sources of air pollution essay

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air pollution

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• United States Environment Protection Agency - Air Pollution: Current and Future Challenges
• Natural Resources Defense Council - Air Pollution: Everything You Need to Know
• National Institute of Environmental Health Sciences - Air Pollution
• National Center for Biotechnology Information - PubMed Central - Air pollution: Impact and prevention
• Frontiers - Air pollution and rhinitis
• Environmental Pollution Centers - What is Air Pollution?
• air pollution - Student Encyclopedia (Ages 11 and up)
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air pollution , release into the atmosphere of various gases , finely divided solids, or finely dispersed liquid aerosols at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. These substances may reach concentrations in the air that cause undesirable health, economic, or aesthetic effects.

Major air pollutants

Criteria pollutants.

Clean, dry air consists primarily of nitrogen and oxygen —78 percent and 21 percent respectively, by volume. The remaining 1 percent is a mixture of other gases, mostly argon (0.9 percent), along with trace (very small) amounts of carbon dioxide , methane , hydrogen , helium , and more. Water vapour is also a normal, though quite variable, component of the atmosphere, normally ranging from 0.01 to 4 percent by volume; under very humid conditions the moisture content of air may be as high as 5 percent.

There are six major air pollutants that have been designated by the U.S. Environmental Protection Agency (EPA) as “criteria” pollutants — criteria meaning that the concentrations of these pollutants in the atmosphere are useful as indicators of overall air quality. The sources, acceptable concentrations, and effects of the criteria pollutants are summarized in the table.

The gaseous criteria air pollutants of primary concern in urban settings include sulfur dioxide , nitrogen dioxide , and carbon monoxide ; these are emitted directly into the air from fossil fuels such as fuel oil , gasoline , and natural gas that are burned in power plants, automobiles, and other combustion sources. Ozone (a key component of smog ) is also a gaseous pollutant; it forms in the atmosphere via complex chemical reactions occurring between nitrogen dioxide and various volatile organic compounds (e.g., gasoline vapours).

Airborne suspensions of extremely small solid or liquid particles called “particulates” (e.g., soot, dust, smokes, fumes, mists), especially those less than 10 micrometres (μm; millionths of a metre) in size, are significant air pollutants because of their very harmful effects on human health. They are emitted by various industrial processes, coal- or oil-burning power plants, residential heating systems, and automobiles. Lead fumes (airborne particulates less than 0.5 μm in size) are particularly toxic and are an important pollutant of many diesel fuels .

Except for lead, criteria pollutants are emitted in industrialized countries at very high rates, typically measured in millions of tons per year. All except ozone are discharged directly into the atmosphere from a wide variety of sources. They are regulated primarily by establishing ambient air quality standards, which are maximum acceptable concentrations of each criteria pollutant in the atmosphere, regardless of its origin. The six criteria pollutants are described in turn below.

ENCYCLOPEDIC ENTRY

Air pollution.

Air pollution consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. It also damages buildings.

Biology, Ecology, Earth Science, Geography

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Air pollution consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. It also damages buildings. Pollutants in the air take many forms. They can be gases , solid particles, or liquid droplets. Sources of Air Pollution Pollution enters the Earth's atmosphere in many different ways. Most air pollution is created by people, taking the form of emissions from factories, cars, planes, or aerosol cans . Second-hand cigarette smoke is also considered air pollution. These man-made sources of pollution are called anthropogenic sources . Some types of air pollution, such as smoke from wildfires or ash from volcanoes , occur naturally. These are called natural sources . Air pollution is most common in large cities where emissions from many different sources are concentrated . Sometimes, mountains or tall buildings prevent air pollution from spreading out. This air pollution often appears as a cloud making the air murky. It is called smog . The word "smog" comes from combining the words "smoke" and " fog ." Large cities in poor and developing nations tend to have more air pollution than cities in developed nations. According to the World Health Organization (WHO) , some of the worlds most polluted cities are Karachi, Pakistan; New Delhi, India; Beijing, China; Lima, Peru; and Cairo, Egypt. However, many developed nations also have air pollution problems. Los Angeles, California, is nicknamed Smog City. Indoor Air Pollution Air pollution is usually thought of as smoke from large factories or exhaust from vehicles. But there are many types of indoor air pollution as well. Heating a house by burning substances such as kerosene , wood, and coal can contaminate the air inside the house. Ash and smoke make breathing difficult, and they can stick to walls, food, and clothing. Naturally-occurring radon gas, a cancer -causing material, can also build up in homes. Radon is released through the surface of the Earth. Inexpensive systems installed by professionals can reduce radon levels. Some construction materials, including insulation , are also dangerous to people's health. In addition, ventilation , or air movement, in homes and rooms can lead to the spread of toxic mold . A single colony of mold may exist in a damp, cool place in a house, such as between walls. The mold's spores enter the air and spread throughout the house. People can become sick from breathing in the spores. Effects On Humans People experience a wide range of health effects from being exposed to air pollution. Effects can be broken down into short-term effects and long-term effects . Short-term effects, which are temporary , include illnesses such as pneumonia or bronchitis . They also include discomfort such as irritation to the nose, throat, eyes, or skin. Air pollution can also cause headaches, dizziness, and nausea . Bad smells made by factories, garbage , or sewer systems are considered air pollution, too. These odors are less serious but still unpleasant . Long-term effects of air pollution can last for years or for an entire lifetime. They can even lead to a person's death. Long-term health effects from air pollution include heart disease , lung cancer, and respiratory diseases such as emphysema . Air pollution can also cause long-term damage to people's nerves , brain, kidneys , liver , and other organs. Some scientists suspect air pollutants cause birth defects . Nearly 2.5 million people die worldwide each year from the effects of outdoor or indoor air pollution. People react differently to different types of air pollution. Young children and older adults, whose immune systems tend to be weaker, are often more sensitive to pollution. Conditions such as asthma , heart disease, and lung disease can be made worse by exposure to air pollution. The length of exposure and amount and type of pollutants are also factors. Effects On The Environment Like people, animals, and plants, entire ecosystems can suffer effects from air pollution. Haze , like smog, is a visible type of air pollution that obscures shapes and colors. Hazy air pollution can even muffle sounds. Air pollution particles eventually fall back to Earth. Air pollution can directly contaminate the surface of bodies of water and soil . This can kill crops or reduce their yield . It can kill young trees and other plants. Sulfur dioxide and nitrogen oxide particles in the air, can create acid rain when they mix with water and oxygen in the atmosphere. These air pollutants come mostly from coal-fired power plants and motor vehicles . When acid rain falls to Earth, it damages plants by changing soil composition ; degrades water quality in rivers, lakes and streams; damages crops; and can cause buildings and monuments to decay . Like humans, animals can suffer health effects from exposure to air pollution. Birth defects, diseases, and lower reproductive rates have all been attributed to air pollution. Global Warming Global warming is an environmental phenomenon caused by natural and anthropogenic air pollution. It refers to rising air and ocean temperatures around the world. This temperature rise is at least partially caused by an increase in the amount of greenhouse gases in the atmosphere. Greenhouse gases trap heat energy in the Earths atmosphere. (Usually, more of Earths heat escapes into space.) Carbon dioxide is a greenhouse gas that has had the biggest effect on global warming. Carbon dioxide is emitted into the atmosphere by burning fossil fuels (coal, gasoline , and natural gas ). Humans have come to rely on fossil fuels to power cars and planes, heat homes, and run factories. Doing these things pollutes the air with carbon dioxide. Other greenhouse gases emitted by natural and artificial sources also include methane , nitrous oxide , and fluorinated gases. Methane is a major emission from coal plants and agricultural processes. Nitrous oxide is a common emission from industrial factories, agriculture, and the burning of fossil fuels in cars. Fluorinated gases, such as hydrofluorocarbons , are emitted by industry. Fluorinated gases are often used instead of gases such as chlorofluorocarbons (CFCs). CFCs have been outlawed in many places because they deplete the ozone layer . Worldwide, many countries have taken steps to reduce or limit greenhouse gas emissions to combat global warming. The Kyoto Protocol , first adopted in Kyoto, Japan, in 1997, is an agreement between 183 countries that they will work to reduce their carbon dioxide emissions. The United States has not signed that treaty . Regulation In addition to the international Kyoto Protocol, most developed nations have adopted laws to regulate emissions and reduce air pollution. In the United States, debate is under way about a system called cap and trade to limit emissions. This system would cap, or place a limit, on the amount of pollution a company is allowed. Companies that exceeded their cap would have to pay. Companies that polluted less than their cap could trade or sell their remaining pollution allowance to other companies. Cap and trade would essentially pay companies to limit pollution. In 2006 the World Health Organization issued new Air Quality Guidelines. The WHOs guidelines are tougher than most individual countries existing guidelines. The WHO guidelines aim to reduce air pollution-related deaths by 15 percent a year. Reduction Anybody can take steps to reduce air pollution. Millions of people every day make simple changes in their lives to do this. Taking public transportation instead of driving a car, or riding a bike instead of traveling in carbon dioxide-emitting vehicles are a couple of ways to reduce air pollution. Avoiding aerosol cans, recycling yard trimmings instead of burning them, and not smoking cigarettes are others.

Downwinders The United States conducted tests of nuclear weapons at the Nevada Test Site in southern Nevada in the 1950s. These tests sent invisible radioactive particles into the atmosphere. These air pollution particles traveled with wind currents, eventually falling to Earth, sometimes hundreds of miles away in states including Idaho, Utah, Arizona, and Washington. These areas were considered to be "downwind" from the Nevada Test Site. Decades later, people living in those downwind areascalled "downwinders"began developing cancer at above-normal rates. In 1990, the U.S. government passed the Radiation Exposure Compensation Act. This law entitles some downwinders to payments of $50,000.

Greenhouse Gases There are five major greenhouse gases in Earth's atmosphere.

• water vapor
• carbon dioxide
• nitrous oxide

London Smog What has come to be known as the London Smog of 1952, or the Great Smog of 1952, was a four-day incident that sickened 100,000 people and caused as many as 12,000 deaths. Very cold weather in December 1952 led residents of London, England, to burn more coal to keep warm. Smoke and other pollutants became trapped by a thick fog that settled over the city. The polluted fog became so thick that people could only see a few meters in front of them.

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Environmental and Health Impacts of Air Pollution: A Review

Ioannis manisalidis.

1 Delphis S.A., Kifisia, Greece

2 Laboratory of Hygiene and Environmental Protection, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece

Elisavet Stavropoulou

3 Centre Hospitalier Universitaire Vaudois (CHUV), Service de Médicine Interne, Lausanne, Switzerland

Agathangelos Stavropoulos

4 School of Social and Political Sciences, University of Glasgow, Glasgow, United Kingdom

Eugenia Bezirtzoglou

One of our era's greatest scourges is air pollution, on account not only of its impact on climate change but also its impact on public and individual health due to increasing morbidity and mortality. There are many pollutants that are major factors in disease in humans. Among them, Particulate Matter (PM), particles of variable but very small diameter, penetrate the respiratory system via inhalation, causing respiratory and cardiovascular diseases, reproductive and central nervous system dysfunctions, and cancer. Despite the fact that ozone in the stratosphere plays a protective role against ultraviolet irradiation, it is harmful when in high concentration at ground level, also affecting the respiratory and cardiovascular system. Furthermore, nitrogen oxide, sulfur dioxide, Volatile Organic Compounds (VOCs), dioxins, and polycyclic aromatic hydrocarbons (PAHs) are all considered air pollutants that are harmful to humans. Carbon monoxide can even provoke direct poisoning when breathed in at high levels. Heavy metals such as lead, when absorbed into the human body, can lead to direct poisoning or chronic intoxication, depending on exposure. Diseases occurring from the aforementioned substances include principally respiratory problems such as Chronic Obstructive Pulmonary Disease (COPD), asthma, bronchiolitis, and also lung cancer, cardiovascular events, central nervous system dysfunctions, and cutaneous diseases. Last but not least, climate change resulting from environmental pollution affects the geographical distribution of many infectious diseases, as do natural disasters. The only way to tackle this problem is through public awareness coupled with a multidisciplinary approach by scientific experts; national and international organizations must address the emergence of this threat and propose sustainable solutions.

Approach to the Problem

The interactions between humans and their physical surroundings have been extensively studied, as multiple human activities influence the environment. The environment is a coupling of the biotic (living organisms and microorganisms) and the abiotic (hydrosphere, lithosphere, and atmosphere).

Pollution is defined as the introduction into the environment of substances harmful to humans and other living organisms. Pollutants are harmful solids, liquids, or gases produced in higher than usual concentrations that reduce the quality of our environment.

Human activities have an adverse effect on the environment by polluting the water we drink, the air we breathe, and the soil in which plants grow. Although the industrial revolution was a great success in terms of technology, society, and the provision of multiple services, it also introduced the production of huge quantities of pollutants emitted into the air that are harmful to human health. Without any doubt, the global environmental pollution is considered an international public health issue with multiple facets. Social, economic, and legislative concerns and lifestyle habits are related to this major problem. Clearly, urbanization and industrialization are reaching unprecedented and upsetting proportions worldwide in our era. Anthropogenic air pollution is one of the biggest public health hazards worldwide, given that it accounts for about 9 million deaths per year ( 1 ).

Without a doubt, all of the aforementioned are closely associated with climate change, and in the event of danger, the consequences can be severe for mankind ( 2 ). Climate changes and the effects of global planetary warming seriously affect multiple ecosystems, causing problems such as food safety issues, ice and iceberg melting, animal extinction, and damage to plants ( 3 , 4 ).

Air pollution has various health effects. The health of susceptible and sensitive individuals can be impacted even on low air pollution days. Short-term exposure to air pollutants is closely related to COPD (Chronic Obstructive Pulmonary Disease), cough, shortness of breath, wheezing, asthma, respiratory disease, and high rates of hospitalization (a measurement of morbidity).

The long-term effects associated with air pollution are chronic asthma, pulmonary insufficiency, cardiovascular diseases, and cardiovascular mortality. According to a Swedish cohort study, diabetes seems to be induced after long-term air pollution exposure ( 5 ). Moreover, air pollution seems to have various malign health effects in early human life, such as respiratory, cardiovascular, mental, and perinatal disorders ( 3 ), leading to infant mortality or chronic disease in adult age ( 6 ).

National reports have mentioned the increased risk of morbidity and mortality ( 1 ). These studies were conducted in many places around the world and show a correlation between daily ranges of particulate matter (PM) concentration and daily mortality. Climate shifts and global planetary warming ( 3 ) could aggravate the situation. Besides, increased hospitalization (an index of morbidity) has been registered among the elderly and susceptible individuals for specific reasons. Fine and ultrafine particulate matter seems to be associated with more serious illnesses ( 6 ), as it can invade the deepest parts of the airways and more easily reach the bloodstream.

Air pollution mainly affects those living in large urban areas, where road emissions contribute the most to the degradation of air quality. There is also a danger of industrial accidents, where the spread of a toxic fog can be fatal to the populations of the surrounding areas. The dispersion of pollutants is determined by many parameters, most notably atmospheric stability and wind ( 6 ).

In developing countries ( 7 ), the problem is more serious due to overpopulation and uncontrolled urbanization along with the development of industrialization. This leads to poor air quality, especially in countries with social disparities and a lack of information on sustainable management of the environment. The use of fuels such as wood fuel or solid fuel for domestic needs due to low incomes exposes people to bad-quality, polluted air at home. It is of note that three billion people around the world are using the above sources of energy for their daily heating and cooking needs ( 8 ). In developing countries, the women of the household seem to carry the highest risk for disease development due to their longer duration exposure to the indoor air pollution ( 8 , 9 ). Due to its fast industrial development and overpopulation, China is one of the Asian countries confronting serious air pollution problems ( 10 , 11 ). The lung cancer mortality observed in China is associated with fine particles ( 12 ). As stated already, long-term exposure is associated with deleterious effects on the cardiovascular system ( 3 , 5 ). However, it is interesting to note that cardiovascular diseases have mostly been observed in developed and high-income countries rather than in the developing low-income countries exposed highly to air pollution ( 13 ). Extreme air pollution is recorded in India, where the air quality reaches hazardous levels. New Delhi is one of the more polluted cities in India. Flights in and out of New Delhi International Airport are often canceled due to the reduced visibility associated with air pollution. Pollution is occurring both in urban and rural areas in India due to the fast industrialization, urbanization, and rise in use of motorcycle transportation. Nevertheless, biomass combustion associated with heating and cooking needs and practices is a major source of household air pollution in India and in Nepal ( 14 , 15 ). There is spatial heterogeneity in India, as areas with diverse climatological conditions and population and education levels generate different indoor air qualities, with higher PM 2.5 observed in North Indian states (557–601 μg/m 3 ) compared to the Southern States (183–214 μg/m 3 ) ( 16 , 17 ). The cold climate of the North Indian areas may be the main reason for this, as longer periods at home and more heating are necessary compared to in the tropical climate of Southern India. Household air pollution in India is associated with major health effects, especially in women and young children, who stay indoors for longer periods. Chronic obstructive respiratory disease (CORD) and lung cancer are mostly observed in women, while acute lower respiratory disease is seen in young children under 5 years of age ( 18 ).

Accumulation of air pollution, especially sulfur dioxide and smoke, reaching 1,500 mg/m3, resulted in an increase in the number of deaths (4,000 deaths) in December 1952 in London and in 1963 in New York City (400 deaths) ( 19 ). An association of pollution with mortality was reported on the basis of monitoring of outdoor pollution in six US metropolitan cities ( 20 ). In every case, it seems that mortality was closely related to the levels of fine, inhalable, and sulfate particles more than with the levels of total particulate pollution, aerosol acidity, sulfur dioxide, or nitrogen dioxide ( 20 ).

Furthermore, extremely high levels of pollution are reported in Mexico City and Rio de Janeiro, followed by Milan, Ankara, Melbourne, Tokyo, and Moscow ( 19 ).

Based on the magnitude of the public health impact, it is certain that different kinds of interventions should be taken into account. Success and effectiveness in controlling air pollution, specifically at the local level, have been reported. Adequate technological means are applied considering the source and the nature of the emission as well as its impact on health and the environment. The importance of point sources and non-point sources of air pollution control is reported by Schwela and Köth-Jahr ( 21 ). Without a doubt, a detailed emission inventory must record all sources in a given area. Beyond considering the above sources and their nature, topography and meteorology should also be considered, as stated previously. Assessment of the control policies and methods is often extrapolated from the local to the regional and then to the global scale. Air pollution may be dispersed and transported from one region to another area located far away. Air pollution management means the reduction to acceptable levels or possible elimination of air pollutants whose presence in the air affects our health or the environmental ecosystem. Private and governmental entities and authorities implement actions to ensure the air quality ( 22 ). Air quality standards and guidelines were adopted for the different pollutants by the WHO and EPA as a tool for the management of air quality ( 1 , 23 ). These standards have to be compared to the emissions inventory standards by causal analysis and dispersion modeling in order to reveal the problematic areas ( 24 ). Inventories are generally based on a combination of direct measurements and emissions modeling ( 24 ).

As an example, we state here the control measures at the source through the use of catalytic converters in cars. These are devices that turn the pollutants and toxic gases produced from combustion engines into less-toxic pollutants by catalysis through redox reactions ( 25 ). In Greece, the use of private cars was restricted by tracking their license plates in order to reduce traffic congestion during rush hour ( 25 ).

Concerning industrial emissions, collectors and closed systems can keep the air pollution to the minimal standards imposed by legislation ( 26 ).

Current strategies to improve air quality require an estimation of the economic value of the benefits gained from proposed programs. These proposed programs by public authorities, and directives are issued with guidelines to be respected.

In Europe, air quality limit values AQLVs (Air Quality Limit Values) are issued for setting off planning claims ( 27 ). In the USA, the NAAQS (National Ambient Air Quality Standards) establish the national air quality limit values ( 27 ). While both standards and directives are based on different mechanisms, significant success has been achieved in the reduction of overall emissions and associated health and environmental effects ( 27 ). The European Directive identifies geographical areas of risk exposure as monitoring/assessment zones to record the emission sources and levels of air pollution ( 27 ), whereas the USA establishes global geographical air quality criteria according to the severity of their air quality problem and records all sources of the pollutants and their precursors ( 27 ).

In this vein, funds have been financing, directly or indirectly, projects related to air quality along with the technical infrastructure to maintain good air quality. These plans focus on an inventory of databases from air quality environmental planning awareness campaigns. Moreover, pollution measures of air emissions may be taken for vehicles, machines, and industries in urban areas.

Technological innovation can only be successful if it is able to meet the needs of society. In this sense, technology must reflect the decision-making practices and procedures of those involved in risk assessment and evaluation and act as a facilitator in providing information and assessments to enable decision makers to make the best decisions possible. Summarizing the aforementioned in order to design an effective air quality control strategy, several aspects must be considered: environmental factors and ambient air quality conditions, engineering factors and air pollutant characteristics, and finally, economic operating costs for technological improvement and administrative and legal costs. Considering the economic factor, competitiveness through neoliberal concepts is offering a solution to environmental problems ( 22 ).

The development of environmental governance, along with technological progress, has initiated the deployment of a dialogue. Environmental politics has created objections and points of opposition between different political parties, scientists, media, and governmental and non-governmental organizations ( 22 ). Radical environmental activism actions and movements have been created ( 22 ). The rise of the new information and communication technologies (ICTs) are many times examined as to whether and in which way they have influenced means of communication and social movements such as activism ( 28 ). Since the 1990s, the term “digital activism” has been used increasingly and in many different disciplines ( 29 ). Nowadays, multiple digital technologies can be used to produce a digital activism outcome on environmental issues. More specifically, devices with online capabilities such as computers or mobile phones are being used as a way to pursue change in political and social affairs ( 30 ).

In the present paper, we focus on the sources of environmental pollution in relation to public health and propose some solutions and interventions that may be of interest to environmental legislators and decision makers.

Sources of Exposure

It is known that the majority of environmental pollutants are emitted through large-scale human activities such as the use of industrial machinery, power-producing stations, combustion engines, and cars. Because these activities are performed at such a large scale, they are by far the major contributors to air pollution, with cars estimated to be responsible for approximately 80% of today's pollution ( 31 ). Some other human activities are also influencing our environment to a lesser extent, such as field cultivation techniques, gas stations, fuel tanks heaters, and cleaning procedures ( 32 ), as well as several natural sources, such as volcanic and soil eruptions and forest fires.

The classification of air pollutants is based mainly on the sources producing pollution. Therefore, it is worth mentioning the four main sources, following the classification system: Major sources, Area sources, Mobile sources, and Natural sources.

Major sources include the emission of pollutants from power stations, refineries, and petrochemicals, the chemical and fertilizer industries, metallurgical and other industrial plants, and, finally, municipal incineration.

Indoor area sources include domestic cleaning activities, dry cleaners, printing shops, and petrol stations.

Mobile sources include automobiles, cars, railways, airways, and other types of vehicles.

Finally, natural sources include, as stated previously, physical disasters ( 33 ) such as forest fire, volcanic erosion, dust storms, and agricultural burning.

However, many classification systems have been proposed. Another type of classification is a grouping according to the recipient of the pollution, as follows:

Air pollution is determined as the presence of pollutants in the air in large quantities for long periods. Air pollutants are dispersed particles, hydrocarbons, CO, CO 2 , NO, NO 2 , SO 3 , etc.

Water pollution is organic and inorganic charge and biological charge ( 10 ) at high levels that affect the water quality ( 34 , 35 ).

Soil pollution occurs through the release of chemicals or the disposal of wastes, such as heavy metals, hydrocarbons, and pesticides.

Air pollution can influence the quality of soil and water bodies by polluting precipitation, falling into water and soil environments ( 34 , 36 ). Notably, the chemistry of the soil can be amended due to acid precipitation by affecting plants, cultures, and water quality ( 37 ). Moreover, movement of heavy metals is favored by soil acidity, and metals are so then moving into the watery environment. It is known that heavy metals such as aluminum are noxious to wildlife and fishes. Soil quality seems to be of importance, as soils with low calcium carbonate levels are at increased jeopardy from acid rain. Over and above rain, snow and particulate matter drip into watery ' bodies ( 36 , 38 ).

Lastly, pollution is classified following type of origin:

Radioactive and nuclear pollution , releasing radioactive and nuclear pollutants into water, air, and soil during nuclear explosions and accidents, from nuclear weapons, and through handling or disposal of radioactive sewage.

Radioactive materials can contaminate surface water bodies and, being noxious to the environment, plants, animals, and humans. It is known that several radioactive substances such as radium and uranium concentrate in the bones and can cause cancers ( 38 , 39 ).

Noise pollution is produced by machines, vehicles, traffic noises, and musical installations that are harmful to our hearing.

The World Health Organization introduced the term DALYs. The DALYs for a disease or health condition is defined as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition or its consequences ( 39 ). In Europe, air pollution is the main cause of disability-adjusted life years lost (DALYs), followed by noise pollution. The potential relationships of noise and air pollution with health have been studied ( 40 ). The study found that DALYs related to noise were more important than those related to air pollution, as the effects of environmental noise on cardiovascular disease were independent of air pollution ( 40 ). Environmental noise should be counted as an independent public health risk ( 40 ).

Environmental pollution occurs when changes in the physical, chemical, or biological constituents of the environment (air masses, temperature, climate, etc.) are produced.

Pollutants harm our environment either by increasing levels above normal or by introducing harmful toxic substances. Primary pollutants are directly produced from the above sources, and secondary pollutants are emitted as by-products of the primary ones. Pollutants can be biodegradable or non-biodegradable and of natural origin or anthropogenic, as stated previously. Moreover, their origin can be a unique source (point-source) or dispersed sources.

Pollutants have differences in physical and chemical properties, explaining the discrepancy in their capacity for producing toxic effects. As an example, we state here that aerosol compounds ( 41 – 43 ) have a greater toxicity than gaseous compounds due to their tiny size (solid or liquid) in the atmosphere; they have a greater penetration capacity. Gaseous compounds are eliminated more easily by our respiratory system ( 41 ). These particles are able to damage lungs and can even enter the bloodstream ( 41 ), leading to the premature deaths of millions of people yearly. Moreover, the aerosol acidity ([H+]) seems to considerably enhance the production of secondary organic aerosols (SOA), but this last aspect is not supported by other scientific teams ( 38 ).

Climate and Pollution

Air pollution and climate change are closely related. Climate is the other side of the same coin that reduces the quality of our Earth ( 44 ). Pollutants such as black carbon, methane, tropospheric ozone, and aerosols affect the amount of incoming sunlight. As a result, the temperature of the Earth is increasing, resulting in the melting of ice, icebergs, and glaciers.

In this vein, climatic changes will affect the incidence and prevalence of both residual and imported infections in Europe. Climate and weather affect the duration, timing, and intensity of outbreaks strongly and change the map of infectious diseases in the globe ( 45 ). Mosquito-transmitted parasitic or viral diseases are extremely climate-sensitive, as warming firstly shortens the pathogen incubation period and secondly shifts the geographic map of the vector. Similarly, water-warming following climate changes leads to a high incidence of waterborne infections. Recently, in Europe, eradicated diseases seem to be emerging due to the migration of population, for example, cholera, poliomyelitis, tick-borne encephalitis, and malaria ( 46 ).

The spread of epidemics is associated with natural climate disasters and storms, which seem to occur more frequently nowadays ( 47 ). Malnutrition and disequilibration of the immune system are also associated with the emerging infections affecting public health ( 48 ).

The Chikungunya virus “took the airplane” from the Indian Ocean to Europe, as outbreaks of the disease were registered in Italy ( 49 ) as well as autochthonous cases in France ( 50 ).

An increase in cryptosporidiosis in the United Kingdom and in the Czech Republic seems to have occurred following flooding ( 36 , 51 ).

As stated previously, aerosols compounds are tiny in size and considerably affect the climate. They are able to dissipate sunlight (the albedo phenomenon) by dispersing a quarter of the sun's rays back to space and have cooled the global temperature over the last 30 years ( 52 ).

Air Pollutants

The World Health Organization (WHO) reports on six major air pollutants, namely particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Air pollution can have a disastrous effect on all components of the environment, including groundwater, soil, and air. Additionally, it poses a serious threat to living organisms. In this vein, our interest is mainly to focus on these pollutants, as they are related to more extensive and severe problems in human health and environmental impact. Acid rain, global warming, the greenhouse effect, and climate changes have an important ecological impact on air pollution ( 53 ).

Particulate Matter (PM) and Health

Studies have shown a relationship between particulate matter (PM) and adverse health effects, focusing on either short-term (acute) or long-term (chronic) PM exposure.

Particulate matter (PM) is usually formed in the atmosphere as a result of chemical reactions between the different pollutants. The penetration of particles is closely dependent on their size ( 53 ). Particulate Matter (PM) was defined as a term for particles by the United States Environmental Protection Agency ( 54 ). Particulate matter (PM) pollution includes particles with diameters of 10 micrometers (μm) or smaller, called PM 10 , and extremely fine particles with diameters that are generally 2.5 micrometers (μm) and smaller.

Particulate matter contains tiny liquid or solid droplets that can be inhaled and cause serious health effects ( 55 ). Particles <10 μm in diameter (PM 10 ) after inhalation can invade the lungs and even reach the bloodstream. Fine particles, PM 2.5 , pose a greater risk to health ( 6 , 56 ) ( Table 1 ).

Penetrability according to particle size.

