Air pollution

Air pollution from a coking oven

2016 air quality indicator – light colors have lower air quality and thus higher air pollution.

Part of a series on
Pollution
Air pollution Acid rain Air quality index Atmospheric dispersion modeling Chlorofluorocarbon Exhaust gas Haze Indoor air Internal combustion engine Global dimming Global distillation Ozone depletion Particulates Persistent organic pollutant Smog Aerosol Soot Volatile organic compound
Biological pollution Biological hazard Genetic pollution Introduced species (Invasive species)
Electromagnetic pollution Light Ecological light pollution Overillumination Radio spectrum pollution
Natural pollution Ozone Radium and radon in the environment Volcanic ash Wildfire
Noise pollution Transportation Land Water Air Rail Sustainable transport Urban Sonar Marine mammals and sonar Industrial Military Abstract Noise control
Radiation pollution Actinides Bioremediation Depleted uranium Fission product Nuclear fallout Plutonium Poisoning Radioactivity Uranium Electromagnetic radiation and health Radioactive waste
Soil pollution Agricultural pollution Herbicides Manure waste Pesticides Land degradation Bioremediation Defecation Electrical resistance heating Guideline values Phytoremediation
Solid waste pollution Biodegradable waste Brown waste Electronic waste Battery recycling Food waste Green waste Hazardous waste Biomedical waste Chemical waste Construction waste Lead poisoning Mercury poisoning Toxic waste Industrial waste Lead smelting Litter Mining Coal mining Gold mining Surface mining Deep sea mining Mining waste Uranium mining Municipal solid waste Garbage Nanomaterials Plastic pollution Microplastics Packaging waste Post-consumer waste Waste management Landfill Thermal treatment
Space pollution Satellite
Thermal pollution Urban heat island
Visual pollution Air travel Clutter (advertising) Traffic signs Overhead power lines Vandalism
War pollution Chemical warfare Herbicidal warfare (Agent Orange) Nuclear holocaust (Nuclear fallout - nuclear famine - nuclear winter) Scorched earth Unexploded ordnance War and environmental law
Water pollution Agricultural wastewater Diseases Eutrophication Firewater Freshwater Groundwater Hypoxia Industrial wastewater Marine debris Monitoring Nonpoint source pollution Nutrient pollution Ocean acidification Oil spill Pharmaceuticals Septic tanks Sewage Septic tanks Pit latrine Shipping Stagnation Sulfur water Surface runoff Turbidity Urban runoff Water quality
Misc Lists Diseases Law by country Most polluted cities Treaties Categories By country
Environment portal  Ecology portal

Part of a series on
Weather
Temperate and polar seasons Winter Spring Summer Autumn
Tropical seasons Dry season Harmattan Wet season
Storms Cloud Cumulonimbus cloud Arcus cloud Downburst Microburst Heat burst Derecho Lightning Volcanic lightning Thunderstorm Air-mass thunderstorm Thundersnow Dry thunderstorm Mesocyclone Supercell Tornado Anticyclonic tornado Landspout Waterspout Dust devil Fire whirl Anticyclone Cyclone Polar low Extratropical cyclone European windstorm Nor'easter Subtropical cyclone Tropical cyclone Atlantic hurricane Typhoon Storm surge Dust storm Simoom Haboob Monsoon Amihan Gale Sirocco Firestorm Winter storm Ice storm Blizzard Ground blizzard Snowsquall
Precipitation Drizzle Freezing Graupel Hail Megacryometeor Ice pellets Diamond dust Rain Freezing Cloudburst Snow Rain and snow mixed Snow grains Snow roller Slush
Topics Air pollution Atmosphere Chemistry Convection Physics River Climate Cloud Physics Fog Fog season Cold wave Heat wave Jet stream Meteorology Severe weather List Extreme Severe weather terminology Canada Japan United States Weather forecasting Weather modification
Glossaries Meteorology Climate change Tornado terms Tropical cyclone terms
Weather portal

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 to materials. There are many different types of air pollutants, such as gases (including ammonia, carbon monoxide, sulfur dioxide, nitrous oxides, methane, carbon dioxide and chlorofluorocarbons), particulates (both organic and inorganic), and biological molecules. Air pollution can cause diseases, allergies, and even death to humans; it can also cause harm to other living organisms such as animals and food crops, and may damage the natural environment (for example, climate change, ozone depletion or habitat degradation) or built environment (for example, acid rain). Both human activity and natural processes can generate air pollution.

Air pollution is a significant risk factor for a number of pollution-related diseases, including respiratory infections, heart disease, COPD, stroke and lung cancer.^[1] Growing evidence suggests that air pollution exposure may be associated with reduced IQ scores, impaired cognition,^[2] increased risk for psychiatric disorders such as depression^[3] and detrimental perinatal health.^[4] The human health effects of poor air quality are far reaching, but principally affect the body's respiratory system and the cardiovascular system. Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, and the individual's health status and genetics.^[5] Outdoor air pollution alone causes 2.1^[6][7] to 4.21 million deaths annually, making it one of the top contributors to human death.^[1][8] Overall, air pollution causes the deaths of around 7 million people worldwide each year, or a global mean loss of life expectancy (LLE) of 2.9 years,^[9] and is the world's largest single environmental health risk.^[1][10][11] Indoor air pollution and poor urban air quality are listed as two of the world's worst toxic pollution problems in the 2008 Blacksmith Institute World's Worst Polluted Places report.^[12] The scope of the air pollution crisis is enormous: 90% of the world's population breathes dirty air to some degree. Although the health consequences are extensive, the way the problem is handled is often haphazard.^[13][14][15]

Productivity losses and degraded quality of life caused by air pollution are estimated to cost the world economy $5 trillion per year^[16][17][18] but, along with health and mortality impacts, are an externality to the contemporary economic system and most human activity, albeit sometimes being moderately regulated and monitored.^[19][20] Various pollution control technologies and strategies are available to reduce air pollution.^[21][22] To reduce the impacts of air pollution, both international and national legislation and regulation have been implemented to regulate air pollution. Local laws, where well enforced, have led to strong public health improvements. At the international level, some of these efforts have been successful – for example the Montreal Protocol was successful at reducing release of harmful ozone depleting chemicals or the 1985 Helsinki Protocol which reduced sulfur emissions, while other attempts have so far been less successful in implementation, such as international action on climate change.

