{{Short description|Presence of dangerous substances in the air}} {{good article}} {{Redirect2|Bad air quality|Air quality|the obsolete medical theory|Miasma theory|the measurement of air pollution|Air quality index}} {{cs1 config|name-list-style=vanc|display-authors=6}} {{Use dmy dates|date=April 2021}} {{Pollution sidebar|Air}}
'''Air pollution''' is the presence of substances in the air that are harmful to humans, other living beings or the environment. Pollutants can be gases, like ozone or nitrogen oxides, or small particles like soot and dust. Both outdoor and indoor air can be polluted.
Outdoor air pollution comes from burning fossil fuels for electricity and transport, wildfires, some industrial processes, waste management, demolition and agriculture. Indoor air pollution is often from burning firewood or agricultural waste for cooking and heating. Other sources of air pollution include dust storms and volcanic eruptions. Many sources of local air pollution, especially burning fossil fuels, also release greenhouse gases that cause global warming. However, air pollution may limit warming locally.
Air pollution kills 7 to 8 million people each year. It is a significant risk factor for a number of diseases, including stroke, heart disease, chronic obstructive pulmonary disease (COPD), asthma, coronavirus and lung cancer. Particulate matter is the most deadly, both for indoor and outdoor air pollution. Ozone affects crops, and forests are damaged by the pollution that causes acid rain. Overall, the World Bank has estimated that welfare losses (premature deaths) and productivity losses (lost labor) caused by air pollution cost the world economy over $8{{nbsp}}trillion per year.
Various technologies and strategies reduce air pollution. Key approaches include clean cookers, fire protection, improved waste management, dust control, industrial scrubbers, electric vehicles and renewable energy. National air quality laws have often been effective, notably the 1956 Clean Air Act in Britain and the 1963 US Clean Air Act. International efforts have had mixed results: the Montreal Protocol almost eliminated harmful ozone-depleting chemicals, while international action on climate change has been less successful.
== Sources ==
===Human sources=== ====Industry and construction ==== [[File:Athlone cooling towers demolition 2010-08-22.gif|thumb|Demolition of the cooling towers of a power station, Athlone, Cape Town, South Africa, 2010.|alt=Dust and debris rise as large concrete cooling towers collapse during a controlled demolition]] [[File:Air pollution by industrial chimneys.jpg|thumb|Before flue-gas desulfurization was installed, the emissions from this power plant in New Mexico contained excessive amounts of sulfur dioxide.|alt=A factory with chimneys releasing smoke.]] Burning fuel to generate electricity causes air pollution; lignite and coal produce the most air pollution, followed by oil, and then by fossil gas and biomass.<ref>{{Cite journal |last1=Markandya |first1=Anil |last2=Wilkinson |first2=Paul |date=2007 |title=Electricity generation and health |url=https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61253-7/abstract |journal=The Lancet |language=English |volume=370 |issue=9591 |pages=979–990 |doi=10.1016/S0140-6736(07)61253-7 |issn=0140-6736 |pmid=17876910 |url-access=subscription |archive-date=22 March 2025 |access-date=20 March 2025 |archive-url=https://web.archive.org/web/20250322230702/https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61253-7/abstract |url-status=live }}</ref><ref name=OWID_SafestEnergy_2021 /> Methane leaks are common in oil and gas production,<ref>{{cite news |last=Rannard |first=Georgina |date=4 February 2022 |title=Climate change: Satellites map huge methane plumes from oil and gas |url=https://www.bbc.com/news/science-environment-60203683 |url-status=live |archive-url=https://web.archive.org/web/20250124225322/https://www.bbc.com/news/science-environment-60203683 |archive-date=24 January 2025 |access-date=16 March 2022 |work=BBC News}}</ref><ref>{{cite journal |last1=Lauvaux |first1=T. |last2=Giron |first2=C. |last3=Mazzolini |first3=M. |last4=d'Aspremont |first4=A. |last5=Duren |first5=R. |last6=Cusworth |first6=D. |last7=Shindell |first7=D. |last8=Ciais |first8=P. |title=Global assessment of oil and gas methane ultra-emitters |journal=Science |date=2022 |volume=375 |issue=6580 |pages=557–561 |doi=10.1126/science.abj4351 |pmid=35113691 |arxiv=2105.06387 |bibcode=2022Sci...375..557L |s2cid=246530897 |issn=0036-8075 |url=https://www.science.org/doi/10.1126/science.abj4351 |url-access=subscription |archive-date=30 November 2022 |access-date=4 August 2022 |archive-url=https://web.archive.org/web/20221130084645/https://www.science.org/doi/10.1126/science.abj4351 |url-status=live }}</ref> and oil refineries emit a wide range of pollutants.{{sfn|Singh|Singh|2019|p=166}} Some hazardous air pollutants are produced in plastic and rubber production, whereas chloroform can be produced during water chlorination, and arsenic is found in the mining industry.{{Sfn|Hill|2020|p=103}} Many polluting industries have been pushed out of richer nations, and China too has started to push its most polluting industries out of the country.<ref>{{Cite journal |last1=Aunan |first1=Kristin |last2=Hansen |first2=Mette Halskov |last3=Wang |first3=Shuxiao |date=2018 |title=Introduction: Air Pollution in China |url=https://www.cambridge.org/core/journals/china-quarterly/article/introduction-air-pollution-in-china/8D36F205FEC68513BC45E2DEC0F2AC26 |journal=The China Quarterly |language=en |volume=234 |pages=279–298 |doi=10.1017/S0305741017001369 |hdl=10852/60033 |issn=0305-7410 |hdl-access=free |archive-date=1 March 2025 |access-date=20 March 2025 |archive-url=https://web.archive.org/web/20250301172946/https://www.cambridge.org/core/journals/china-quarterly/article/introduction-air-pollution-in-china/8D36F205FEC68513BC45E2DEC0F2AC26 |url-status=live }}</ref>
Construction and demolition produces dust, but also other pollutants. The direct particles from construction and demolition are relatively coarse.<ref name="DEFRA_PM">{{Cite web |title=Emissions of air pollutants in the UK – Particulate matter (PM{{sub|10}} and PM{{sub|2.5}}) |url=https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-particulate-matter-pm10-and-pm25#major-emission-sources-for-pm10-and-pm25-in-the-uk |url-status=live |archive-url=https://web.archive.org/web/20230122102456/https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-particulate-matter-pm10-and-pm25#major-emission-sources-for-pm10-and-pm25-in-the-uk |archive-date=22 January 2023 |access-date=22 January 2023 |website= |publisher=DEFRA}}</ref><ref>{{cite journal |last1=Azarmi |first1=Farhad |last2=Kumar |first2=Prashant |date=July 2016 |title=Ambient exposure to coarse and fine particle emissions from building demolition |journal=Atmospheric Environment |volume=137 |pages=62–79 |bibcode=2016AtmEn.137...62A |doi=10.1016/j.atmosenv.2016.04.029}}</ref> Construction also has an indirect impact on air quality, as cement production is one of the main sources of particle pollution.{{sfn|Singh|Singh|2019|p=166}} Though banned in many countries, asbestos persists in older buildings, where it poses a risk of lung disease when disturbed.<ref>{{Cite journal |last1=Caceres |first1=Jose Diego |last2=Venkata |first2=Anand N. |date=2023-03-01 |title=Asbestos-associated pulmonary disease |journal=Current Opinion in Pulmonary Medicine |volume=29 |issue=2 |pages=76–82 |doi=10.1097/MCP.0000000000000939 |issn=1531-6971 |pmid=36630203}}</ref> Building materials including carpeting and plywood emit formaldehyde, a gas which can cause difficulty breathing and nausea.<ref name=":6">{{Cite web |date=5 June 2015 |title=Taking an Exposure History: What Are Possible Sources of Indoor Air Pollution |url=https://www.atsdr.cdc.gov/csem/exposure-history/Indoor-Air-Pollution-Sources.html |archive-url=https://web.archive.org/web/20241009071645/https://www.atsdr.cdc.gov/csem/exposure-history/Indoor-Air-Pollution-Sources.html |archive-date=9 October 2024 |access-date=2024-07-08 |website= |publisher=ATSDR, CDC |language=en-us}}{{Source-attribution}}</ref>