Multiple epidemiological studies have been performed on the health effects of PM. A positive relation was shown between both short-term and long-term exposures of PM 2.5 and acute nasopharyngitis ( 56 ). In addition, long-term exposure to PM for years was found to be related to cardiovascular diseases and infant mortality.

Those studies depend on PM 2.5 monitors and are restricted in terms of study area or city area due to a lack of spatially resolved daily PM 2.5 concentration data and, in this way, are not representative of the entire population. Following a recent epidemiological study by the Department of Environmental Health at Harvard School of Public Health (Boston, MA) ( 57 ), it was reported that, as PM 2.5 concentrations vary spatially, an exposure error (Berkson error) seems to be produced, and the relative magnitudes of the short- and long-term effects are not yet completely elucidated. The team developed a PM 2.5 exposure model based on remote sensing data for assessing short- and long-term human exposures ( 57 ). This model permits spatial resolution in short-term effects plus the assessment of long-term effects in the whole population.

Moreover, respiratory diseases and affection of the immune system are registered as long-term chronic effects ( 58 ). It is worth noting that people with asthma, pneumonia, diabetes, and respiratory and cardiovascular diseases are especially susceptible and vulnerable to the effects of PM. PM 2.5 , followed by PM 10 , are strongly associated with diverse respiratory system diseases ( 59 ), as their size permits them to pierce interior spaces ( 60 ). The particles produce toxic effects according to their chemical and physical properties. The components of PM 10 and PM 2.5 can be organic (polycyclic aromatic hydrocarbons, dioxins, benzene, 1-3 butadiene) or inorganic (carbon, chlorides, nitrates, sulfates, metals) in nature ( 55 ).

Particulate Matter (PM) is divided into four main categories according to type and size ( 61 ) ( Table 2 ).

Types and sizes of particulate Matter (PM).

Gas contaminants include PM in aerial masses.

Particulate contaminants include contaminants such as smog, soot, tobacco smoke, oil smoke, fly ash, and cement dust.

Biological Contaminants are microorganisms (bacteria, viruses, fungi, mold, and bacterial spores), cat allergens, house dust and allergens, and pollen.

Types of Dust include suspended atmospheric dust, settling dust, and heavy dust.

Finally, another fact is that the half-lives of PM 10 and PM 2.5 particles in the atmosphere is extended due to their tiny dimensions; this permits their long-lasting suspension in the atmosphere and even their transfer and spread to distant destinations where people and the environment may be exposed to the same magnitude of pollution ( 53 ). They are able to change the nutrient balance in watery ecosystems, damage forests and crops, and acidify water bodies.

As stated, PM 2.5 , due to their tiny size, are causing more serious health effects. These aforementioned fine particles are the main cause of the “haze” formation in different metropolitan areas ( 12 , 13 , 61 ).

Ozone Impact in the Atmosphere

Ozone (O 3 ) is a gas formed from oxygen under high voltage electric discharge ( 62 ). It is a strong oxidant, 52% stronger than chlorine. It arises in the stratosphere, but it could also arise following chain reactions of photochemical smog in the troposphere ( 63 ).

Ozone can travel to distant areas from its initial source, moving with air masses ( 64 ). It is surprising that ozone levels over cities are low in contrast to the increased amounts occuring in urban areas, which could become harmful for cultures, forests, and vegetation ( 65 ) as it is reducing carbon assimilation ( 66 ). Ozone reduces growth and yield ( 47 , 48 ) and affects the plant microflora due to its antimicrobial capacity ( 67 , 68 ). In this regard, ozone acts upon other natural ecosystems, with microflora ( 69 , 70 ) and animal species changing their species composition ( 71 ). Ozone increases DNA damage in epidermal keratinocytes and leads to impaired cellular function ( 72 ).

Ground-level ozone (GLO) is generated through a chemical reaction between oxides of nitrogen and VOCs emitted from natural sources and/or following anthropogenic activities.

Ozone uptake usually occurs by inhalation. Ozone affects the upper layers of the skin and the tear ducts ( 73 ). A study of short-term exposure of mice to high levels of ozone showed malondialdehyde formation in the upper skin (epidermis) but also depletion in vitamins C and E. It is likely that ozone levels are not interfering with the skin barrier function and integrity to predispose to skin disease ( 74 ).

Due to the low water-solubility of ozone, inhaled ozone has the capacity to penetrate deeply into the lungs ( 75 ).

Toxic effects induced by ozone are registered in urban areas all over the world, causing biochemical, morphologic, functional, and immunological disorders ( 76 ).

The European project (APHEA2) focuses on the acute effects of ambient ozone concentrations on mortality ( 77 ). Daily ozone concentrations compared to the daily number of deaths were reported from different European cities for a 3-year period. During the warm period of the year, an observed increase in ozone concentration was associated with an increase in the daily number of deaths (0.33%), in the number of respiratory deaths (1.13%), and in the number of cardiovascular deaths (0.45%). No effect was observed during wintertime.

Carbon Monoxide (CO)

Carbon monoxide is produced by fossil fuel when combustion is incomplete. The symptoms of poisoning due to inhaling carbon monoxide include headache, dizziness, weakness, nausea, vomiting, and, finally, loss of consciousness.

The affinity of carbon monoxide to hemoglobin is much greater than that of oxygen. In this vein, serious poisoning may occur in people exposed to high levels of carbon monoxide for a long period of time. Due to the loss of oxygen as a result of the competitive binding of carbon monoxide, hypoxia, ischemia, and cardiovascular disease are observed.

Carbon monoxide affects the greenhouses gases that are tightly connected to global warming and climate. This should lead to an increase in soil and water temperatures, and extreme weather conditions or storms may occur ( 68 ).

However, in laboratory and field experiments, it has been seen to produce increased plant growth ( 78 ).

Nitrogen Oxide (NO 2 )

Nitrogen oxide is a traffic-related pollutant, as it is emitted from automobile motor engines ( 79 , 80 ). It is an irritant of the respiratory system as it penetrates deep in the lung, inducing respiratory diseases, coughing, wheezing, dyspnea, bronchospasm, and even pulmonary edema when inhaled at high levels. It seems that concentrations over 0.2 ppm produce these adverse effects in humans, while concentrations higher than 2.0 ppm affect T-lymphocytes, particularly the CD8+ cells and NK cells that produce our immune response ( 81 ).It is reported that long-term exposure to high levels of nitrogen dioxide can be responsible for chronic lung disease. Long-term exposure to NO 2 can impair the sense of smell ( 81 ).

However, systems other than respiratory ones can be involved, as symptoms such as eye, throat, and nose irritation have been registered ( 81 ).

High levels of nitrogen dioxide are deleterious to crops and vegetation, as they have been observed to reduce crop yield and plant growth efficiency. Moreover, NO 2 can reduce visibility and discolor fabrics ( 81 ).

Sulfur Dioxide (SO 2 )

Sulfur dioxide is a harmful gas that is emitted mainly from fossil fuel consumption or industrial activities. The annual standard for SO 2 is 0.03 ppm ( 82 ). It affects human, animal, and plant life. Susceptible people as those with lung disease, old people, and children, who present a higher risk of damage. The major health problems associated with sulfur dioxide emissions in industrialized areas are respiratory irritation, bronchitis, mucus production, and bronchospasm, as it is a sensory irritant and penetrates deep into the lung converted into bisulfite and interacting with sensory receptors, causing bronchoconstriction. Moreover, skin redness, damage to the eyes (lacrimation and corneal opacity) and mucous membranes, and worsening of pre-existing cardiovascular disease have been observed ( 81 ).

Environmental adverse effects, such as acidification of soil and acid rain, seem to be associated with sulfur dioxide emissions ( 83 ).

Lead is a heavy metal used in different industrial plants and emitted from some petrol motor engines, batteries, radiators, waste incinerators, and waste waters ( 84 ).

Moreover, major sources of lead pollution in the air are metals, ore, and piston-engine aircraft. Lead poisoning is a threat to public health due to its deleterious effects upon humans, animals, and the environment, especially in the developing countries.

Exposure to lead can occur through inhalation, ingestion, and dermal absorption. Trans- placental transport of lead was also reported, as lead passes through the placenta unencumbered ( 85 ). The younger the fetus is, the more harmful the toxic effects. Lead toxicity affects the fetal nervous system; edema or swelling of the brain is observed ( 86 ). Lead, when inhaled, accumulates in the blood, soft tissue, liver, lung, bones, and cardiovascular, nervous, and reproductive systems. Moreover, loss of concentration and memory, as well as muscle and joint pain, were observed in adults ( 85 , 86 ).

Children and newborns ( 87 ) are extremely susceptible even to minimal doses of lead, as it is a neurotoxicant and causes learning disabilities, impairment of memory, hyperactivity, and even mental retardation.

Elevated amounts of lead in the environment are harmful to plants and crop growth. Neurological effects are observed in vertebrates and animals in association with high lead levels ( 88 ).

Polycyclic Aromatic Hydrocarbons(PAHs)

The distribution of PAHs is ubiquitous in the environment, as the atmosphere is the most important means of their dispersal. They are found in coal and in tar sediments. Moreover, they are generated through incomplete combustion of organic matter as in the cases of forest fires, incineration, and engines ( 89 ). PAH compounds, such as benzopyrene, acenaphthylene, anthracene, and fluoranthene are recognized as toxic, mutagenic, and carcinogenic substances. They are an important risk factor for lung cancer ( 89 ).

Volatile Organic Compounds(VOCs)

Volatile organic compounds (VOCs), such as toluene, benzene, ethylbenzene, and xylene ( 90 ), have been found to be associated with cancer in humans ( 91 ). The use of new products and materials has actually resulted in increased concentrations of VOCs. VOCs pollute indoor air ( 90 ) and may have adverse effects on human health ( 91 ). Short-term and long-term adverse effects on human health are observed. VOCs are responsible for indoor air smells. Short-term exposure is found to cause irritation of eyes, nose, throat, and mucosal membranes, while those of long duration exposure include toxic reactions ( 92 ). Predictable assessment of the toxic effects of complex VOC mixtures is difficult to estimate, as these pollutants can have synergic, antagonistic, or indifferent effects ( 91 , 93 ).

Dioxins originate from industrial processes but also come from natural processes, such as forest fires and volcanic eruptions. They accumulate in foods such as meat and dairy products, fish and shellfish, and especially in the fatty tissue of animals ( 94 ).

Short-period exhibition to high dioxin concentrations may result in dark spots and lesions on the skin ( 94 ). Long-term exposure to dioxins can cause developmental problems, impairment of the immune, endocrine and nervous systems, reproductive infertility, and cancer ( 94 ).

Without any doubt, fossil fuel consumption is responsible for a sizeable part of air contamination. This contamination may be anthropogenic, as in agricultural and industrial processes or transportation, while contamination from natural sources is also possible. Interestingly, it is of note that the air quality standards established through the European Air Quality Directive are somewhat looser than the WHO guidelines, which are stricter ( 95 ).

Effect of Air Pollution on Health

The most common air pollutants are ground-level ozone and Particulates Matter (PM). Air pollution is distinguished into two main types:

Outdoor pollution is the ambient air pollution.

Indoor pollution is the pollution generated by household combustion of fuels.

People exposed to high concentrations of air pollutants experience disease symptoms and states of greater and lesser seriousness. These effects are grouped into short- and long-term effects affecting health.

Susceptible populations that need to be aware of health protection measures include old people, children, and people with diabetes and predisposing heart or lung disease, especially asthma.

As extensively stated previously, according to a recent epidemiological study from Harvard School of Public Health, the relative magnitudes of the short- and long-term effects have not been completely clarified ( 57 ) due to the different epidemiological methodologies and to the exposure errors. New models are proposed for assessing short- and long-term human exposure data more successfully ( 57 ). Thus, in the present section, we report the more common short- and long-term health effects but also general concerns for both types of effects, as these effects are often dependent on environmental conditions, dose, and individual susceptibility.

Short-term effects are temporary and range from simple discomfort, such as irritation of the eyes, nose, skin, throat, wheezing, coughing and chest tightness, and breathing difficulties, to more serious states, such as asthma, pneumonia, bronchitis, and lung and heart problems. Short-term exposure to air pollution can also cause headaches, nausea, and dizziness.

These problems can be aggravated by extended long-term exposure to the pollutants, which is harmful to the neurological, reproductive, and respiratory systems and causes cancer and even, rarely, deaths.

The long-term effects are chronic, lasting for years or the whole life and can even lead to death. Furthermore, the toxicity of several air pollutants may also induce a variety of cancers in the long term ( 96 ).

As stated already, respiratory disorders are closely associated with the inhalation of air pollutants. These pollutants will invade through the airways and will accumulate at the cells. Damage to target cells should be related to the pollutant component involved and its source and dose. Health effects are also closely dependent on country, area, season, and time. An extended exposure duration to the pollutant should incline to long-term health effects in relation also to the above factors.

Particulate Matter (PMs), dust, benzene, and O 3 cause serious damage to the respiratory system ( 97 ). Moreover, there is a supplementary risk in case of existing respiratory disease such as asthma ( 98 ). Long-term effects are more frequent in people with a predisposing disease state. When the trachea is contaminated by pollutants, voice alterations may be remarked after acute exposure. Chronic obstructive pulmonary disease (COPD) may be induced following air pollution, increasing morbidity and mortality ( 99 ). Long-term effects from traffic, industrial air pollution, and combustion of fuels are the major factors for COPD risk ( 99 ).

Multiple cardiovascular effects have been observed after exposure to air pollutants ( 100 ). Changes occurred in blood cells after long-term exposure may affect cardiac functionality. Coronary arteriosclerosis was reported following long-term exposure to traffic emissions ( 101 ), while short-term exposure is related to hypertension, stroke, myocardial infracts, and heart insufficiency. Ventricle hypertrophy is reported to occur in humans after long-time exposure to nitrogen oxide (NO 2 ) ( 102 , 103 ).

Neurological effects have been observed in adults and children after extended-term exposure to air pollutants.

Psychological complications, autism, retinopathy, fetal growth, and low birth weight seem to be related to long-term air pollution ( 83 ). The etiologic agent of the neurodegenerative diseases (Alzheimer's and Parkinson's) is not yet known, although it is believed that extended exposure to air pollution seems to be a factor. Specifically, pesticides and metals are cited as etiological factors, together with diet. The mechanisms in the development of neurodegenerative disease include oxidative stress, protein aggregation, inflammation, and mitochondrial impairment in neurons ( 104 ) ( Figure 1 ).

Impact of air pollutants on the brain.

Brain inflammation was observed in dogs living in a highly polluted area in Mexico for a long period ( 105 ). In human adults, markers of systemic inflammation (IL-6 and fibrinogen) were found to be increased as an immediate response to PNC on the IL-6 level, possibly leading to the production of acute-phase proteins ( 106 ). The progression of atherosclerosis and oxidative stress seem to be the mechanisms involved in the neurological disturbances caused by long-term air pollution. Inflammation comes secondary to the oxidative stress and seems to be involved in the impairment of developmental maturation, affecting multiple organs ( 105 , 107 ). Similarly, other factors seem to be involved in the developmental maturation, which define the vulnerability to long-term air pollution. These include birthweight, maternal smoking, genetic background and socioeconomic environment, as well as education level.

However, diet, starting from breast-feeding, is another determinant factor. Diet is the main source of antioxidants, which play a key role in our protection against air pollutants ( 108 ). Antioxidants are free radical scavengers and limit the interaction of free radicals in the brain ( 108 ). Similarly, genetic background may result in a differential susceptibility toward the oxidative stress pathway ( 60 ). For example, antioxidant supplementation with vitamins C and E appears to modulate the effect of ozone in asthmatic children homozygous for the GSTM1 null allele ( 61 ). Inflammatory cytokines released in the periphery (e.g., respiratory epithelia) upregulate the innate immune Toll-like receptor 2. Such activation and the subsequent events leading to neurodegeneration have recently been observed in lung lavage in mice exposed to ambient Los Angeles (CA, USA) particulate matter ( 61 ). In children, neurodevelopmental morbidities were observed after lead exposure. These children developed aggressive and delinquent behavior, reduced intelligence, learning difficulties, and hyperactivity ( 109 ). No level of lead exposure seems to be “safe,” and the scientific community has asked the Centers for Disease Control and Prevention (CDC) to reduce the current screening guideline of 10 μg/dl ( 109 ).

It is important to state that impact on the immune system, causing dysfunction and neuroinflammation ( 104 ), is related to poor air quality. Yet, increases in serum levels of immunoglobulins (IgA, IgM) and the complement component C3 are observed ( 106 ). Another issue is that antigen presentation is affected by air pollutants, as there is an upregulation of costimulatory molecules such as CD80 and CD86 on macrophages ( 110 ).

As is known, skin is our shield against ultraviolet radiation (UVR) and other pollutants, as it is the most exterior layer of our body. Traffic-related pollutants, such as PAHs, VOCs, oxides, and PM, may cause pigmented spots on our skin ( 111 ). On the one hand, as already stated, when pollutants penetrate through the skin or are inhaled, damage to the organs is observed, as some of these pollutants are mutagenic and carcinogenic, and, specifically, they affect the liver and lung. On the other hand, air pollutants (and those in the troposphere) reduce the adverse effects of ultraviolet radiation UVR in polluted urban areas ( 111 ). Air pollutants absorbed by the human skin may contribute to skin aging, psoriasis, acne, urticaria, eczema, and atopic dermatitis ( 111 ), usually caused by exposure to oxides and photochemical smoke ( 111 ). Exposure to PM and cigarette smoking act as skin-aging agents, causing spots, dyschromia, and wrinkles. Lastly, pollutants have been associated with skin cancer ( 111 ).

Higher morbidity is reported to fetuses and children when exposed to the above dangers. Impairment in fetal growth, low birth weight, and autism have been reported ( 112 ).

Another exterior organ that may be affected is the eye. Contamination usually comes from suspended pollutants and may result in asymptomatic eye outcomes, irritation ( 112 ), retinopathy, or dry eye syndrome ( 113 , 114 ).

Environmental Impact of Air Pollution

Air pollution is harming not only human health but also the environment ( 115 ) in which we live. The most important environmental effects are as follows.

Acid rain is wet (rain, fog, snow) or dry (particulates and gas) precipitation containing toxic amounts of nitric and sulfuric acids. They are able to acidify the water and soil environments, damage trees and plantations, and even damage buildings and outdoor sculptures, constructions, and statues.

Haze is produced when fine particles are dispersed in the air and reduce the transparency of the atmosphere. It is caused by gas emissions in the air coming from industrial facilities, power plants, automobiles, and trucks.

Ozone , as discussed previously, occurs both at ground level and in the upper level (stratosphere) of the Earth's atmosphere. Stratospheric ozone is protecting us from the Sun's harmful ultraviolet (UV) rays. In contrast, ground-level ozone is harmful to human health and is a pollutant. Unfortunately, stratospheric ozone is gradually damaged by ozone-depleting substances (i.e., chemicals, pesticides, and aerosols). If this protecting stratospheric ozone layer is thinned, then UV radiation can reach our Earth, with harmful effects for human life (skin cancer) ( 116 ) and crops ( 117 ). In plants, ozone penetrates through the stomata, inducing them to close, which blocks CO 2 transfer and induces a reduction in photosynthesis ( 118 ).

Global climate change is an important issue that concerns mankind. As is known, the “greenhouse effect” keeps the Earth's temperature stable. Unhappily, anthropogenic activities have destroyed this protecting temperature effect by producing large amounts of greenhouse gases, and global warming is mounting, with harmful effects on human health, animals, forests, wildlife, agriculture, and the water environment. A report states that global warming is adding to the health risks of poor people ( 119 ).

People living in poorly constructed buildings in warm-climate countries are at high risk for heat-related health problems as temperatures mount ( 119 ).

Wildlife is burdened by toxic pollutants coming from the air, soil, or the water ecosystem and, in this way, animals can develop health problems when exposed to high levels of pollutants. Reproductive failure and birth effects have been reported.

Eutrophication is occurring when elevated concentrations of nutrients (especially nitrogen) stimulate the blooming of aquatic algae, which can cause a disequilibration in the diversity of fish and their deaths.

Without a doubt, there is a critical concentration of pollution that an ecosystem can tolerate without being destroyed, which is associated with the ecosystem's capacity to neutralize acidity. The Canada Acid Rain Program established this load at 20 kg/ha/yr ( 120 ).

Hence, air pollution has deleterious effects on both soil and water ( 121 ). Concerning PM as an air pollutant, its impact on crop yield and food productivity has been reported. Its impact on watery bodies is associated with the survival of living organisms and fishes and their productivity potential ( 121 ).

An impairment in photosynthetic rhythm and metabolism is observed in plants exposed to the effects of ozone ( 121 ).

Sulfur and nitrogen oxides are involved in the formation of acid rain and are harmful to plants and marine organisms.

Last but not least, as mentioned above, the toxicity associated with lead and other metals is the main threat to our ecosystems (air, water, and soil) and living creatures ( 121 ).

In 2018, during the first WHO Global Conference on Air Pollution and Health, the WHO's General Director, Dr. Tedros Adhanom Ghebreyesus, called air pollution a “silent public health emergency” and “the new tobacco” ( 122 ).

Undoubtedly, children are particularly vulnerable to air pollution, especially during their development. Air pollution has adverse effects on our lives in many different respects.

Diseases associated with air pollution have not only an important economic impact but also a societal impact due to absences from productive work and school.

Despite the difficulty of eradicating the problem of anthropogenic environmental pollution, a successful solution could be envisaged as a tight collaboration of authorities, bodies, and doctors to regularize the situation. Governments should spread sufficient information and educate people and should involve professionals in these issues so as to control the emergence of the problem successfully.

Technologies to reduce air pollution at the source must be established and should be used in all industries and power plants. The Kyoto Protocol of 1997 set as a major target the reduction of GHG emissions to below 5% by 2012 ( 123 ). This was followed by the Copenhagen summit, 2009 ( 124 ), and then the Durban summit of 2011 ( 125 ), where it was decided to keep to the same line of action. The Kyoto protocol and the subsequent ones were ratified by many countries. Among the pioneers who adopted this important protocol for the world's environmental and climate “health” was China ( 3 ). As is known, China is a fast-developing economy and its GDP (Gross Domestic Product) is expected to be very high by 2050, which is defined as the year of dissolution of the protocol for the decrease in gas emissions.

A more recent international agreement of crucial importance for climate change is the Paris Agreement of 2015, issued by the UNFCCC (United Nations Climate Change Committee). This latest agreement was ratified by a plethora of UN (United Nations) countries as well as the countries of the European Union ( 126 ). In this vein, parties should promote actions and measures to enhance numerous aspects around the subject. Boosting education, training, public awareness, and public participation are some of the relevant actions for maximizing the opportunities to achieve the targets and goals on the crucial matter of climate change and environmental pollution ( 126 ). Without any doubt, technological improvements makes our world easier and it seems difficult to reduce the harmful impact caused by gas emissions, we could limit its use by seeking reliable approaches.

Synopsizing, a global prevention policy should be designed in order to combat anthropogenic air pollution as a complement to the correct handling of the adverse health effects associated with air pollution. Sustainable development practices should be applied, together with information coming from research in order to handle the problem effectively.

At this point, international cooperation in terms of research, development, administration policy, monitoring, and politics is vital for effective pollution control. Legislation concerning air pollution must be aligned and updated, and policy makers should propose the design of a powerful tool of environmental and health protection. As a result, the main proposal of this essay is that we should focus on fostering local structures to promote experience and practice and extrapolate these to the international level through developing effective policies for sustainable management of ecosystems.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest

IM is employed by the company Delphis S.A. The remaining authors declare that the present review paper was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Lisa Hupp/USFWS

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Air Pollution: Everything You Need to Know

How smog, soot, greenhouse gases, and other top air pollutants are affecting the planet—and your health.

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What is air pollution?

What causes air pollution, effects of air pollution, air pollution in the united states, air pollution and environmental justice, controlling air pollution, how to help reduce air pollution, how to protect your health.

Air pollution  refers to the release of pollutants into the air—pollutants that are detrimental to human health and the planet as a whole. According to the  World Health Organization (WHO) , each year, indoor and outdoor air pollution is responsible for nearly seven million deaths around the globe. Ninety-nine percent of human beings currently breathe air that exceeds the WHO’s guideline limits for pollutants, with those living in low- and middle-income countries suffering the most. In the United States, the  Clean Air Act , established in 1970, authorizes the U.S. Environmental Protection Agency (EPA) to safeguard public health by regulating the emissions of these harmful air pollutants.

“Most air pollution comes from energy use and production,” says  John Walke , director of the Clean Air team at NRDC. Driving a car on gasoline, heating a home with oil, running a power plant on  fracked gas : In each case, a fossil fuel is burned and harmful chemicals and gases are released into the air.

“We’ve made progress over the last 50 years in improving air quality in the United States, thanks to the Clean Air Act. But climate change will make it harder in the future to meet pollution standards, which are designed to  protect health ,” says Walke.

Air pollution is now the world’s fourth-largest risk factor for early death. According to the 2020  State of Global Air  report —which summarizes the latest scientific understanding of air pollution around the world—4.5 million deaths were linked to outdoor air pollution exposures in 2019, and another 2.2 million deaths were caused by indoor air pollution. The world’s most populous countries, China and India, continue to bear the highest burdens of disease.

“Despite improvements in reducing global average mortality rates from air pollution, this report also serves as a sobering reminder that the climate crisis threatens to worsen air pollution problems significantly,” explains  Vijay Limaye , senior scientist in NRDC’s Science Office. Smog, for instance, is intensified by increased heat, forming when the weather is warmer and there’s more ultraviolet radiation. In addition, climate change increases the production of allergenic air pollutants, including mold (thanks to damp conditions caused by extreme weather and increased flooding) and pollen (due to a longer pollen season). “Climate change–fueled droughts and dry conditions are also setting the stage for dangerous wildfires,” adds Limaye. “ Wildfire smoke can linger for days and pollute the air with particulate matter hundreds of miles downwind.”

The effects of air pollution on the human body vary, depending on the type of pollutant, the length and level of exposure, and other factors, including a person’s individual health risks and the cumulative impacts of multiple pollutants or stressors.

Smog and soot

These are the two most prevalent types of air pollution. Smog (sometimes referred to as ground-level ozone) occurs when emissions from combusting fossil fuels react with sunlight. Soot—a type of  particulate matter —is made up of tiny particles of chemicals, soil, smoke, dust, or allergens that are carried in the air. The sources of smog and soot are similar. “Both come from cars and trucks, factories, power plants, incinerators, engines, generally anything that combusts fossil fuels such as coal, gasoline, or natural gas,” Walke says.

Smog can irritate the eyes and throat and also damage the lungs, especially those of children, senior citizens, and people who work or exercise outdoors. It’s even worse for people who have asthma or allergies; these extra pollutants can intensify their symptoms and trigger asthma attacks. The tiniest airborne particles in soot are especially dangerous because they can penetrate the lungs and bloodstream and worsen bronchitis, lead to heart attacks, and even hasten death. In  2020, a report from Harvard’s T.H. Chan School of Public Health showed that COVID-19 mortality rates were higher in areas with more particulate matter pollution than in areas with even slightly less, showing a correlation between the virus’s deadliness and long-term exposure to air pollution. 

These findings also illuminate an important  environmental justice issue . Because highways and polluting facilities have historically been sited in or next to low-income neighborhoods and communities of color, the negative effects of this pollution have been  disproportionately experienced by the people who live in these communities.

Hazardous air pollutants

A number of air pollutants pose severe health risks and can sometimes be fatal, even in small amounts. Almost 200 of them are regulated by law; some of the most common are mercury,  lead , dioxins, and benzene. “These are also most often emitted during gas or coal combustion, incineration, or—in the case of benzene—found in gasoline,” Walke says. Benzene, classified as a carcinogen by the EPA, can cause eye, skin, and lung irritation in the short term and blood disorders in the long term. Dioxins, more typically found in food but also present in small amounts in the air, is another carcinogen that can affect the liver in the short term and harm the immune, nervous, and endocrine systems, as well as reproductive functions.  Mercury  attacks the central nervous system. In large amounts, lead can damage children’s brains and kidneys, and even minimal exposure can affect children’s IQ and ability to learn.

Another category of toxic compounds, polycyclic aromatic hydrocarbons (PAHs), are by-products of traffic exhaust and wildfire smoke. In large amounts, they have been linked to eye and lung irritation, blood and liver issues, and even cancer.  In one study , the children of mothers exposed to PAHs during pregnancy showed slower brain-processing speeds and more pronounced symptoms of ADHD.

Greenhouse gases

While these climate pollutants don’t have the direct or immediate impacts on the human body associated with other air pollutants, like smog or hazardous chemicals, they are still harmful to our health. By trapping the earth’s heat in the atmosphere, greenhouse gases lead to warmer temperatures, which in turn lead to the hallmarks of climate change: rising sea levels, more extreme weather, heat-related deaths, and the increased transmission of infectious diseases. In 2021, carbon dioxide accounted for roughly 79 percent of the country’s total greenhouse gas emissions, and methane made up more than 11 percent. “Carbon dioxide comes from combusting fossil fuels, and methane comes from natural and industrial sources, including large amounts that are released during oil and gas drilling,” Walke says. “We emit far larger amounts of carbon dioxide, but methane is significantly more potent, so it’s also very destructive.” 