Sources of air pollution

Anthropogenic (human-made) sources

Aviation is a major source of air pollution.

Controlled burning of a field outside of Statesboro, Georgia, in preparation for spring planting

Smoking of fish over an open fire in Ghana, 2018

These are mostly related to the burning of fuel.

• Stationary sources include:
  • smoke stacks of fossil fuels and biomass power stations (see for example environmental impact of the coal industry)
  • burning of traditional biomass such as wood, crop waste and dung. (In developing and poor countries, traditional biomass burning is the major source of air pollutants.^[23][24] It is also the main source of particulate pollution in many developed areas including the UK & New South Wales.^[25][26] Its pollutants include PAHs.^[27])
  • manufacturing facilities (factories)
    • a 2014 study found that in China equipment-, machinery-, and devices-manufacturing and construction sectors contributed more than 50% of air pollutant emissions^[28]
  • waste incineration (incinerators as well as open and uncontrolled fires of mismanaged waste, making up about a fourth of municipal solid terrestrial waste)^[29][30]
  • furnaces and other types of fuel-burning heating devices
• Mobile sources include motor vehicles, trains (particularly diesel locomotives and DMUs), marine vessels and aircraft.
• Controlled burn practices in agriculture and forest management. Controlled or prescribed burning is a technique sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement. Fire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters. Controlled burning stimulates the germination of some desirable forest trees, thus renewing the forest.

There are also sources from processes other than combustion:

• Fumes from paint, hair spray, varnish, aerosol sprays and other solvents. These can be substantial; emissions from these sources was estimated to account for almost half of pollution from volatile organic compounds in the Los Angeles basin in the 2010s.^[31]
• Waste deposition in landfills, which generate methane. Methane is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia or suffocation may result if the oxygen concentration is reduced to below 19.5% by displacement.
• Military resources, such as nuclear weapons, toxic gases, germ warfare and rocketry.
• Agricultural emissions contribute substantially to air pollution^[32][33]
  • Fertilized farmland may be a major source of nitrogen oxides.^[34]

Mean acidifying emissions (air pollution) of different foods per 100g of protein^[35]

Food Types	Acidifying Emissions (g SO2eq per 100g protein)
Beef	343.6
Cheese	165.5
Pork	142.7
Lamb and mutton	139.0
Farmed crustaceans	133.1
Poultry	102.4
Farmed fish	65.9
Eggs	53.7
Groundnuts	22.6
Peas	8.5
Tofu	6.7

Natural sources

Dust storm approaching Stratford, Texas

• Dust from natural sources, usually large areas of land with little vegetation or no vegetation
• Methane, emitted by the digestion of food by animals, for example cattle
• Radon gas from radioactive decay within the Earth's crust. Radon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. It is considered to be a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking.
• Smoke and carbon monoxide from wildfires. During periods of active wildfires, smoke from uncontrolled biomass combustion can make up almost 75% of all air pollution by concentration.^[36]
• Vegetation, in some regions, emits environmentally significant amounts of volatile organic compounds (VOCs) on warmer days. These VOCs react with primary anthropogenic pollutants – specifically, NO_x, SO₂, and anthropogenic organic carbon compounds – to produce a seasonal haze of secondary pollutants.^[37] Black gum, poplar, oak and willow are some examples of vegetation that can produce abundant VOCs. The VOC production from these species result in ozone levels up to eight times higher than the low-impact tree species.^[38]
• Volcanic activity, which produces sulfur, chlorine, and ash particulates

Emission factors

Beijing air in 2005 after rain (left) and a smoggy day (right)

Air pollutant emission factors are reported representative values that attempt to relate the quantity of a pollutant released to the ambient air with an activity associated with the release of that pollutant. These factors are usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant (e.g., kilograms of particulate emitted per tonne of coal burned). Such factors facilitate estimation of emissions from various sources of air pollution. In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages.

There are 12 compounds in the list of persistent organic pollutants. Dioxins and furans are two of them and intentionally created by combustion of organics, like open burning of plastics. These compounds are also endocrine disruptors and can mutate the human genes.

E-waste processing in Agbogbloshie, Ghana using open-burning of electronics to access valuable metals like coper. Open burning of plastics is common in many parts of the world without the capacity for processing. Especially without proper protections, heavy metals and other contaminates can seep into the soil, and create water pollution and air pollution.

The United States Environmental Protection Agency has published a compilation of air pollutant emission factors for a wide range of industrial sources.^[39] The United Kingdom, Australia, Canada and many other countries have published similar compilations, as well as the European Environment Agency.^{[40][41][42][43]}

Pollutants

Schematic drawing, causes and effects of air pollution: (1) greenhouse effect, (2) particulate contamination, (3) increased UV radiation, (4) acid rain, (5) increased ground-level ozone concentration, (6) increased levels of nitrogen oxides

An air pollutant is a material in the air that can have adverse effects on humans and the ecosystem. The substance can be solid particles, liquid droplets, or gases. A pollutant can be of natural origin or man-made. Pollutants are classified as primary or secondary. Primary pollutants are usually produced by processes such as ash from a volcanic eruption. Other examples include carbon monoxide gas from motor vehicle exhausts or sulfur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. Ground level ozone is a prominent example of a secondary pollutant. Some pollutants may be both primary and secondary: they are both emitted directly and formed from other primary pollutants.