====Transportation ==== {{See Also|Exhaust gas#Main motor vehicle emissions}} Road vehicles produce a significant amount of all air pollution. For instance, they may be responsible for a third to half of all nitrogen dioxide emissions,<ref name="pmid31143547">{{cite journal |vauthors=Wang J, Wu Q, Liu J, Yang H, Yin M, Chen S, etal |year=2019 |title=Vehicle emission and atmospheric pollution in China: problems, progress, and prospects. |journal=PeerJ |volume=7 |issue= |doi=10.7717/peerj.6932 |pmc=6526014 |pmid=31143547 |doi-access=free |article-number=e6932 |bibcode=2019PeerJ...7e6932W }}</ref><ref name="pmid26142107">{{cite journal |author=Aggarwal P, Jain S |year=2015 |title=Impact of air pollutants from surface transport sources on human health: A modeling and epidemiological approach. |url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=26142107 |journal=Environ Int |volume=83 |issue= |pages=146–57 |bibcode=2015EnInt..83..146A |doi=10.1016/j.envint.2015.06.010 |pmc= |pmid=26142107}}</ref> and are a major cause of climate change.<ref>{{Cite journal |last=Ritchie |first=Hannah |date=6 October 2020 |title=Cars, planes, trains: where do CO₂ emissions from transport come from? |url=https://ourworldindata.org/co2-emissions-from-transport |url-status=live |journal=Our World in Data |language=en |archive-url=https://web.archive.org/web/20250302075540/https://ourworldindata.org/co2-emissions-from-transport |archive-date=2 March 2025}}</ref> Vehicles with petrol and diesel engines produce about half of their emissions from their exhaust gas, and the other half from non-exhaust emissions (tire and brake wear and erosion or disturbance of the road surface); electric vehicles produce no tailpipe emissions, but still produce the other emissions.{{sfn|Amato|2018|p=4}} Diesel trains, ships, and planes also cause air pollution.<ref>{{cite web |date=15 December 2021 |title=Overview of Air Pollution from Transportation |url=https://www.epa.gov/transportation-air-pollution-and-climate-change/overview-air-pollution-transportation |url-status=live |archive-url=https://web.archive.org/web/20250726002536/https://www.epa.gov/transportation-air-pollution-and-climate-change/overview-air-pollution-transportation |archive-date=26 July 2025 |access-date=16 June 2022 |publisher=US Environmental Protection Agency}}</ref>
====Agriculture and waste==== [[File:BurningOffFieldsInTheEveningInSouthGeorgia.jpg|thumb|Controlled burning of a field outside of Statesboro, Georgia, US, in preparation for spring planting.|alt=Smoke rises from a fire, and is dispersed by wind]] [[File:Agbogbloshie,_Ghana_2019.jpg|thumb|E-waste processing in Agbogbloshie, Ghana, using open-burning of electronics to access valuable metals like copper.|alt=Several people are working on a heap of rubbish, with smoke rising from it.]]
Agricultural emissions, both from crops and from animal agriculture, contribute substantially to air pollution.<ref>{{cite journal |last1=Sun |first1=Feifei |last2=Dai |first2=Yun |last3=Yu |first3=Xiaohua |date=2017 |title=Air pollution, food production and food security: A review from the perspective of food system |journal=Journal of Integrative Agriculture |volume=16 |issue=12 |pages=2945–2962 |bibcode=2017JIAgr..16.2945S |doi=10.1016/S2095-3119(17)61814-8 |doi-access=free}}</ref><ref name="10.1038/nature15371">{{cite journal |last1=Lelieveld |first1=J. |last2=Evans |first2=J. S. |last3=Fnais |first3=M. |last4=Giannadaki |first4=D. |last5=Pozzer |first5=A. |date=2015 |title=The contribution of outdoor air pollution sources to premature mortality on a global scale |journal=Nature |language=en |volume=525 |issue=7569 |pages=367–371 |bibcode=2015Natur.525..367L |doi=10.1038/nature15371 |issn=1476-4687 |pmid=26381985 |hdl=20.500.14279/9356 |s2cid=4460927 |quote=Whereas in much of the USA and in a few other countries emissions from traffic and power generation are important, in eastern USA, Europe, Russia and East Asia agricultural emissions make the largest relative contribution to PM2.5, with the estimate of overall health impact depending on assumptions regarding particle toxicity.|hdl-access=free }}</ref> For instance, methane is emitted by the digestion of food by cattle, causing ground-level ozone.<ref>{{cite web |date=5 February 2025 |title=Methane, climate change and air quality in Europe: exploring the connections |url=https://www.eea.europa.eu/en/analysis/publications/methane-climate-change-and-air-quality-in-europe-exploring-the-connections |url-status=live |archive-url=https://web.archive.org/web/20250723064104/https://www.eea.europa.eu/en/analysis/publications/methane-climate-change-and-air-quality-in-europe-exploring-the-connections |archive-date=23 July 2025 |access-date=7 March 2025 |publisher=European Environment Agency}}</ref> Agriculture is also a major source of ammonia, which can form fine particulate matter.<ref>{{Cite journal |last1=Giannadaki |first1=Despina |last2=Giannakis |first2=Elias |last3=Pozzer |first3=Andrea |last4=Lelieveld |first4=Jos |date=2018 |title=Estimating health and economic benefits of reductions in air pollution from agriculture |url=https://www.sciencedirect.com/science/article/pii/S0048969717334836 |journal=Science of the Total Environment |volume=622-623 |pages=1304–1316 |bibcode=2018ScTEn.622.1304G |doi=10.1016/j.scitotenv.2017.12.064 |issn=0048-9697 |pmid=29890597 |url-access=subscription |archive-date=8 April 2020 |access-date=27 May 2025 |archive-url=https://web.archive.org/web/20200408021012/https://www.sciencedirect.com/science/article/pii/S0048969717334836 |url-status=live }}</ref> Practices like slash-and-burn in forests like the Amazon cause large air pollution alongside deforestation.<ref>{{cite web |title=NASA's AIRS Maps Carbon Monoxide from Brazil Fires |url=https://www.jpl.nasa.gov/images/pia23356-nasas-airs-maps-carbon-monoxide-from-brazil-fires |url-status=live |archive-url=https://web.archive.org/web/20250313005700/https://www.jpl.nasa.gov/images/pia23356-nasas-airs-maps-carbon-monoxide-from-brazil-fires/ |archive-date=13 March 2025 |access-date=4 August 2022 |website=NASA Jet Propulsion Laboratory (JPL)}}</ref>
Open dumps of waste are a common source of air pollution in low-income countries. They can be a source of toxins and can promote the growth of microbes that pollute water and air. Through open burning of waste—whether self-ignited or burned on purpose—soot, methane, and other pollutants are released.{{sfn|United Nations Environmental Programme|2021|pp=37–39}} Organic waste in landfills itself also produces methane as it decomposes.<ref>{{cite web |date=15 April 2016 |title=Basic Information about Landfill Gas |url=https://www.epa.gov/lmop/basic-information-about-landfill-gas |url-status=live |archive-url=https://web.archive.org/web/20250420164416/https://www.epa.gov/lmop/basic-information-about-landfill-gas |archive-date=20 April 2025 |access-date=9 August 2022 |website=US Environmental Protection Agency |quote=Landfill gas (LFG) is a natural byproduct of the decomposition of organic material in landfills. LFG is composed of roughly 50 percent methane...}}</ref> Globally, a quarter of solid waste is not collected and another quarter is not disposed of properly.{{sfn|Cook|Velis|2020|p=7}}
==== Household sources ==== {{Main|Household air pollution|Indoor air quality|Energy poverty and cooking}}
thumb|Smoking fish over an open fire in Ghana, 2018.|alt=a round metal open fire with small fish As of 2023, more than 2.3 billion people in developing countries rely on burning polluting fuels such as firewood, agricultural waste, dry dung, coal, or charcoal for cooking, which causes harmful household air pollution.<ref>{{Cite web |title=Executive summary – A Vision for Clean Cooking Access for All – Analysis |url=https://www.iea.org/reports/a-vision-for-clean-cooking-access-for-all/executive-summary |url-status=live |archive-url=https://web.archive.org/web/20250430065454/https://www.iea.org/reports/a-vision-for-clean-cooking-access-for-all/executive-summary |archive-date=30 April 2025 |access-date=9 January 2025 |website=IEA |language=en-GB}}</ref> Kerosene, another polluting fuel, is used in many countries for lighting and sometimes for space heating or cooking. Globally, 12% of outdoor fine particle pollution comes from household cooking. Health effects are concentrated among women, who are likely to be responsible for cooking, and young children.{{sfn|World Health Organization|2016|pp=vii–xi}}