Another class of greenhouse gases,  hydrofluorocarbons (HFCs) , are thousands of times more powerful than carbon dioxide in their ability to trap heat. In October 2016, more than 140 countries signed the Kigali Agreement to reduce the use of these chemicals—which are found in air conditioners and refrigerators—and develop greener alternatives over time. (The United States officially signed onto the  Kigali Agreement in 2022.)

Pollen and mold

Mold and allergens from trees, weeds, and grass are also carried in the air, are exacerbated by climate change, and can be hazardous to health. Though they aren’t regulated, they can be considered a form of air pollution. “When homes, schools, or businesses get water damage, mold can grow and produce allergenic airborne pollutants,” says Kim Knowlton, professor of environmental health sciences at Columbia University and a former NRDC scientist. “ Mold exposure can precipitate asthma attacks  or an allergic response, and some molds can even produce toxins that would be dangerous for anyone to inhale.”

Pollen allergies are worsening  because of climate change . “Lab and field studies are showing that pollen-producing plants—especially ragweed—grow larger and produce more pollen when you increase the amount of carbon dioxide that they grow in,” Knowlton says. “Climate change also extends the pollen production season, and some studies are beginning to suggest that ragweed pollen itself might be becoming a more potent allergen.” If so, more people will suffer runny noses, fevers, itchy eyes, and other symptoms. “And for people with allergies and asthma, pollen peaks can precipitate asthma attacks, which are far more serious and can be life-threatening.”

More than one in three U.S. residents—120 million people—live in counties with unhealthy levels of air pollution, according to the  2023  State of the Air  report by the American Lung Association (ALA). Since the annual report was first published, in 2000, its findings have shown how the Clean Air Act has been able to reduce harmful emissions from transportation, power plants, and manufacturing.

Recent findings, however, reflect how climate change–fueled wildfires and extreme heat are adding to the challenges of protecting public health. The latest report—which focuses on ozone, year-round particle pollution, and short-term particle pollution—also finds that people of color are 61 percent more likely than white people to live in a county with a failing grade in at least one of those categories, and three times more likely to live in a county that fails in all three.

In rankings for each of the three pollution categories covered by the ALA report, California cities occupy the top three slots (i.e., were highest in pollution), despite progress that the Golden State has made in reducing air pollution emissions in the past half century. At the other end of the spectrum, these cities consistently rank among the country’s best for air quality: Burlington, Vermont; Honolulu; and Wilmington, North Carolina. 

No one wants to live next door to an incinerator, oil refinery, port, toxic waste dump, or other polluting site. Yet millions of people around the world do, and this puts them at a much higher risk for respiratory disease, cardiovascular disease, neurological damage, cancer, and death. In the United States, people of color are 1.5 times more likely than whites to live in areas with poor air quality, according to the ALA.

Historically, racist zoning policies and discriminatory lending practices known as  redlining  have combined to keep polluting industries and car-choked highways away from white neighborhoods and have turned communities of color—especially low-income and working-class communities of color—into sacrifice zones, where residents are forced to breathe dirty air and suffer the many health problems associated with it. In addition to the increased health risks that come from living in such places, the polluted air can economically harm residents in the form of missed workdays and higher medical costs.

Environmental racism isn't limited to cities and industrial areas. Outdoor laborers, including the estimated three million migrant and seasonal farmworkers in the United States, are among the most vulnerable to air pollution—and they’re also among the least equipped, politically, to pressure employers and lawmakers to affirm their right to breathe clean air.

Recently,  cumulative impact mapping , which uses data on environmental conditions and demographics, has been able to show how some communities are overburdened with layers of issues, like high levels of poverty, unemployment, and pollution. Tools like the  Environmental Justice Screening Method  and the EPA’s  EJScreen  provide evidence of what many environmental justice communities have been explaining for decades: that we need land use and public health reforms to ensure that vulnerable areas are not overburdened and that the people who need resources the most are receiving them.

In the United States, the  Clean Air Act  has been a crucial tool for reducing air pollution since its passage in 1970, although fossil fuel interests aided by industry-friendly lawmakers have frequently attempted to  weaken its many protections. Ensuring that this bedrock environmental law remains intact and properly enforced will always be key to maintaining and improving our air quality.

But the best, most effective way to control air pollution is to speed up our transition to cleaner fuels and industrial processes. By switching over to renewable energy sources (such as wind and solar power), maximizing fuel efficiency in our vehicles, and replacing more and more of our gasoline-powered cars and trucks with electric versions, we'll be limiting air pollution at its source while also curbing the global warming that heightens so many of its worst health impacts.

And what about the economic costs of controlling air pollution? According to a report on the Clean Air Act commissioned by NRDC, the annual  benefits of cleaner air  are up to 32 times greater than the cost of clean air regulations. Those benefits include up to 370,000 avoided premature deaths, 189,000 fewer hospital admissions for cardiac and respiratory illnesses, and net economic benefits of up to $3.8 trillion for the U.S. economy every year.

“The less gasoline we burn, the better we’re doing to reduce air pollution and the harmful effects of climate change,” Walke explains. “Make good choices about transportation. When you can, ride a bike, walk, or take public transportation. For driving, choose a car that gets better miles per gallon of gas or  buy an electric car .” You can also investigate your power provider options—you may be able to request that your electricity be supplied by wind or solar. Buying your food locally cuts down on the fossil fuels burned in trucking or flying food in from across the world. And most important: “Support leaders who push for clean air and water and responsible steps on climate change,” Walke says.

• “When you see in the news or hear on the weather report that pollution levels are high, it may be useful to limit the time when children go outside or you go for a jog,” Walke says. Generally, ozone levels tend to be lower in the morning.
• If you exercise outside, stay as far as you can from heavily trafficked roads. Then shower and wash your clothes to remove fine particles.
• The air may look clear, but that doesn’t mean it’s pollution free. Utilize tools like the EPA’s air pollution monitor,  AirNow , to get the latest conditions. If the air quality is bad, stay inside with the windows closed.
• If you live or work in an area that’s prone to wildfires,  stay away from the harmful smoke  as much as you’re able. Consider keeping a small stock of masks to wear when conditions are poor. The most ideal masks for smoke particles will be labelled “NIOSH” (which stands for National Institute for Occupational Safety and Health) and have either “N95” or “P100” printed on it.
• If you’re using an air conditioner while outdoor pollution conditions are bad, use the recirculating setting to limit the amount of polluted air that gets inside. 

This story was originally published on November 1, 2016, and has been updated with new information and links.

This NRDC.org story is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the story was originally published by NRDC.org and link to the original; the story cannot be edited (beyond simple things such as grammar); you can’t resell the story in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select stories individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our stories.

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REVIEW article

Environmental and health impacts of air pollution: a review.

• 1 Delphis S.A., Kifisia, Greece
• 2 Laboratory of Hygiene and Environmental Protection, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece
• 3 Centre Hospitalier Universitaire Vaudois (CHUV), Service de Médicine Interne, Lausanne, Switzerland
• 4 School of Social and Political Sciences, University of Glasgow, Glasgow, United Kingdom

One of our era's greatest scourges is air pollution, on account not only of its impact on climate change but also its impact on public and individual health due to increasing morbidity and mortality. There are many pollutants that are major factors in disease in humans. Among them, Particulate Matter (PM), particles of variable but very small diameter, penetrate the respiratory system via inhalation, causing respiratory and cardiovascular diseases, reproductive and central nervous system dysfunctions, and cancer. Despite the fact that ozone in the stratosphere plays a protective role against ultraviolet irradiation, it is harmful when in high concentration at ground level, also affecting the respiratory and cardiovascular system. Furthermore, nitrogen oxide, sulfur dioxide, Volatile Organic Compounds (VOCs), dioxins, and polycyclic aromatic hydrocarbons (PAHs) are all considered air pollutants that are harmful to humans. Carbon monoxide can even provoke direct poisoning when breathed in at high levels. Heavy metals such as lead, when absorbed into the human body, can lead to direct poisoning or chronic intoxication, depending on exposure. Diseases occurring from the aforementioned substances include principally respiratory problems such as Chronic Obstructive Pulmonary Disease (COPD), asthma, bronchiolitis, and also lung cancer, cardiovascular events, central nervous system dysfunctions, and cutaneous diseases. Last but not least, climate change resulting from environmental pollution affects the geographical distribution of many infectious diseases, as do natural disasters. The only way to tackle this problem is through public awareness coupled with a multidisciplinary approach by scientific experts; national and international organizations must address the emergence of this threat and propose sustainable solutions.

Approach to the Problem

The interactions between humans and their physical surroundings have been extensively studied, as multiple human activities influence the environment. The environment is a coupling of the biotic (living organisms and microorganisms) and the abiotic (hydrosphere, lithosphere, and atmosphere).

Pollution is defined as the introduction into the environment of substances harmful to humans and other living organisms. Pollutants are harmful solids, liquids, or gases produced in higher than usual concentrations that reduce the quality of our environment.

Human activities have an adverse effect on the environment by polluting the water we drink, the air we breathe, and the soil in which plants grow. Although the industrial revolution was a great success in terms of technology, society, and the provision of multiple services, it also introduced the production of huge quantities of pollutants emitted into the air that are harmful to human health. Without any doubt, the global environmental pollution is considered an international public health issue with multiple facets. Social, economic, and legislative concerns and lifestyle habits are related to this major problem. Clearly, urbanization and industrialization are reaching unprecedented and upsetting proportions worldwide in our era. Anthropogenic air pollution is one of the biggest public health hazards worldwide, given that it accounts for about 9 million deaths per year ( 1 ).

Without a doubt, all of the aforementioned are closely associated with climate change, and in the event of danger, the consequences can be severe for mankind ( 2 ). Climate changes and the effects of global planetary warming seriously affect multiple ecosystems, causing problems such as food safety issues, ice and iceberg melting, animal extinction, and damage to plants ( 3 , 4 ).

Air pollution has various health effects. The health of susceptible and sensitive individuals can be impacted even on low air pollution days. Short-term exposure to air pollutants is closely related to COPD (Chronic Obstructive Pulmonary Disease), cough, shortness of breath, wheezing, asthma, respiratory disease, and high rates of hospitalization (a measurement of morbidity).

The long-term effects associated with air pollution are chronic asthma, pulmonary insufficiency, cardiovascular diseases, and cardiovascular mortality. According to a Swedish cohort study, diabetes seems to be induced after long-term air pollution exposure ( 5 ). Moreover, air pollution seems to have various malign health effects in early human life, such as respiratory, cardiovascular, mental, and perinatal disorders ( 3 ), leading to infant mortality or chronic disease in adult age ( 6 ).

National reports have mentioned the increased risk of morbidity and mortality ( 1 ). These studies were conducted in many places around the world and show a correlation between daily ranges of particulate matter (PM) concentration and daily mortality. Climate shifts and global planetary warming ( 3 ) could aggravate the situation. Besides, increased hospitalization (an index of morbidity) has been registered among the elderly and susceptible individuals for specific reasons. Fine and ultrafine particulate matter seems to be associated with more serious illnesses ( 6 ), as it can invade the deepest parts of the airways and more easily reach the bloodstream.

Air pollution mainly affects those living in large urban areas, where road emissions contribute the most to the degradation of air quality. There is also a danger of industrial accidents, where the spread of a toxic fog can be fatal to the populations of the surrounding areas. The dispersion of pollutants is determined by many parameters, most notably atmospheric stability and wind ( 6 ).

In developing countries ( 7 ), the problem is more serious due to overpopulation and uncontrolled urbanization along with the development of industrialization. This leads to poor air quality, especially in countries with social disparities and a lack of information on sustainable management of the environment. The use of fuels such as wood fuel or solid fuel for domestic needs due to low incomes exposes people to bad-quality, polluted air at home. It is of note that three billion people around the world are using the above sources of energy for their daily heating and cooking needs ( 8 ). In developing countries, the women of the household seem to carry the highest risk for disease development due to their longer duration exposure to the indoor air pollution ( 8 , 9 ). Due to its fast industrial development and overpopulation, China is one of the Asian countries confronting serious air pollution problems ( 10 , 11 ). The lung cancer mortality observed in China is associated with fine particles ( 12 ). As stated already, long-term exposure is associated with deleterious effects on the cardiovascular system ( 3 , 5 ). However, it is interesting to note that cardiovascular diseases have mostly been observed in developed and high-income countries rather than in the developing low-income countries exposed highly to air pollution ( 13 ). Extreme air pollution is recorded in India, where the air quality reaches hazardous levels. New Delhi is one of the more polluted cities in India. Flights in and out of New Delhi International Airport are often canceled due to the reduced visibility associated with air pollution. Pollution is occurring both in urban and rural areas in India due to the fast industrialization, urbanization, and rise in use of motorcycle transportation. Nevertheless, biomass combustion associated with heating and cooking needs and practices is a major source of household air pollution in India and in Nepal ( 14 , 15 ). There is spatial heterogeneity in India, as areas with diverse climatological conditions and population and education levels generate different indoor air qualities, with higher PM 2.5 observed in North Indian states (557–601 μg/m 3 ) compared to the Southern States (183–214 μg/m 3 ) ( 16 , 17 ). The cold climate of the North Indian areas may be the main reason for this, as longer periods at home and more heating are necessary compared to in the tropical climate of Southern India. Household air pollution in India is associated with major health effects, especially in women and young children, who stay indoors for longer periods. Chronic obstructive respiratory disease (CORD) and lung cancer are mostly observed in women, while acute lower respiratory disease is seen in young children under 5 years of age ( 18 ).

Accumulation of air pollution, especially sulfur dioxide and smoke, reaching 1,500 mg/m3, resulted in an increase in the number of deaths (4,000 deaths) in December 1952 in London and in 1963 in New York City (400 deaths) ( 19 ). An association of pollution with mortality was reported on the basis of monitoring of outdoor pollution in six US metropolitan cities ( 20 ). In every case, it seems that mortality was closely related to the levels of fine, inhalable, and sulfate particles more than with the levels of total particulate pollution, aerosol acidity, sulfur dioxide, or nitrogen dioxide ( 20 ).

Furthermore, extremely high levels of pollution are reported in Mexico City and Rio de Janeiro, followed by Milan, Ankara, Melbourne, Tokyo, and Moscow ( 19 ).

Based on the magnitude of the public health impact, it is certain that different kinds of interventions should be taken into account. Success and effectiveness in controlling air pollution, specifically at the local level, have been reported. Adequate technological means are applied considering the source and the nature of the emission as well as its impact on health and the environment. The importance of point sources and non-point sources of air pollution control is reported by Schwela and Köth-Jahr ( 21 ). Without a doubt, a detailed emission inventory must record all sources in a given area. Beyond considering the above sources and their nature, topography and meteorology should also be considered, as stated previously. Assessment of the control policies and methods is often extrapolated from the local to the regional and then to the global scale. Air pollution may be dispersed and transported from one region to another area located far away. Air pollution management means the reduction to acceptable levels or possible elimination of air pollutants whose presence in the air affects our health or the environmental ecosystem. Private and governmental entities and authorities implement actions to ensure the air quality ( 22 ). Air quality standards and guidelines were adopted for the different pollutants by the WHO and EPA as a tool for the management of air quality ( 1 , 23 ). These standards have to be compared to the emissions inventory standards by causal analysis and dispersion modeling in order to reveal the problematic areas ( 24 ). Inventories are generally based on a combination of direct measurements and emissions modeling ( 24 ).

As an example, we state here the control measures at the source through the use of catalytic converters in cars. These are devices that turn the pollutants and toxic gases produced from combustion engines into less-toxic pollutants by catalysis through redox reactions ( 25 ). In Greece, the use of private cars was restricted by tracking their license plates in order to reduce traffic congestion during rush hour ( 25 ).

Concerning industrial emissions, collectors and closed systems can keep the air pollution to the minimal standards imposed by legislation ( 26 ).

Current strategies to improve air quality require an estimation of the economic value of the benefits gained from proposed programs. These proposed programs by public authorities, and directives are issued with guidelines to be respected.

In Europe, air quality limit values AQLVs (Air Quality Limit Values) are issued for setting off planning claims ( 27 ). In the USA, the NAAQS (National Ambient Air Quality Standards) establish the national air quality limit values ( 27 ). While both standards and directives are based on different mechanisms, significant success has been achieved in the reduction of overall emissions and associated health and environmental effects ( 27 ). The European Directive identifies geographical areas of risk exposure as monitoring/assessment zones to record the emission sources and levels of air pollution ( 27 ), whereas the USA establishes global geographical air quality criteria according to the severity of their air quality problem and records all sources of the pollutants and their precursors ( 27 ).

In this vein, funds have been financing, directly or indirectly, projects related to air quality along with the technical infrastructure to maintain good air quality. These plans focus on an inventory of databases from air quality environmental planning awareness campaigns. Moreover, pollution measures of air emissions may be taken for vehicles, machines, and industries in urban areas.

Technological innovation can only be successful if it is able to meet the needs of society. In this sense, technology must reflect the decision-making practices and procedures of those involved in risk assessment and evaluation and act as a facilitator in providing information and assessments to enable decision makers to make the best decisions possible. Summarizing the aforementioned in order to design an effective air quality control strategy, several aspects must be considered: environmental factors and ambient air quality conditions, engineering factors and air pollutant characteristics, and finally, economic operating costs for technological improvement and administrative and legal costs. Considering the economic factor, competitiveness through neoliberal concepts is offering a solution to environmental problems ( 22 ).

The development of environmental governance, along with technological progress, has initiated the deployment of a dialogue. Environmental politics has created objections and points of opposition between different political parties, scientists, media, and governmental and non-governmental organizations ( 22 ). Radical environmental activism actions and movements have been created ( 22 ). The rise of the new information and communication technologies (ICTs) are many times examined as to whether and in which way they have influenced means of communication and social movements such as activism ( 28 ). Since the 1990s, the term “digital activism” has been used increasingly and in many different disciplines ( 29 ). Nowadays, multiple digital technologies can be used to produce a digital activism outcome on environmental issues. More specifically, devices with online capabilities such as computers or mobile phones are being used as a way to pursue change in political and social affairs ( 30 ).

In the present paper, we focus on the sources of environmental pollution in relation to public health and propose some solutions and interventions that may be of interest to environmental legislators and decision makers.

Sources of Exposure

It is known that the majority of environmental pollutants are emitted through large-scale human activities such as the use of industrial machinery, power-producing stations, combustion engines, and cars. Because these activities are performed at such a large scale, they are by far the major contributors to air pollution, with cars estimated to be responsible for approximately 80% of today's pollution ( 31 ). Some other human activities are also influencing our environment to a lesser extent, such as field cultivation techniques, gas stations, fuel tanks heaters, and cleaning procedures ( 32 ), as well as several natural sources, such as volcanic and soil eruptions and forest fires.

The classification of air pollutants is based mainly on the sources producing pollution. Therefore, it is worth mentioning the four main sources, following the classification system: Major sources, Area sources, Mobile sources, and Natural sources.

Major sources include the emission of pollutants from power stations, refineries, and petrochemicals, the chemical and fertilizer industries, metallurgical and other industrial plants, and, finally, municipal incineration.

Indoor area sources include domestic cleaning activities, dry cleaners, printing shops, and petrol stations.

Mobile sources include automobiles, cars, railways, airways, and other types of vehicles.

Finally, natural sources include, as stated previously, physical disasters ( 33 ) such as forest fire, volcanic erosion, dust storms, and agricultural burning.

However, many classification systems have been proposed. Another type of classification is a grouping according to the recipient of the pollution, as follows:

Air pollution is determined as the presence of pollutants in the air in large quantities for long periods. Air pollutants are dispersed particles, hydrocarbons, CO, CO 2 , NO, NO 2 , SO 3 , etc.

Water pollution is organic and inorganic charge and biological charge ( 10 ) at high levels that affect the water quality ( 34 , 35 ).

Soil pollution occurs through the release of chemicals or the disposal of wastes, such as heavy metals, hydrocarbons, and pesticides.

Air pollution can influence the quality of soil and water bodies by polluting precipitation, falling into water and soil environments ( 34 , 36 ). Notably, the chemistry of the soil can be amended due to acid precipitation by affecting plants, cultures, and water quality ( 37 ). Moreover, movement of heavy metals is favored by soil acidity, and metals are so then moving into the watery environment. It is known that heavy metals such as aluminum are noxious to wildlife and fishes. Soil quality seems to be of importance, as soils with low calcium carbonate levels are at increased jeopardy from acid rain. Over and above rain, snow and particulate matter drip into watery ' bodies ( 36 , 38 ).

Lastly, pollution is classified following type of origin:

Radioactive and nuclear pollution , releasing radioactive and nuclear pollutants into water, air, and soil during nuclear explosions and accidents, from nuclear weapons, and through handling or disposal of radioactive sewage.

Radioactive materials can contaminate surface water bodies and, being noxious to the environment, plants, animals, and humans. It is known that several radioactive substances such as radium and uranium concentrate in the bones and can cause cancers ( 38 , 39 ).

Noise pollution is produced by machines, vehicles, traffic noises, and musical installations that are harmful to our hearing.

The World Health Organization introduced the term DALYs. The DALYs for a disease or health condition is defined as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition or its consequences ( 39 ). In Europe, air pollution is the main cause of disability-adjusted life years lost (DALYs), followed by noise pollution. The potential relationships of noise and air pollution with health have been studied ( 40 ). The study found that DALYs related to noise were more important than those related to air pollution, as the effects of environmental noise on cardiovascular disease were independent of air pollution ( 40 ). Environmental noise should be counted as an independent public health risk ( 40 ).

Environmental pollution occurs when changes in the physical, chemical, or biological constituents of the environment (air masses, temperature, climate, etc.) are produced.

Pollutants harm our environment either by increasing levels above normal or by introducing harmful toxic substances. Primary pollutants are directly produced from the above sources, and secondary pollutants are emitted as by-products of the primary ones. Pollutants can be biodegradable or non-biodegradable and of natural origin or anthropogenic, as stated previously. Moreover, their origin can be a unique source (point-source) or dispersed sources.

Pollutants have differences in physical and chemical properties, explaining the discrepancy in their capacity for producing toxic effects. As an example, we state here that aerosol compounds ( 41 – 43 ) have a greater toxicity than gaseous compounds due to their tiny size (solid or liquid) in the atmosphere; they have a greater penetration capacity. Gaseous compounds are eliminated more easily by our respiratory system ( 41 ). These particles are able to damage lungs and can even enter the bloodstream ( 41 ), leading to the premature deaths of millions of people yearly. Moreover, the aerosol acidity ([H+]) seems to considerably enhance the production of secondary organic aerosols (SOA), but this last aspect is not supported by other scientific teams ( 38 ).

Climate and Pollution

Air pollution and climate change are closely related. Climate is the other side of the same coin that reduces the quality of our Earth ( 44 ). Pollutants such as black carbon, methane, tropospheric ozone, and aerosols affect the amount of incoming sunlight. As a result, the temperature of the Earth is increasing, resulting in the melting of ice, icebergs, and glaciers.

In this vein, climatic changes will affect the incidence and prevalence of both residual and imported infections in Europe. Climate and weather affect the duration, timing, and intensity of outbreaks strongly and change the map of infectious diseases in the globe ( 45 ). Mosquito-transmitted parasitic or viral diseases are extremely climate-sensitive, as warming firstly shortens the pathogen incubation period and secondly shifts the geographic map of the vector. Similarly, water-warming following climate changes leads to a high incidence of waterborne infections. Recently, in Europe, eradicated diseases seem to be emerging due to the migration of population, for example, cholera, poliomyelitis, tick-borne encephalitis, and malaria ( 46 ).

The spread of epidemics is associated with natural climate disasters and storms, which seem to occur more frequently nowadays ( 47 ). Malnutrition and disequilibration of the immune system are also associated with the emerging infections affecting public health ( 48 ).

The Chikungunya virus “took the airplane” from the Indian Ocean to Europe, as outbreaks of the disease were registered in Italy ( 49 ) as well as autochthonous cases in France ( 50 ).

An increase in cryptosporidiosis in the United Kingdom and in the Czech Republic seems to have occurred following flooding ( 36 , 51 ).

As stated previously, aerosols compounds are tiny in size and considerably affect the climate. They are able to dissipate sunlight (the albedo phenomenon) by dispersing a quarter of the sun's rays back to space and have cooled the global temperature over the last 30 years ( 52 ).

Air Pollutants

The World Health Organization (WHO) reports on six major air pollutants, namely particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Air pollution can have a disastrous effect on all components of the environment, including groundwater, soil, and air. Additionally, it poses a serious threat to living organisms. In this vein, our interest is mainly to focus on these pollutants, as they are related to more extensive and severe problems in human health and environmental impact. Acid rain, global warming, the greenhouse effect, and climate changes have an important ecological impact on air pollution ( 53 ).

Particulate Matter (PM) and Health

Studies have shown a relationship between particulate matter (PM) and adverse health effects, focusing on either short-term (acute) or long-term (chronic) PM exposure.

Particulate matter (PM) is usually formed in the atmosphere as a result of chemical reactions between the different pollutants. The penetration of particles is closely dependent on their size ( 53 ). Particulate Matter (PM) was defined as a term for particles by the United States Environmental Protection Agency ( 54 ). Particulate matter (PM) pollution includes particles with diameters of 10 micrometers (μm) or smaller, called PM 10 , and extremely fine particles with diameters that are generally 2.5 micrometers (μm) and smaller.

Particulate matter contains tiny liquid or solid droplets that can be inhaled and cause serious health effects ( 55 ). Particles <10 μm in diameter (PM 10 ) after inhalation can invade the lungs and even reach the bloodstream. Fine particles, PM 2.5 , pose a greater risk to health ( 6 , 56 ) ( Table 1 ).

Table 1 . Penetrability according to particle size.

Multiple epidemiological studies have been performed on the health effects of PM. A positive relation was shown between both short-term and long-term exposures of PM 2.5 and acute nasopharyngitis ( 56 ). In addition, long-term exposure to PM for years was found to be related to cardiovascular diseases and infant mortality.

Those studies depend on PM 2.5 monitors and are restricted in terms of study area or city area due to a lack of spatially resolved daily PM 2.5 concentration data and, in this way, are not representative of the entire population. Following a recent epidemiological study by the Department of Environmental Health at Harvard School of Public Health (Boston, MA) ( 57 ), it was reported that, as PM 2.5 concentrations vary spatially, an exposure error (Berkson error) seems to be produced, and the relative magnitudes of the short- and long-term effects are not yet completely elucidated. The team developed a PM 2.5 exposure model based on remote sensing data for assessing short- and long-term human exposures ( 57 ). This model permits spatial resolution in short-term effects plus the assessment of long-term effects in the whole population.

Moreover, respiratory diseases and affection of the immune system are registered as long-term chronic effects ( 58 ). It is worth noting that people with asthma, pneumonia, diabetes, and respiratory and cardiovascular diseases are especially susceptible and vulnerable to the effects of PM. PM 2.5 , followed by PM 10 , are strongly associated with diverse respiratory system diseases ( 59 ), as their size permits them to pierce interior spaces ( 60 ). The particles produce toxic effects according to their chemical and physical properties. The components of PM 10 and PM 2.5 can be organic (polycyclic aromatic hydrocarbons, dioxins, benzene, 1-3 butadiene) or inorganic (carbon, chlorides, nitrates, sulfates, metals) in nature ( 55 ).

Particulate Matter (PM) is divided into four main categories according to type and size ( 61 ) ( Table 2 ).

Table 2 . Types and sizes of particulate Matter (PM).

Gas contaminants include PM in aerial masses.

Particulate contaminants include contaminants such as smog, soot, tobacco smoke, oil smoke, fly ash, and cement dust.

Biological Contaminants are microorganisms (bacteria, viruses, fungi, mold, and bacterial spores), cat allergens, house dust and allergens, and pollen.

Types of Dust include suspended atmospheric dust, settling dust, and heavy dust.

Finally, another fact is that the half-lives of PM 10 and PM 2.5 particles in the atmosphere is extended due to their tiny dimensions; this permits their long-lasting suspension in the atmosphere and even their transfer and spread to distant destinations where people and the environment may be exposed to the same magnitude of pollution ( 53 ). They are able to change the nutrient balance in watery ecosystems, damage forests and crops, and acidify water bodies.

As stated, PM 2.5 , due to their tiny size, are causing more serious health effects. These aforementioned fine particles are the main cause of the “haze” formation in different metropolitan areas ( 12 , 13 , 61 ).

Ozone Impact in the Atmosphere

Ozone (O 3 ) is a gas formed from oxygen under high voltage electric discharge ( 62 ). It is a strong oxidant, 52% stronger than chlorine. It arises in the stratosphere, but it could also arise following chain reactions of photochemical smog in the troposphere ( 63 ).

Ozone can travel to distant areas from its initial source, moving with air masses ( 64 ). It is surprising that ozone levels over cities are low in contrast to the increased amounts occuring in urban areas, which could become harmful for cultures, forests, and vegetation ( 65 ) as it is reducing carbon assimilation ( 66 ). Ozone reduces growth and yield ( 47 , 48 ) and affects the plant microflora due to its antimicrobial capacity ( 67 , 68 ). In this regard, ozone acts upon other natural ecosystems, with microflora ( 69 , 70 ) and animal species changing their species composition ( 71 ). Ozone increases DNA damage in epidermal keratinocytes and leads to impaired cellular function ( 72 ).

Ground-level ozone (GLO) is generated through a chemical reaction between oxides of nitrogen and VOCs emitted from natural sources and/or following anthropogenic activities.