Pollutants emitted into the atmosphere by human activity include:

• Carbon dioxide (CO₂): Because of its role as a greenhouse gas it has been described as "the leading pollutant"^[44] and "the worst climate pollutant".^[45] Carbon dioxide is a natural component of the atmosphere, essential for plant life and given off by the human respiratory system.^[46] This question of terminology has practical effects, for example as determining whether the U.S. Clean Air Act is deemed to regulate CO₂ emissions.^[47] CO₂ currently forms about 410 parts per million (ppm) of earth's atmosphere, compared to about 280 ppm in pre-industrial times,^[48] and billions of metric tons of CO₂ are emitted annually by burning of fossil fuels.^[49] CO₂ increase in earth's atmosphere has been accelerating.^[50]
• Sulfur oxides (SO_x): particularly sulfur dioxide, a chemical compound with the formula SO₂. SO₂ is produced by volcanoes and in various industrial processes. Coal and petroleum often contain sulfur compounds, and their combustion generates sulfur dioxide. Further oxidation of SO₂, usually in the presence of a catalyst such as NO₂, forms H₂SO₄, and thus acid rain is formed. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
• Nitrogen oxides (NO_x): Nitrogen oxides, particularly nitrogen dioxide, are expelled from high temperature combustion, and are also produced during thunderstorms by electric discharge. They can be seen as a brown haze dome above or a plume downwind of cities. Nitrogen dioxide is a chemical compound with the formula NO₂. It is one of several nitrogen oxides. One of the most prominent air pollutants, this reddish-brown toxic gas has a characteristic sharp, biting odor.
• Carbon monoxide (CO): CO is a colorless, odorless, toxic gas.^[51] It is a product of combustion of fuel such as natural gas, coal or wood. Vehicular exhaust contributes to the majority of carbon monoxide let into the atmosphere. It creates a smog type formation in the air that has been linked to many lung diseases and disruptions to the natural environment and animals.
• Volatile organic compounds (VOC): VOCs are a well-known outdoor air pollutant. They are categorized as either methane (CH₄) or non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases because of their role in creating ozone and prolonging the life of methane in the atmosphere. This effect varies depending on local air quality. The aromatic NMVOCs benzene, toluene and xylene are suspected carcinogens and may lead to leukemia with prolonged exposure. 1,3-butadiene is another dangerous compound often associated with industrial use.
• Particulate matter/particles, alternatively referred to as particulate matter (PM), atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to combined particles and gas. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged worldwide, anthropogenic aerosols – those made by human activities – currently account for approximately 10% of our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease,^[52] altered lung function and lung cancer. Particulates are related to respiratory infections and can be particularly harmful to those already suffering from conditions like asthma.^[53]
• Persistent free radicals connected to airborne fine particles are linked to cardiopulmonary disease.^[54][55]
• Toxic metals, such as lead and mercury, especially their compounds.
• Chlorofluorocarbons (CFCs): Harmful to the ozone layer; Emitted from products that are currently banned from use. These are gases which are released from air conditioners, refrigerators, aerosol sprays, etc. On release into the air, CFCs rise to the stratosphere. Here they come in contact with other gases and damage the ozone layer. This allows harmful UV rays to reach the earth's surface. This can lead to skin cancer, eye disease and can even cause damage to plants.
• Ammonia: Emitted mainly by agricultural waste. Ammonia is a compound with the formula NH₃. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous.^[56] In the atmosphere, ammonia reacts with oxides of nitrogen and sulfur to form secondary particles.^[57]
• Odors: Such as from garbage, sewage, and industrial processes.
• Radioactive pollutants: Produced by nuclear explosions, nuclear events, war explosives, and natural processes such as the radioactive decay of radon.

Secondary pollutants include:

• Particulates created from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution. Classic smog results from large amounts of coal burning in an area, which produces a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog.
• Ground level ozone (O₃): Ozone is formed from NO_x and VOCs. It is a key constituent of the troposphere. It is also an important constituent of certain regions of the stratosphere commonly known as the ozone layer. Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuel), it is a pollutant and a constituent of smog.
• Peroxyacetyl nitrate (C₂H₃NO₅): similarly formed from NO_x and VOCs.

Minor air pollutants include:

• A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework Directive.
• A variety of persistent organic pollutants, which can attach to particulates

Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potentially significant impacts on human health and the environment.

• 
  Before flue-gas desulfurization was installed, the emissions from this power plant in New Mexico contained excessive amounts of sulfur dioxide.
• 
  Thermal oxidisers are air pollution abatement options for hazardous air pollutants (HAPs), volatile organic compounds (VOCs), and odorous emissions.

Exposure

Up to 30% of Europeans living in cities are exposed to air pollutant levels exceeding EU air quality standards. Around 98% of Europeans living in cities are exposed to levels of air pollutants deemed damaging to health by the World Health Organization's more stringent guidelines.^[58]

Air pollution risk is a function of the hazard of the pollutant and the exposure to that pollutant. Air pollution exposure can be expressed for an individual, for certain groups (e.g. neighbourhoods or children living in a country), or for entire populations. For example, one may want to calculate the exposure to a hazardous air pollutant for a geographic area, which includes the various microenvironments and age groups. This can be calculated^[5] as an inhalation exposure. This would account for daily exposure in various settings (e.g. different indoor micro-environments and outdoor locations). The exposure needs to include different age and other demographic groups, especially infants, children, pregnant women and other sensitive subpopulations. The exposure to an air pollutant must integrate the concentrations of the air pollutant with respect to the time spent in each setting and the respective inhalation rates for each subgroup for each specific time that the subgroup is in the setting and engaged in particular activities (playing, cooking, reading, working, spending time in traffic, etc.). For example, a small child's inhalation rate will be less than that of an adult. A child engaged in vigorous exercise will have a higher respiration rate than the same child in a sedentary activity. The daily exposure, then, needs to reflect the time spent in each micro-environmental setting and the type of activities in these settings. The air pollutant concentration in each microactivity/microenvironmental setting is summed to indicate the exposure.^[5] For some pollutants such as black carbon, traffic related exposures may dominate total exposure despite short exposure times since high concentrations coincide with proximity to major roads or participation to (motorized) traffic.^[59] A large portion of total daily exposure occurs as short peaks of high concentrations, but it remains unclear how to define peaks and determine their frequency and health impact.^[60]