Gas stoves for cooking contribute to indoor air pollution by emitting {{NOx|x=2}}, benzene, and carbon monoxide.<ref>{{Cite news |last=Niranjan |first=Ajit |date=28 October 2024 |title=Pollutants from gas stoves kill 40,000 Europeans each year, report finds |url=https://www.theguardian.com/environment/2024/oct/28/pollutants-from-gas-stoves-kill-40000-europeans-each-year-report-finds |url-status=live |archive-url=https://web.archive.org/web/20250725054937/https://www.theguardian.com/environment/2024/oct/28/pollutants-from-gas-stoves-kill-40000-europeans-each-year-report-finds |archive-date=25 July 2025 |access-date=21 March 2025 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref> Toasters can produce particulate pollution.<ref>{{Cite magazine |last=Twilley |first=Nicola |date=1 April 2019 |title=The Hidden Air Pollution in Our Homes |url=https://www.newyorker.com/magazine/2019/04/08/the-hidden-air-pollution-in-our-homes |archive-url=https://web.archive.org/web/20240727073125/https://www.newyorker.com/magazine/2019/04/08/the-hidden-air-pollution-in-our-homes |archive-date=27 July 2024 |magazine=The New Yorker |via=www.newyorker.com}}</ref> Similarly, heating systems such as furnaces and other types of fuel-burning heating devices release pollutants into the air.<ref>{{cite web |title=Combustion Pollutants in Your Home - Guidelines |url=https://ww2.arb.ca.gov/resources/documents/combustion-pollutants-your-home-guidelines |url-status=live |archive-url=https://web.archive.org/web/20250524102500/https://ww2.arb.ca.gov/resources/documents/combustion-pollutants-your-home-guidelines |archive-date=24 May 2025 |access-date=16 June 2022 |publisher=California Air Resources Board |quote="... most furnaces, wood stoves, fireplaces, gas water heaters, and gas clothes dryers, usually vent (exhaust) the combustion pollutants directly to the outdoors. However, if the vent system is not properly designed, installed, and maintained, indoor pollutants can build up quickly inside the home.}}</ref> In some developed countries, including the UK and Sydney, Australia, wood stoves are the major source of particulate pollution in urban areas.<ref>{{Cite web |date=13 March 2025 |title=Emissions of air pollutants in the UK – Particulate matter (PM10 and PM2.5) |url=https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-particulate-matter-pm10-and-pm25 |url-status=live |archive-url=https://web.archive.org/web/20250727062327/https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-particulate-matter-pm10-and-pm25 |archive-date=27 July 2025 |access-date=27 January 2025 |website=GOV.UK |language=en}}</ref><ref name="auto">{{cite web |date=7 May 2024 |title=Wood burning heaters and your health |url=https://www.health.nsw.gov.au/environment/factsheets/Pages/wood-smoke.aspx |url-status=live |archive-url=https://web.archive.org/web/20250619120922/https://www.health.nsw.gov.au/environment/factsheets/Pages/wood-smoke.aspx |archive-date=19 June 2025 |access-date=11 February 2025 |website=New South Wales Health |publisher=NSW Government}}</ref> Wood stoves can also emit carbon monoxide and {{NOx}}.<ref name=":6" />
Other sources of indoor air pollution are building materials, biological material and tobacco smoke. Biological material, such as dander, house dust mite, mold and pollen, can come from humans, animals or plants. Some of this material can trigger allergies, such as allergic rhinitis.<ref name=":6" /> Fumes from pesticides, paints, cleaning products and personal care products can be substantial, and make up an increasing share of outdoor and indoor air pollution as transportation is getting cleaner.<ref>{{Cite journal |last1=McDonald |first1=Brian C. |last2=de Gouw |first2=Joost A. |last3=Gilman |first3=Jessica B. |last4=Jathar |first4=Shantanu H. |last5=Akherati |first5=Ali |last6=Cappa |first6=Christopher D. |last7=Jimenez |first7=Jose L. |last8=Lee-Taylor |first8=Julia |last9=Hayes |first9=Patrick L. |last10=McKeen |first10=Stuart A. |last11=Cui |first11=Yu Yan |last12=Kim |first12=Si-Wan |last13=Gentner |first13=Drew R. |last14=Isaacman-VanWertz |first14=Gabriel |last15=Goldstein |first15=Allen H. |date=2018 |title=Volatile chemical products emerging as largest petrochemical source of urban organic emissions |url=https://www.science.org/doi/10.1126/science.aaq0524 |journal=Science |language=en |volume=359 |issue=6377 |pages=760–764 |doi=10.1126/science.aaq0524 |pmid=29449485 |bibcode=2018Sci...359..760M |issn=0036-8075}}</ref>
=== Natural sources === [[File:Dust storm approaching Stratford, Texas.jpg|thumb|Dust storm approaching Stratford, Texas, in 1935.|alt=A dust storm approaches a collection of houses, dwarfing them in height.]] Dust from desert can cause poor air quality far from its source. For instance, dust from the Gobi Desert in China and Mongolia can reach Hawaii, and dust from the Sahara reaches the Amazon rainforest in South America.<ref>{{Cite web |date=10 May 2022 |title=What is desert dust and how does it change atmosphere and the air we breathe? |url=https://atmosphere.copernicus.eu/what-saharan-dust-and-how-does-it-change-atmosphere-and-air-we-breathe |url-status=live |archive-url=https://web.archive.org/web/20250723062415/https://atmosphere.copernicus.eu/what-saharan-dust-and-how-does-it-change-atmosphere-and-air-we-breathe |archive-date=23 July 2025 |access-date=21 March 2025 |website=Copernicus Atmosphere |language=en}}</ref>
Radon is a radioactive gas that can build up in buildings from the soil. It can cause lung cancer, especially in smokers. Levels are generally low, but can be elevated in buildings with "leaky" foundations or areas with soils rich in uranium.{{sfn|Harrison|Hester|2019|pp=57-58}} Volcanic eruptions can be a large source of sulfur dioxide and also produce particle pollution.<ref>{{Citation |title=Emissions of Air Pollutants and Emission Control Technologies |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |pages=8–9 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/air-pollution/emissions-of-air-pollutants-and-emission-control-technologies/4CA3AB4F3F9D17F531345212A5677DDB |access-date=2025-06-04 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.002 |isbn=978-1-108-48163-2 |url-access=subscription}}</ref>
Vegetation can emit gases that contribute to ozone formation and particle pollution. This is especially true in warmer climates and during the growth season.<ref>{{Cite journal |last1=Wang |first1=Luxi |last2=Lun |first2=Xiaoxiu |last3=Wang |first3=Qiang |last4=Wu |first4=Ju |date=2024 |title=Biogenic volatile organic compounds emissions, atmospheric chemistry, and environmental implications: a review |url=https://link.springer.com/10.1007/s10311-024-01785-5 |journal=Environmental Chemistry Letters |language=en |volume=22 |issue=6 |pages=3033–3058 |bibcode=2024EnvCL..22.3033W |doi=10.1007/s10311-024-01785-5 |issn=1610-3653 |url-access=subscription}}</ref> These gases react with human pollution sources to produce a seasonal haze.<ref>{{cite journal|title=Biogenic carbon and anthropogenic pollutants combine to form a cooling haze over the southeastern United States |journal=Proceedings of the National Academy of Sciences |last1=Goldstein |first1=Allen H. |first2=Charles D. |last2=Koven |first3=Colette L. |last3=Heald |author3-link=Colette Heald |first4=Inez Y. |last4=Fung |date=5 May 2009 |doi=10.1073/pnas.0904128106 |pmid=19451635 |volume=106 |issue=22 |pages=8835–40 |pmc=2690056 |bibcode=2009PNAS..106.8835G |doi-access=free}}</ref> Black gum, poplar, oak and willow emit gases that can raise ozone levels up to eight times more than low-impact tree species.<ref>{{cite journal|title=Trees That Pollute |first=Mark |last=Fischetti |journal=Scientific American |volume=310 |issue=6 |page=14 |doi=10.1038/scientificamerican0614-14 |pmid=25004561 |year=2014 |bibcode=2014SciAm.310f..14F}}</ref> Wildfires, which have become more severe and more common due to climate change, release fine particles. They are a major source of air pollution.<ref>{{Cite journal |last1=Knorr |first1=Wolfgang |last2=Dentener |first2=Frank |last3=Lamarque |first3=Jean-François |last4=Jiang |first4=Leiwen |last5=Arneth |first5=Almut |date=2017-07-31 |title=Wildfire air pollution hazard during the 21st century |url=https://acp.copernicus.org/articles/17/9223/2017/ |journal=Atmospheric Chemistry and Physics |language=English |volume=17 |issue=14 |pages=9223–9236 |doi=10.5194/acp-17-9223-2017 |doi-access=free |bibcode=2017ACP....17.9223K |issn=1680-7316 |archive-date=10 July 2025 |access-date=5 June 2025 |archive-url=https://web.archive.org/web/20250710064330/https://acp.copernicus.org/articles/17/9223/2017/ |url-status=live }}</ref>
== Major pollutants == {{Main|Pollutant|Greenhouse gas emissions}}
[[File:Air Pollution-Causes&Effects.svg|thumb|upright=1.3|Major pollutants, their sources and effects: (1) greenhouse gases, (2) particulate pollution, (3) ozone-depleting gases, (4) acid rain, (5) ground-level ozone, (6) nitrogen oxides|alt=Schematic showing (1) CO2 and CH4 from heating, driving and livestock causing warming (2) PM pollution from driving (3) CFCs from buildings depleting ozone, causing UV to come through (4) SO2 from combustion causing acid rain and (5) ground-level ozone from nitrous oxides and (6) nitrous oxides from car exhausts.]]