Ozone uptake usually occurs by inhalation. Ozone affects the upper layers of the skin and the tear ducts ( 73 ). A study of short-term exposure of mice to high levels of ozone showed malondialdehyde formation in the upper skin (epidermis) but also depletion in vitamins C and E. It is likely that ozone levels are not interfering with the skin barrier function and integrity to predispose to skin disease ( 74 ).

Due to the low water-solubility of ozone, inhaled ozone has the capacity to penetrate deeply into the lungs ( 75 ).

Toxic effects induced by ozone are registered in urban areas all over the world, causing biochemical, morphologic, functional, and immunological disorders ( 76 ).

The European project (APHEA2) focuses on the acute effects of ambient ozone concentrations on mortality ( 77 ). Daily ozone concentrations compared to the daily number of deaths were reported from different European cities for a 3-year period. During the warm period of the year, an observed increase in ozone concentration was associated with an increase in the daily number of deaths (0.33%), in the number of respiratory deaths (1.13%), and in the number of cardiovascular deaths (0.45%). No effect was observed during wintertime.

Carbon Monoxide (CO)

Carbon monoxide is produced by fossil fuel when combustion is incomplete. The symptoms of poisoning due to inhaling carbon monoxide include headache, dizziness, weakness, nausea, vomiting, and, finally, loss of consciousness.

The affinity of carbon monoxide to hemoglobin is much greater than that of oxygen. In this vein, serious poisoning may occur in people exposed to high levels of carbon monoxide for a long period of time. Due to the loss of oxygen as a result of the competitive binding of carbon monoxide, hypoxia, ischemia, and cardiovascular disease are observed.

Carbon monoxide affects the greenhouses gases that are tightly connected to global warming and climate. This should lead to an increase in soil and water temperatures, and extreme weather conditions or storms may occur ( 68 ).

However, in laboratory and field experiments, it has been seen to produce increased plant growth ( 78 ).

Nitrogen Oxide (NO 2 )

Nitrogen oxide is a traffic-related pollutant, as it is emitted from automobile motor engines ( 79 , 80 ). It is an irritant of the respiratory system as it penetrates deep in the lung, inducing respiratory diseases, coughing, wheezing, dyspnea, bronchospasm, and even pulmonary edema when inhaled at high levels. It seems that concentrations over 0.2 ppm produce these adverse effects in humans, while concentrations higher than 2.0 ppm affect T-lymphocytes, particularly the CD8+ cells and NK cells that produce our immune response ( 81 ).It is reported that long-term exposure to high levels of nitrogen dioxide can be responsible for chronic lung disease. Long-term exposure to NO 2 can impair the sense of smell ( 81 ).

However, systems other than respiratory ones can be involved, as symptoms such as eye, throat, and nose irritation have been registered ( 81 ).

High levels of nitrogen dioxide are deleterious to crops and vegetation, as they have been observed to reduce crop yield and plant growth efficiency. Moreover, NO 2 can reduce visibility and discolor fabrics ( 81 ).

Sulfur Dioxide (SO 2 )

Sulfur dioxide is a harmful gas that is emitted mainly from fossil fuel consumption or industrial activities. The annual standard for SO 2 is 0.03 ppm ( 82 ). It affects human, animal, and plant life. Susceptible people as those with lung disease, old people, and children, who present a higher risk of damage. The major health problems associated with sulfur dioxide emissions in industrialized areas are respiratory irritation, bronchitis, mucus production, and bronchospasm, as it is a sensory irritant and penetrates deep into the lung converted into bisulfite and interacting with sensory receptors, causing bronchoconstriction. Moreover, skin redness, damage to the eyes (lacrimation and corneal opacity) and mucous membranes, and worsening of pre-existing cardiovascular disease have been observed ( 81 ).

Environmental adverse effects, such as acidification of soil and acid rain, seem to be associated with sulfur dioxide emissions ( 83 ).

Lead is a heavy metal used in different industrial plants and emitted from some petrol motor engines, batteries, radiators, waste incinerators, and waste waters ( 84 ).

Moreover, major sources of lead pollution in the air are metals, ore, and piston-engine aircraft. Lead poisoning is a threat to public health due to its deleterious effects upon humans, animals, and the environment, especially in the developing countries.

Exposure to lead can occur through inhalation, ingestion, and dermal absorption. Trans- placental transport of lead was also reported, as lead passes through the placenta unencumbered ( 85 ). The younger the fetus is, the more harmful the toxic effects. Lead toxicity affects the fetal nervous system; edema or swelling of the brain is observed ( 86 ). Lead, when inhaled, accumulates in the blood, soft tissue, liver, lung, bones, and cardiovascular, nervous, and reproductive systems. Moreover, loss of concentration and memory, as well as muscle and joint pain, were observed in adults ( 85 , 86 ).

Children and newborns ( 87 ) are extremely susceptible even to minimal doses of lead, as it is a neurotoxicant and causes learning disabilities, impairment of memory, hyperactivity, and even mental retardation.

Elevated amounts of lead in the environment are harmful to plants and crop growth. Neurological effects are observed in vertebrates and animals in association with high lead levels ( 88 ).

Polycyclic Aromatic Hydrocarbons(PAHs)

The distribution of PAHs is ubiquitous in the environment, as the atmosphere is the most important means of their dispersal. They are found in coal and in tar sediments. Moreover, they are generated through incomplete combustion of organic matter as in the cases of forest fires, incineration, and engines ( 89 ). PAH compounds, such as benzopyrene, acenaphthylene, anthracene, and fluoranthene are recognized as toxic, mutagenic, and carcinogenic substances. They are an important risk factor for lung cancer ( 89 ).

Volatile Organic Compounds(VOCs)

Volatile organic compounds (VOCs), such as toluene, benzene, ethylbenzene, and xylene ( 90 ), have been found to be associated with cancer in humans ( 91 ). The use of new products and materials has actually resulted in increased concentrations of VOCs. VOCs pollute indoor air ( 90 ) and may have adverse effects on human health ( 91 ). Short-term and long-term adverse effects on human health are observed. VOCs are responsible for indoor air smells. Short-term exposure is found to cause irritation of eyes, nose, throat, and mucosal membranes, while those of long duration exposure include toxic reactions ( 92 ). Predictable assessment of the toxic effects of complex VOC mixtures is difficult to estimate, as these pollutants can have synergic, antagonistic, or indifferent effects ( 91 , 93 ).

Dioxins originate from industrial processes but also come from natural processes, such as forest fires and volcanic eruptions. They accumulate in foods such as meat and dairy products, fish and shellfish, and especially in the fatty tissue of animals ( 94 ).

Short-period exhibition to high dioxin concentrations may result in dark spots and lesions on the skin ( 94 ). Long-term exposure to dioxins can cause developmental problems, impairment of the immune, endocrine and nervous systems, reproductive infertility, and cancer ( 94 ).

Without any doubt, fossil fuel consumption is responsible for a sizeable part of air contamination. This contamination may be anthropogenic, as in agricultural and industrial processes or transportation, while contamination from natural sources is also possible. Interestingly, it is of note that the air quality standards established through the European Air Quality Directive are somewhat looser than the WHO guidelines, which are stricter ( 95 ).

Effect of Air Pollution on Health

The most common air pollutants are ground-level ozone and Particulates Matter (PM). Air pollution is distinguished into two main types:

Outdoor pollution is the ambient air pollution.

Indoor pollution is the pollution generated by household combustion of fuels.

People exposed to high concentrations of air pollutants experience disease symptoms and states of greater and lesser seriousness. These effects are grouped into short- and long-term effects affecting health.

Susceptible populations that need to be aware of health protection measures include old people, children, and people with diabetes and predisposing heart or lung disease, especially asthma.

As extensively stated previously, according to a recent epidemiological study from Harvard School of Public Health, the relative magnitudes of the short- and long-term effects have not been completely clarified ( 57 ) due to the different epidemiological methodologies and to the exposure errors. New models are proposed for assessing short- and long-term human exposure data more successfully ( 57 ). Thus, in the present section, we report the more common short- and long-term health effects but also general concerns for both types of effects, as these effects are often dependent on environmental conditions, dose, and individual susceptibility.

Short-term effects are temporary and range from simple discomfort, such as irritation of the eyes, nose, skin, throat, wheezing, coughing and chest tightness, and breathing difficulties, to more serious states, such as asthma, pneumonia, bronchitis, and lung and heart problems. Short-term exposure to air pollution can also cause headaches, nausea, and dizziness.

These problems can be aggravated by extended long-term exposure to the pollutants, which is harmful to the neurological, reproductive, and respiratory systems and causes cancer and even, rarely, deaths.

The long-term effects are chronic, lasting for years or the whole life and can even lead to death. Furthermore, the toxicity of several air pollutants may also induce a variety of cancers in the long term ( 96 ).

As stated already, respiratory disorders are closely associated with the inhalation of air pollutants. These pollutants will invade through the airways and will accumulate at the cells. Damage to target cells should be related to the pollutant component involved and its source and dose. Health effects are also closely dependent on country, area, season, and time. An extended exposure duration to the pollutant should incline to long-term health effects in relation also to the above factors.

Particulate Matter (PMs), dust, benzene, and O 3 cause serious damage to the respiratory system ( 97 ). Moreover, there is a supplementary risk in case of existing respiratory disease such as asthma ( 98 ). Long-term effects are more frequent in people with a predisposing disease state. When the trachea is contaminated by pollutants, voice alterations may be remarked after acute exposure. Chronic obstructive pulmonary disease (COPD) may be induced following air pollution, increasing morbidity and mortality ( 99 ). Long-term effects from traffic, industrial air pollution, and combustion of fuels are the major factors for COPD risk ( 99 ).

Multiple cardiovascular effects have been observed after exposure to air pollutants ( 100 ). Changes occurred in blood cells after long-term exposure may affect cardiac functionality. Coronary arteriosclerosis was reported following long-term exposure to traffic emissions ( 101 ), while short-term exposure is related to hypertension, stroke, myocardial infracts, and heart insufficiency. Ventricle hypertrophy is reported to occur in humans after long-time exposure to nitrogen oxide (NO 2 ) ( 102 , 103 ).

Neurological effects have been observed in adults and children after extended-term exposure to air pollutants.

Psychological complications, autism, retinopathy, fetal growth, and low birth weight seem to be related to long-term air pollution ( 83 ). The etiologic agent of the neurodegenerative diseases (Alzheimer's and Parkinson's) is not yet known, although it is believed that extended exposure to air pollution seems to be a factor. Specifically, pesticides and metals are cited as etiological factors, together with diet. The mechanisms in the development of neurodegenerative disease include oxidative stress, protein aggregation, inflammation, and mitochondrial impairment in neurons ( 104 ) ( Figure 1 ).

Figure 1 . Impact of air pollutants on the brain.

Brain inflammation was observed in dogs living in a highly polluted area in Mexico for a long period ( 105 ). In human adults, markers of systemic inflammation (IL-6 and fibrinogen) were found to be increased as an immediate response to PNC on the IL-6 level, possibly leading to the production of acute-phase proteins ( 106 ). The progression of atherosclerosis and oxidative stress seem to be the mechanisms involved in the neurological disturbances caused by long-term air pollution. Inflammation comes secondary to the oxidative stress and seems to be involved in the impairment of developmental maturation, affecting multiple organs ( 105 , 107 ). Similarly, other factors seem to be involved in the developmental maturation, which define the vulnerability to long-term air pollution. These include birthweight, maternal smoking, genetic background and socioeconomic environment, as well as education level.

However, diet, starting from breast-feeding, is another determinant factor. Diet is the main source of antioxidants, which play a key role in our protection against air pollutants ( 108 ). Antioxidants are free radical scavengers and limit the interaction of free radicals in the brain ( 108 ). Similarly, genetic background may result in a differential susceptibility toward the oxidative stress pathway ( 60 ). For example, antioxidant supplementation with vitamins C and E appears to modulate the effect of ozone in asthmatic children homozygous for the GSTM1 null allele ( 61 ). Inflammatory cytokines released in the periphery (e.g., respiratory epithelia) upregulate the innate immune Toll-like receptor 2. Such activation and the subsequent events leading to neurodegeneration have recently been observed in lung lavage in mice exposed to ambient Los Angeles (CA, USA) particulate matter ( 61 ). In children, neurodevelopmental morbidities were observed after lead exposure. These children developed aggressive and delinquent behavior, reduced intelligence, learning difficulties, and hyperactivity ( 109 ). No level of lead exposure seems to be “safe,” and the scientific community has asked the Centers for Disease Control and Prevention (CDC) to reduce the current screening guideline of 10 μg/dl ( 109 ).

It is important to state that impact on the immune system, causing dysfunction and neuroinflammation ( 104 ), is related to poor air quality. Yet, increases in serum levels of immunoglobulins (IgA, IgM) and the complement component C3 are observed ( 106 ). Another issue is that antigen presentation is affected by air pollutants, as there is an upregulation of costimulatory molecules such as CD80 and CD86 on macrophages ( 110 ).

As is known, skin is our shield against ultraviolet radiation (UVR) and other pollutants, as it is the most exterior layer of our body. Traffic-related pollutants, such as PAHs, VOCs, oxides, and PM, may cause pigmented spots on our skin ( 111 ). On the one hand, as already stated, when pollutants penetrate through the skin or are inhaled, damage to the organs is observed, as some of these pollutants are mutagenic and carcinogenic, and, specifically, they affect the liver and lung. On the other hand, air pollutants (and those in the troposphere) reduce the adverse effects of ultraviolet radiation UVR in polluted urban areas ( 111 ). Air pollutants absorbed by the human skin may contribute to skin aging, psoriasis, acne, urticaria, eczema, and atopic dermatitis ( 111 ), usually caused by exposure to oxides and photochemical smoke ( 111 ). Exposure to PM and cigarette smoking act as skin-aging agents, causing spots, dyschromia, and wrinkles. Lastly, pollutants have been associated with skin cancer ( 111 ).

Higher morbidity is reported to fetuses and children when exposed to the above dangers. Impairment in fetal growth, low birth weight, and autism have been reported ( 112 ).

Another exterior organ that may be affected is the eye. Contamination usually comes from suspended pollutants and may result in asymptomatic eye outcomes, irritation ( 112 ), retinopathy, or dry eye syndrome ( 113 , 114 ).

Environmental Impact of Air Pollution

Air pollution is harming not only human health but also the environment ( 115 ) in which we live. The most important environmental effects are as follows.

Acid rain is wet (rain, fog, snow) or dry (particulates and gas) precipitation containing toxic amounts of nitric and sulfuric acids. They are able to acidify the water and soil environments, damage trees and plantations, and even damage buildings and outdoor sculptures, constructions, and statues.

Haze is produced when fine particles are dispersed in the air and reduce the transparency of the atmosphere. It is caused by gas emissions in the air coming from industrial facilities, power plants, automobiles, and trucks.

Ozone , as discussed previously, occurs both at ground level and in the upper level (stratosphere) of the Earth's atmosphere. Stratospheric ozone is protecting us from the Sun's harmful ultraviolet (UV) rays. In contrast, ground-level ozone is harmful to human health and is a pollutant. Unfortunately, stratospheric ozone is gradually damaged by ozone-depleting substances (i.e., chemicals, pesticides, and aerosols). If this protecting stratospheric ozone layer is thinned, then UV radiation can reach our Earth, with harmful effects for human life (skin cancer) ( 116 ) and crops ( 117 ). In plants, ozone penetrates through the stomata, inducing them to close, which blocks CO 2 transfer and induces a reduction in photosynthesis ( 118 ).

Global climate change is an important issue that concerns mankind. As is known, the “greenhouse effect” keeps the Earth's temperature stable. Unhappily, anthropogenic activities have destroyed this protecting temperature effect by producing large amounts of greenhouse gases, and global warming is mounting, with harmful effects on human health, animals, forests, wildlife, agriculture, and the water environment. A report states that global warming is adding to the health risks of poor people ( 119 ).

People living in poorly constructed buildings in warm-climate countries are at high risk for heat-related health problems as temperatures mount ( 119 ).

Wildlife is burdened by toxic pollutants coming from the air, soil, or the water ecosystem and, in this way, animals can develop health problems when exposed to high levels of pollutants. Reproductive failure and birth effects have been reported.

Eutrophication is occurring when elevated concentrations of nutrients (especially nitrogen) stimulate the blooming of aquatic algae, which can cause a disequilibration in the diversity of fish and their deaths.

Without a doubt, there is a critical concentration of pollution that an ecosystem can tolerate without being destroyed, which is associated with the ecosystem's capacity to neutralize acidity. The Canada Acid Rain Program established this load at 20 kg/ha/yr ( 120 ).

Hence, air pollution has deleterious effects on both soil and water ( 121 ). Concerning PM as an air pollutant, its impact on crop yield and food productivity has been reported. Its impact on watery bodies is associated with the survival of living organisms and fishes and their productivity potential ( 121 ).

An impairment in photosynthetic rhythm and metabolism is observed in plants exposed to the effects of ozone ( 121 ).

Sulfur and nitrogen oxides are involved in the formation of acid rain and are harmful to plants and marine organisms.

Last but not least, as mentioned above, the toxicity associated with lead and other metals is the main threat to our ecosystems (air, water, and soil) and living creatures ( 121 ).

In 2018, during the first WHO Global Conference on Air Pollution and Health, the WHO's General Director, Dr. Tedros Adhanom Ghebreyesus, called air pollution a “silent public health emergency” and “the new tobacco” ( 122 ).

Undoubtedly, children are particularly vulnerable to air pollution, especially during their development. Air pollution has adverse effects on our lives in many different respects.

Diseases associated with air pollution have not only an important economic impact but also a societal impact due to absences from productive work and school.

Despite the difficulty of eradicating the problem of anthropogenic environmental pollution, a successful solution could be envisaged as a tight collaboration of authorities, bodies, and doctors to regularize the situation. Governments should spread sufficient information and educate people and should involve professionals in these issues so as to control the emergence of the problem successfully.

Technologies to reduce air pollution at the source must be established and should be used in all industries and power plants. The Kyoto Protocol of 1997 set as a major target the reduction of GHG emissions to below 5% by 2012 ( 123 ). This was followed by the Copenhagen summit, 2009 ( 124 ), and then the Durban summit of 2011 ( 125 ), where it was decided to keep to the same line of action. The Kyoto protocol and the subsequent ones were ratified by many countries. Among the pioneers who adopted this important protocol for the world's environmental and climate “health” was China ( 3 ). As is known, China is a fast-developing economy and its GDP (Gross Domestic Product) is expected to be very high by 2050, which is defined as the year of dissolution of the protocol for the decrease in gas emissions.

A more recent international agreement of crucial importance for climate change is the Paris Agreement of 2015, issued by the UNFCCC (United Nations Climate Change Committee). This latest agreement was ratified by a plethora of UN (United Nations) countries as well as the countries of the European Union ( 126 ). In this vein, parties should promote actions and measures to enhance numerous aspects around the subject. Boosting education, training, public awareness, and public participation are some of the relevant actions for maximizing the opportunities to achieve the targets and goals on the crucial matter of climate change and environmental pollution ( 126 ). Without any doubt, technological improvements makes our world easier and it seems difficult to reduce the harmful impact caused by gas emissions, we could limit its use by seeking reliable approaches.

Synopsizing, a global prevention policy should be designed in order to combat anthropogenic air pollution as a complement to the correct handling of the adverse health effects associated with air pollution. Sustainable development practices should be applied, together with information coming from research in order to handle the problem effectively.

At this point, international cooperation in terms of research, development, administration policy, monitoring, and politics is vital for effective pollution control. Legislation concerning air pollution must be aligned and updated, and policy makers should propose the design of a powerful tool of environmental and health protection. As a result, the main proposal of this essay is that we should focus on fostering local structures to promote experience and practice and extrapolate these to the international level through developing effective policies for sustainable management of ecosystems.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest

IM is employed by the company Delphis S.A.

The remaining authors declare that the present review paper was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords: air pollution, environment, health, public health, gas emission, policy

Citation: Manisalidis I, Stavropoulou E, Stavropoulos A and Bezirtzoglou E (2020) Environmental and Health Impacts of Air Pollution: A Review. Front. Public Health 8:14. doi: 10.3389/fpubh.2020.00014

Received: 17 October 2019; Accepted: 17 January 2020; Published: 20 February 2020.

Reviewed by:

Copyright © 2020 Manisalidis, Stavropoulou, Stavropoulos and Bezirtzoglou. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Ioannis Manisalidis, giannismanisal@gmail.com ; Elisavet Stavropoulou, elisabeth.stavropoulou@gmail.com

† These authors have contributed equally to this work

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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by Chris Woodford . Last updated: November 22, 2022.

Photo: Air pollution is obvious when it pours from a smokestack (chimney), but it's not always so easy to spot. This is an old photo of the kind of smoke that used to come from coal-fired power plants and, apart from soot (unburned carbon particles), its pollutants include sulfur dioxide and the greenhouse gas carbon dioxide. Thanks to tougher pollution controls, modern power plants produce only a fraction as much pollution. Modern pollution made by traffic consists of gases like nitrogen dioxide and "particulates" (microscopic soot and dust fragments) that are largely invisible.

What is air pollution?

Air pollution is a gas (or a liquid or solid dispersed through ordinary air) released in a big enough quantity to harm the health of people or other animals, kill plants or stop them growing properly, damage or disrupt some other aspect of the environment (such as making buildings crumble), or cause some other kind of nuisance (reduced visibility, perhaps, or an unpleasant odor).

Natural air pollution

Photo: Forest fires are a completely natural cause of air pollution. We'll never be able to prevent them breaking out or stop the pollution they cause; our best hope is to manage forests, where we can, so fires don't spread. Ironically, that can mean deliberately burning areas of forest, as shown here, to create firebreaks. Forests are also deliberately burned to regenerate ecosystems. Photo by courtesy of US Fish and Wildlife Service .

Top-ten kinds of air pollution Photo: Flying molecules—if you could see air pollution close up, this is what it would look like. Image courtesy of US Department of Energy. Any gas could qualify as pollution if it reached a high enough concentration to do harm. Theoretically, that means there are dozens of different pollution gases. It's important to note that not all the things we think of as pollution are gases: some are aerosols (liquids or solids dispersed through gases). In practice, about ten different substances cause most concern: Sulfur dioxide : Coal, petroleum, and other fuels are often impure and contain sulfur as well as organic (carbon-based) compounds. When sulfur (spelled "sulphur" in some countries) burns with oxygen from the air, sulfur dioxide (SO 2 ) is produced. Coal-fired power plants are the world's biggest source of sulfur-dioxide air pollution, which contributes to smog, acid rain, and health problems that include lung disease. [5] Large amounts of sulfur dioxide are also produced by ships, which use dirtier diesel fuel than cars and trucks. [6] Carbon monoxide : This highly dangerous gas forms when fuels have too little oxygen to burn completely. It spews out in car exhausts and it can also build up to dangerous levels inside your home if you have a poorly maintained gas boiler , stove, or fuel-burning appliance. (Always fit a carbon monoxide detector if you burn fuels indoors.) [7] Carbon dioxide : This gas is central to everyday life and isn't normally considered a pollutant: we all produce it when we breathe out and plants such as crops and trees need to "breathe" it in to grow. However, carbon dioxide is also a greenhouse gas released by engines and power plants. Since the beginning of the Industrial Revolution, it's been building up in Earth's atmosphere and contributing to the problem of global warming and climate change . [8] Nitrogen oxides : Nitrogen dioxide (NO 2 ) and nitrogen oxide (NO) are pollutants produced as an indirect result of combustion, when nitrogen and oxygen from the air react together. Nitrogen oxide pollution comes from vehicle engines and power plants, and plays an important role in the formation of acid rain, ozone and smog. Nitrogen oxides are also "indirect greenhouse gases" (they contribute to global warming by producing ozone, which is a greenhouse gas). [9] Volatile organic compounds (VOCs) : These carbon-based (organic) chemicals evaporate easily at ordinary temperatures and pressures, so they readily become gases. That's precisely why they're used as solvents in many different household chemicals such as paints , waxes, and varnishes. Unfortunately, they're also a form of air pollution: they're believed to have long-term (chronic) effects on people's health and they play a role in the formation of ozone and smog. VOCs are also released by tobacco smoke and wildfires. [10] Particulates : There are many different kinds of particulates, from black soot in diesel exhaust to dust and organic matter from the desert. Airborne liquid droplets from farm pollution also count as particulates. Particulates of different sizes are often referred to by the letters PM followed by a number, so PM 10 means soot particles of less than 10 microns (10 millionths of a meter or 10µm in diameter, roughly 10 times thinner than a thick human hair). The smaller ("finer") the particulates, the deeper they travel into our lungs and the more dangerous they are. PM 2.5 particulates are much more dangerous (they're less than 2.5 millionths of a meter or about 40 times thinner than a typical hair). In cities, most particulates come from traffic fumes. [11] Ozone : Also called trioxygen, this is a type of oxygen gas whose molecules are made from three oxygen atoms joined together (so it has the chemical formula O 3 ), instead of just the two atoms in conventional oxygen (O 2 ). In the stratosphere (upper atmosphere), a band of ozone ("the ozone layer") protects us by screening out harmful ultraviolet radiation (high-energy blue light) beaming down from the Sun. At ground level, it's a toxic pollutant that can damage health. It forms when sunlight strikes a cocktail of other pollution and is a key ingredient of smog (see box below). [12] Chlorofluorocarbons (CFCs) : Once thought to be harmless, these gases were widely used in refrigerators and aerosol cans until it was discovered that they damaged Earth's ozone layer. We discuss this in more detail down below. [13] Unburned hydrocarbons : Petroleum and other fuels are made of organic compounds based on chains of carbon and hydrogen atoms. When they burn properly, they're completely converted into harmless carbon dioxide and water ; when they burn incompletely, they can release carbon monoxide or float into the air in their unburned form, contributing to smog. Lead and heavy metals : Lead and other toxic "heavy metals" can be spread into the air either as toxic compounds or as aerosols (when solids or liquids are dispersed through gases and carried through the air by them) in such things as exhaust fumes and the fly ash (contaminated waste dust) from incinerator smokestacks. [14] What are the causes of air pollution?

Photo: Even in the age of electric cars, traffic remains a major cause of air pollution. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL) (NREL photo id#46361).

Photo: Brown smog lingers over Denver, Colorado. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL) (NREL photo id#56919).

Chart: Most of the world's major cities routinely exceed World Health Organization (WHO) air pollution guidelines, though progress is being made: you can see that the 2022 figures (green) show a marked improvement on the 2016 ones (orange) in almost every case. This chart compares annual mean PM 2.5 levels in 12 representative cities around the world with the recently revised (2021) WHO guideline value of 5μg per cubic meter (dotted line). PM 2.5 particulates are those smaller than 2.5 microns and believed to be most closely linked with adverse health effects. For more about this chart and the data sources used, see note [22] .

Photo: Smokestacks billowing pollution over Moscow, Russia in 1994. Factory pollution is much less of a problem than it used to be in the world's "richer" countries—partly because a lot of their industry has been exported to nations such as China, India, and Mexico. Photo by Roger Taylor courtesy of US DOE National Renewable Energy Laboratory (NREL) .

What effects does air pollution have?

Photo: Air pollution can cause a variety of lung diseases and other respiratory problems. This chest X ray shows a lung disease called emphysema in the patient's left lung. A variety of things can cause it, including smoking and exposure to air pollution. Photo courtesy of National Heart, Lung and Blood Institute (NHLBI) and National Institutes of Health.

" In 2016, 91% of the world population was living in places where the WHO air quality guidelines levels were not met." World Health Organization , 2018

Photo: For many years, the stonework on the Parthenon in Athens, Greece has been blackened by particulates from traffic pollution, but other sources of pollution, such as wood-burning stoves, are increasingly significant. Photo by Michael M. Reddy courtesy of U.S. Geological Survey .

How air pollution works on different scales

Indoor air pollution.

Photo: Air freshener—or air polluter?

Further reading

Acid rain—a closer look.

Photo: Acid rain can turn lakes so acidic that fish no longer survive. Picture courtesy of U.S. Fish and Wildlife Service Division of Public Affairs. Why does that matter? Pure water is neither acidic nor alkaline but completely neutral (we say it has an acidity level or pH of 7.0). Ordinary rainwater is a little bit more acidic than this with about the same acidity as bananas (roughly pH 5.5), but if rain falls through sulfur dioxide pollution it can turn much more acidic (with a pH of 4.5 or lower, which is the same acidity as orange or lemon juice). When acid rain accumulates in lakes or rivers, it gradually turns the entire water more acidic. That's a real problem because fish thrive only in water that is neutral or slightly acidic (typically with a pH of 6.5–7.0). Once the acidity drops below about pH 6.0, fish soon start to die—and if the pH drops to about 4.0 or less, all the fish will be killed. Acid rain has caused major problems in lakes throughout North America and Europe. It also causes the death of forests, reduces the fertility of soil, and damages buildings by eating away stonework (the marble on the US Capitol in Washington, DC has been eroded by acid-rain, for example). One of the biggest difficulties in tackling acid rain is that it can happen over very long distances. In one notable case, sulfur dioxide air pollution produced by power plants in the UK was blamed for causing acid rain that fell on Scandinavian countries such as Norway, producing widespread damage to forests and the deaths of thousands of fish in acidified lakes. The British government refused to acknowledge the problem and that was partly why the UK became known as the "dirty man of Europe" in the 1980s and 1990s. [18] Acid rain was a particular problem in the last 30–40 years of the 20th century. Thanks to the decline in coal-fired power plants, and the sulfur dioxide they spewed out, it's less of a problem for western countries today. But it's still a big issue in places like India, where coal remains a major source of energy. Global air pollution It's hard to imagine doing anything so dramatic and serious that it would damage our entire, enormous planet—but, remarkable though it may seem, we all do things like this everyday, contributing to problems such as global warming and the damage to the ozone layer (two separate issues that are often confused). Global warming Every time you ride in a car, turn on the lights, switch on your TV , take a shower, microwave a meal, or use energy that's come from burning a fossil fuel such as oil, coal, or natural gas, you're almost certainly adding to the problem of global warming and climate change: unless it's been produced in some environmentally friendly way, the energy you're using has most likely released carbon dioxide gas into the air. While it's not an obvious pollutant, carbon dioxide has gradually built up in the atmosphere, along with other chemicals known as greenhouse gases . Together, these gases act a bit like a blanket surrounding our planet that is slowly making the mean global temperature rise, causing the climate (the long-term pattern of our weather) to change, and producing a variety of different effects on the natural world, including rising sea levels. Read more in our main article about global warming and climate change . Ozone holes

How can we solve the problem of air pollution?