In 2021, the WHO halved its recommended guideline limit for tiny particles from burning fossil fuels. The new limit for nitrogen dioxide (NO₂) is 75% lower.^[61]

Indoor air quality

Share of deaths from indoor air pollution

Air quality monitoring, New Delhi, India

A lack of ventilation indoors concentrates air pollution where people often spend the majority of their time. Radon (Rn) gas, a carcinogen, is exuded from the Earth in certain locations and trapped inside houses. Building materials including carpeting and plywood emit formaldehyde (H₂CO) gas. Paint and solvents give off volatile organic compounds (VOCs) as they dry. Lead paint can degenerate into dust and be inhaled. Intentional air pollution is introduced with the use of air fresheners, incense, and other scented items. Controlled wood fires in cook stoves and fireplaces can add significant amounts of harmful smoke particulates into the air, inside and out.^[62][63] Indoor pollution fatalities may be caused by using pesticides and other chemical sprays indoors without proper ventilation.

Carbon monoxide poisoning and fatalities are often caused by faulty vents and chimneys, or by the burning of charcoal indoors or in a confined space, such as a tent.^[64] Chronic carbon monoxide poisoning can result even from poorly-adjusted pilot lights. Traps are built into all domestic plumbing to keep sewer gas and hydrogen sulfide, out of interiors. Clothing emits tetrachloroethylene, or other dry cleaning fluids, for days after dry cleaning.

Though its use has now been banned in many countries, the extensive use of asbestos in industrial and domestic environments in the past has left a potentially very dangerous material in many localities. Asbestosis is a chronic inflammatory medical condition affecting the tissue of the lungs. It occurs after long-term, heavy exposure to asbestos from asbestos-containing materials in structures. Sufferers have severe dyspnea (shortness of breath) and are at an increased risk regarding several different types of lung cancer. As clear explanations are not always stressed in non-technical literature, care should be taken to distinguish between several forms of relevant diseases. According to the World Health Organization (WHO),^[65] these may be defined as asbestosis, lung cancer, and peritoneal mesothelioma (generally a very rare form of cancer, when more widespread it is almost always associated with prolonged exposure to asbestos).

Biological sources of air pollution are also found indoors, as gases and airborne particulates. Pets produce dander, people produce dust from minute skin flakes and decomposed hair, dust mites in bedding, carpeting and furniture produce enzymes and micrometre-sized fecal droppings, inhabitants emit methane, mold forms on walls and generates mycotoxins and spores, air conditioning systems can incubate Legionnaires' disease and mold, and houseplants, soil and surrounding gardens can produce pollen, dust, and mold. Indoors, the lack of air circulation allows these airborne pollutants to accumulate more than they would otherwise occur in nature.

Health effects

Even at levels lower than those considered safe by United States regulators, exposure to three components of air pollution, fine particulate matter, nitrogen dioxide and ozone, correlates with cardiac and respiratory illness.^[66] In 2020, pollution (including air pollution) was a contributing factor to one in eight deaths in Europe, and was a significant risk factor for pollution-related diseases including heart disease, stroke and lung cancer.^[67] The health effects caused by air pollution may include difficulty in breathing, wheezing, coughing, asthma^[68] and worsening of existing respiratory and cardiac conditions. These effects can result in increased medication use, increased doctor or emergency department visits, more hospital admissions and premature death. The human health effects of poor air quality are far reaching, but principally affect the body's respiratory system and the cardiovascular system. Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, and the individual's health status and genetics.^[5] The most common sources of air pollution include particulates, ozone, nitrogen dioxide, and sulfur dioxide. Children aged less than five years who live in developing countries are the most vulnerable population in terms of total deaths attributable to indoor and outdoor air pollution.^[69]

Mortality

Share of deaths from outdoor air pollution, OWID

The World Health Organization estimated in 2014 that every year air pollution causes the premature death of some 7 million people worldwide.^[1] Studies published in March 2019 indicated that the number may be around 8.8 million.^[70] Causes of deaths include strokes, heart disease, COPD, lung cancer, and lung infections.^[1]

Urban outdoor air pollution is estimated to cause 1.3 million deaths worldwide per year.^[71] Children are particularly at risk due to the immaturity of their respiratory organ systems.^[72] In 2015, outdoor air pollution, mostly by PM_2.5, was estimated to lead to 3.3 (95% CI 1.61–4.81) million premature deaths per year worldwide, predominantly in Asia.^[33] In 2021, the WHO reported that outdoor air pollution was estimated to cause 4.2 million premature deaths worldwide in 2016.^[73] A 2020 study indicates that the global mean loss of life expectancy (LLE) from air pollution in 2015 was 2.9 years, substantially more than, for example, 0.3 years from all forms of direct violence, albeit a significant fraction of the LLE is unavoidable.^[9] Moreover, communities with the most exceptional aging have low ambient air pollution, suggesting a link between air pollution levels and longevity.^[74]

By region

India and China have the highest death rate due to air pollution.^[75][76] India also has more deaths from asthma than any other nation according to the World Health Organization. In December 2013 air pollution was estimated to kill 500,000 people in China each year.^[77] There is a positive correlation between pneumonia-related deaths and air pollution from motor vehicle emissions.^[78]