Air pollutants can be tiny solid or liquid particles dispersed in the air (called aerosols), or gases.{{sfn|Pearson|Derwent|2022|pp=1,6}} Pollutants are classified as primary or secondary. Primary pollutants are produced directly by a source and remain in the same chemical form after they have been emitted into the atmosphere. Examples include carbon monoxide gas from car exhausts and sulfur dioxide from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react with each other or with other parts of the atmosphere. Ground-level ozone is one example of a secondary pollutant. Some pollutants may be both primary and secondary — both are emitted directly and formed from other primary pollutants.<ref>{{cite book |last1=Harrison |first1=Roy M. |author1-link=Roy M. Harrison |url=https://iris.who.int/bitstream/handle/10665/107823/9789289021920-eng.pdf?sequence=1&isAllowed=y |title=Air Quality Guidelines: Global Update 2005: Particulate Matter, Ozone, Nitrogen Dioxide, and Sulfur Dioxide |date=2005 |publisher=World Health Organization |isbn=92-890-2192-6 |location=Copenhagen |pages=9–10, 13 |chapter=1: Sources of Air Pollution |archive-url=https://web.archive.org/web/20250706041122/https://iris.who.int/bitstream/handle/10665/107823/9789289021920-eng.pdf?sequence=1&isAllowed=y |archive-date=6 July 2025 |url-status=live}}</ref>
=== Ammonia === Ammonia ({{chem|NH|3}}) is emitted mainly by overuse of synthetic nitrogen fertilizers on farmland, and from manure and urine from livestock.<ref>{{Cite news |last=Carrington |first=Damian |date=4 November 2021 |title=Ammonia from farms behind 60% of UK particulate air pollution – study |url=https://www.theguardian.com/environment/2021/nov/04/ammonia-from-farms-behind-60-of-uk-particulate-air-pollution-study |url-status=live |archive-url=https://web.archive.org/web/20250722145113/https://www.theguardian.com/environment/2021/nov/04/ammonia-from-farms-behind-60-of-uk-particulate-air-pollution-study |archive-date=22 July 2025 |access-date=7 November 2021 |work=The Guardian}}</ref> At typical concentrations in the air, it is not harmful to health directly. However, ammonia can react with other pollutants in the air to form ammonium sulfate or nitrate salts, contributing to particulate matter pollution. Furthermore, when ammonia is deposited onto the soil, it can harm ecosystems via eutrophication.<ref>{{Citation |title=Gaseous Pollutants |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |page=149 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/abs/air-pollution/gaseous-pollutants/66D443B7442EC23035C17FBF3EEDAAB2 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.008 |isbn=978-1-108-48163-2 |url-access=subscription}}</ref>
=== Carbon dioxide === Carbon dioxide ({{CO2}}) is mainly emitted by the burning of fossil fuels.<ref>{{Cite web |last1=Hausfather |first1=Zeke |last2=Pierre |first2=Friedlichstein |date=11 November 2022 |title=Analysis: Global CO2 emissions from fossil fuels hit record high in 2022 |url=https://www.carbonbrief.org/analysis-global-co2-emissions-from-fossil-fuels-hit-record-high-in-2022/ |url-status=live |archive-url=https://web.archive.org/web/20250726011140/https://www.carbonbrief.org/analysis-global-co2-emissions-from-fossil-fuels-hit-record-high-in-2022/ |archive-date=26 July 2025 |access-date=25 July 2025 |website=Carbon Brief |language=en}}</ref> {{CO2}} is sometimes called an air pollutant, because it is the main greenhouse gas responsible for climate change.<ref>{{cite web |last1=Vaidyanathan |first1=Gayathri |date=4 November 2014 |title=The Worst Climate Pollution Is Carbon Dioxide |url=https://www.scientificamerican.com/article/the-worst-climate-pollution-is-carbon-dioxide/ |url-status=live |archive-url=https://web.archive.org/web/20250602210215/https://www.scientificamerican.com/article/the-worst-climate-pollution-is-carbon-dioxide/ |archive-date=2 June 2025 |access-date=1 August 2025 |publisher=Scientific American}}</ref><ref>{{Cite book |last=Vallero |first=Daniel A. |title=Fundamentals of Air Pollution |date=2014 |publisher=Academic Press |isbn=978-0-12-401733-7 |edition=5th |page=421}}</ref> Although the World Health Organization recognizes {{CO2}} as a climate pollutant, it does not include the gas in its ''Air Quality Guidelines'' or set recommended targets for it.<ref>{{cite book |title=Air Quality Guidelines Global Update 2005: Particulate matter, ozone, nitrogen dioxide and sulfur dioxide |publisher=World Health Organization |year=2006 |isbn=92-890-2192-6 |location=Copenhagen |page=12 |quote="Some pollutants, and especially those associated with greenhouse warming effects (carbon dioxide, nitrous oxide and methane)..."}}</ref> This question of terminology has practical consequences, for example, in determining whether the U.S. Clean Air Act (which is designed to improve air quality) is deemed to regulate {{CO2}} emissions. The Inflation Reduction Act of 2022 amended the Clean Air Act to define {{CO2}} from fossil fuel burning explicitly as an air pollutant.<ref>{{cite news |last1=Friedman |first1=Lisa |date=22 August 2022 |title=Democrats Designed the Climate Law to Be a Game Changer. Here's How. |url=https://www.nytimes.com/2022/08/22/climate/epa-supreme-court-pollution.html |url-status=live |archive-url=https://web.archive.org/web/20250721021508/https://www.nytimes.com/2022/08/22/climate/epa-supreme-court-pollution.html |archive-date=21 July 2025 |access-date=19 April 2023 |work=The New York Times}}</ref>
=== Carbon monoxide === Carbon monoxide (CO) is a colorless, odorless, and toxic gas.<ref>{{Cite web |date=17 October 2017 |title=Carbon Monoxide Poisoning |url=https://www.nhs.uk/conditions/carbon-monoxide-poisoning/ |url-status=live |archive-url=https://web.archive.org/web/20250709025308/https://www.nhs.uk/conditions/Carbon-monoxide-poisoning/ |archive-date=9 July 2025 |access-date=1 August 2025 |website=National Health Service}}</ref> It is a product of combustion of fuel such as natural gas, coal, or wood. In the past, emissions from vehicles were the main source of CO, but modern vehicles do not emit much of it. Now, wildfires and bonfires are the main source of outdoors CO.{{sfn|Pearson|Derwent|2022|p=2}} Indoors, CO is a larger problem and mainly comes from cooking and heating.{{sfn|Pearson|Derwent|2022|pp=19-20}} In poorly ventilated spaces, CO can accumulate to dangerous levels, and exposure may cause people to lose consciousness and die. When CO is destroyed in the atmosphere, it can raise levels of {{CO2}} and {{CH4}}.{{Sfn|Hill|2020|p=99}}
=== Ground-level ozone === thumb|alt=leaves showing patches of white between the veins|Leaves damaged by exposure to ozone.