Photo: Pollution solution: an electrostatic smoke precipitator helps to prevent air pollution from this smokestack at the McNeil biomass power plant in Burlington, VT. Photo by Warren Gretz courtesy of US DOE National Renewable Energy Laboratory (NREL).

What can you do to help reduce air pollution?

Photo: Buying organic food reduces the use of sprayed pesticides and other chemicals, so it helps to reduce air (as well as water) pollution.

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• Climate change and global warming
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• Breathless: Why Air Pollution Matters—and How it Affects You by Chris Woodford. Icon, 2021. My new book explores the problem in much more depth than I've been able to go into here. You can also read a bonus chapter called Angels with dirty faces: How air pollution blackens our buildings and monuments .
• The Invisible Killer: The Rising Global Threat of Air Pollution and How We Can Fight Back by Gary Fuller. Melville House, 2018.
• Reducing Pollution and Waste by Jen Green. Raintree/Capstone, 2011. A 48-page introduction for ages 9–12. The emphasis here is on getting children to think about pollution: where it comes from, who makes it, and who should solve the problem.
• Pollution Crisis by Russ Parker. Rosen, 2009. A 32-page guide for ages 8–10. It starts with a global survey of the problem; looks at air, water, and land pollution; then considers how we all need to be part of the solution.
• Earth Matters by Lynn Dicks et al. Dorling Kindersley, 2008. This isn't specifically about pollution. Instead, it explores how a range of different environmental problems are testing life to the limit in the planet's major biomes (oceans, forests, and so on). I wrote the section of this book that covers the polar regions.
• State of Global Air : One of the best sources of global air pollution data.
• American Lung Association: State of the Air Report : A good source of data about the United States.
• European Environment Agency: Air quality in Europe : A definitive overview of the situation in the European countries.
• World Health Organization (WHO) Ambient (outdoor) air pollution in cities database : A spreadsheet of pollution data for most major cities in the world (a little out of date, but a new version is expected soon).
• Our World in Data : Accessible guides to global data from Oxford University.
• The New York Times Topics: Air Pollution
• The Guardian: Pollution
• Wired: Pollution
• 'Invisible killer': fossil fuels caused 8.7m deaths globally in 2018, research finds by Oliver Milman. The Guardian, February 9, 2021. Pollution of various kinds causes something like one in five of all deaths.
• Millions of masks distributed to students in 'gas chamber' Delhi : BBC News, 1 November 2019.
• 90% of world's children are breathing toxic air, WHO study finds by Matthew Taylor. The Guardian, October 29, 2018. The air pollution affecting billions of children could continue to harm their health throughout their lives.
• Pollution May Dim Thinking Skills, Study in China Suggests by Mike Ives. The New York Times, August 29, 2018. Long-term exposure to air pollution seems to cause a decline in cognitive skills.
• Global pollution kills 9m a year and threatens 'survival of human societies' by Damian Carrington. The Guardian, October 19, 2017. Air, water, and land pollution kill millions, cost trillions, and threaten the very survival of humankind, a new study reveals.
• India's Air Pollution Rivals China's as World's Deadliest by Geeta Anand. The New York Times, February 14, 2017. High levels of pollution could be killing 1.1 million Indians each year.
• More Than 9 in 10 People Breathe Bad Air, WHO Study Says by Mike Ives. The New York Times, September 27, 2016. New WHO figures suggest the vast majority of us are compromising our health by breathing bad air.
• Study Links 6.5 Million Deaths Each Year to Air Pollution by Stanley Reed. The New York Times, June 26, 2016. Air pollution deaths are far greater than previously supposed according to a new study by the International Energy Agency.
• UK air pollution 'linked to 40,000 early deaths a year' by Michelle Roberts, BBC News, February 23, 2016. Diesel engines, cigarette smoke, and even air fresheners are among the causes of premature death from air pollution.
• This Wearable Detects Pollution to Build Air Quality Maps in Real Time by Davey Alba. Wired, November 19, 2014. A wearable pollution gadget lets people track their exposure to air pollution through a smartphone app.
• Air pollution and public health: emerging hazards and improved understanding of risk by Frank J. Kelly and Julia C. Fussell, Environmental Geochemistry and Health, 2015
• Health effects of fine particulate air pollution: lines that connect by C.A. Pope and D.W. Dockery. Journal of the Air and Waste Management Association, 2006
• Ambient and household air pollution: complex triggers of disease by Stephen A. Farmer et al, Am J Physiol Heart Circ Physiol, 2014

Text copyright © Chris Woodford 2010, 2022. All rights reserved. Full copyright notice and terms of use .

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Air pollution, explained

Pollutants in the air aren't always visible and come from many different sources.

Despite decades of progress, the air quality in the United States has started to decline over the past few years, according to data provided in summer 2019 by the Environmental Protection Agency . The agency recorded 15 percent more days with unhealthy air in the country in 2018 and 2017 compared to the average from 2013 to 2016.

The reasons for the recent decline in air quality remain unclear, says the agency, but may be related to high numbers of wildfires , a warming climate, and increasing human consumption patterns driven by population growth and a strong economy. The long-term outlook also remains unclear, even as politicians debate air pollution standards.

What is air pollution?

Air pollution is a mix of particles and gases that can reach harmful concentrations both outside and indoors. Its effects can range from higher disease risks to rising temperatures. Soot, smoke, mold, pollen, methane, and carbon dioxide are a just few examples of common pollutants.

In the U.S., one measure of outdoor air pollution is the Air Quality Index, or AQI which rates air conditions across the country based on concentrations of five major pollutants: ground-level ozone, particle pollution (or particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Some of those also contribute to indoor air pollution , along with radon, cigarette smoke, volatile organic compounds (VOCs), formaldehyde, asbestos, and other substances.

A global health hazard

Poor air quality kills people. Worldwide, bad outdoor air caused an estimated 4.2 million premature deaths in 2016 , about 90 percent of them in low- and middle-income countries, according to the World Health Organization. Indoor smoke is an ongoing health threat to the 3 billion people who cook and heat their homes by burning biomass, kerosene, and coal. Air pollution has been linked to higher rates of cancer, heart disease, stroke, and respiratory diseases such as asthma. In   the U.S. nearly 134 million people—over 40 percent of the population—are at risk of disease and premature death because of air pollution, according to American Lung Association estimates .

While those effects emerge from long-term exposure, air pollution can also cause short-term problems such as sneezing and coughing, eye irritation, headaches, and dizziness. Particulate matter smaller than 10 micrometers (classified as PM 10 and the even smaller PM 2.5 ) pose higher health risks because they can be breathed deeply into the lungs and may cross into the bloodstream.

Air pollutants cause less-direct health effects when they contribute to climate change . Heat waves, extreme weather, food supply disruptions, and other effects related to increased greenhouse gases can have negative impacts on human health. The U.S. Fourth National Climate Assessment released in 2018 noted, for example, that a changing climate "could expose more people in North America to ticks that carry Lyme disease and mosquitoes that transmit viruses such as West Nile, chikungunya, dengue, and Zika."

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Environmental impacts.

Though many living things emit carbon dioxide when they breathe, the gas is widely considered to be a pollutant when associated with cars, planes, power plants, and other human activities that involve the burning of fossil fuels such as gasoline and natural gas. That's because carbon dioxide is the most common of the greenhouse gases, which trap heat in the atmosphere and contribute to climate change. Humans have pumped enough carbon dioxide into the atmosphere over the past 150 years to raise its levels higher than they have been for hundreds of thousands of years .

Other greenhouse gases include methane —which comes from such sources as landfills, the natural gas industry, and gas emitted by livestock —and chlorofluorocarbons (CFCs), which were used in refrigerants and aerosol propellants until they were banned in the late 1980s because of their deteriorating effect on Earth's ozone layer.

Another pollutant associated with climate change is sulfur dioxide, a component of smog. Sulfur dioxide and closely related chemicals are known primarily as a cause of acid rain . But they also reflect light when released in the atmosphere, which keeps sunlight out and creates a cooling effect. Volcanic eruptions can spew massive amounts of sulfur dioxide into the atmosphere, sometimes causing cooling that lasts for years. In fact, volcanoes used to be the main source of atmospheric sulfur dioxide; today, people are.

Airborne particles, depending on their chemical makeup, can also have direct effects separate from climate change. They can change or deplete nutrients in soil and waterways, harm forests and crops, and damage cultural icons such as monuments and statues.

What can be done?

Countries around the world are tackling various forms of air pollution. China, for example, is making strides in cleaning up smog-choked skies from years of rapid industrial expansion, partly by closing or canceling coal-fired power plants. In the U.S., California has been a leader in setting emissions standards aimed at improving air quality, especially in places like famously hazy Los Angeles. And a variety of efforts aim to bring cleaner cooking options to places where hazardous cookstoves are prevalent.

In any home, people can safeguard against indoor air pollution by increasing ventilation, testing for radon gas, using air purifiers, running kitchen and bathroom exhaust fans, and avoiding smoking. When working on home projects, look for paint and other products low in volatile organic compounds: organizations such as Green Seal , UL (GREENGUARD) , and the U.S. Green Building Council can help.

To curb global warming, a variety of measures need to be taken , such as adding more renewable energy and replacing gasoline-fueled cars with zero-emissions vehicles such as electric ones. On a larger scale, governments at all levels are making commitments to limit emissions of carbon dioxide and other greenhouse gases. The Paris Agreement , ratified on November 4, 2016, is one effort to combat climate change on a global scale. And the Kigali Amendment seeks to further the progress made by the Montreal Protocol , banning heat-trapping hydrofluorocarbons (HFCs) in addition to CFCs.

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Air Pollution

Our overview of indoor and outdoor air pollution.

By: Hannah Ritchie and Max Roser

This article was first published in October 2017 and last revised in February 2024.

Air pollution is one of the world's largest health and environmental problems. It develops in two contexts: indoor (household) air pollution and outdoor air pollution.

In this topic page, we look at the aggregate picture of air pollution – both indoor and outdoor. We also have dedicated topic pages that look in more depth at these subjects:

Indoor Air Pollution

Look in detail at the data and research on the health impacts of Indoor Air Pollution, attributed deaths, and its causes across the world

Outdoor Air Pollution

Look in detail at the data and research on exposure to Outdoor Air Pollution, its health impacts, and attributed deaths across the world

Look in detail at the data and research on energy consumption, its impacts around the world today, and how this has changed over time

See all interactive charts on Air Pollution ↓

Other research and writing on air pollution on Our World in Data:

• Air pollution: does it get worse before it gets better?
• Data Review: How many people die from air pollution?
• Energy poverty and indoor air pollution: a problem as old as humanity that we can end within our lifetime
• How many people do not have access to clean fuels for cooking?
• What are the safest and cleanest sources of energy?
• What the history of London’s air pollution can tell us about the future of today’s growing megacities
• When will countries phase out coal power?

Air pollution is one of the world's leading risk factors for death

Air pollution is responsible for millions of deaths each year.

Air pollution – the combination of outdoor and indoor particulate matter and ozone – is a risk factor for many of the leading causes of death, including heart disease, stroke, lower respiratory infections, lung cancer, diabetes, and chronic obstructive pulmonary disease (COPD).

The Institute for Health Metrics and Evaluation (IHME), in its Global Burden of Disease study, provides estimates of the number of deaths attributed to the range of risk factors for disease. 1

In the visualization, we see the number of deaths per year attributed to each risk factor. This chart shows the global total but can be explored for any country or region using the "change country" toggle.

Air pollution is one of the leading risk factors for death. In low-income countries, it is often very near the top of the list (or is the leading risk factor).

Air pollution contributes to one in ten deaths globally

In recent years, air pollution has contributed to one in ten deaths globally. 2

In the map shown here, we see the share of deaths attributed to air pollution across the world.

Air pollution is one of the leading risk factors for disease burden

Air pollution is one of the leading risk factors for death. But its impacts go even further; it is also one of the main contributors to the global disease burden.

Global disease burden takes into account not only years of life lost to early death but also the number of years lived in poor health.

In the visualization, we see risk factors ranked in order of DALYs – disability-adjusted life years – the metric used to assess disease burden. Again, air pollution is near the top of the list, making it one of the leading risk factors for poor health across the world.

Air pollution not only takes years from people's lives but also has a large effect on the quality of life while they're still living.

Who is most affected by air pollution?

Death rates from air pollution are highest in low-to-middle-income countries.

Air pollution is a health and environmental issue across all countries of the world but with large differences in severity.

In the interactive map, we show death rates from air pollution across the world, measured as the number of deaths per 100,000 people in a given country or region.

The burden of air pollution tends to be greater across both low and middle-income countries for two reasons: indoor pollution rates tend to be high in low-income countries due to a reliance on solid fuels for cooking, and outdoor air pollution tends to increase as countries industrialize and shift from low to middle incomes.

A map of the number of deaths from air pollution by country can be found here .

How are death rates from air pollution changing?

Death rates from air pollution are falling – mainly due to improvements in indoor pollution.

In the visualization, we show global death rates from air pollution over time – shown as the total air pollution – in addition to the individual contributions from outdoor and indoor pollution.

Globally, we see that in recent decades, the death rates from total air pollution have declined: since 1990, death rates have nearly halved. But, as we see from the breakdown, this decline has been primarily driven by improvements in indoor air pollution.

Death rates from indoor air pollution have seen an impressive decline, while improvements in outdoor pollution have been much more modest.

You can explore this data for any country or region using the "change country" toggle on the interactive chart.

Interactive charts on air pollution

Murray, C. J., Aravkin, A. Y., Zheng, P., Abbafati, C., Abbas, K. M., Abbasi-Kangevari, M., ... & Borzouei, S. (2020). Global burden of 87 risk factors in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019 .  The Lancet ,  396 (10258), 1223-1249.

Here, we use the term 'contributes,' meaning it was one of the attributed risk factors for a given disease or cause of death. There can be multiple risk factors for a given disease that can amplify one another. This means that in some cases, air pollution was not the only risk factor but one of several.

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How air pollution is destroying our health

WHO data show that almost all of the global population (99%) breathe air that exceeds WHO  guideline limits  and contains high levels of  pollutants , with low- and middle-income countries (LMIC) suffering from the highest exposures.

Ambient (outdoor) air pollution in both cities and rural areas is causing fine particulate matter which results in strokes, heart diseases, lung cancer, and acute and chronic respiratory diseases.  

Additionally, around 2.6 billion people are exposed to dangerous levels of household air pollution from using polluting open fires or simple stoves for cooking fuelled by kerosene, biomass (wood, animal dung and crop waste) and coal.

First Global Conference on Air Pollution and Health

To rally the world towards major commitments to fight this problem, WHO and partners convened the first  Global Conference on Air Pollution and Health  in Geneva on 29 October – 1 November 2018. The conference raised awareness of this growing public health challenge and shared information and tools on the health risks of air pollution and its interventions.

This conference showcased some of WHO’s work on air pollution, including the findings of its Global Platform on Air Quality and Health. This platform, whose diverse membership includes researchers, civil society, UN agencies and other partner institutions, reviewed the data on air quality and health. For example, the platform worked on techniques to more accurately attribute air pollution coming from different sources of pollution. Ongoing work includes improving estimates of air quality by combining the data from various air quality monitoring networks, atmospheric modelling and satellite remote sensing.

Health impacts of air pollution

There are two main types of air pollution: ambient air pollution (outdoor pollution) and household air pollution (indoor air pollution). Ambient air pollution is a major environmental health problem affecting everyone in low-, middle-, and high-income countries as its source – combustion of fossil fuel – is ubiquitous. Household air pollution is mainly caused by the use of solid fuels (such as wood, crop wastes, charcoal, coal and dung) and kerosene in open fires and inefficient stoves. Most of these people are poor and live in low- and middle-income countries.

Exposure to smoke from cooking fires causes 3.2 million premature deaths each year, mostly in low- and middle-income countries, where polluting fuels and technologies are used every day, particularly at home for cooking, heating and lighting. Women and children, who tend to spend more time indoors, are affected the most. LMIC also suffer the greatest from exposure ambient air pollution with 3.68 million premature deaths each year, which is almost 8 times the mortality rates in high income countries (0.47 million).

The main pollutants are:

-  particulate matter, a mix of solid and liquid droplets, with larger particles (PM 10 ) arising from pollen, sea spray and wind-blown dust from erosion, agricultural spaces, roadways and mining operations, while finer particles (PM2.5) can be derived from primary sources (for example combustion of fuels in power generation facilities, industries or vehicles) and secondary sources (for example chemical reactions between gases)

-  nitrogen dioxide (NO 2 ), a gas from combustion of fuels in processes such as those used for furnaces, gas stoves, transportation, industry and power generation;

-  sulfur dioxide, another gas mainly from the combustion of fossil fuels for domestic heating, industries and power generation; and

-  ozone at ground level, caused by a chemical reaction of gases, such as NO 2 , in the presence of sunlight. The pollutant that is most commonly monitored by regulatory frameworks and for which a lot of evidence of adverse health impact is available is particulate matter followed by nitrogen dioxide.

Ambient (outdoor) air pollution

Household air pollution

How air pollution affects our body

Particles with a diameter of 10 microns or less (≤ PM 10 ) can penetrate and lodge deep inside the lungs, causing irritation, inflammation and damaging the lining of the respiratory tract. Smaller, more health-damaging particles with a diameter of 2.5 microns or less (≤ PM 2.5 – 60 of them make up the width of a human hair) can penetrate the lung barrier and enter the blood system, affecting all major organs of the body. These pollutants increase the risk of heart and respiratory diseases, as well as lung cancer and strokes.

Ozone is a major factor in causing asthma (or making it worse), and nitrogen dioxide and sulfur dioxide can also cause asthma, bronchial symptoms, lung inflammation and reduced lung function. In 2021 WHO updated the Global Air Quality Guidelines, which recommend the maximum safe level for PM 2.5 annual average concentration of 5 μg/m 3  or less. The guidelines provide evidence of the damage air pollution inflicts on human health, at even lower concentrations than previously understood. The updated guidelines provide recommendations on air quality guideline levels as well as interim targets for six key air pollutants. They also offer qualitative statements on good practices for the management of certain types of particulate matter (PM), for example, black carbon/elemental carbon, ultrafine particles, and particles originating from sand and dust storms, for which there is insufficient quantitative evidence to derive AQG levels.

Air pollution has a disastrous effect on children; there were more than 5 million deaths of children under the age of 5 years. More than 27% of those deaths – 1.7 million – were attributable to environmental factors, with air pollution foremost among them. Globally, lower respiratory infections are the second leading cause of death for children under 5 years. Every year, 442 000 children (as of 2022) younger than 5 years die prematurely from breathing polluted air. Evidence suggests that air pollution could also harm children before they are born (reduced birth weight) through their mothers' exposure. There is emerging evidence linking air pollution exposure to cancer, neurodevelopmental and metabolic diseases in children.

As well as affecting our health, pollutants in the air are also causing long-term environmental damage by driving climate change, itself a major threat to health and well-being. 

Already in 2018, the UN Intergovernmental Panel on Climate Change warned that coal-fired electricity must end by 2050 if we are to limit global warming rises to 1.5 °C. If not, we may see a major climate crisis in just 20 years.

Affordable strategies exist to reduce emissions from energy, transport, waste management, housing and industrial sectors. These interventions often carry other benefits like reduced traffic and noise, increased physical activity and better land use – all of which contribute to improving health and well-being. WHO also supports cities with the data, tools and capacity to select, implement and track clean and healthy policies at the city level. Better air quality will benefit all of us, everywhere.

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4 Causes and Effects of Air Pollution

Air pollution refers to the release of pollutants into the air, which can be harmful and impose significant health risks to the population, including increased chances of coronary and respiratory diseases, as well as preliminary deaths. Made up of chemicals and pollutant particles, air pollution is one of the biggest environmental problems of our lifetime . Read on to learn about the major causes and effects of air pollution. 

Sources of Air Pollution

1. burning fossil fuels.

The biggest contributors of air pollution are from industry sources and power plants to generate power, as well as fossil fuel motor vehicles. The continuous burning of fossil fuels releases air pollutants, emissions and chemicals into the air and atmosphere. 

In 2020, the Environmental Protection Agency reported that about 68 million tons of air pollution were emitted into the atmosphere in the US, contributing to the “formation of ozone and particles, the deposition of acids, and visibility impairment.”

The World Health Organization (WHO) estimates around 91% of the world’s population lives in places where air quality levels exceed limits. Developing and low-income countries experienced the greatest impacts from outdoor air pollution, particularly in the Western Pacific and South-East Asia regions. 

Climate change has an interrelated relationship with the environment and air pollution. As more air pollutants and greenhouse gases are released, this alters the energy balance between the atmosphere and the Earth’s surface , which leads to global warming. The global temperature increase in turns raises the production of allergenic air pollutants such as mold and extends pollen seasons. 

2. Ozone and Smog

Ozone is a gas that when it forms air pollution and reaches too close to the ground, it significantly reduces visibility. We call this smog. This form of air pollution occurs when sunlight reacts with nitrogen oxides released from car exhausts and coal power plants. The ozone typically forms a protective layer in the atmosphere to protect the population from ultraviolet radiation (UV), but as it transforms into smog, it is harmful to human health and poses higher risks of respiratory illnesses like asthma and lung cancer. 

3. Weather Conditions

Air pollution and poor air quality can be attributed to changing weather conditions. For example, dust storms in China would carry clouds of industrial pollutants and particulate pollution across the Gobi desert into neighbouring countries such as Korea and Japan during spring season. Likewise during periods of high air pressure, air becomes stagnant and pollutants are more concentrated over certain areas. 

4. Heatwaves and Wildfires

Heatwaves not only lead to an increase of temperature, but are some of the causes and effects of air pollution. Hotter, stagnant air during a heat wave increases the concentration of particle pollutants. Extreme heat wave events also have higher risks of large-scale wildfires, which in turn, releases more carbon emissions, smog and pollutants into the air. 

You might also like: 15 Most Polluted Cities in the World

Effects of Air Pollution 

Air pollution contributes to the death of 5 million every year and about 6% of the global population, according to Our World in Data . The lethal combination of outdoor air pollution and toxic emissions from burning fossil fuel has been one of the leading causes of chronic and often terminal health issues including heart disease, stroke, lung cancer, and lower respiratory infections. 

The WHO estimates that nine out of 10 people breathe air that contains high levels of pollutants. In 2017, close to 15% of population deaths in low income countries like South and East Asia are attributed to air pollution, while the higher income countries experience only about 2%. 

The drastic difference in mortality numbers can be linked to legislations such as the Clean Air Act implemented by high-income countries like the US. Such legislations usually establishes national air quality standards and regulations on hazardous air pollutants. The UK in particular, saw a sharp 60% decline in air pollutant emissions between the 1970 and 2016. 

The environmental effects of air pollution are also vast, ranging from acid rain to contributing to birth defects, reproductive failure, and diseases in wildlife animals. Agriculture is also a victim of air pollution as increased pollutants can affect crop and forest yields, reduce growth  and increased plant susceptibility to disease from increased UV radiation caused by ozone depletion.

In the wake of the COVID-19 pandemic, air pollution has once again returned to the spotlight in relation to its role in transmitting virus molecules. Preliminary studies have identified a positive correlation between COVID-19-related mortalities and air pollution. China, being one of the most polluted countries in the world, can potentially link its high death toll during the pandemic to its poor air quality. Although, more research needs to be conducted to make any substantive correlation.

You might also like: History of Air Pollution: Have We Reached the Point of No Return?

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Essay on Air Pollution for Students: Check Samples of 100 Words to 250 Words

• Updated on  
• Jun 2, 2024

Essay on Air Pollution : Invisible but insidious, air pollution silently infiltrates our lives, impacting health, the environment, and future generations. Through this blog, let’s explore its roots, repercussions, and remedies, which are essential in our quest for cleaner, healthier skies. Essay writing here becomes more crucial, to raise awareness about air pollution’s dire consequences and drive action for cleaner air.

Table of Contents

• 1 10-Line Essay on Air Pollution
• 2 What are the Causes of Air Pollution?
• 3 What are the effects of Air Pollution?
• 4 Essay on Air Pollution: How to Tackle Air Pollution?
• 5 Essay on Air Pollution Sample (100 Words)
• 6 Essay on Air Pollution Sample (250 Words)

Quick Read: Essay on Child Labour

10-Line Essay on Air Pollution

Below mentioned is a 10-lined essay on air pollution:

• Air pollution is caused by harmful substances known as pollutants.
• The pollutant comes from various sources, like vehicle gasses, forest fires, and other human activities.
• The two biggest sources of air pollution are the burning of fossil fuels and deforestation.
• Air pollution is harmful to humans because it can cause skin and respiratory diseases.
• Air pollution is equally harmful to plants and animals.
• Air pollution can also damage non-living things, such as ancient monuments constructed from marble and limestone.
• Air pollution leads to ozone layer depletion, climate change and global warming.
• Air pollution can damage ecosystems in forests.
• We must take effective steps to reduce air pollution.
• We can reduce air pollution by planting more trees and burning less fossil fuels.

What are the Causes of Air Pollution?

Air pollution is caused by various factors, including:

• Industrial Emissions: Factories and manufacturing processes release pollutants like chemicals and particulate matter into the air.
• Vehicle Emissions: Combustion engines in cars, trucks, and aeroplanes emit exhaust gases, including carbon monoxide and nitrogen oxides.
• Burning Fossil Fuels: The use of coal, oil, and natural gas for energy generation and heating releases pollutants and greenhouse gases.
• Agricultural Activities: Pesticides and fertilizers release chemicals, while livestock emit methane.
• Deforestation: Cutting down trees reduces the planet’s capacity to absorb pollutants.
• Waste Disposal: Improper disposal of waste leads to the release of harmful substances into the air.
• Natural Sources: Volcanic eruptions, dust storms, and wildfires can also contribute to air pollution.

What are the effects of Air Pollution?

Air pollution poses severe health and environmental risks. Short-term exposure can lead to respiratory issues, eye irritation, and exacerbation of pre-existing conditions. Long-term exposure is linked to chronic diseases such as lung cancer, heart disease, and respiratory disorders. 

Additionally, air pollution harms ecosystems, causing acid rain, damaging vegetation, and polluting water bodies. It also contributes to climate change by increasing greenhouse gas concentrations. Addressing air pollution is crucial to safeguard the human health and protecting the planet’s ecosystems and climate.

Essay on Air Pollution: How to Tackle Air Pollution?

Addressing air pollution is paramount for a healthier planet. By curbing emissions, adopting clean technologies, and fostering sustainable practices, we can safeguard our environment and public health. Here are some key points on how to tackle air pollution:

• Reduce Vehicle Emissions
• Improve Industrial Practices
• Plant more trees
• Reduce Indoor Air Pollution
• Promote Renewable Energy
• Encourage Sustainable Practices
• Raise Public Awareness
• Reduce Open Burning
• International Cooperation

Tackling air pollution requires a multi-faceted approach involving government policies, community engagement, and individual responsibility.

Must Read: Essay On Global Warming

Essay on Air Pollution Sample (100 Words)

Air pollution is a pressing environmental issue with far-reaching consequences. It occurs when harmful substances, such as particulate matter and toxic gases, contaminate the atmosphere. These pollutants result from various sources, including industrial emissions, vehicular exhaust, and agricultural activities.

The consequences of air pollution are severe, impacting both human health and the environment. Prolonged exposure to polluted air can lead to respiratory diseases, cardiovascular issues, and even premature death. Additionally, air pollution harms ecosystems, leading to reduced crop yields and biodiversity loss.

Mitigating air pollution requires collective efforts, including stricter emission regulations, cleaner energy sources, and promoting public awareness. By addressing this issue, we can safeguard our health and preserve the environment for future generations.

Essay on Air Pollution Sample (250 Words)

Air pollution is a pressing global issue that affects the health and well-being of people and the environment. It occurs when harmful substances, such as particulate matter, nitrogen oxides, sulfur dioxide, and volatile organic compounds, are released into the atmosphere. This pollution can have dire consequences for both humans and the planet.

First and foremost, air pollution poses a significant threat to human health. Particulate matter and toxic gases can enter the respiratory system, leading to various respiratory diseases like asthma and bronchitis. Long-term exposure to polluted air has also been linked to cardiovascular diseases, lung cancer, and premature death. Vulnerable populations such as children, the elderly, and those with pre-existing health conditions are at higher risk.