Annual premature European deaths caused by air pollution are estimated at 430,000^[79] to 800,000.^[70] An important cause of these deaths is nitrogen dioxide and other nitrogen oxides (NOx) emitted by road vehicles.^[79] In a 2015 consultation document the UK government disclosed that nitrogen dioxide is responsible for 23,500 premature UK deaths per annum.^[80] Across the European Union, air pollution is estimated to reduce life expectancy by almost nine months.^[81]

Guidelines

Main article: Air quality guideline

The US EPA has estimated that limiting ground-level ozone concentration to 65 parts per billion (ppb), would avert 1,700 to 5,100 premature deaths nationwide in 2020 compared with the 75 ppb standard. The agency projected the more protective standard would also prevent an additional 26,000 cases of aggravated asthma, and more than a million cases of missed work or school.^[82][83] Following this assessment, the EPA acted to protect public health by lowering the National Ambient Air Quality Standards (NAAQS) for ground-level ozone to 70 ppb.^[84] A new economic study of the health impacts and associated costs of air pollution in the Los Angeles Basin and San Joaquin Valley of Southern California shows that more than 3,800 people die prematurely (approximately 14 years earlier than normal) each year because air pollution levels violate federal standards. The number of annual premature deaths is considerably higher than the fatalities related to auto collisions in the same area, which average fewer than 2,000 per year.^[85][86][87] A 2021 study found that outdoor air pollution is associated with substantially increased mortality "even at low pollution levels below the current European and North American standards and WHO guideline values" shortly before the WHO adjusted its guidelines.^[88][89]

Major causes

Further information: § Sources

Comparison of footprint-based and transboundary pollution-based relationships among G20 nations for the number of PM_2.5-related premature deaths.^[90]

The largest cause is air pollution generated by fossil fuel combustion^[91] – mostly the production and use of cars, electricity production and heating. A study by Greenpeace estimates there are 4.5 million annual premature deaths worldwide because of pollutants released by high-emission power stations and vehicle exhausts.^[92]

Diesel exhaust (DE) is a major contributor to combustion-derived particulate matter air pollution. In several human experimental studies, using a well-validated exposure chamber setup, DE has been linked to acute vascular dysfunction and increased thrombus formation.^[93][94]

A study concluded that PM_2.5 air pollution induced by the contemporary free trade and consumption by the 19 G20 nations causes two million premature deaths annually, suggesting that the average lifetime consumption of about ~28 people in these countries causes at least one premature death (average age ~67) while developing countries "cannot be expected" to implement or be able to implement countermeasures without external support or internationally coordinated efforts.^[95][90]

Primary mechanisms

The WHO estimates that in 2016, ~58% of outdoor air pollution-related premature deaths were due to ischaemic heart disease and stroke.^[73] The mechanisms linking air pollution to increased cardiovascular mortality are uncertain, but probably include pulmonary and systemic inflammation.^[96]

Contemporary annual deaths

A study by scientists of U.K. and U.S. universities that uses a high spatial resolution model and an updated concentration-response function concluded in 2021 that 10.4 million global excess deaths in 2012 and 8.7 million in 2018 – or a fifth – were due to air pollution generated by fossil fuel combustion, significantly higher than earlier estimates and with spatially subdivided mortality impacts.^[97][91]

According to the WHO air pollution accounts for 1 in 8 deaths worldwide.^[98]

Cancer (lung cancer)

Unprotected exposure to PM2.5 air pollution can be equivalent to smoking multiple cigarettes per day,^[115] potentially increasing the risk of cancer, which is mainly the result of environmental factors.^[116]

A review of evidence regarding whether ambient air pollution exposure is a risk factor for cancer in 2007 found solid data to conclude that long-term exposure to PM2.5 (fine particulates) increases the overall risk of non-accidental mortality by 6% per a 10 microg/m³ increase. Exposure to PM2.5 was also associated with an increased risk of mortality from lung cancer (range: 15% to 21% per 10 microg/m³ increase) and total cardiovascular mortality (range: 12% to 14% per a 10 microg/m³ increase). The review further noted that living close to busy traffic appears to be associated with elevated risks of these three outcomes – increase in lung cancer deaths, cardiovascular deaths, and overall non-accidental deaths. The reviewers also found suggestive evidence that exposure to PM2.5 is positively associated with mortality from coronary heart diseases and exposure to SO₂ increases mortality from lung cancer, but the data was insufficient to provide solid conclusions.^[117] Another investigation showed that higher activity level increases deposition fraction of aerosol particles in human lung and recommended avoiding heavy activities like running in outdoor space at polluted areas.^[118]

In 2011, a large Danish epidemiological study found an increased risk of lung cancer for people who lived in areas with high nitrogen oxide concentrations. In this study, the association was higher for non-smokers than smokers.^[119] An additional Danish study, also in 2011, likewise noted evidence of possible associations between air pollution and other forms of cancer, including cervical cancer and brain cancer.^[120]

"Clean" areas

Share of the population exposed to air pollution levels above WHO guidelines, OWID

Even in areas with relatively low levels of air pollution, public health effects can be significant and costly, since a large number of people breathe in such pollutants. A study published in 2017 found that even in areas of the U.S. where ozone and PM_2.5 meet federal standards, Medicare recipients who are exposed to more air pollution have higher mortality rates.^[134] A 2005 scientific study for the British Columbia Lung Association showed that a small improvement in air quality (1% reduction of ambient PM_2.5 and ozone concentrations) would produce $29 million in annual savings in the Metro Vancouver region in 2010.^[135] This finding is based on health valuation of lethal (death) and sub-lethal (illness) affects.