Ground-level ozone ({{chem|O|3}}) is mostly created when {{chem|NO|x}} and volatile organic compounds mix in the presence of sunlight. It can also form from carbon monoxide or methane.<ref name="EEA-ozone">{{Cite web |date=17 March 2025 |title=Ground-level ozone |url=https://climate-adapt.eea.europa.eu/en/observatory/evidence/health-effects/ground-level-ozone#:~:text=Ground-level%20ozone%20affects%20human,use,%20and%20even%20premature%20mortality. |url-status=live |archive-url=https://web.archive.org/web/20250622234704/https://climate-adapt.eea.europa.eu/en/observatory/evidence/health-effects/ground-level-ozone/ |archive-date=22 June 2025 |access-date=21 April 2025 |publisher=European Climate and Health Observatory |language=en}}</ref> Due to the influence of temperature and sunlight on this reaction, high ozone levels are most common on hot summer afternoons.<ref>{{Cite web |title=Cars and Air Pollution |url=https://www.adeq.state.ar.us/air/planning/ozone/cars.aspx |url-status=live |archive-url=https://web.archive.org/web/20250602090226/https://www.adeq.state.ar.us/air/planning/ozone/cars.aspx |archive-date=2 June 2025 |access-date=24 August 2024 |website=Arkansas Energy Department of Energy and Environment}}</ref> It is the main gas in photochemical smog.<ref>{{Citation |title=Gaseous Pollutants |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |page=147 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/abs/air-pollution/gaseous-pollutants/66D443B7442EC23035C17FBF3EEDAAB2 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.008 |isbn=978-1-108-48163-2 |url-access=subscription |archive-date=2 June 2025 |archive-url=https://web.archive.org/web/20250602181951/https://www.cambridge.org/core/books/abs/air-pollution/gaseous-pollutants/66D443B7442EC23035C17FBF3EEDAAB2 |url-status=live }}</ref>
{{chem|O|3}} can be harmful to human health, but also to some materials, forests, plants, and crops.<ref>{{Cite web |title=Ozone (O3) |url=https://www.gov.uk/government/statistics/air-quality-statistics/concentrations-of-ozone |url-status=live |archive-url=https://web.archive.org/web/20241225145207/https://www.gov.uk/government/statistics/air-quality-statistics/concentrations-of-ozone |archive-date=25 December 2024 |access-date=21 April 2025 |website=GOV.UK |language=en}}</ref> Smog is a particular problem in big cities where it cannot easily be transported away by wind (e.g. cities built in valleys surrounded by mountains).<ref>{{Cite web |title=smog {{!}} National Geographic Society |url=https://education.nationalgeographic.org/resource/smog/ |url-status=live |archive-url=https://web.archive.org/web/20250531082512/https://education.nationalgeographic.org/resource/smog/ |archive-date=31 May 2025 |access-date=7 June 2022 |website= |publisher=National Geographic}}</ref> When ground-level ozone is produced, it can linger in the air for days or weeks, and therefore be transported far from where it was first formed.<ref name="EEA-ozone" />
=== Nitrogen oxides === [[File:NASA - Human Fingerprint on Global Air Quality.webm|thumb|right|upright=1.2|A NASA video on satellite measurement of nitrogen oxides, showing declining levels due to regulation. However, some regions did see rising levels of NO<sub>2</sub> pollution, for instance, those with fracking or civil unrest.]]
Nitrogen oxides ({{chem|NO|x}}), particularly nitric oxide ({{chem|NO}}), are mostly created by the burning of fossil fuels, and in lesser amounts by lightning. Nitrogen dioxide ({{chem|NO|2}}) is formed from NO in a reaction with other atmospheric gases.<ref>{{Cite journal |last1=Pérez-Invernón |first1=Francisco J. |last2=Huntrieser |first2=Heidi |last3=Erbertseder |first3=Thilo |last4=Loyola |first4=Diego |last5=Valks |first5=Pieter |last6=Liu |first6=Song |last7=Allen |first7=Dale J. |last8=Pickering |first8=Kenneth E. |last9=Bucsela |first9=Eric J. |last10=Jöckel |first10=Patrick |last11=van Geffen |first11=Jos |last12=Eskes |first12=Henk |last13=Soler |first13=Sergio |last14=Gordillo-Vázquez |first14=Francisco J. |last15=Lapierre |first15=Jeff |date=2022-06-08 |title=Quantification of lightning-produced NOx over the Pyrenees and the Ebro Valley by using different TROPOMI-NO2 and cloud research products |url=https://amt.copernicus.org/articles/15/3329/2022/ |journal=Atmospheric Measurement Techniques |language=English |volume=15 |issue=11 |pages=3329–3351 |doi=10.5194/amt-15-3329-2022 |doi-access=free |issn=1867-1381 |hdl=10261/282028 |hdl-access=free |archive-date=19 March 2025 |access-date=15 March 2025 |archive-url=https://web.archive.org/web/20250319100438/https://amt.copernicus.org/articles/15/3329/2022/ |url-status=live }}</ref><ref>{{Cite web |title=Emissions of air pollutants in the UK – Nitrogen oxides (NOx) |url=https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-nitrogen-oxides-nox |url-status=live |archive-url=https://web.archive.org/web/20250424011229/https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-nitrogen-oxides-nox |archive-date=24 April 2025 |access-date=15 March 2025 |website=GOV.UK |language=en}}</ref> {{chem|NO}} and {{chem|NO|2}} can form acid rain, can form into a haze, and can cause nutrient pollution in water.<ref>{{Cite web |date=16 July 2024 |title=Basic Information about NO<sub>2</sub> |url=https://www.epa.gov/no2-pollution/basic-information-about-no2 |url-status=live |archive-url=https://web.archive.org/web/20250726031947/https://www.epa.gov/no2-pollution/basic-information-about-no2 |archive-date=26 July 2025 |access-date=15 March 2025 |website=Environmental Protection Agency |language=en}}</ref> {{chem|NO|2}} is a reddish-brown toxic gas with a strong odor, whereas {{chem|NO}} is odorless and colorless.<ref>{{Cite web |title=Nitrogen oxides, NOx |url=https://www.eea.europa.eu/help/glossary/eper-chemicals-glossary/nitrogen-oxides-nox |url-status=live |archive-url=https://web.archive.org/web/20250520204117/https://www.eea.europa.eu/help/glossary/eper-chemicals-glossary/nitrogen-oxides-nox |archive-date=20 May 2025 |access-date=15 March 2025 |website=European Environment Agency |language=en}}</ref>
=== Particulate matter === Particulate matter (PM), also known as particle pollution, includes all airborne substances that are not gases.<ref name="DEFRA_PM" /><ref name="EPA_PM">{{Cite web |date=19 April 2016 |title=Particulate Matter (PM) Basics |url=https://www.epa.gov/pm-pollution/particulate-matter-pm-basics |url-status=live |archive-url=https://web.archive.org/web/20250726002416/https://www.epa.gov/pm-pollution/particulate-matter-pm-basics |archive-date=26 July 2025 |access-date=19 April 2025 |website=Environmental Protection Agency |language=en}}</ref> It is a mix of microscopic solid particles or droplets suspended in a gas.<ref>{{Cite web |date=March 29, 2022 |title=What is Particulate Matter? {{!}} Urban Environmental Program in New England |url=https://www3.epa.gov/region1/eco/uep/particulatematter.html |url-status=deviated |archive-url=https://web.archive.org/web/20220607141238/https://www3.epa.gov/region1/eco/uep/particulatematter.html |archive-date=7 June 2022 |access-date=7 June 2022 |website=Environmental Protection Agency |language=en}}</ref>