Additionally, air pollution has adverse effects on the environment. It contributes to climate change by increasing the concentration of greenhouse gases in the atmosphere, leading to rising global temperatures and more frequent extreme weather events. Moreover, pollutants can harm ecosystems, contaminate water bodies, and damage crops, impacting food security.

The sources of air pollution are diverse, including industrial processes, transportation, agriculture, and energy production. To combat this problem, governments, industries, and individuals must take collective action. Implementing stricter emission standards for vehicles and industrial facilities, transitioning to cleaner energy sources, and promoting public transportation are essential steps in reducing air pollution.

In conclusion, air pollution is a critical issue that affects human health and the environment. Its detrimental effects on respiratory health and its contributions to climate change necessitate urgent action. By adopting sustainable practices and reducing emissions, we can mitigate the impact of air pollution and create a healthier and more sustainable future for all.

Ans. Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or materials.

Ans. To prevent air pollution, reduce vehicle emissions by using public transport, carpooling, or opting for electric vehicles. Promote clean energy sources like wind and solar power. Implement strict industrial emissions standards. Encourage reforestation and green spaces. Educate the public about responsible waste disposal and advocate for clean energy policies.

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Home Essay Samples Environment Air Pollution

The Causes and Effects of Air Pollution: A Comprehensive Analysis

Table of contents, causes of air pollution, effects of air pollution, addressing air pollution, 1. industrial emissions, 2. vehicle emissions, 3. deforestation and land use, 1. health impacts, 2. environmental degradation, 3. climate change, 4. economic costs, 1. regulatory measures, 2. transition to clean energy, 3. reforestation and conservation.

• Brauer, M., Freedman, G., & Frostad, J. (2019). Ambient air pollution exposure estimation for the Global Burden of Disease 2013. Environmental Science & Technology, 50(1), 79-88.
• Chen, L., Yang, C., & Huang, C. (2020). Air pollution and stroke: Association and effect modifiers. International Journal of Environmental Research and Public Health, 17(6), 1959.
• Khaniabadi, Y. O., Daryanoosh, S. M., Hopke, P. K., Ferrante, M., & De Marco, A. (2017). Exposure to PM10, NO2, and O3 and impacts on human health. Environmental Science and Pollution Research, 24(3), 2781-2789.
• Pope III, C. A., & Dockery, D. W. (2006). Health effects of fine particulate air pollution: Lines that connect. Journal of the Air & Waste Management Association, 56(6), 709-742.
• World Health Organization. (2018). Ambient (outdoor) air quality and health. https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health

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Essay on Air Pollution for Students and Children

500+ words essay on air pollution.

Essay on Air Pollution – Earlier the air we breathe in use to be pure and fresh. But, due to increasing industrialization and concentration of poisonous gases in the environment the air is getting more and more toxic day by day. Also, these gases are the cause of many respiratory and other diseases . Moreover, the rapidly increasing human activities like the burning of fossil fuels, deforestation is the major cause of air pollution.

How Air Gets Polluted?

The fossil fuel , firewood, and other things that we burn produce oxides of carbons which got released into the atmosphere. Earlier there happens to be a large number of trees which can easily filter the air we breathe in. But with the increase in demand for land, the people started cutting down of trees which caused deforestation. That ultimately reduced the filtering capacity of the tree.

Moreover, during the last few decades, the numbers of fossil fuel burning vehicle increased rapidly which increased the number of pollutants in the air .

Causes Of Air Pollution

Its causes include burning of fossil fuel and firewood, smoke released from factories , volcanic eruptions, forest fires, bombardment, asteroids, CFCs (Chlorofluorocarbons), carbon oxides and many more.

Besides, there are some other air pollutants like industrial waste, agricultural waste, power plants, thermal nuclear plants, etc.

Greenhouse Effect

The greenhouse effect is also the cause of air pollution because air pollution produces the gases that greenhouse involves. Besides, it increases the temperature of earth surface so much that the polar caps are melting and most of the UV rays are easily penetrating the surface of the earth.

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Effects Of Air Pollution On Health

Moreover, it increases the rate of aging of lungs, decreases lungs function, damage cells in the respiratory system.

Ways To Reduce Air Pollution

Although the level of air pollution has reached a critical point. But, there are still ways by which we can reduce the number of air pollutants from the air.

Reforestation- The quality of air can be improved by planting more and more trees as they clean and filter the air.

Policy for industries- Strict policy for industries related to the filter of gases should be introduced in the countries. So, we can minimize the toxins released from factories.

Use of eco-friendly fuel-  We have to adopt the usage of Eco-friendly fuels such as LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas), bio-gas, and other eco-friendly fuels. So, we can reduce the amount of harmful toxic gases.

To sum it up, we can say that the air we breathe is getting more and more polluted day by day. The biggest contribution to the increase in air pollution is of fossil fuels which produce nitric and sulphuric oxides. But, humans have taken this problem seriously and are devotedly working to eradicate the problem that they have created.

Above all, many initiatives like plant trees, use of eco-friendly fuel are promoted worldwide.

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National Institute of Environmental Health Sciences

Your environment. your health., air pollution and your health, introduction.

Air Pollution

Air pollution is a familiar environmental health hazard. We know what we’re looking at when brown haze settles over a city, exhaust billows across a busy highway, or a plume rises from a smokestack. Some air pollution is not seen, but its pungent smell alerts you.

It is a major threat to global health and prosperity. Air pollution, in all forms, is responsible for more than 6.5 million deaths each year globally , a number that has increased over the past two decades.

What Is Air Pollution?

Air pollution is a mix of hazardous substances from both human-made and natural sources.

Vehicle emissions, fuel oils and natural gas to heat homes, by-products of manufacturing and power generation, particularly coal-fueled power plants, and fumes from chemical production are the primary sources of human-made air pollution.

Nature releases hazardous substances into the air, such as smoke from wildfires, which are often caused by people; ash and gases from volcanic eruptions; and gases, like methane, which are emitted from decomposing organic matter in soils.

Traffic-Related Air Pollution (TRAP), a mixture of gasses and particles, has most of the elements of human-made air pollution: ground-level ozone, various forms of carbon, nitrogen oxides, sulfur oxides, volatile organic compounds, polycyclic aromatic hydrocarbons, and fine particulate matter.

Ozone , an atmospheric gas, is often called smog when at ground level. It is created when pollutants emitted by cars, power plants, industrial boilers, refineries, and other sources chemically react in the presence of sunlight.

Noxious gases , which include carbon dioxide, carbon monoxide, nitrogen oxides (NOx), and sulfur oxides (SOx), are components of motor vehicle emissions and byproducts of industrial processes.

Particulate matter (PM) is composed of chemicals such as sulfates, nitrates, carbon, or mineral dusts. Vehicle and industrial emissions from fossil fuel combustion, cigarette smoke, and burning organic matter, such as wildfires, all contain PM.

A subset of PM, fine particulate matter (PM 2.5) is 30 times thinner than a human hair. It can be inhaled deeply into lung tissue and contribute to serious health problems. PM 2.5 accounts for most health effects due to air pollution in the U.S.

Volatile organic compounds (VOC) vaporize at or near room temperature—hence, the designation volatile. They are called organic because they contain carbon. VOCs are given off by paints, cleaning supplies, pesticides, some furnishings, and even craft materials like glue. Gasoline and natural gas are major sources of VOCs, which are released during combustion.

Polycyclic aromatic hydrocarbons (PAH) are organic compounds containing carbon and hydrogen. Of more than 100 PAHs known to be widespread in the environment, 15 are listed in the Report on Carcinogens . In addition to combustion, many industrial processes, such as iron, steel, and rubber product manufacturing, as well as power generation, also produce PAHs as a by-product. PAHs are also found in particulate matter.

Air Pollution and Climate Change

Air pollution and climate change affect each other through complex interactions in the atmosphere. Air pollution is intricately linked with climate change because both problems come largely from the same sources, such as emissions from burning fossil fuels. Both are threats to people’s health and the environment worldwide. Read more: Health Impacts of Air Quality .

What is NIEHS Doing?

Over its 50-plus year history, NIEHS has been a leader in air pollution research. The institute continues to fund and conduct research into how air pollution affects health and the population groups who are most affected.

How does air pollution affect our health?

When the National Ambient Air Quality Standards were established in 1970, air pollution was regarded primarily as a threat to respiratory health. In 1993, NIEHS researchers published the landmark Six Cities Study , which established an association between fine particulate matter and mortality.

Air pollution exposure is associated with oxidative stress and inflammation in human cells, which may lay a foundation for chronic diseases and cancer. In 2013, the International Agency for Research on Cancer of the World Health Organization (WHO) classified air pollution as a human carcinogen .

Many studies have established that short-term exposure to higher levels of outdoor air pollution is associated with reduced lung function, asthma, cardiac problems, emergency department visits, and hospital admissions . Mortality rates related to air pollution are also a concern. Exposure to the air pollutant PM2.5 is associated with an increased risk of death .

A team of researchers, partially funded by NIEHS, found that deaths decreased after air pollution regulations were implemented and coal-powered plants were retired. The study data covered 21 years. More specifically, they found exposure to PM2.5 from coal was associated with a mortality risk that was twice as high as the risk from exposure to PM2.5 from all sources. PM2.5 from coal is high in sulfur dioxide, black carbon, and metals.

Public health concerns related to high air pollution exposures include cancer, cardiovascular disease, respiratory diseases, diabetes mellitus, obesity, and reproductive, neurological, and immune system disorders.

Research on air pollution and health effects continually advances.

• A large study of more than 57,000 women found living near major roadways may increase a woman’s risk for breast cancer .
• Occupational exposure to benzene, an industrial chemical and component of gasoline, can cause leukemia and is associated with non-Hodgkin’s Lymphoma .
• A long-term study, 2000-2016, found an association between lung cancer incidence and increased reliance on coal for energy generation.
• Using a national dataset of older adults, researchers found that 10-year long exposures to PM2.5 and NO2 increased the risks of colorectal and prostate cancers .

Cardiovascular Disease

• Fine particulate matter can impair blood vessel function and speed up calcification in arteries .
• NIEHS researchers established links between short-term daily exposure by post-menopausal women to nitrogen oxides and increased risk of hemorrhagic stroke .
• For some older Americans, exposure to TRAP can result in lowered levels of high-density lipoprotein , sometimes called good cholesterol, increasing their risk for cardiovascular disease.
• According to a National Toxicology Program (NTP) report , TRAP exposure also increases a pregnant woman’s risk for dangerous changes in blood pressure, known as hypertensive disorders, which are a leading cause of pre-term birth, low birth weight, and maternal and fetal illness and death.

Respiratory Disease

• Air pollution can affect lung development and is implicated in the development of emphysema , asthma, and other respiratory diseases, such as chronic obstructive pulmonary disease (COPD).
• Increases in asthma prevalence and severity are linked to urbanization and outdoor air pollution. Children living in low-income urban areas tend to have more asthma cases than others. Research published in 2023 tied two air pollutants, ozone and PM2.5, to asthma-related changes in children’s airways.
• In a study of 50,000 women across the country, long-term exposure to PM2.5, PM10, and nitrogen dioxide were linked to chronic bronchitis .
• In 2020, a major public health challenge was confluence of the COVID-19 pandemic and wildfires across the western U.S. Building on a well-established connection between air pollution and respiratory-tract infections, a study linked exposure to wildfire smoke with more severe cases of COVID-19 and deaths .

Whom does air pollution affect the most?

Air pollution affects everyone’s health, but certain groups may be harmed more. Almost 9 out of 10 people who live in urban areas worldwide are affected by air pollution.

NIEHS-funded research indicates there are racial or ethnic and socioeconomic disparities in air pollution emissions. Air pollution emissions have decreased over past decades but the changes vary by demographics . This research found that people with annual incomes above $70,000 generally experience greater declines in industry, energy, transportation, residential, and commercial-related emissions than do people with lower incomes.

The NIEHS-funded Children’s Health Study at the University of Southern California is one of the largest studies of the long-term effects of air pollution on children’s respiratory health. Among its findings:

• Higher air pollution levels increase short-term respiratory infections, which lead to more school absences.
• Children who play several outdoor sports and live in high ozone communities are more likely to develop asthma.
• Children living near busy roads have an increased chance of developing asthma.
• Children who were exposed to high levels of air pollutants were more likely to develop bronchitis symptoms in adulthood .
• Living in communities with higher pollution levels can cause lung damage .

Other studies on women and children

• Breathing PM 2.5, even at relatively low levels, may alter the size of a child's developing brain , which may ultimately increase the risk for cognitive and emotional problems later in adolescence.
• In a large-scale study that looked at more than 1 million birth records, prenatal PM2.5 exposure was associated with an increased risk of cerebral palsy . While this finding adds to knowledge about environmental risk factors for cerebral palsy development and how to reduce the chance of it developing, further studies are needed. Prenatal exposure to PAHs was associated with brain development effects, slower processing speed, attention-deficit and hyperactivity disorder (ADHD) symptoms, and other neurobehavioral problems in urban youth .
• Prenatal exposure to air pollution may play a role in the development of ADHD-related behavior problems in childhood.
• Prenatal exposure to particulate matter was associated with low birth weight .
• Women exposed to high levels of fine particulate matter during pregnancy, particularly in the third trimester, may have up to twice the risk of having a child with autism .
• Second and third trimester exposure to PM2.5 might increase the chance of those children having high blood pressure in early life .
• A large study of more than 300,000 women found long-term exposure to air pollution, especially ozone and PM2.5, during and after pregnancy increases the risk of postpartum depression .
• The study with data on more than 5 million babies assessed associations between prenatal exposure to wildfire smoke and the risk of preterm birth. The researchers found that exposure to high levels of wildfire particulate matter during any period of pregnancy was associated with a greater chance of preterm birth .

Older adults

• Alzheimer’s disease and related dementias are a public health challenge for aging populations. NIEHS-funded researchers at the University of Washington identified a link between air pollution and dementias. This well-conducted study adds considerable evidence that ambient air fine particles increase risk of dementias . Conversely, a multi-year study published in 2022 shows improved air quality is associated with lower risk of dementia in older women. The researchers also stated this decline in dementia risk was equivalent to taking nearly 2 1/2 years off the age of the women studied.
• A large, nationally representative study looked at PM2.5 from many sources and incident dementia. Emissions from agriculture, traffic, coal combustion, and wildfires, in particular, were associated with increased rates of dementia .
• Air pollution was linked to a greater chance of developing several neurological disorders , including Parkinson's disease, Alzheimer's disease, and other dementias. Hospital admissions data from 63 million older adults in the U.S., obtained over 17 years (2000-2016), was analyzed along with estimated PM2.5 concentrations by zip code to conduct the study. Another study with data from 10-year long exposures also found a relationship between CO and PM2.5 and an increased chance of developing Parkinson’s disease .
• Osteoporosis affects women more than men. A large study associated high levels of air pollutants with bone damage , particularly in the lumbar spine, among postmenopausal women. This study expands previous findings linking air pollution and bone damage.
• Nutrients may counter some harmful effects from air pollution. A 2020 study found omega-3 fatty acids , obtained by eating certain fish, may protect against PM2.5-associated brain shrinkage in older women.

Rural dwellers

• NIEHS supported a translational research project,  Addressing Air Pollution and Asthma (1MB) , that may lead to improved health for children suffering from asthma. They found that certain agricultural practices contribute to poor air quality and asthma among children. The team combined high-efficiency particulate air (HEPA) cleaners and a home-based education program to reduce children’s exposure to pollutants in the home.
• Exposure to smoke from agricultural burns for as little as two weeks per year may worsen children's respiratory health outcomes, according to research supported by NIEHS. The study was conducted in response to community concerns about children's heath in Imperial Valley, a rural, agricultural area in southern California. Such agricultural burning is done to clear post-harvest crop remnants. This form of clearing is inexpensive, and farmers in the area do not have other economical methods for disposing of waste.
• In the rural U.S., large-scale animal feeding operations might compromise regional air quality through emission of pollutants, such as ammonia gas. A study found acute lung function problems in children with asthma in such areas.

NIEHS and community involvement

NIEHS supports community participation in the research process and encourages collaborative approaches that build capacity in communities to address environmental health concerns. Community-engaged research and citizen science are two types of collaborative research approaches.

For example, NIEHS grant recipients developed community-level tactics and public policies for reducing exposure to TRAP:

• Using high-efficiency particulate air (HEPA) filtration.
• Building land-use buffers and vegetation barriers.
• Improving urban design with gardens, parks, and street-side trees.
• Creating active-travel options, such as bicycling and walking paths.

Why improving air quality matters

• Air pollution and birth outcomes are linked as global public health concerns. Researchers analyzed indoor and outdoor air pollution data from all inhabited continents along with key pregnancy outcomes. Their findings indicate efforts to reduce PM2.5 exposure could lead to significant reductions in the number of low-birth weight and pre-term birth infants worldwide . Air pollution reduction would be especially beneficial for children born in low- and middle-income countries.
• Among children in Southern California, decreases in ambient nitrogen dioxide and PM 2.5 were associated with fewer cases of asthma .
• Bronchitis symptoms declined as pollution levels dropped in the Los Angeles region.
• Improving air quality may improve cognitive function and reduce dementia risk, according to studies supported in part by NIH and the Alzheimer's Association.
• When fossil-fuel power plants close, nearby air pollution is reduced. A study found the incidence of preterm births went down within 5 kilometers of retired coal and oil-powered plant locations.

Further Reading

Stories from the environmental factor (niehs newsletter).

• Wildfire Smoke: Effects on Male Fertility, Offspring Studied by Expert (August 2024)
• Air Pollution May Trigger DNA Modifications Tied to Alzheimer’s Disease (April 2024)
• Scientific Journeys: Using AI to Track a Major Source of Pollution (March 2024)
• Burn Pits’ Complex Emissions Simulated in NIEHS Grantee’s Laboratory (December 2023)
• Indoor Wood-burning May Be Linked to Lung Cancer in U.S. Women (September 2023)
• Everyday Air Pollution Can Harm Brain Development in Adolescents (September 2023)
• Wildfire Smoke, Other Air Pollution Can Harm Brain Health, Expert Says (August 2023)
• Burning Plastic Can Affect Air Quality, Public Health (August 2022)
• Interventions Needed to Slow Climate-driven Air Pollution, Researchers Note (March 2022)
• Air Pollution and Forever Chemicals Continue to Pose Health Risks (March 2022)
• Air Pollution Affects Children’s Brain Structure (February 2022)
• Increasing Evidence Links Air Pollution With Breast Cancer (November 2021)
• Fine Particulate Air Pollution Associated With Higher Dementia Risk (September 2021)

Printable Fact Sheets

Fact sheets.

Breast Cancer: Why the Environment Matters

Climate Change and Human Health

Lung Health and Your Environment

Partnerships for Environmental Public Health (PEPH)

• When Wildfires Hit Close to Home is about NIEHS-funded research on the complexity of urban wildfires and how they may affect human health.
• Wildfire Smoke and Children's Health

Additional Resources

• Air Pollution Linked to Dementia Cases (September 2023) – In this edition of NIH Research Matters, read about findings from the Health and Retirement Study, funded by the National Institute on Aging, that showed higher air pollution exposure was linked to an increased risk of dementia. After consideration of all sources, fine particulate matter, or PM2.5, from agriculture and wildfires were specifically associated with an increased risk of dementia. Reducing such exposures might help lower the incidence of dementia. The study was published in JAMA Internal Medicine.
• AirNow , a tool developed in partnership by several government agencies, allows you to monitor air quality in real time anywhere in the U.S. Simply enter your zip code as indicated on the website.
• EPA's Air Sensor Toolbox provides information on the operation and use of air-sensor monitoring systems for technology developers, air-quality managers, citizen scientists, and the public.
• NIH Climate Change and Health Initiative – This solutions-focused research initiative aims to reduce the health consequences associated with extreme weather events and evolving climate conditions. NIH has a strong history of creating innovative tools, technologies, and data-driven solutions to address global environmental problems.
• Smoke-ready Toolbox for Wildfires is a compendium of resources from the EPA to help educate you about the risks of smoke exposure and actions that protect your health.

Related Health Topics

• Exposure Science
• Gene and Environment Interaction
• Lung Diseases

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Air Pollution: Current and Future Challenges

Despite dramatic progress cleaning the air since 1970, air pollution in the United States continues to harm people’s health and the environment. Under the Clean Air Act, EPA continues to work with state, local and tribal governments, other federal agencies, and stakeholders to reduce air pollution and the damage that it causes.

• Learn about more about air pollution, air pollution programs, and what you can do.

Outdoor air pollution challenges facing the United States today include:

• Meeting health-based standards for common air pollutants
• Limiting climate change
• Reducing risks from toxic air pollutants
• Protecting the stratospheric ozone layer against degradation

Indoor air pollution, which arises from a variety of causes, also can cause health problems. For more information on indoor air pollution, which is not regulated under the Clean Air Act, see EPA’s indoor air web site .

Air Pollution Challenges: Common Pollutants

Great progress has been made in achieving national air quality standards, which EPA originally established in 1971 and updates periodically based on the latest science. One sign of this progress is that visible air pollution is less frequent and widespread than it was in the 1970s.

However, air pollution can be harmful even when it is not visible. Newer scientific studies have shown that some pollutants can harm public health and welfare even at very low levels. EPA in recent years revised standards for five of the six common pollutants subject to national air quality standards. EPA made the standards more protective because new, peer-reviewed scientific studies showed that existing standards were not adequate to protect public health and the environment.

Status of common pollutant problems in brief

Today, pollution levels in many areas of the United States exceed national air quality standards for at least one of the six common pollutants:

• Although levels of particle pollution and ground-level ozone pollution are substantially lower than in the past, levels are unhealthy in numerous areas of the country. Both pollutants are the result of emissions from diverse sources, and travel long distances and across state lines. An extensive body of scientific evidence shows that long- and short-term exposures to fine particle pollution, also known as fine particulate matter (PM 2.5 ), can cause premature death and harmful effects on the cardiovascular system, including increased hospital admissions and emergency department visits for heart attacks and strokes. Scientific evidence also links PM to harmful respiratory effects, including asthma attacks. Ozone can increase the frequency of asthma attacks, cause shortness of breath, aggravate lung diseases, and cause permanent damage to lungs through long-term exposure. Elevated ozone levels are linked to increases in hospitalizations, emergency room visits and premature death. Both pollutants cause environmental damage, and fine particles impair visibility. Fine particles can be emitted directly or formed from gaseous emissions including sulfur dioxide or nitrogen oxides. Ozone, a colorless gas, is created when emissions of nitrogen oxides and volatile organic compounds react.  
• For unhealthy peak levels of sulfur dioxide and nitrogen dioxide , EPA is working with states and others on ways to determine where and how often unhealthy peaks occur. Both pollutants cause multiple adverse respiratory effects including increased asthma symptoms, and are associated with increased emergency department visits and hospital admissions for respiratory illness. Both pollutants cause environmental damage, and are byproducts of fossil fuel combustion.  
• Airborne lead pollution, a nationwide health concern before EPA phased out lead in motor vehicle gasoline under Clean Air Act authority, now meets national air quality standards except in areas near certain large lead-emitting industrial facilities. Lead is associated with neurological effects in children, such as behavioral problems, learning deficits and lowered IQ, and high blood pressure and heart disease in adults.  
• The entire nation meets the carbon monoxide air quality standards, largely because of emissions standards for new motor vehicles under the Clean Air Act.

In Brief: How EPA is working with states and tribes to limit common air pollutants

• EPA's air research provides the critical science to develop and implement outdoor air regulations under the Clean Air Act and puts new tools and information in the hands of air quality managers and regulators to protect the air we breathe.  
• To reflect new scientific studies, EPA revised the national air quality standards for fine particles (2006, 2012), ground-level ozone (2008, 2015), sulfur dioxide (2010), nitrogen dioxide (2010), and lead (2008). After the scientific review, EPA decided to retain the existing standards for carbon monoxide.  EPA strengthened the air quality standards for ground-level ozone in October 2015 based on extensive scientific evidence about ozone’s effects.

EPA has designated areas meeting and not meeting the air quality standards for the 2006 and 2012 PM standards and the 2008 ozone standard, and has completed an initial round of area designations for the 2010 sulfur dioxide standard. The agency also issues rules or guidance for state implementation of the various ambient air quality standards – for example, in March 2015, proposing requirements for implementation of current and future fine particle standards. EPA is working with states to improve data to support implementation of the 2010 sulfur dioxide and nitrogen dioxide standards.

For areas not meeting the national air quality standards, states are required to adopt state implementation plan revisions containing measures needed to meet the standards as expeditiously as practicable and within time periods specified in the Clean Air Act (except that plans are not required for areas with “marginal” ozone levels).

• EPA is helping states to meet standards for common pollutants by issuing federal emissions standards for new motor vehicles and non-road engines, national emissions standards for categories of new industrial equipment (e.g., power plants, industrial boilers, cement manufacturing, secondary lead smelting), and technical and policy guidance for state implementation plans. EPA and state rules already on the books are projected to help 99 percent of counties with monitors meet the revised fine particle standards by 2020. The Mercury and Air Toxics Standards for new and existing power plants issued in December 2011 are achieving reductions in fine particles and sulfur dioxide as a byproduct of controls required to cut toxic emissions.  
• Vehicles and their fuels continue to be an important contributor to air pollution. EPA in 2014 issued standards commonly known as Tier 3, which consider the vehicle and its fuel as an integrated system, setting new vehicle emissions standards and a new gasoline sulfur standard beginning in 2017. The vehicle emissions standards will reduce both tailpipe and evaporative emissions from passenger cars, light-duty trucks, medium-duty passenger vehicles, and some heavy-duty vehicles. The gasoline sulfur standard will enable more stringent vehicle emissions standards and will make emissions control systems more effective. These rules further cut the sulfur content of gasoline. Cleaner fuel makes possible the use of new vehicle emission control technologies and cuts harmful emissions in existing vehicles. The standards will reduce atmospheric levels of ozone, fine particles, nitrogen dioxide, and toxic pollution.

Learn more about common pollutants, health effects, standards and implementation:

• fine particles
• ground-level ozone
• sulfur dioxide
• nitrogen dioxide
• carbon monoxide

Air Pollution Challenges: Climate Change

EPA determined in 2009 that emissions of carbon dioxide and other long-lived greenhouse gases that build up in the atmosphere endanger the health and welfare of current and future generations by causing climate change and ocean acidification. Long-lived greenhouse gases , which trap heat in the atmosphere, include carbon dioxide, methane, nitrous oxide, and fluorinated gases. These gases are produced by a numerous and diverse human activities.

In May 2010, the National Research Council, the operating arm of the National Academy of Sciences, published an assessment which concluded that “climate change is occurring, is caused largely by human activities, and poses significant risks for - and in many cases is already affecting - a broad range of human and natural systems.” 1 The NRC stated that this conclusion is based on findings that are consistent with several other major assessments of the state of scientific knowledge on climate change. 2

Climate change impacts on public health and welfare

The risks to public health and the environment from climate change are substantial and far-reaching. Scientists warn that carbon pollution and resulting climate change are expected to lead to more intense hurricanes and storms, heavier and more frequent flooding, increased drought, and more severe wildfires - events that can cause deaths, injuries, and billions of dollars of damage to property and the nation’s infrastructure.

Carbon dioxide and other greenhouse gas pollution leads to more frequent and intense heat waves that increase mortality, especially among the poor and elderly. 3 Other climate change public health concerns raised in the scientific literature include anticipated increases in ground-level ozone pollution 4 , the potential for enhanced spread of some waterborne and pest-related diseases 5 , and evidence for increased production or dispersion of airborne allergens. 6

Other effects of greenhouse gas pollution noted in the scientific literature include ocean acidification, sea level rise and increased storm surge, harm to agriculture and forests, species extinctions and ecosystem damage. 7 Climate change impacts in certain regions of the world (potentially leading, for example, to food scarcity, conflicts or mass migration) may exacerbate problems that raise humanitarian, trade and national security issues for the United States. 8

The U.S. government's May 2014 National Climate Assessment concluded that climate change impacts are already manifesting themselves and imposing losses and costs. 9 The report documents increases in extreme weather and climate events in recent decades, with resulting damage and disruption to human well-being, infrastructure, ecosystems, and agriculture, and projects continued increases in impacts across a wide range of communities, sectors, and ecosystems.

Those most vulnerable to climate related health effects - such as children, the elderly, the poor, and future generations - face disproportionate risks. 10 Recent studies also find that certain communities, including low-income communities and some communities of color (more specifically, populations defined jointly by ethnic/racial characteristics and geographic location), are disproportionately affected by certain climate-change-related impacts - including heat waves, degraded air quality, and extreme weather events - which are associated with increased deaths, illnesses, and economic challenges. Studies also find that climate change poses particular threats to the health, well-being, and ways of life of indigenous peoples in the U.S.