In 2020, scientists found that the boundary layer air over the Southern Ocean around Antarctica is 'unpolluted' by humans.^[136]

Agricultural effects

In India in 2014, it was reported that air pollution by black carbon and ground level ozone had reduced crop yields in the most affected areas by almost half in 2011 when compared to 1980 levels.^[149]

Economic effects

Air pollution costs the world economy $5 trillion per year as a result of productivity losses and degraded quality of life, according to a joint study by the World Bank and the Institute for Health Metrics and Evaluation (IHME) at the University of Washington.^[16][17][18] These productivity losses are caused by deaths due to diseases caused by air pollution. One out of ten deaths in 2013 was caused by diseases associated with air pollution and the problem is getting worse. The problem is even more acute in the developing world. "Children under age 5 in lower-income countries are more than 60 times as likely to die from exposure to air pollution as children in high-income countries."^[16][17] The report states that additional economic losses caused by air pollution, including health costs^[150] and the adverse effect on agricultural and other productivity were not calculated in the report, and thus the actual costs to the world economy are far higher than $5 trillion.

Other effects

Artist's illustration of an advanced ET civilization with industrial pollution

Artificial air pollution may be detectable on Earth from distant vantage points such as other planetary systems via atmospheric SETI – including NO₂ pollution levels and with telescopic technology close to today. It may also be possible to detect extraterrestrial civilizations this way.^{[151][152][153]}

Historical disasters

The world's worst short-term civilian pollution crisis was the 1984 Bhopal Disaster in India.^[154] Leaked industrial vapours from the Union Carbide factory, belonging to Union Carbide, Inc., U.S.A. (later bought by Dow Chemical Company), killed at least 3787 people and injured from 150,000 to 600,000. The United Kingdom suffered its worst air pollution event when the 4 December Great Smog of 1952 formed over London. In six days more than 4,000 died and more recent estimates put the figure at nearer 12,000.^[155] An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 near Sverdlovsk is believed to have caused at least 64 deaths.^[156] The worst single incident of air pollution to occur in the US occurred in Donora, Pennsylvania, in late October 1948, when 20 people died and over 7,000 were injured.^[157]

Reduction and regulation

Pollution prevention seeks to prevent pollution such as air pollution and could include adjustments to industrial and business activities such as designing sustainable manufacturing processes (and the products' designs)^[158] and related legal regulations as well as efforts towards renewable energy transitions.^[159][160]

Efforts to reduce particulate matter in the air may result in better health.^[161]

Alternatives to pollution

Support for a ban on high-emission vehicles in city centres in Europe, China and the US from respondents to the European Investment Bank Climate Survey

Support, use and infrastructure-expansion of forms of public transport that do not cause air pollution may be a critical key alternative to pollution

There are now practical alternatives to the principal causes of air pollution:

• Strategic substitution of air pollution sources in transport with lower-emission or, during lifecycle, emission-free forms of public transport^[165][166] and bicycle use and infrastructure (as well as with remote work, reductions of work, relocations and localizations)
  • Phase-out of fossil fuel vehicles are a critical component of a shift to sustainable transport; however, similar infrastructure and design decisions like electric vehicles may be associated with similar pollution for production as well as mining and resource exploitation for large numbers of needed batteries as well as the energy for their recharging^[167][168]
• Areas downwind (over 20 miles) of major airports have more than double total particulate emissions in air than other areas, even when factoring in areas with frequent ship calls, and heavy freeway and city traffic like Los Angeles.^[169] Aviation biofuel mixed in with jetfuel at a 50/50 ratio can reduce jet derived cruise altitude particulate emissions by 50–70%, according to a NASA led 2017 study (however, this should imply ground level benefits to urban air pollution as well).^[170]
• Ship propulsion and idling can be switched to much cleaner fuels like natural gas. (Ideally a renewable source but not practical yet)
• Combustion of fossil fuels for space heating can be replaced by using ground source heat pumps and seasonal thermal energy storage.^[171]
• Electric power generation from burning fossil fuels can be replaced by power generation from nuclear and renewable. For poor nations, heating and home stoves that contribute much to regional air pollution can be replaced by a much cleaner fossil fuel like natural gas, or ideally, renewables.
• Motor vehicles driven by fossil fuels, a key factor in urban air pollution, can be replaced by electric vehicles. Though lithium supply and cost is a limitation, there are alternatives. Herding more people into clean public transit such as electric trains can also help. Nevertheless, even in emission-free electric vehicles, rubber tires produce significant amounts of air pollution themselves, ranking as 13th worst pollutant in Los Angeles.^[172]
• Reducing travel in vehicles can curb pollution. After Stockholm reduced vehicle traffic in the central city with a congestion tax, nitrogen dioxide and PM10 pollution declined, as did acute pediatric asthma attacks.^[173]
• Biodigesters can be utilized in poor nations where slash and burn is prevalent, turning a useless commodity into a source of income. The plants can be gathered and sold to a central authority that will break it down in a large modern biodigester, producing much needed energy to use.
• Induced humidity and ventilation both can greatly dampen air pollution in enclosed spaces, which was found to be relatively high inside subway lines due to braking and friction and relatively less ironically inside transit buses than lower sitting passenger automobiles or subways.^[174]

Further information: § Sources

Control devices

Tarps and netting are often used to reduce the amount of dust released from construction sites.

The following items are commonly used as pollution control devices in industry and transportation. They can either destroy contaminants or remove them from an exhaust stream before it is emitted into the atmosphere.