Particulate matter can contain a large variety of materials and chemical compounds including toxic substances, which can vary strongly in size.<ref name="DEFRA_PM" /> Coarse PM (PM<sub>10</sub>) is 10 micrometer (μm) or smaller in diameter, fine PM (PM<sub>2.5</sub>) is smaller than 2.5 μm, and ultrafine particles are 0.1 μm or smaller.<ref name=":16">{{Cite journal |last1=Garcia-Marlès |first1=Meritxell |last2=Lara |first2=Rosa |last3=Reche |first3=Cristina |last4=Pérez |first4=Noemí |last5=Tobías |first5=Aurelio |last6=Savadkoohi |first6=Marjan |last7=Beddows |first7=David |last8=Salma |first8=Imre |last9=Vörösmarty |first9=Máté |last10=Weidinger |first10=Tamás |last11=Hueglin |first11=Christoph |last12=Mihalopoulos |first12=Nikos |last13=Grivas |first13=Georgios |last14=Kalkavouras |first14=Panayiotis |last15=Ondráček |first15=Jakub |date=1 March 2024 |title=Inter-annual trends of ultrafine particles in urban Europe |url=https://linkinghub.elsevier.com/retrieve/pii/S0160412024000965 |journal=Environment International |volume=185 |bibcode=2024EnInt.18508510G |doi=10.1016/j.envint.2024.108510 |issn=0160-4120 |pmid=38460241 |article-number=108510 |archive-date=16 May 2025 |access-date=19 April 2025 |archive-url=https://web.archive.org/web/20250516015151/https://linkinghub.elsevier.com/retrieve/pii/S0160412024000965 |url-status=live |hdl=10261/350656 |hdl-access=free }}</ref> Smaller particles pose more risk to health, as they can reach the bloodstream.<ref name="EPA_PM" /><ref name=":16" /> A definitive link between fine particulate pollution and higher death rates in urban areas was established by the Harvard Six Cities study, published in 1993.<ref name="laden">{{cite journal |last1=Laden |first1=F |date=October 2019 |title=A Tale of Six Cities: The Landmark Harvard Six Cities Study |journal=Environmental Epidemiology |volume=3 |page=221 |bibcode=2019EnEpi...3Q.221L |doi=10.1097/01.EE9.0000608272.94008.7b |s2cid=210638367 |doi-access=free}}</ref>
Sea spray, wildfires, volcanoes and dust storms are the main natural sources of PM. Meanwhile, human sources include the burning of biomass and fossil fuels, as well as road emissions and dust resuspension. Human PM is usually finer than natural PM.<ref>{{Cite journal |last1=Mukherjee |first1=Arideep |last2=Agrawal |first2=Madhoolika |date=2017-06-01 |title=World air particulate matter: sources, distribution and health effects |url=https://link.springer.com/article/10.1007/s10311-017-0611-9 |journal=Environmental Chemistry Letters |language=en |volume=15 |issue=2 |pages=283–309 |bibcode=2017EnvCL..15..283M |doi=10.1007/s10311-017-0611-9 |issn=1610-3661 |url-access=subscription}}</ref> Most particulate matter is formed in the atmosphere from precursor gases. For instance, sulfate comes from {{chem|SO|2}}, nitrate from {{chem|NO|2}}, and ammonium is formed from ammonia. Soot on the other hand is directly emitted from combustion, and consists of black carbon and organic compounds.<ref>{{Cite book |last=Seigneur |first=Christian |url=https://www.cambridge.org/core/product/identifier/9781108674614/type/book |title=Air Pollution: Concepts, Theory, and Applications |date=2019 |publisher=Cambridge University Press |isbn=978-1-108-67461-4 |edition=1 |pages=190–191, 204 |doi=10.1017/9781108674614.009}}</ref> Particulate matter can have a cooling effect locally on the climate, as it reflects sunlight away from Earth's surface.<ref>{{Cite news |title=If India chokes less, it will fry more |url=https://www.economist.com/interactive/asia/2025/05/28/if-india-chokes-less-it-will-fry-more |url-access=subscription |url-status=live |archive-url=https://web.archive.org/web/20250723212302/https://www.economist.com/interactive/asia/2025/05/28/if-india-chokes-less-it-will-fry-more |archive-date=23 July 2025 |access-date=26 June 2025 |newspaper=The Economist |issn=0013-0613 |quote=Sulphate particles, soot and other aerosols intercept sunlight before it reaches the surface, either reflecting it back out to space or absorbing it. Aerosols can also change cloud cover further shielding the ground from the sun.}}</ref><ref>{{Cite journal |last=Ritchie |first=Hannah |last2=Rosado |first2=Pablo |date=2025-03-31 |title=Air pollution kills millions every year — where does it come from? |url=https://ourworldindata.org/air-pollution-sources |journal=Our World in Data |language=en}}</ref><ref>{{Cite web |title=Air pollution: The invisible health threat |url=https://www.who.int/news-room/feature-stories/detail/air-pollution--the-invisible-health-threat |access-date=2025-12-10 |website=www.who.int |language=en}}</ref><ref>{{Cite web |title=Air Pollution and Your Health |url=https://www.niehs.nih.gov/health/topics/agents/air-pollution |access-date=2025-12-10 |website=National Institute of Environmental Health Sciences |language=en}}</ref><ref>{{Cite web |date=2015-07-09 |title=National Institute of Environmental Health Sciences (NIEHS) |url=https://stagetestdomain3.nih.gov/about-nih/what-we-do/nih-almanac/national-institute-environmental-health-sciences-niehs |access-date=2025-12-10 |website=National Institutes of Health (NIH) |language=EN}}</ref>
=== Sulfur dioxide === Sulfur dioxide (SO<sub>2</sub>), an acidic and corrosive gas, is produced mostly by burning crude oil and coal. These fossil fuels often contain sulfur compounds, and their combustion generates sulfur dioxide.<ref>{{Cite web |title=Emissions of air pollutants in the UK – Sulphur dioxide (SO2) |url=https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-sulphur-dioxide-so2 |access-date=2025-04-21 |website=GOV.UK |language=en |archive-date=25 April 2025 |archive-url=https://web.archive.org/web/20250425021721/https://www.gov.uk/government/statistics/emissions-of-air-pollutants/emissions-of-air-pollutants-in-the-uk-sulphur-dioxide-so2 |url-status=live }}</ref> In Europe and North America, SO<sub>2</sub> is mostly found in areas with significant shipping and industry, as road traffic fuels are regulated.<ref>{{Citation |title=Gaseous Pollutants |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |page=146 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/abs/air-pollution/gaseous-pollutants/66D443B7442EC23035C17FBF3EEDAAB2 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.008 |isbn=978-1-108-48163-2 |url-access=subscription |archive-date=2 June 2025 |archive-url=https://web.archive.org/web/20250602181951/https://www.cambridge.org/core/books/abs/air-pollution/gaseous-pollutants/66D443B7442EC23035C17FBF3EEDAAB2 |url-status=live }}</ref> Smaller amounts of SO<sub>2</sub> are released from smelting and volcanoes.<ref name="usepaso2" />
High concentrations of SO<sub>2</sub> in the air generally also lead to the formation of other sulfur oxides (SO<sub>x</sub>). SO<sub>x</sub> can react with other compounds in the atmosphere to form small particles and contribute to particulate matter pollution. At high concentrations, gaseous SO<sub>x</sub> can harm plants by damaging leafs and decreasing growth.<ref name="usepaso2">{{cite web |date=2 Jun 2016 |title=Sulfur Dioxide Basics |url=https://www.epa.gov/so2-pollution/sulfur-dioxide-basics |url-status=live |archive-url=https://web.archive.org/web/20250101120025/https://www.epa.gov/so2-pollution/sulfur-dioxide-basics |archive-date=2025-01-01 |access-date=12 Jan 2025 |website=US EPA}} {{PD-notice}}</ref> Further oxidation of SO<sub>2</sub>, mostly taking place in cloud droplets, forms sulfuric acid (H<sub>2</sub>SO<sub>4</sub>), which is one of the components of acid rain.<ref>{{Cite book |last=Seigneur |first=Christian |title=Air pollution: concepts, theory, and applications |date=2019 |publisher=Cambridge University Press |isbn=978-1-108-48163-2 |location=Cambridge, United Kingdom ; New York, NY |pages=249–250, 254}}</ref> [[File:Pollution de l'air.jpg|thumb|Smog polluting the air.]]