The National Research Council (NRC) and other scientific bodies have emphasized that it is important to take initial steps to reduce greenhouse gases without delay because, once emitted, greenhouse gases persist in the atmosphere for long time periods. As the NRC explained in a recent report, “The sooner that serious efforts to reduce greenhouse gas emissions proceed, the lower the risks posed by climate change, and the less pressure there will be to make larger, more rapid, and potentially more expensive reductions later.” 11

In brief: What EPA is doing about climate change

Under the Clean Air Act, EPA is taking initial common sense steps to limit greenhouse gas pollution from large sources:

EPA and the National Highway and Traffic Safety Administration between 2010 and 2012 issued the first national greenhouse gas emission standards and fuel economy standards for cars and light trucks for model years 2012-2025, and for medium- and heavy-duty trucks for 2014-2018.  Proposed truck standards for 2018 and beyond were announced in June 2015.  EPA is also responsible for developing and implementing regulations to ensure that transportation fuel sold in the United States contains a minimum volume of renewable fuel. Learn more about clean vehicles

EPA and states in 2011 began requiring preconstruction permits that limit greenhouse gas emissions from large new stationary sources - such as power plants, refineries, cement plants, and steel mills - when they are built or undergo major modification. Learn more about GHG permitting

• On August 3, 2015, President Obama and EPA announced the Clean Power Plan – a historic and important step in reducing carbon pollution from power plants that takes real action on climate change. Shaped by years of unprecedented outreach and public engagement, the final Clean Power Plan is fair, flexible and designed to strengthen the fast-growing trend toward cleaner and lower-polluting American energy. With strong but achievable standards for power plants, and customized goals for states to cut the carbon pollution that is driving climate change, the Clean Power Plan provides national consistency, accountability and a level playing field while reflecting each state’s energy mix. It also shows the world that the United States is committed to leading global efforts to address climate change. Learn more about the Clean Power Plan, the Carbon Pollution Standards, the Federal Plan, and model rule for states

The Clean Power Plan will reduce carbon pollution from existing power plants, the nation’s largest source, while maintaining energy reliability and affordability.  The Clean Air Act creates a partnership between EPA, states, tribes and U.S. territories – with EPA setting a goal, and states and tribes choosing how they will meet it.  This partnership is laid out in the Clean Power Plan.

Also on August 3, 2015, EPA issued final Carbon Pollution Standards for new, modified, and constructed power plants, and proposed a Federal Plan and model rules to assist states in implementing the Clean Power Plan.

On February 9, 2016, the Supreme Court stayed implementation of the Clean Power Plan pending judicial review. The Court’s decision was not on the merits of the rule. EPA firmly believes the Clean Power Plan will be upheld when the merits are considered because the rule rests on strong scientific and legal foundations.

On October 16, 2017, EPA  proposed to repeal the CPP and rescind the accompanying legal memorandum.

EPA is implementing its Strategy to Reduce Methane Emissions released in March 2014. In January 2015 EPA announced a new goal to cut methane emissions from the oil and gas sector by 40 – 45 percent from 2012 levels by 2025, and a set of actions by EPA and other agencies to put the U.S. on a path to achieve this ambitious goal. In August 2015, EPA proposed new common-sense measures to cut methane emissions, reduce smog-forming air pollution and provide certainty for industry through proposed rules for the oil and gas industry . The agency also proposed to further reduce emissions of methane-rich gas from municipal solid waste landfills . In March 2016 EPA launched the National Gas STAR Methane Challenge Program under which oil and gas companies can make, track and showcase ambitious commitments to reduce methane emissions.

EPA in July 2015 finalized a rule to prohibit certain uses of hydrofluorocarbons -- a class of potent greenhouse gases used in air conditioning, refrigeration and other equipment -- in favor of safer alternatives. The U.S. also has proposed amendments to the Montreal Protocol to achieve reductions in HFCs internationally.

Learn more about climate science, control efforts, and adaptation on EPA’s climate change web site

Air Pollution Challenges: Toxic Pollutants

While overall emissions of air toxics have declined significantly since 1990, substantial quantities of toxic pollutants continue to be released into the air. Elevated risks can occur in urban areas, near industrial facilities, and in areas with high transportation emissions.

Numerous toxic pollutants from diverse sources

Hazardous air pollutants, also called air toxics, include 187 pollutants listed in the Clean Air Act. EPA can add pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or to cause adverse environmental effects.

Examples of air toxics include benzene, which is found in gasoline; perchloroethylene, which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint stripper by a number of industries. Other examples of air toxics include dioxin, asbestos, and metals such as cadmium, mercury, chromium, and lead compounds.

Most air toxics originate from manmade sources, including mobile sources such as motor vehicles, industrial facilities and small “area” sources. Numerous categories of stationary sources emit air toxics, including power plants, chemical manufacturing, aerospace manufacturing and steel mills. Some air toxics are released in large amounts from natural sources such as forest fires.

Health risks from air toxics

EPA’s most recent national assessment of inhalation risks from air toxics 12 estimated that the whole nation experiences lifetime cancer risks above ten in a million, and that almost 14 million people in more than 60 urban locations have lifetime cancer risks greater than 100 in a million. Since that 2005 assessment, EPA standards have required significant further reductions in toxic emissions.

Elevated risks are often found in the largest urban areas where there are multiple emission sources, communities near industrial facilities, and/or areas near large roadways or transportation facilities. Benzene and formaldehyde are two of the biggest cancer risk drivers, and acrolein tends to dominate non-cancer risks.

In brief: How EPA is working with states and communities to reduce toxic air pollution

EPA standards based on technology performance have been successful in achieving large reductions in national emissions of air toxics. As directed by Congress, EPA has completed emissions standards for all 174 major source categories, and 68 categories of small area sources representing 90 percent of emissions of 30 priority pollutants for urban areas. In addition, EPA has reduced the benzene content in gasoline, and has established stringent emission standards for on-road and nonroad diesel and gasoline engine emissions that significantly reduce emissions of mobile source air toxics. As required by the Act, EPA has completed residual risk assessments and technology reviews covering numerous regulated source categories to assess whether more protective air toxics standards are warranted. EPA has updated standards as appropriate. Additional residual risk assessments and technology reviews are currently underway.

EPA also encourages and supports area-wide air toxics strategies of state, tribal and local agencies through national, regional and community-based initiatives. Among these initiatives are the National Clean Diesel Campaign , which through partnerships and grants reduces diesel emissions for existing engines that EPA does not regulate; Clean School Bus USA , a national partnership to minimize pollution from school buses; the SmartWay Transport Partnership to promote efficient goods movement; wood smoke reduction initiatives; a collision repair campaign involving autobody shops; community-scale air toxics ambient monitoring grants ; and other programs including Community Action for a Renewed Environment (CARE). The CARE program helps communities develop broad-based local partnerships (that include business and local government) and conduct community-driven problem solving as they build capacity to understand and take effective actions on addressing environmental problems.

Learn more about air toxics, stationary sources of emissions, and control efforts Learn more about mobile source air toxics and control efforts

Air Pollution Challenges: Protecting the Stratospheric Ozone Layer

The  ozone (O 3 ) layer  in the stratosphere protects life on earth by filtering out harmful ultraviolet radiation (UV) from the sun. When chlorofluorocarbons (CFCs) and other ozone-degrading chemicals  are emitted, they mix with the atmosphere and eventually rise to the stratosphere. There, the chlorine and the bromine they contain initiate chemical reactions that destroy ozone. This destruction has occurred at a more rapid rate than ozone can be created through natural processes, depleting the ozone layer.

The toll on public health and the environment

Higher levels of  ultraviolet radiation  reaching Earth's surface lead to health and environmental effects such as a greater incidence of skin cancer, cataracts, and impaired immune systems. Higher levels of ultraviolet radiation also reduce crop yields, diminish the productivity of the oceans, and possibly contribute to the decline of amphibious populations that is occurring around the world.

In brief: What’s being done to protect the ozone layer

Countries around the world are phasing out the production of chemicals that destroy ozone in the Earth's upper atmosphere under an international treaty known as the Montreal Protocol . Using a flexible and innovative regulatory approach, the United States already has phased out production of those substances having the greatest potential to deplete the ozone layer under Clean Air Act provisions enacted to implement the Montreal Protocol. These chemicals include CFCs, halons, methyl chloroform and carbon tetrachloride. The United States and other countries are currently phasing out production of hydrochlorofluorocarbons (HCFCs), chemicals being used globally in refrigeration and air-conditioning equipment and in making foams. Phasing out CFCs and HCFCs is also beneficial in protecting the earth's climate, as these substances are also very damaging greenhouse gases.

Also under the Clean Air Act, EPA implements regulatory programs to:

Ensure that refrigerants and halon fire extinguishing agents are recycled properly.

Ensure that alternatives to ozone-depleting substances (ODS) are evaluated for their impacts on human health and the environment.

Ban the release of ozone-depleting refrigerants during the service, maintenance, and disposal of air conditioners and other refrigeration equipment.

Require that manufacturers label products either containing or made with the most harmful ODS.

These vital measures are helping to protect human health and the global environment.

The work of protecting the ozone layer is not finished. EPA plans to complete the phase-out of ozone-depleting substances that continue to be produced, and continue efforts to minimize releases of chemicals in use. Since ozone-depleting substances persist in the air for long periods of time, the past use of these substances continues to affect the ozone layer today. In our work to expedite the recovery of the ozone layer, EPA plans to augment CAA implementation by:

Continuing to provide forecasts of the expected risk of overexposure to UV radiation from the sun through the UV Index, and to educate the public on how to protect themselves from over exposure to UV radiation.

Continuing to foster domestic and international partnerships to protect the ozone layer.

Encouraging the development of products, technologies, and initiatives that reap co-benefits in climate change and energy efficiency.

Learn more About EPA’s Ozone Layer Protection Programs

Some of the following links exit the site

1 National Research Council (2010), Advancing the Science of Climate Change , National Academy Press, Washington, D.C., p. 3.

2 National Research Council (2010), Advancing the Science of Climate Change , National Academy Press, Washington, D.C., p. 286.

3 USGCRP (2009).  Global Climate Change Impacts in the United States . Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

4 CCSP (2008).  Analyses of the effects of global change on human health and welfare and human systems . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Gamble, J.L. (ed.), K.L. Ebi, F.G. Sussman, T.J. Wilbanks, (Authors). U.S. Environmental Protection Agency, Washington, DC, USA.

5 Confalonieri, U., B. Menne, R. Akhtar, K.L. Ebi, M. Hauengue, R.S. Kovats, B. Revich and A. Woodward (2007). Human health. In:  Climate Change 2007: Impacts, Adaptation and Vulnerability  .  Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change  Parry, M.L., O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, (eds.), Cambridge University Press, Cambridge, United Kingdom.

7 An explanation of observed and projected climate change and its associated impacts on health, society, and the environment is included in the EPA’s Endangerment Finding and associated technical support document (TSD). See EPA, “ Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act ,” 74 FR 66496, Dec. 15, 2009. Both the Federal Register Notice and the Technical Support Document (TSD) for Endangerment and Cause or Contribute Findings are found in the public docket, Docket No. EPA-OAR-2009-0171.

8 EPA, Endangerment Finding , 74 FR 66535.

9 . U.S. Global Change Research Program, Climate Change Impacts in the United States: The Third National Climate Assessment , May 2014.

10 EPA, Endangerment Finding , 74 FR 66498.

11 National Research Council (2011) America’s Climate Choices: Report in Brief , Committee on America’s Climate Choices, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., p. 2.

12 EPA, 2005 National-Scale Air Toxics Assessment (2011).

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Essay on Air Pollution: Sources, Types and Effects

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Essay on Air Pollution: Sources, Types and Effects!

The earth’s atmosphere contains various gases, water vapor and suspended particles. The dry air of the atmosphere is composed of four major gases nitrogen, oxygen, argon and carbon dioxide that account for more than 99.5% (Table 55.1).

The other gases found in traces in the air include helium, methane, krypton, hydrogen, carbon monoxide, nitrous oxide (N 2 O), nitrogen dioxide (NO 2 ), ammonia, ozone, sulfur dioxide and hydrogen sulfide.

The lower part of the atmosphere (up to about 12 km) also contains water vapor at a concentration, ranging from 0.01 to 5.0%. This water is mostly contributed by evaporation from the hydrosphere.

The air is getting contaminated by pollution due the natural and unnatural activities of man. Air pollution is basically the presence of foreign substances in the air at a concentration that will adversely affect the health and property of the individual.

As per the World Health Organization (WHO) criteria, air pollution refers to ‘the substances put into the air by the activity of mankind into concentration sufficient to cause harmful effects to his health, vegetables, property or to interfere with the enjoyment of his property.’

According to Indian Standards Institution ‘air pollution is the presence in ambient atmosphere of substances generally resulting from the activity of man, in sufficient concentration, present for sufficient time and under circumstances which interfere significantly with the comfort, health or welfare of a person or with the full use or enjoyment of his property.’

The term pollutant refers to a substance which increases in quantity in the air and adversely affects the environment e.g. carbon monoxide, sulfur dioxide, lead. On the other hand, a contaminant is a substance which is not present in nature, but released due to human activity e.g. methyl isocyanate. DDT, malathion. However, this distinction is not very rigid, and most authors use the term pollutant to represent both (pollutant as well as contaminant).

Sources of Air Pollutants :

The sources that contribute to air pollution may be broadly categorized into two types:

1. Natural sources:

These include volcanic eruptions, sand storms, and decomposition of organic matter, forest fire, pollen grains and cormic dust. The problem of pollution due to natural sources in general, is considered to be minimal.

2. Anthropogenic (man-made) sources:

Air pollution due to human-induced activities is very high. The sources of pollution include industries, burning of fossil fuels, emissions from vehicles, agricultural activities and warfare’s. The sources of air pollution may also considered as stationary (industries, open combustion) or mobile (motor vehicles, trains, aircraft) in nature.

Industrial pollutants :

The major problem of air pollution is due to industrial activities. Among the several industries, nine types of industries are considered to be the major air pollutant generating industries (Table 55.2). Among these, thermal power plants, steel industries, petroleum refineries and metal smelters are the most dangerous polluting industries.

Classification of Air Pollutants :

Air pollutants are classified based on their origin, chemical composition and the state of the matter.

Classification based on origin :

Air pollutants are divided into two categories, based on their origin-primary and secondary.

Primary air pollutants:

These pollutants are directly emitted into the atmosphere and present there as such (i.e. in the form they are originally emitted). Primary air pollutants contribute to as much as 90% global air pollution. Particulates, carbon monoxide, (CO), oxides of sulfur (SO x ), oxides of nitrogen (NO x ), hydrocarbons (HCs), radioactive compounds, pollen and bacteria are the major primary air pollutants.

Secondary air pollutants:

These are produced in the air as a result of interaction among the primary pollutants, or by a reaction that occurs between a primary pollutant and a normal constituent of the atmosphere. Good examples of secondary air pollutants are ozone (O 3 ), peroxyacetyl nitrate (PAN), formaldehyde and smog.

Classification based on chemical composition:

According to chemical composition, air pollutants are categorized as organic and inorganic.

Organic air pollutants:

These pollutants are mainly composed of carbon and hydrogen. In addition, oxygen, nitrogen, sulfur and phosphorus may also be present e.g. hydrocarbons, organic sulfur compounds, aldehydes, ketones, carboxylic acids.

Inorganic air pollutants:

These are purely inorganic in nature e.g. carbon dioxide, carbon monoxide, oxides of sulfur, oxides of nitrogen, ozone.

Classification based on the state of matter:

Air pollutants may be divided into two types, based on the state in which they exist-particulate and gaseous.

Particulate air pollutants:

The solids and liquids dispersed in the atmosphere constitute the particulate air pollutants. Solid particulates e.g. smoke, dust, fly ash. Liquid particulates e.g. mist, fog, spray.

Gaseous air pollutants:

These are the organic and inorganic gases that are present in the air as pollutants. Organic gases e.g. methane, butane, aldehydes. Inorganic gases e.g. CO 2 , SO 2 , NO 2 , NH 3 , and H 2 S.

Effects of Air Pollution:

Majority of the air pollutants are present normally in the atmosphere, although at low concentrations. Such pollutants are unlikely to cause any significant harmful effects. When the concentrations of the air pollutants go beyond the acceptable limits (variable for each pollutant) they are dangerous and cause several harmful effects. The WHO has set guidelines and fixed threshold limit values (TLV) for each air pollutant. The general effects of air pollutants on humans, plants, animals, materials and global climate are briefly described.

Effects of air pollutants on humans :

On an average, man breathes around 22,000 times and inhales about 16 kg of air each day. Primarily, the air we breathe is life sustaining. However, pollutants present in the air often cause harmful effects. The nature of the pollutant, its concentration and duration of exposure are among the factors that affect the health of humans.

In general, infants, elderly people and those with respiratory diseases are more susceptible to air pollution. Further, adverse health effects of air pollutants are maximum during winter compared to other seasons. Some of the important air pollutants and their effects on human health are given in Table 55.3. Sulfur dioxide is the most dangerous pollutant gas to man. It is produced in many industries and causes respiratory disorders.

Oxides of nitrogen and carbon monoxide reduce O 2 supply to the tissues. Lead pollution is associated with tissue damage and abnormal behavioural pattern. Suspended particulate matter (SPM) mainly causes chronic pulmonary diseases. Prolonged exposure to radioactive isotopes results in anemia, besides a heavy risk of cancer and genetic defects.

Effects of air pollutants on plants:

At low concentration, the air pollutants may not cause any visible damage to the plants. However, even at this level, the pollutants may be stored and introduced into the food chain. This in turn, may affect animals as well as humans.

The entry of the gas air pollutants (SO 2 , NO 2 ) predominantly occurs through the stomata, openings on the leaves. Stomata are located at the bottom of the leaves through which CO 2 enters for photosynthesis. In the same way as CO 2 enters the leaves, the gaseous pollutants also enter and cause various effects.

The solid particles are adsorbed on the surfaces of leaves. This may result in clogging of the stomata and a reduced intake of CO 2 . Further, the suspended particles deposited on the leaves, may adversely affect the leaf functions (reduced exposure to sun light, decrease in chlorophyll content, interruption of gaseous exchange).

The effects of common air pollutants on leaves are given in Table 55.4. The sensitivity of plants to pollutants depends on many factors such as climatic conditions (light, temperature, and humidity), soil and water, and the individual plant’s response to a particular pollutant. The major air pollutants affecting plants are SO 2 , NO 2 , O 3 , fluorides, ammonia and ethylene, besides the particulates. They may damage the plants to varying degrees as outlined in Table 55.4.

The sensitivity of certain selected plants to air pollutants can be used for bio-monitoring of air pollution.

Effects of air pollutants on animals :

The effect of air pollution on animals is mostly indirect, as it occurs after they eat polluted plants or foliage. Fluorine, lead and arsenic are three main air pollutants that cause harmful effects to livestock.

Fluorine causes loss of weight, muscular weakness, diarrhea, wearing of teeth, and even death. Fluorosis mainly affects the ruminants, particularly dairy cows.

Lead poisoning is commonly observed in animals grazing near lead mines. It is associated with loss of appetite, difficulty in breathing, diarrhea and paralysis.

Arsenic toxicity in animals is associated with increased salivation, thirst, irregular pulses, abnormal body temperature and paralysis. Chronic poisoning may result in anemia, diarrhea, paralysis and even death.

Effects of air pollutants on materials :

Air pollutants cause immense damage to various materials — stone, metal, paint work, fibre materials, glass, ceramic, textiles, rubber, architecture etc. The adverse effects of air pollution on materials and properties are associated with severe economic losses throughout the world.

Effects of air pollutants on global climatic changes :

Air pollution is associated with significant changes in global climate and the related processes e.g., ozone depletion, green house effects, acid rain.

Bio Monitoring of Air Pollution :

Plants are used to monitor (bio monitoring) air pollution and such plants are referred to as indicator plants. This is based on the principle of sensitivity and response of the plants to air pollutants. A list of the plants used for bio monitoring and the corresponding air pollutants is given in Table 55.5. Among these, lichens and mosses are most commonly used to check the quality of air. The pattern of occurrence of patches on lichens serves as an index for bio monitoring of air pollution.

Bioluminescence in air pollution monitoring :

Bioluminescence is the phenomenon of emission of visible light by an organism. It occurs as an enzymatically catalysed light emitting reaction in living cells. Bioluminescence is an indicator for the analysis of atmospheric gases such as SO 2 , formaldehyde and ethyl acetate. The microorganism, Photo bacterium phosphoreum can be used as a special photo detector. The changes in the emission of light due to a pollutant can be detected by a sensor, amplified and recorded.

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• Published: 01 August 2024

Impact of air pollution on human morality: A multinational perspective

• Tomoaki Nakaishi   ORCID: orcid.org/0000-0001-9199-7480 1 ,
• Sunbin Yoo 2 ,
• Shigemi Kagawa 1 &
• Shunsuke Managi 2  

Humanities and Social Sciences Communications volume  11 , Article number:  991 ( 2024 ) Cite this article

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This study aimed to investigate whether global air pollution harms human morals beyond physiological and psychological health. To accomplish this, we conducted an original survey involving over 80,000 individuals across 30 countries, inquiring about their recent perceived unethical behaviors. Through regression analyses, we identified global evidence of a positive correlation between local monthly average concentrations of nitrogen dioxide (NO 2 ) and perceptions of unethical behavior. This finding suggests that air pollution may potentially elicit unethical behavior through a complex response mechanism. It is noteworthy that the impact of air pollution on the inclination to perceive unethical behavior is heterogeneous across categories of unethical behavior and countries. For example, the effects of increasing air pollution concentrations vary even within the same European country: an increase in NO 2 concentration in Greece and the Netherlands augments the inclination to perceive fatal unethical behaviors such as murder, terrorism, and suicide, while in Germany, NO 2 concentration diminishes the inclination to perceive the same types of unethical behaviors. Overall, the societal costs of air pollution may be even more far-reaching than previously acknowledged, and further research is necessary to unveil the intricate response mechanisms underlying this issue.

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Introduction.

In 2019, approximately 6.7 million premature deaths were caused by air pollution, making it the most significant health risk factor compared to other factors such as child and maternal malnutrition, drug and alcohol use, AIDS, tuberculosis, malaria, road injuries, and interpersonal violence (Fuller et al., 2022 ). Furthermore, Fuller et al. ( 2022 ) reported that the number of deaths attributed to air pollution was approximately equivalent to those caused by smoking. Existing epidemiological literature summarizes that both short- and long-term exposure to air pollution contribute to respiratory and cardiovascular diseases (Brunekreef and Holgate, 2002 ; Seaton et al., 1995 ). According to Manisalidis et al. ( 2020 ), short-term exposure to air pollutants is associated with chronic obstructive pulmonary disease, coughing, shortness of breath, wheezing, asthma, and other respiratory diseases, leading to high hospitalization rates. Long-term effects are closely associated with chronic asthma, pulmonary dysfunction, cardiovascular disease, and cardiovascular mortality. Thus, it is widely recognized in public and ambient health contexts that exposure to air pollution is related to various diseases (Sass et al., 2017 ).

In addition to these well-established health effects, recent epidemiological literature suggests a potential link between air pollution and mental health (Sass et al., 2017 ). Previous studies on humans and animals have demonstrated that exposure to air pollution can lead to neuroinflammation, oxidative stress, cerebrovascular disorders, and neurodegenerative pathologies, which could potentially lead to psychiatric disorders such as depression, anxiety, and suicidal ideation among humans (Block, Calderón-Garcidueñas, 2009 ; Sass et al., 2017 ).

Previous studies have also shown that exposure to air pollution decreases well-being and life satisfaction (Li et al., 2019 ; Zheng et al., 2019 ; Yerema and Managi, 2021 ; Li and Managi, 2022 ), increases anxiety and discomfort (Power et al., 2015 ; Sass et al., 2017 ; Lu et al., 2018 ), and contributes to mental disorders such as depression, schizophrenia, and autism (Pedersen et al., 2004 ; Volk et al., 2013 ; Cho et al., 2014 ). It has also been reported that air pollution is a significant risk factor for substance abuse, self-harm, and suicide (Yang et al., 2011 ; Liu et al., 2018 ; Szyszkowicz et al., 2018 ; Lu, 2020 ; Okuyama et al., 2022 ).

This study explores a novel question: Does air pollution influence human moral perceptions and behavior? While extensive research has demonstrated the detrimental effects of air pollution on physical and mental health, this study aims to extend this understanding into the realm of moral psychology. Several medical and psychological studies served as motivation to test the hypothesis. Studies on mice by Rammal et al. ( 2008 ) showed a strong positive correlation between oxidative stress and neuroinflammation with anxiety levels. Kouchaki and Desai ( 2015 ), along with Corrigan and Watson ( 2005 ), found that anxiety symptoms could elicit unethical behavior in humans, regardless of its violent nature. Li et al. ( 2017 ) further demonstrated that exposure to particulate matter significantly increases cortisol levels (the stress hormone) in the body; Lee et al. ( 2015 ) reported that cortisol levels decreased after individuals engaged in unethical behavior. The anxiety engendered by air pollution exacerbates the perception of threat and fosters selfish and unethical behavior (Kouchaki and Desai, 2015 ; Lu et al., 2018 ).

Building upon this medical and psychological research, this study seeks to contribute to the field by examining how these physical and psychological effects of air pollution may impact moral judgments and behaviors—a relatively unexplored area in environmental health research. Specifically, this study surveyed over 80,000 individuals across 30 countries using a custom-designed online questionnaire to assess their perceptions of unethical behavior across 16 types of experiences. We then analyzed the relationship between these measured individual-level perceptions of unethical behavior and air pollution, specifically monthly average nitrogen dioxide (NO 2 ) concentrations in respondents’ residential areas, while controlling for various personal and regional characteristics. To the best of our knowledge, this study is the first multinational demonstration of the impact of air pollution on unethical behavior based on individual-level data, shedding light on the potential for further research to elucidate its underlying mechanisms.

Methodology

Data acquisition.

Garcia-Moreno et al., ( 2006 ) highlighted that the reported number of incidents of domestic violence considered unethical behavior may be significantly lower than the actual occurrences due to victims’ fear of retaliation from abusers if they file a complaint with the police. Furthermore, individuals may have different perceptions of what constitutes reportable behavior. Aradabiliy et al. ( 2011 ) noted that domestic violence may be considered by some as a form of family discipline despite its unethical nature. Therefore, we decided to directly inquire about individuals’ recent unethical behaviors rather than relying on reported crime statistics. Unlike studies based on city-level crime arrest data (Herrnstadt et al., 2021 ; Lu et al., 2018 ), our questionnaire-based study allows us to consider three types of unethical behaviors: (1) crimes such as prostitution, rape, child abuse, and domestic violence, which people may be hesitant to disclose; (2) acts such as theft and pilferage, which may not always result in criminal charges; and (3) acts such as racial and gender discrimination, which may not be illegal everywhere but are nonetheless malicious. As a result, our definition of unethical behavior includes a range of malicious acts beyond strictly criminal behavior. This study provides the first multinational evidence that air pollution affects not only criminal behavior but also unethical behavior.

To ensure the representativeness and completeness of the dataset, this study utilized an extensive international survey conducted by Nikkei Research, Inc., covering 89,266 respondents across 30 countries selected based on their work capacity and research budget constraints (Chapman et al., 2019 ). The surveyed countries included Australia, Brazil, Canada, Chile, China, Colombia, the Czech Republic, France, Germany, Greece, Hungary, India, Indonesia, Italy, Japan, Malaysia, Mexico, Myanmar, the Netherlands, Philippines, Poland, Romania, Russia, South Africa, Spain, Sweden, Thailand, Turkey, the United States, and Vietnam. See Table A1 in the Supplementary Information for sample sizes for each country. It is important to note that samples from Canada, the Czech Republic, Poland, and Romania, which exhibit significantly lower rates of reported unethical behavior, were excluded from the empirical analysis. After filtering out respondents who chose not to answer certain relevant questions (e.g., income, criminal experience), the final sample size for analysis was refined to 48,836.

The survey was carefully designed to capture a wide range of sociodemographic variables by randomly selecting respondents to reflect the demographic characteristics of each country in terms of age and sex. To mitigate potential biases in data collection, particularly those arising from Internet-based survey methods, our approach included both online and in-person surveys. Specifically, in certain countries such as Myanmar, we utilized in-person surveys to ensure the representation of underrepresented groups in rural areas and slums. This combination of methods was crucial for capturing diverse perspectives. The survey content underwent rigorous checks for accuracy and cultural relevance and was translated and reviewed by professional translators. The survey was conducted between June 2015 and March 2017 according to the schedule noted in Table A1 . To maintain the integrity and quality of the dataset, strict quality control procedures overseen by Nikkei were implemented to ensure that responses accurately reflected the specified sociodemographic categories.

The questionnaire included prompts such as, ‘Please select items that describe what has happened recently in your neighborhood or among the people around you.’ Respondents could select all 21 items that applied to them: theft/stealing , fraud , murder , terrorism , suicide , gang violence/assault , privacy violation by police/military , racial discrimination , gender discrimination , drug trafficking , ownership of gun(s)/rifle(s) , abortion , prostitution , pregnancy/delivery by unmarried women , rape , bribing/corruption , child abuse , domestic violence , single parenting , homosexuality , or none of the above . Four items ( abortion , pregnancy/delivery by unmarried women , single parenting , and homosexuality ) were excluded from the analysis as they do not constitute unethical behaviors. It should be noted here that the term “recently” may have varied in interpretation across individuals. Its use aimed to reduce stress and elicit intuitive responses from the respondents. Following Jessup et al. ( 2017 ), our analysis assumed that the term “recently” corresponded to a period of “one month” throughout. While recognizing that this assumption may introduce bias, particularly in questionnaire-based studies, we acknowledge it as a limitation.