• Particulate control
  • Mechanical collectors (dust cyclones, multicyclones)
  • Electrostatic precipitators: An electrostatic precipitator (ESP), or electrostatic air cleaner, is a particulate collection device that removes particles from a flowing gas (such as air), using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulates such as dust and smoke from the air stream.
  • Baghouses: Designed to handle heavy dust loads, a dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust).
  • Particulate scrubbers: A wet scrubber is a form of pollution control technology. The term describes a variety of devices that use pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, so as to remove the pollutants.
• Scrubbers
  • Baffle spray scrubber
  • Cyclonic spray scrubber
  • Ejector venturi scrubber
  • Mechanically aided scrubber
  • Spray tower
  • Wet scrubber
• NO_x control
  • LO-NOx burners
  • Selective catalytic reduction (SCR)
  • Selective non-catalytic reduction (SNCR)
  • NOx scrubbers
  • Exhaust gas recirculation
  • Catalytic converter (also for VOC control)
• VOC abatement
  • Adsorption systems, using activated carbon, such as Fluidized Bed Concentrator
  • Flares
  • Thermal oxidizers
  • Catalytic converters
  • Biofilters
  • Absorption (scrubbing)
  • Cryogenic condensers
  • Vapor recovery systems
• Acid gas/SO₂ control
  • Wet scrubbers
  • Dry scrubbers
  • Flue-gas desulfurization
• Mercury control
  • Sorbent injection technology
  • Electro-catalytic oxidation (ECO)
  • K-Fuel
• Dioxin and furan control
• Miscellaneous associated equipment
  • Source capturing systems
  • Continuous emissions monitoring systems (CEMS)

Regulations

Smog in Cairo

In general, there are two types of air quality standards. The first class of standards (such as the U.S. National Ambient Air Quality Standards and E.U. Air Quality Directive^[185]) set maximum atmospheric concentrations for specific pollutants. Environmental agencies enact regulations which are intended to result in attainment of these target levels. The second class (such as the North American air quality index) take the form of a scale with various thresholds, which is used to communicate to the public the relative risk of outdoor activity. The scale may or may not distinguish between different pollutants.

Canada

In Canada, air pollution and associated health risks are measured with the Air Quality Health Index (AQHI). It is a health protection tool used to make decisions to reduce short-term exposure to air pollution by adjusting activity levels during increased levels of air pollution.

The AQHI is a federal program jointly coordinated by Health Canada and Environment Canada. However, the AQHI program would not be possible without the commitment and support of the provinces, municipalities and NGOs. From air quality monitoring to health risk communication and community engagement, local partners are responsible for the vast majority of work related to AQHI implementation. The AQHI provides a number from 1 to 10+ to indicate the level of health risk associated with local air quality. Occasionally, when the amount of air pollution is abnormally high, the number may exceed 10. The AQHI provides a local air quality current value as well as a local air quality maximums forecast for today, tonight and tomorrow and provides associated health advice.

1

2

3

4

5

6

7

8

9

10

+

Risk:

Low (1–3)

Moderate (4–6)

High (7–10)

Very high (above 10)

As it is now known that even low levels of air pollution can trigger discomfort for the sensitive population, the index has been developed as a continuum: The higher the number, the greater the health risk and need to take precautions. The index describes the level of health risk associated with this number as 'low', 'moderate', 'high' or 'very high', and suggests steps that can be taken to reduce exposure.^[186]

Health risk	Air Quality Health Index	Health messages[187]
		At risk population	General population
Low	1–3	Enjoy your usual outdoor activities.	Ideal air quality for outdoor activities
Moderate	4–6	Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms.	No need to modify your usual outdoor activities unless you experience symptoms such as coughing and throat irritation.
High	7–10	Reduce or reschedule strenuous activities outdoors. Children and the elderly should also take it easy.	Consider reducing or rescheduling strenuous activities outdoors if you experience symptoms such as coughing and throat irritation.
Very high	Above 10	Avoid strenuous activities outdoors. Children and the elderly should also avoid outdoor physical exertion and should stay indoors.	Reduce or reschedule strenuous activities outdoors, especially if you experience symptoms such as coughing and throat irritation.

The measurement is based on the observed relationship of nitrogen dioxide (NO₂), ground-level ozone (O₃) and particulates (PM_2.5) with mortality, from an analysis of several Canadian cities. Significantly, all three of these pollutants can pose health risks, even at low levels of exposure, especially among those with pre-existing health problems.

When developing the AQHI, Health Canada's original analysis of health effects included five major air pollutants: particulates, ozone, and nitrogen dioxide (NO₂), as well as sulfur dioxide (SO₂), and carbon monoxide (CO). The latter two pollutants provided little information in predicting health effects and were removed from the AQHI formulation.

The AQHI does not measure the effects of odour, pollen, dust, heat or humidity.

Germany

TA Luft is the German air quality regulation.

Hotspots

Air pollution hotspots are areas where air pollution emissions expose individuals to increased negative health effects.^[199] They are particularly common in highly populated, urban areas, where there may be a combination of stationary sources (e.g. industrial facilities) and mobile sources (e.g. cars and trucks) of pollution. Emissions from these sources can cause respiratory disease, childhood asthma,^[68] cancer, and other health problems. Fine particulate matter such as diesel soot, which contributes to more than 3.2 million premature deaths around the world each year, is a significant problem. It is very small and can lodge itself within the lungs and enter the bloodstream. Diesel soot is concentrated in densely populated areas, and one in six people in the U.S. live near a diesel pollution hot spot.^[200]

External video
AirVisual Earth – realtime map of global wind and air pollution[201]

While air pollution hotspots affect a variety of populations, some groups are more likely to be located in hotspots. Previous studies have shown disparities in exposure to pollution by race and/or income. Hazardous land uses (toxic storage and disposal facilities, manufacturing facilities, major roadways) tend to be located where property values and income levels are low. Low socioeconomic status can be a proxy for other kinds of social vulnerability, including race, a lack of ability to influence regulation and a lack of ability to move to neighborhoods with less environmental pollution. These communities bear a disproportionate burden of environmental pollution and are more likely to face health risks such as cancer or asthma.^[202]