=== Volatile organic compounds === Volatile organic compounds (VOCs) are a class of carbon-based chemicals that exist as gases at room temperature, found both indoors and outdoors.<ref name="epa-voc">{{cite web |date=24 February 2025 |title=Technical Overview of Volatile Organic Compounds |url=https://www.epa.gov/indoor-air-quality-iaq/technical-overview-volatile-organic-compounds |access-date=1 April 2025 |website=US Environmental Protection Agency}}</ref> They can cause photochemical smog and form aerosols impacting climate. The group includes methane, acetone, and toluene. Some can cause cancer, such as butadiene and benzene,<ref>{{Cite journal |last=Lewis |first=Alastair C. |date=2018-02-16 |title=The changing face of urban air pollution |url=https://www.science.org/doi/10.1126/science.aar4925 |journal=Science |language=en |volume=359 |issue=6377 |pages=744–745 |doi=10.1126/science.aar4925 |pmid=29449479 |bibcode=2018Sci...359..744L |issn=0036-8075 |url-access=subscription |archive-date=26 September 2024 |access-date=1 April 2025 |archive-url=https://web.archive.org/web/20240926131517/https://www.science.org/doi/10.1126/science.aar4925 |url-status=live }}</ref> with benzene being released from cigarette smoking. Methane is a greenhouse gas and the second-largest driver of global warming. Other VOCs contribute to climate warming because they help form ground-level ozone, a greenhouse gas.{{sfn|Pearson|Derwent|2022|pp=4-5}}
=== Other pollutants === Some heavy metals can be bad for health. For instance, lead exposure can lead to learning disabilities in children. In the atmosphere, heavy metals can exist in different states, such as particles or gases. One of the forms of chromium can cause cancer. Mercury is harmful both as an element and in an organic compound. In the atmosphere, it comes mostly from cement production, coal burning, and incinerators.<ref>{{Citation |title=Environmental Impacts |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |pages=311–316 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/abs/air-pollution/environmental-impacts/8F47851775A4681857CEB599B3C32DF5 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.013 |isbn=978-1-108-48163-2 |url-access=subscription |archive-date=2 June 2025 |archive-url=https://web.archive.org/web/20250602182130/https://www.cambridge.org/core/books/abs/air-pollution/environmental-impacts/8F47851775A4681857CEB599B3C32DF5 |url-status=live }}</ref>
Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation. They persist in the environment, are capable of long-range transmission, bioaccumulate in humans and animals, and biomagnify in food chains.<ref name=":17">{{cite book |last1=Singh |first1=Ritu |url=https://books.google.com/books?id=NiRAEAAAQBAJ |title=Persistent Organic Pollutants in the Environment: Origin and Role |last2=Kumar |first2=Sanjeev |last3=Karmakar |first3=Susmita |last4=Siddiqui |first4=Arif J. |last5=Mathur |first5=Ankita |last6=Adnan |first6=Mohd. |last7=Rajput |first7=Vishnu D. |last8=Rani |first8=Anita |last9=Kumar |first9=Narendra |date=2021 |publisher=CRC Press |isbn=978-1-003-05317-0 |editor1-last=Kumar |editor1-first=Narendra |pages=31–54 |chapter=2: Causes, Consequences, and Control of Persistent Organic Pollutants |access-date=11 June 2022 |editor2-last=Shukla |editor2-first=Vertika}}</ref> The Stockholm Convention on Persistent Organic Pollutants identified pesticides and other POPs of concern. These include dioxins and furans which are created by waste combustion. POPs are usually either semi-volatile (gaseous only at higher temperatures) or non-volatile (emitted as particles). The harmful effects of the pesticide DDT, a POP, were popularized by Rachel Carson's 1962 book ''Silent Spring''.<ref>{{Citation |title=Environmental Impacts |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |pages=309–311 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/abs/air-pollution/environmental-impacts/8F47851775A4681857CEB599B3C32DF5 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.013 |isbn=978-1-108-48163-2 |url-access=subscription |archive-date=2 June 2025 |archive-url=https://web.archive.org/web/20250602182130/https://www.cambridge.org/core/books/abs/air-pollution/environmental-impacts/8F47851775A4681857CEB599B3C32DF5 |url-status=live }}</ref> PFASs and polycyclic aromatic hydrocarbons (PAHs) are other examples of POPs.<ref>{{Cite journal |last1=Negrete-Bolagay |first1=Daniela |last2=Zamora-Ledezma |first2=Camilo |last3=Chuya-Sumba |first3=Cristina |last4=De Sousa |first4=Frederico B. |last5=Whitehead |first5=Daniel |last6=Alexis |first6=Frank |last7=Guerrero |first7=Victor H. |date=2021-12-15 |title=Persistent organic pollutants: The trade-off between potential risks and sustainable remediation methods |url=https://linkinghub.elsevier.com/retrieve/pii/S0301479721017990 |journal=Journal of Environmental Management |volume=300 |article-number=113737 |doi=10.1016/j.jenvman.2021.113737 |pmid=34536739 |bibcode=2021JEnvM.30013737N |issn=0301-4797 |url-access=subscription |archive-date=2 June 2025 |access-date=12 May 2025 |archive-url=https://web.archive.org/web/20250602182201/https://linkinghub.elsevier.com/retrieve/pii/S0301479721017990 |url-status=live }}</ref>
Chlorofluorocarbons (CFCs) are a group of compounds which harm the ozone layer. They were widely used in aerosol sprays, refrigerants, and fire suppression. Due to their chemical stability, CFCs persist in the atmosphere and eventually reach the stratosphere (the upper atmosphere).<ref>{{Cite web |last=US EPA |date=2025-03-05 |title=Basic Ozone Layer Science |url=https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science |access-date=2025-06-11 |website=www.epa.gov |publisher=US Environmental Protection Agency |archive-date=7 November 2022 |archive-url=https://web.archive.org/web/20221107150120/https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science |url-status=live }}</ref> There, they break down under the impact of UV light, which releases chlorine. This in turn reacts with ozone, destroying it. As the ozone layer blocks harmful UV radiation from reaching the Earth's surface, its depletion leads to health risks such as skin ageing and skin cancer.<ref>{{Citation |title=The Stratospheric Ozone Layer |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |pages=139–140 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/air-pollution/stratospheric-ozone-layer/E7D02160D69CF8747E451244D8C80C90 |access-date=2025-06-11 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.007 |isbn=978-1-108-48163-2|url-access=subscription }}</ref>
== Exposure == thumb|PM<sub>2.5</sub> Levels Across the World's 5 Most Populated Nations in 2019.|alt=Air pollution levels for urban, rural areas and cities and town. India and Pakistan have concentrations of about 50 microgram PM2.5 per cubic meter. China has levels around 35, Indonesia around 15, and the US around 8. Rural areas typically have somewhat cleaner air than urban areas.Exposure to air pollution varies widely across the world and across groups.<ref>{{Cite journal |last1=Hajat |first1=Anjum |last2=Hsia |first2=Charlene |last3=O'Neill |first3=Marie S. |date=2015 |title=Socioeconomic Disparities and Air Pollution Exposure: a Global Review |journal=Current Environmental Health Reports |language=en |volume=2 |issue=4 |pages=440–450 |doi=10.1007/s40572-015-0069-5 |issn=2196-5412 |pmc=4626327 |pmid=26381684|bibcode=2015CEHR....2..440H }}</ref> Children, for example, are more exposed because they breathe more rapidly than adults and closer to the ground, where pollution from vehicle exhaust and dust is more concentrated.<ref name="HEI_2024_p21-23" /> Similarly, people engaging in strenuous exercise inhale more pollutants than those at rest.<ref name=":7">{{Cite book |last=Vallero |first=Daniel A. |url=https://shop.elsevier.com/books/fundamentals-of-air-pollution/vallero/978-0-12-373615-4 |title=Fundamentals of Air Pollution |date=1 October 2007 |publisher=Academic Press |isbn=978-0-12-405481-3 |edition=4th |archive-date=5 April 2024 |access-date=16 August 2024 |archive-url=https://web.archive.org/web/20240405223437/https://shop.elsevier.com/books/fundamentals-of-air-pollution/vallero/978-0-12-373615-4 }}</ref> People can reduce their exposure by wearing high-quality face masks or by using air purifiers.<ref>{{Cite journal |last1=Allen |first1=Ryan W. |last2=Barn |first2=Prabjit |date=2020 |title=Individual- and Household-Level Interventions to Reduce Air Pollution Exposures and Health Risks: a Review of the Recent Literature |journal=Current Environmental Health Reports |language=en |volume=7 |issue=4 |pages=424–440 |doi=10.1007/s40572-020-00296-z |pmid=33241434 |issn=2196-5412|pmc=7749091 |bibcode=2020CEHR....7..424A }}</ref>