Figure A1 in the Supplementary Information illustrates an example question from our survey. This table presents a hypothetical scenario where respondents indicate they have experienced (1) murder, (2) fraud, or (3) gang violence/assault. In this case, respondents are guided to select the corresponding items in the table. Table 1 elucidates the extent of crime exposure among our respondents. This table categorizes the types of criminal activities encountered by participants, specifying the percentage (%) of individuals who reported each experience. The data reveal that theft is the most frequently reported crime, with 39.47% of respondents acknowledging such incidents. Other notable criminal experiences include fraud (12.50%), drug trafficking (12.29%), and murder (6.75%).

In addition to the key question listed above, the questionnaire survey also simultaneously examined the respondents’ sociodemographic variables (address, age, sex, occupation, income, education, religion). These individual-level data were utilized to control for factors that may have influenced the perceptions of unethical behavior. Socioeconomic factors are likely to influence exposure to unethical behavior, as they can shape an individual’s criteria for judging right and wrong and the frequency of exposure to unethical behavior. For example, studies have shown that women tend to be harsher on crime than men, and people become more negative about crime as they age (Borg and Hermann, 2023 ). In addition, a positive correlation exists between regional income inequality and individuals’ fear of crime (Clément and Piaser, 2021 ). Furthermore, individuals with higher levels of education are less exposed to violence against women (Sen and Bolsoy, 2017 ). Additionally, it is widely recognized that certain aspects of religion reduce participation in criminal activity, as indicated by a literature review by Sumter et al. ( 2018 ).

Air pollution data were obtained from measurements of vertical column concentrations of NO 2 particles from the surface to the lower troposphere by the Global Ozone Monitoring Experiment (GOME-2) satellite (ESA, EUMETSAT 2000 ). The GOME-2 satellite measures the vertical column concentrations of NO 2 in the troposphere on a daily basis through an optical process and accurately models monthly average NO 2 values with a resolution of 80 × 40 km. In our study, the monthly average NO 2 concentration data (molecules/cm 2 ) obtained from the GOME-2 satellite were matched to the geographic information (ZIP code) of the survey respondents at the grid level to obtain air pollution concentration data around them. Satellite (rather than surface) observation data were utilized because the sample included several developing countries and regions that lacked adequate air pollution monitoring facilities, and it was necessary to evaluate these countries and regions in the same manner as developed countries (Yerema and Managi. 2021 ; Vohra et al., 2022).

The choice of NO 2 as the primary air pollutant for examination in our study was guided by both practical and scientific considerations. NO 2 is a prevalent urban pollutant, often used as a key indicator of air quality due to its significant health impacts and ubiquity in urban environments. This choice was further reinforced by the availability of consistent global satellite data for NO 2 , which was particularly crucial given our study’s extensive geographical scope, including many developing countries. These regions often lack comprehensive, ground-based monitoring systems for a variety of air pollutants, making satellite-derived NO 2 data the most reliable and accessible proxy for assessing air pollution levels across different countries (Yerema and Managi, 2021 ). While we acknowledge that other pollutants such as SO 2 and particulate matter also carry important health and behavioral implications, focusing on NO 2 enabled us to conduct a more uniform and globally applicable analysis, essential for understanding the broader implications of air pollution on human moral perceptions and behaviors.

In addition to data on reported unethical behavior and air pollution concentrations, several meteorological variables were included as control variables in the empirical model. Previous studies have indicated that weather conditions (e.g., temperature, humidity, and wind speed) may influence unethical behavior (Baron and Bell, 1976 ; Rotton and Frey, 1985 ). In the present study, average wind speed, precipitation, vapor pressure, and monthly minimum and maximum temperatures for the study period in each country, collected at a 4-km resolution from the TerraClimate data set (Abatzoglou et al., 2018 ), were used as control variables in the model. Additionally, distance to the coast was included as a control variable because of geographic and climatic factors that could affect air quality and pollution patterns, potentially influencing the analysis of the relationship between air pollution and human moral perceptions and behavior. This methodological choice is consistent with established practices in environmental research. Controlling for variations in residential choices and local climates due to proximity to coastlines is a recognized approach, as demonstrated in studies by Banzhaf, Randall ( 2008 ), and Kalkuhl and Wenz ( 2020 ).

To address the possibility of endogenous biases, such as increased pollutant emissions from police cars dispatched during criminal events, the monthly planetary boundary layer height (PBLH) was employed as an instrumental variable in the empirical model. PBLH is known to have a negative impact on local air pollution concentrations (Schwartz et al., 2017 ). As such, a lower boundary layer results in higher local pollution concentrations for the same local emissions, and vice versa (Seinfeld and Pandis 1998 ). There is no known evidence that PBLH affects people’s unethical behavior. Given these arguments, we justified using PBLH as an instrumental variable in this study. PBLH data with a resolution of 0.5̊ × 0.625̊ collected from NASA ( 2010 ) were matched with the locations of survey respondents at the grid level.

Model specifications

Our empirical model was designed to test whether monthly average NO 2 concentrations significantly correlated with perceptions of unethical behavior at the corresponding locations, even after controlling for various variables that could contribute to the experience and perception of unethical behavior, such as personal attributes and heterogeneity associated with the residential area. Specifically, a two-stage instrumental variable model was employed with the respondent’s perception of unethical behavior as the dependent variable, the ZIP code-level monthly average NO 2 concentration as the independent variable, and the ZIP code-level PBLH as the control variable. The model included ZIP code-level weather-related variables (e.g., monthly average temperature, precipitation, wind speed, and wind direction) and respondents’ socioeconomic variables (e.g., income, sex, age, education, family structure, and religion) as control variables. Various fixed effects related to country, region (e.g., Asia, Europe), first-level administrative district (e.g., state, province), second-level administrative district (e.g., city, town, village), year, and month were also considered (Tanaka and Okamoto, 2021 ).

To measure respondents’ perceptions of unethical behavior, we employed two types of indicators following the frameworks proposed by Chai et al. ( 2015 ) and Melo et al. ( 2018 ). The first indicator utilized a relatively straightforward approach by counting the number of unethical behaviors perceived or experienced by respondents in the recent past. We considered a total of 16 unethical behaviors; therefore, the maximum value of this straightforward index was 16, and the minimum value was 0. The second approach was based on item response theory (IRT), which is often used in educational testing to measure potential difficulties. While the straightforward approach assumed equal weights (i.e., equal difficulty) for all 16 unethical behaviors, the IRT-based approach relaxed these assumptions by assigning individual weights based on the perceived difficulty of each unethical behavior. The actual loadings (coefficients) for each unethical behavior were estimated using the IRT binary response model (one-parameter logistic), as presented in Table A2 in the Supplementary Information. Table A5 shows that a large loading coefficient (2.900) was estimated for unethical behaviors with high difficulty (e.g., terrorism ), while a small loading coefficient (0.388) was estimated for unethical behaviors with low difficulty (e.g., theft/stealing ). These coefficients were multiplied by each unethical behavior as weights and aggregated for each respondent to produce the IRT-based index of perceptions of unethical behavior. It is worth noting that since no significant differences were found between the regression results from the straightforward and IRT-based approaches, the results from the former approach are presented in the Results section due to space limitations. See Table A3 in the Supplementary Information for the estimation results from the IRT-based approach. For a summary of the means and standard deviations for each variable included in the model, see the summary of descriptive statistics in Table 2 .

Main result

Table 3 displays the estimated parameters of the main statistical model, presenting the average impact of monthly average NO 2 concentration on perceptions of unethical behavior. As indicated by the first column in Table 3 , a statistically significant positive correlation was observed between monthly average NO 2 concentration and perceptions of unethical behavior at the corresponding location. In other words, as the monthly average NO 2 concentration increased, the average perceptions of unethical behavior at the corresponding locations also increased. Unethical behavior, as defined by Jones (1991) and Lu et al. ( 2018 ), refers to “behavior that is illegal or morally unacceptable to the larger community.” The unethical behaviors considered in this study included prostitution, rape, child abuse, domestic violence, murder, terrorism, suicide, gender discrimination, racial discrimination, theft/stealing, gang violence/gang assault, privacy violation by police/military, drug trafficking, ownership of guns/rifles, fraud, and bribery/corruption. These unethical behaviors were divided into five groups through factor analysis: fatal (murder, terrorism, and suicide); assault (prostitution, rape, child abuse, and domestic violence); discrimination (gender and racial discrimination); financial (fraud and bribery/corruption); and organized (theft/stealing, gang violence/gang assault, drug trafficking, and ownership of guns/rifles). The estimates in the second and subsequent columns of Table 3 indicate that monthly average NO 2 concentrations were significantly positively correlated with fatal , assault , and organized unethical behavior perceptions.

In the following sections, we conduct a detailed comparative analysis, intertwining economic indicators such as gross domestic product (GDP) with environmental metrics, particularly air pollution levels. We hypothesize that individuals in wealthier nations may exhibit increased sensitivity to slight rises in air pollution due to their infrequent exposure to such conditions. Nevertheless, these communities often possess greater resources to mitigate the effects of pollution, including the utilization of air purifiers.

Our study investigates the diverse responses to air pollution, specifically examining its correlation with perceptions of unethical behavior in relation to national NO 2 pollution levels. A key aspect of our analysis is the concept of “pollution habituation,” prompting an in-depth examination of how varying exposure levels to environmental pollutants influence societal norms and ethical viewpoints. The following sections will thoroughly assess the varied impacts of air pollution, shedding light on the intricate relationship between environmental conditions and unethical behavior patterns.

Our findings reveal that: (1) Overall, the impact of air pollution on the perception of unethical behavior tends to differ by economic status, indicating a heightened sensitivity to pollution in more economically developed countries. (2) The analysis underscores the diversity in the marginal effects of air pollution on perceptions of unethical behavior across different national pollution levels, offering some evidence for the population’s adaptation to pollution. We will delve into these results in greater detail in the subsequent sections.

Heterogeneous effects on the national economic level

Table 4 illustrates the impact of monthly average NO 2 concentration on perceptions of unethical behavior for each economic level category. The parameter estimates listed in each column of Table 4 were derived from a sub-model that included the interaction of three dummy variables (corresponding to percentiles of economic level categories based on GDP per capita) with the main model presented in Table 3 (a list of countries included in each category is presented in Table A5 in the Supplementary Information). The baseline for this analysis was countries with the lowest GDP per capita.

Overall, the impact of air pollution on the perception of unethical behavior appeared to vary across economic levels, suggesting that individuals in countries with higher economic status may be more sensitive to pollution. The first column of Table 4 indicates that the monthly average concentration of NO 2 had a significant positive effect on the perception of unethical behavior for countries at the baseline and first and third percentile GDP per capita. Additionally, this column highlights that the marginal effects of increasing the monthly average concentration of NO 2 on perceptions of unethical behavior were particularly pronounced in the wealthiest countries.

Furthermore, the second and subsequent columns of Table 4 demonstrate a significant positive correlation between monthly average NO 2 concentration and perceptions of unethical behavior in wealthy countries. Perceptions related to fatal , assault , and organized unethical behaviors showed significant positive correlations with monthly average NO 2 concentration, consistent with the main model findings (Table 1 ). Additionally, discrimination and financial unethical behaviors, which did not yield significant results in the main model, exhibited significant positive correlations with monthly average NO 2 concentration in relatively wealthier countries (Table 4 , columns 4 and 5).

Heterogeneous effects on national pollution level

We investigated the heterogeneity of the effects of air pollution on perceptions of unethical behavior based on national pollution levels to provide further evidence of pollution habituation. Table 5 illustrates the effect of monthly average NO 2 concentrations on perceptions of unethical behavior for each category of national pollution levels. The parameter estimates in each column of Table 5 result from estimation with a sub-model that includes a cross-term with a dummy variable based on national pollution levels (total annual pollution by NO 2 ) from the main model presented in Table 1 (A list of countries included in each category is presented in Table A5 in the Supplementary Information). The baseline in this case comprises countries with the lowest total annual NO 2 pollution.

Overall, the results underscore the heterogeneity of the marginal effects of air pollution on perceptions of unethical behavior across national pollution levels, with partial evidence suggesting pollution habituation within the population. The first column of Table 5 illustrates that the influence of monthly average NO 2 concentration on respondents’ perceptions of unethical behavior at their corresponding location was significantly positive at the baseline (representing the cleanest countries) and for categories with national annual pollution in the second and third percentiles. The effect of increasing monthly average NO 2 concentration on perceptions of unethical behavior was particularly pronounced at the baseline and for the second percentile of national annual pollution (Table 5 , column 1). Conversely, a negative correlation (albeit non-statistically significant) between air pollution and perceptions of unethical behavior was observed in the first percentile for national annual pollution. This suggests that people in countries with elevated pollution levels may have developed a degree of tolerance, leading to a diminished effect of pollution on their perceptions of unethical behavior.

In the second and subsequent columns of Table 5 , consistent with the main model findings (Table 1 ), statistically significant positive correlations were observed between monthly average NO 2 concentrations and perceptions of fatal , assault , and organized unethical behaviors. In addition, statistically significant positive effects were observed in the baseline categories for financial unethical behavior (Table 5 , column 5), for which no significant effects were identified in the main model (Table 3 ). However, for discriminatory unethical behavior (Table 5 , column 4), similar to the main model (Table 3 ), no statistically significant relationship was found for any pollution category. Notably, for the first percentile of national annual pollution, the monthly average NO 2 concentration was negatively correlated with all types of perceptions of unethical behavior, although not statistically significant.

Heterogeneous effects on specific countries

The relationship between air pollution and perceptions of unethical behavior may vary significantly by country. Table 6 presents the country-specific effects of monthly average NO 2 concentration on perceptions of unethical behavior. The estimates in Table 6 were derived from country-specific sub-models that maintained the specifications of the main model (Table 3 ) while only sampling respondents from individual countries. In Table 6 , the values of the estimated parameters are denoted by positive and negative symbols, and the statistical significance of each parameter is indicated by the color depth of the corresponding cell. The darker the cell, the higher the statistical significance of the estimates.

The first column of Table 6 illustrates the overall impact of monthly average NO 2 concentration on perceptions of unethical behavior at the corresponding locations. According to this column, a significant positive correlation was observed between monthly average NO 2 concentration and the tendency of respondents in Brazil, France, Spain, and Turkey to perceive unethical behavior. In essence, a marginal increase in the monthly average NO 2 concentration in these countries led to an average increase in the perception of unethical behavior.

The second and subsequent columns in Table 6 show the impact of monthly average NO 2 concentration on perceptions of five different types of unethical behavior. It is noteworthy that in some countries (Brazil, China, Germany, Hungary, Indonesia, Myanmar, Russia, and the United States), a significant negative correlation was observed between monthly average NO 2 concentration and the tendency to perceive specific unethical behavior. Therefore, a slight increase in monthly average NO 2 concentration in these countries led to a decrease (on average) in the tendency to perceive specific unethical behavior. Additionally, it should be noted that the impact of monthly average NO 2 concentration on perceptions of unethical behavior was not consistent across specific regions or types of unethical behavior. For example, a slight increase in monthly average NO 2 concentration in Greece and the Netherlands led to an increase (on average) in the tendency to perceive fatal unethical behavior, while Germany, another European country, exhibited the opposite trend with a decrease in the tendency to perceive the same unethical behavior.

Discussion and implications

In this section, we discuss potential mechanisms for the positive correlation between NO 2 concentrations and perceptions of unethical behavior identified in this study. First, NO 2 exposure could induce anxiety symptoms, which can stimulate unethical behavior (Kouchaki and Desai, 2015 ; Corrigan and Watson, 2005 ). Mehta et al. ( 2015 ) and Lin et al. ( 2017 ) demonstrated that exposure to NO 2 can lead to anxiety and stress disorders. Additionally, there is a known association between mental illness and unethical behavior, particularly violent behavior (Corrigan and Watson, 2005 ). Exposure to NO 2 can increase susceptibility to psychiatric disorders such as depression, schizophrenia, and substance abuse, thereby contributing to unethical behavior (Cho et al., 2014 ; Pedersen et al., 2004 ; Szyszkowicz et al., 2018 ). Swanson, and Holzer ( 1992 ) found that individuals suffering from psychiatric disorders (e.g., schizophrenia) and substance abuse disorders exhibit a four- and ten-fold increase in violent behavior, respectively, compared to those without these disorders. Corrigan and Watson ( 2005 ) also found that individuals diagnosed with anxiety disorders or depression are three to four times more likely than those without such disorders to engage in violent behavior, while those with bipolar disorder or drug or alcohol abuse are eight times more likely.

Furthermore, physical discomfort caused by NO 2 exposure may also incite unethical behavior. Air pollution can lead to irritation of the eyes, throat, and nose, as well as olfactory abnormalities (Chen et al., 2007 ); this discomfort may increase aggression and prompt unethical behavior (Rotton and White, 1996 ). Psychological studies by Rotton et al. ( 1978 , 1979 ) and Rotton ( 1983 ) demonstrated that physical discomfort from odors, a component of air pollution, diminishes participants’ cognitive abilities and interpersonal attractiveness while increasing frustration and aggression. An indoor experiment by Rotton et al. ( 1979 ) confirmed that participants experiencing discomfort from pollution tended to administer stronger electric shocks to their peers on average than did other participants. Similar results have been observed in studies involving cigarette smoke (Jones and Bogat, 1978 ; Zillman et al., 1981 ).

Colored air pollutants, such as NO 2 , may also visually stimulate individuals (Lu, 2020 ), potentially influencing unethical behavior as a result of the obscured visibility caused by NO 2 smog (Lu et al., 2018 ). Psychological studies conducted by Zhong et al. ( 2010 ) indicate that people are more likely to act dishonestly or selfishly in the dark, as darkness may create a sense of illusory anonymity. Similarly, Doleac and Sanders ( 2015 ) confirmed that ambient light reduces criminal behavior. Additionally, visual environmental disturbances due to air pollution may induce social and moral disturbances (Lu et al., 2018 ). The well-known “broken window theory” argues that public wrongdoing and degradation, such as broken windows and graffiti, can lead to an increase in serious crime (Wilson and Kelling, 1982 ). Indeed, according to a field experiment by Keizer et al. ( 2008 ), individuals who observe others violating social norms and rules are more likely to violate other norms and rules. Similarly, a psychological experiment by Gino et al. ( 2009 ) found that when unethical behavior is committed by members of the same group, it is more likely to be transmitted to other members. The disorder in urban neighborhoods caused by NO 2 smog may have led to the spread of disorder through such psychological mechanisms.

While there are mechanisms that may account for the positive correlation between air pollution and perceived propensity for unethical behavior, mechanisms that support a negative correlation should also be noted. For instance, extremely high levels of air pollution may reduce aggression in individuals (Baron and Bell, 1976 ; Rotton et al., 1979 ; Rotton and White, 1996 ). Baron and Bell ( 1976 ) and Rotton and White ( 1996 ) proposed that moderate levels of stimulation can increase aggression, whereas extremely high levels of stimulation can elicit escape and withdrawal behaviors in individuals, consequently decreasing aggression. In the aforementioned psychological study by Rotton et al. ( 1979 ), participants exposed to moderately unpleasant odors exhibited strong aggression, while those exposed to odorless air or extremely unpleasant odors did not exhibit such strong aggression.

High concentrations of air pollution can alter people’s habitual behavior, thereby impacting the frequency of unethical behavior. Bresnahan et al. ( 1997 ) and Wen et al., ( 2009 ) demonstrated that individuals tended to engage in avoidance behavior, specifically refraining from going out on days when air pollution was severe and warnings were issued. This change in behavior could serve as the driving force behind both the increase and decrease in individuals’ encounters with unethical behavior. For example, increased time spent indoors because of pollution may increase the risk of encountering roommate conflicts, such as domestic violence and child abuse, and suicide due to loneliness and vitamin D deficiency (Anglin et al., 2013 ). However, a reduction in time spent outdoors also lowers the risk of encountering unethical behavior in outdoor settings, such as terrorism and theft. Additionally, the temporary reduction of the urban population due to pollution could create an ideal environment for individuals motivated by unethical behavior, given the absence of outdoor observers. However, such a phenomenon could simultaneously act as a disincentive for their unethical behavior to succeed, as there may not be suitable targets available.

This study confirms that individuals in locations with higher air pollution concentrations tend to perceive and experience more unethical behavior, and vice versa. Consequently, air pollution may incur even greater social costs than those directly attributable to health risks by inducing individual unethical behaviors. As such, it is important to reevaluate the additional social costs resulting from unethical behaviors and rebuild our social system to accurately reflect the costs of air pollution, based on a renewed recognition of its risks. Specifically, environmental regulatory guidelines developed solely based on the health risks of air pollution (e.g., WHO, 2006 ) and environmental taxation systems that fail to internalize the additional external costs of unethical conduct induced by air pollution are typical examples of existing social systems that need modification. For instance, new pollution guidelines based on criteria for the occurrence of unethical behavior could be developed and applied to alert citizens to prevent them from encountering unethical behavior and reduce extra social spending in response to unethical behavior.

The results also indicate that the impact of air pollution on perceptions of unethical behavior was heterogeneous, depending on the type of unethical behavior, national economic and pollution levels, and the country itself. The finding that increased air pollution in some countries had a negative impact on certain unethical behaviors (i.e., contributing to a decrease in unethical behavior) is crucial from a policymaking perspective. This is because, contrary to our general conclusion, air pollution could have unintended social benefits in such countries. In essence, mitigating air pollution in such countries and regions could inadvertently increase unethical behavior, which policymakers need to consider before implementing air pollution mitigation measures. Specifically, countries and regions where such phenomena are experienced need to implement air pollution mitigation policies while considering the potential increase in unethical (particularly criminal) behavior.

The current findings offer significant insights for policymaking in public health, urban planning, and environmental regulation. This study identified a positive correlation between air pollution, specifically NO 2 , and the perception of unethical behavior, suggesting that the social costs of air pollution extend beyond the traditionally recognized physical and mental health impacts, in line with previous research (Xue et al., 2019 ; Antonsen et al., 2020 ). Accordingly, we propose several key policy implications across diverse sectors.

Firstly, in public health, our findings support the integration of air quality considerations into broader health strategies. Policymakers are encouraged to prioritize reducing air pollution, not only to address health issues but also to mitigate social and behavioral concerns. This could entail implementing stricter emissions regulations, encouraging cleaner transportation options, and enhancing public awareness regarding the wide-ranging impacts of air pollution. In addition, facilitating an eco-surplus culture among urban residents can improve their willingness to pay for nature conservation (Nguyen, Jones 2022 ; Vuong, 2021 ; 2023 ).

Secondly, regarding urban planning, our research highlights the necessity of designing cities to minimize exposure to air pollution. Supporting literature indicates that urban air pollution, typically higher than rural levels, can lead to mental distress in urban populations (Bakolis et al., 2021 ; Glaeser et al., 2016 ). Following recommendations by Khreis et al., ( 2023 ) and Yoo et al., ( 2023 ), strategies such as congestion charging, developing urban green spaces, enhancing public transit systems, and promoting policies that reduce reliance on private vehicles are crucial. Such measures are instrumental in reducing NO 2 levels, which can positively affect social behaviors and enhance urban well-being.

Additionally, our global evidence pinpoints specific countries particularly vulnerable to the impact of air pollution on unethical behaviors. This insight underscores the need for targeted interventions in areas with high NO 2 concentrations. Community-level initiatives aimed at promoting ethical behavior and social cohesion are vital, especially in heavily polluted urban areas. In conclusion, our study advocates for comprehensive policy measures and thoughtful urban planning to address air pollution. Such initiatives promise not only health benefits but are also crucial in cultivating a more ethically conscious and socially cohesive society.

Although the present study reveals important findings, several limitations highlight the need for further research. First, the effect of air pollution on unethical behavior identified in our empirical model may be underestimated due to the possibility that not all respondents reported their actual perceived unethical behaviors. We acknowledge such limitations as a common problem of a questionnaire-based approach. Nevertheless, our survey offers significant advantages in recognizing and considering illegal unethical behavior (e.g., racism, gender discrimination, etc.), too sensitive to disclose (e.g., prostitution, rape, child abuse, domestic violence, etc.), or not treated as a criminal case because of the small amount of damage (e.g., larceny, theft, etc.). The bias of underreporting must be compensated for through future research using psychological experiments in a laboratory setting.

Another limitation of our study is our inability to consider air pollutants other than NO 2 (e.g., SO 2 and PM) due to data limitations. We utilized satellite observations of NO 2 as a proxy for air pollution because our sample included many countries and regions, particularly developing countries, lacking sufficient monitoring facilities for air pollutants (Yerema and Managi, 2021 ). Differences in air pollutants are important, and we anticipate that the potential mechanisms influencing unethical behavior may vary depending on the type of pollutant. For example, related studies (Herrnstadt et al., 2021 ; Jones, 2022 ) also suggest that air pollution may affect serotonin levels in the brain, potentially leading to unethical behavior. Serotonin, a neurotransmitter, plays an important role in emotion regulation during social decision-making (Crockett et al., 2008 ). Although previous research has examined the correlation between serotonin depletion and impulsive aggression (Krakowski, 2003 ; Duke et al., 2013 ; Cunha-Bang and Knudsen, 2021 ), our literature review found no evidence that NO 2 decreases brain serotonin levels. Therefore, it is unlikely that NO 2 increases unethical behavior through a serotonin-related mechanism. Further studies should examine and compare multiple air pollutants with different properties.

Finally, our study did not identify statistically significant correlations between air pollution and certain unethical behaviors in some countries, especially those with limited sample sizes. It should be noted, however, that this result does not imply an absence of association between air pollution and unethical behaviors in such countries. In general, more localized studies focusing on specific unethical behaviors, air pollutants, countries, or regions should be conducted in the future to better understand the complex mechanisms between air pollution and unethical behavior. The results of this study can underscore the importance of such complementary research endeavors.

Data availability

Because of privacy concerns, the datasets created and/or examined for this project are not accessible to the general public. Making the entire data set publicly accessible may violate both the study’s ethical approval and the participants’ pledge of privacy when they consented to participate. Upon reasonable request, the data can be obtained from its corresponding author.

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Nakaishi, T., Yoo, S., Kagawa, S. et al. Impact of air pollution on human morality: A multinational perspective. Humanit Soc Sci Commun 11 , 991 (2024). https://doi.org/10.1057/s41599-024-03186-z

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Air pollution may be a leading cause for antibiotic resistance globally, new study finds

A new study is linking air pollution to the global amount of antibiotic resistance, when medicines used to treat bacterial infections become less effective.

Scientists found a connection between the two after analyzing data from over 116 countries over nearly two decades and shared their findings Monday in the journal The Lancet Planetary Health . In the model created by the researchers, air pollution was found to be responsible for 11% of changes in average antibiotic resistance levels globally, possibly making particle pollution a leading driver.

“Antibiotic resistance and air pollution are each in their own right among the greatest threats to global health,” wrote the study's lead author Hong Chen.

However, the study, which examined nine bacterial pathogens and 43 types of antibiotics, is observational and can't prove a connection or explain what the connection would be.

Not 'if' but 'when': Antibiotic resistance poses existential threat for modern medicine

Antibiotic resistance is considered to be one of the most harmful threats to global health as infections like pneumonia and tuberculosis are becoming harder to treat, the  World Health Organization (WHO) states .

Chen and the other researchers created a model to view antibiotic resistance levels and air pollution levels called PM2.5. The researchers found that particle pollution rose with the levels of antibiotic resistance.

What is particle pollution and antibiotic resistance?

The US Environmental Protection Agency defines PM2.5, also called particle pollution or particulate matter pollution, as the combination of solid and liquid droplets found in the air. Coal, cars, unpaved roads, construction sites, natural gas-fired plants and wildfires can create particulate pollution. Dirt, dust, soot and smoke are forms of particulate pollution.

WHO defines antibiotic resistance, also called antimicrobial resistance or  AMR,  as what happens when a particular pathogen like a bacteria, fungi or parasite - is less affected by medicine, making battling infections difficult.

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The study's authors said air pollution needs to be considered a significant cause of antibiotic resistance just like other activities scientists have found including poor sanitation, poor infection control in hospitals, the misuse of antibiotics and the overuse in farm animals. The study suggests every 1% increase in air pollution can be linked to a rise in antibiotic resistance between 0.5 and 1.9%, based on the pathogen.

While the possible connection needs to be further studied, the researchers said if their model's analysis is accurate and consistent, then the level of antibiotic resistance around the world could be 17% higher by 2050, meaning around 840,000 people could die due to ineffective antibiotics.

Antimicrobial-resistant cases and deaths in the US

In 2019, the last year for which data is available, more than 2.8 million Americans had antimicrobial-resistant infections and more than 35,000 died, according to the CDC. Worldwide, deaths already top 5 million a year and are expected to grow into the tens of millions within a few decades.

"We are truly right now in the midst of this crisis," Brenda Wilson, a professor of microbiology at the University of Illinois said in a recent American Society for Microbiology talk.

More: Drug-resistant superbugs are killing thousands of Americans. Here's what you need to know about them

The U.S. was making solid progress against antibiotic resistance before the coronavirus pandemic. Thanks to improved infection prevention and control and better stewardship, deaths from antimicrobial resistance declined by 18% overall and 30% in hospitals from 2012 to 2017.

But the pandemic pushed hospitals and other health care facilities near their breaking point in 2020, leading to an increase in antibiotic use, trouble following infection prevention and a significant increase in resistant infections in U.S. hospitals, the CDC found. Resistant hospital-onset infections and deaths increased at least 15% that year, although data outside hospitals is lacking.

Contributing: Karen Weintraub and Adrianna Rodriguez