Studies show that patterns in race and income disparities not only indicate a higher exposure to pollution but also higher risk of adverse health outcomes.^[203] Communities characterized by low socioeconomic status and racial minorities can be more vulnerable to cumulative adverse health impacts resulting from elevated exposure to pollutants than more privileged communities.^[203] Blacks and Latinos generally face more pollution than whites and Asians, and low-income communities bear a higher burden of risk than affluent ones.^[202] Racial discrepancies are particularly distinct in suburban areas of the Southern United States and metropolitan areas of the Midwestern and Western United States.^[204] Residents in public housing, who are generally low-income and cannot move to healthier neighborhoods, are highly affected by nearby refineries and chemical plants.^[205]

Cities

Nitrogen dioxide concentrations as measured from satellite 2002–2004

Deaths from air pollution in 2004

Air pollution is usually concentrated in densely populated metropolitan areas, especially in developing countries where environmental regulations are relatively lax or nonexistent. However, even populated areas in developed countries attain unhealthy levels of pollution, with Los Angeles and Rome being two examples.^[206] Between 2002 and 2011 the incidence of lung cancer in Beijing near doubled. While smoking remains the leading cause of lung cancer in China, the number of smokers is falling while lung cancer rates are rising.^[207]

Projections

According to a projection, by 2030 half of the world's pollution emissions could be generated by Africa.^[209] Potential contributors to such an outcome include increased burning activities (such as the burning of open waste), traffic, agri-food and chemical industries, sand dust from the Sahara, and overall population growth.

According to OECD, by 2050 outdoor air pollution (particulate matter and ground-level ozone) is projected to become the top cause of environmentally related deaths worldwide.^[210]

See also

References

Further reading

• Brimblecombe, Peter. The Big Smoke: A History of Air Pollution in London Since Medieval Times (Methuen, 1987)
• Brimblecombe, Peter. "History of air pollution." in Composition, Chemistry and Climate of the Atmosphere (Van Nostrand Reinhold (1995): 1–18
• Brimblecombe, Peter; Makra, László (2005). "Selections from the history of environmental pollution, with special attention to air pollution. Part 2*: From medieval times to the 19th century". International Journal of Environment and Pollution. 23 (4): 351–67. doi:10.1504/ijep.2005.007599.
• Cherni, Judith A. Economic Growth versus the Environment: The Politics of Wealth, Health and Air Pollution (2002) online
• Corton, Christine L. London Fog: The Biography (2015)
• Currie, Donya. "WHO: Air Pollution a Continuing Health Threat in World's Cities," The Nation's Health (February 2012) 42#1 online
• Dewey, Scott Hamilton. Don't Breathe the Air: Air Pollution and US Environmental Politics, 1945–1970 (Texas A & M University Press, 2000)
• Gonzalez, George A. The politics of air pollution: Urban growth, ecological modernization, and symbolic inclusion (SUNY Press, 2012)
• Grinder, Robert Dale (1978). "From Insurgency to Efficiency: The Smoke Abatement Campaign in Pittsburgh before World War I.". Western Pennsylvania Historical Magazine. 61 (3): 187–202.
• Grinder, Robert Dale. "The Battle for Clean Air: The Smoke Problem in Post-Civil War America" in Martin V. Melosi, ed., Pollution & Reform in American Cities, 1870–1930 (1980), pp. 83–103.
• Mingle, Jonathan, "Our Lethal Air" [review of Gary Fuller, The Invisible Killer...; Beth Gardiner, Choked...; Tim Smedley, Clearing the Air...; U.S. Environmental Protection Agency, Integrated Science Assessment for Particulate Matter (External Review Draft, 2018); and Chartered Clean Air Scientific Advisory Committee, Letter to EPA Administrator on the EPA's Integrated Science Assessment for Particulate Matter, 11 April 2019], The New York Review of Books, vol. LXVI, no. 14 (26 September 2019), pp. 64–66, 68. "Today, 91 percent of people worldwide live in areas where air pollution levels exceed the World Health Organization's recommended limits. ... [T]here is no safe level of exposure to fine particulate matter. ... Most of these fine particles are a by-product of ... burning ... coal, gasoline, diesel, wood, trash ... These particles can get past the defenses of our upper airways to penetrate deep into our lungs and reach the alveoli ... From there, they cross into the bloodstream and spread throughout the body. They can travel through the nose, up the olfactory nerve, and lodge ... in the brain. They can form deposits on the lining of arteries, constricting blood vessels and raising the likelihood of ... strokes and heart attacks. [T]hey exacerbate respiratory illnesses like asthma and chronic obstructive pulmonary disease ... There's ... evidence linking air pollution exposure to an increased risk of Alzheimer's and other forms of dementia." (p. 64.)
• Mosley, Stephen. The chimney of the world: a history of smoke pollution in Victorian and Edwardian Manchester. Routledge, 2013.
• Schreurs, Miranda A. Environmental Politics in Japan, Germany, and the United States (Cambridge University Press, 2002) online
• Thorsheim, Peter. Inventing Pollution: Coal, Smoke, and Culture in Britain since 1800 (2009)

External links

Wikimedia Commons has media related to Air pollution.

Wikivoyage has travel information for Air pollution.

• Air Pollution: Everything You Need to Know Guide by the Natural Resources Defense Council (NRDC)
• Global real-time air quality index map
• Air Quality Index (AQI) Basics
• AQI Calculator AQI to Concentration and Concentration to AQI for five pollutants
• International Conference on Urban Air Quality Archived 16 December 2008 at the Wayback Machine.
• UNEP Urban environmental planning
• European Commission > Environment > Air > Air Quality
• Database: outdoor air pollution in cities from the World Health Organization
• World Health Organization Fact Sheet on Air quality and health
• Centre for Research on Energy and Clean Air
• The Mortality Effects of Long-Term Exposure to Particulate Air Pollution in the United Kingdom, UK Committee on the Medical Effects of Air Pollution, 2010.
• Ground Level Ozone Pollution at EPA.gov