thumb|Share of the population exposed to air pollution levels above WHO guidelines, 2017.|alt=most regions show that 100% of the population was exposed to unhealthy air pollution using the less strict 2017 WHO guidelines.For some pollutants, low exposure can be seen as safe, whereas other pollutants have negative health effects even at low levels.<ref name='WHO_energy_health'>{{cite web |title=Air quality, energy and health |url=https://www.who.int/teams/environment-climate-change-and-health/air-quality-energy-and-health/health-impacts |access-date=16 January 2025 |publisher=World Health Organization |archive-date=16 January 2025 |archive-url=https://web.archive.org/web/20250116061716/https://www.who.int/teams/environment-climate-change-and-health/air-quality-energy-and-health/health-impacts |url-status=live }}</ref> As evidence has grown that even very low levels of air pollutants hurt human health, the WHO halved its recommended safe limit for particulate matter from 10 μg/m<sup>3</sup> to 5 μg/m<sup>3</sup> in 2021. Under the new guideline, nearly the entire global population—97%—is classified as exposed to unsafe levels of fine particles (PM<sub>2.5)</sub>.<ref>{{Cite web |date=2022-06-14 |title=Most of the World Breathes Unsafe Air, Taking More Than 2 Years Off Global Life Expectancy |url=https://aqli.epic.uchicago.edu/news/most-of-the-world-breathes-unsafe-air-taking-more-than-2-years-off-global-life-expectancy/ |access-date=2022-07-12 |website=AQLI |archive-date=25 October 2022 |archive-url=https://web.archive.org/web/20221025042621/https://aqli.epic.uchicago.edu/news/most-of-the-world-breathes-unsafe-air-taking-more-than-2-years-off-global-life-expectancy/ |url-status=live }}</ref> The new limit for nitrogen dioxide (NO<sub>2</sub>) became 75% lower.<ref>{{Cite web |last=Carrington |first=Damian |date=2021-09-22 |title=WHO slashes guideline limits on air pollution from fossil fuels |url=https://www.theguardian.com/environment/2021/sep/22/who-cuts-guideline-limits-on-air-pollution-from-fossil-fuels |access-date=2021-09-22 |website=The Guardian |archive-date=5 December 2022 |archive-url=https://web.archive.org/web/20221205141212/https://www.theguardian.com/environment/2021/sep/22/who-cuts-guideline-limits-on-air-pollution-from-fossil-fuels |url-status=live }}</ref> For all pollutants together, the World Health Organization concluded that 99% of the world population is exposed to harmful air pollution.<ref name=":13">{{Cite web |title=Billions of people still breathe unhealthy air: new WHO data |url=https://www.who.int/news/item/04-04-2022-billions-of-people-still-breathe-unhealthy-air-new-who-data |access-date=2025-01-14 |publisher=World Health Organization |language=en |archive-date=15 January 2025 |archive-url=https://web.archive.org/web/20250115023645/https://www.who.int/news/item/04-04-2022-billions-of-people-still-breathe-unhealthy-air-new-who-data |url-status=live }}</ref>
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 in (motorized) traffic.<ref name="Dons et al.">{{cite journal|last=Dons |first=E. |title=Impact of time-activity patterns on personal exposure to black carbon |journal=Atmospheric Environment |volume=45 |issue=21 |pages=3594–3602 |year=2011 |doi=10.1016/j.atmosenv.2011.03.064 |bibcode=2011AtmEn..45.3594D}}</ref> A large portion of total daily exposure occurs as short peaks of high concentrations.<ref name="Dons et al. 2019">{{cite journal |last=Dons |first=E. |title=Transport most likely to cause air pollution peak exposures in everyday life: Evidence from over 2000 days of personal monitoring |journal=Atmospheric Environment |volume=213 |pages=424–432 |year=2019 |doi=10.1016/j.atmosenv.2019.06.035 |bibcode=2019AtmEn.213..424D |hdl=10044/1/80194 |s2cid=197131423 |hdl-access=free}}</ref>
=== By socioeconomic group === {{Main|Toxic hotspot|Environmental justice}}
While air pollution affects a variety of populations, some groups are more exposed. In many regions, there are disparities in exposure to pollution by race and income. This is especially true in countries with high inequalities in incomes and healthcare, such as the United States. Polluting industries and roads are more likely to be placed in poorer communities, and people in these communities are more likely to work outdoors, leading to additional exposure.<ref name=":10" /> Residents in public housing, who are generally low-income and cannot easily move to healthier neighborhoods, are highly affected by nearby refineries and chemical plants.<ref>{{cite journal |last=Lerner |first=Steve |year=2010 |title=Sacrifice Zones: The Front Lines of Toxic Chemical Exposure in the United States |journal=Port Arthur, Texas: Public Housing Residents Breathe Contaminated Air from Nearby Refineries and Chemical Plants |publisher=MIT Press}}</ref> Additionally, lower-income communities more often perform polluting activities, such as using solid biofuels for cooking.<ref>{{Cite journal |last1=Reddington |first1=C. L. |last2=Turnock |first2=S. T. |last3=Conibear |first3=L. |last4=Forster |first4=P. M. |last5=Lowe |first5=J. A. |last6=Ford |first6=L. Berrang |last7=Weaver |first7=C. |last8=van Bavel |first8=B. |last9=Dong |first9=H. |last10=Alizadeh |first10=M. R. |last11=Arnold |first11=S. R. |date=2023 |title=Inequalities in Air Pollution Exposure and Attributable Mortality in a Low Carbon Future |journal=Earth's Future |language=en |volume=11 |issue=12 |article-number=e2023EF003697 |doi=10.1029/2023EF003697 |bibcode=2023EaFut..1103697R |issn=2328-4277|doi-access=free }}</ref><ref>{{Cite journal |last1=Rao |first1=Narasimha D. |last2=Kiesewetter |first2=Gregor |last3=Min |first3=Jihoon |last4=Pachauri |first4=Shonali |last5=Wagner |first5=Fabian |date=2021-07-26 |title=Household contributions to and impacts from air pollution in India |url=https://www.nature.com/articles/s41893-021-00744-0 |journal=Nature Sustainability |language=en |volume=4 |issue=10 |pages=859–867 |doi=10.1038/s41893-021-00744-0 |bibcode=2021NatSu...4..859R |issn=2398-9629 |url-access=subscription |archive-date=6 March 2025 |access-date=18 May 2025 |archive-url=https://web.archive.org/web/20250306175726/https://www.nature.com/articles/s41893-021-00744-0 |url-status=live }}</ref> In the United States, Blacks and Latinos generally face more pollution than Whites and Asians.<ref name="Drury">{{cite journal |last1=Drury |first1=Richard |last2=Belliveau |first2=Michael |last3=Kuhn |first3=J. Scott |last4=Shipra |first4=Bansal |date=Spring 1999 |title=Pollution Trading and Environmental Justice: Los Angeles' Failed Experiment in Air Pollution Policy |journal=Duke Environmental Law & Policy Forum |volume=9 |issue=231}}</ref>
=== By geographic area === {{further information|List of most polluted cities in the world by particulate matter concentration|List of least polluted cities by particulate matter concentration}} {| class="wikitable floatright" |+Top 5 most polluted cities in 2024<ref>{{Cite web |date=2025 |title=World's Most Polluted Cities - PM2.5 Ranking {{!}} AirVisual |url=https://www.iqair.com/us/world-most-polluted-cities |access-date=2025-04-24 |website=IQAir |archive-date=6 December 2022 |archive-url=https://web.archive.org/web/20221206065325/https://www.iqair.com/us/world-most-polluted-cities |url-status=live }}</ref> !City !PM<sub>2.5</sub> concentration |- |Byrnihat, India |128 |- |Delhi, India |108 |- |Karaganda, Kazakhstan |105 |- |Mullanpur, India |102 |- |Lahore, Pakistan |102 |} Exposure to outdoor air pollution is worst in lower-middle income countries in line with the environmental Kuznets curve, which postulates that pollution is worst in economies that rely on manufacturing but have not yet been able to prioritize environmental regulation.<ref name=":10">{{cite journal |last1=Rentschler |first1=Jun |last2=Leonova |first2=Nadezda |date=2023 |title=Global air pollution exposure and poverty |journal=Nature Communications |volume=14 |issue=1 |page=4432 |bibcode=2023NatCo..14.4432R |doi=10.1038/s41467-023-39797-4 |pmc=10363163 |pmid=37481598 |doi-access=free}}</ref> Indoor air pollution is worst in low-income countries, in particularly south-east Asia, the western Pacific, and Africa.{{sfn|World Health Organization|2016|pp=17-18}}
Outdoor air pollution is usually concentrated in densely populated metropolitan areas. Urbanization leads to a rapid rise in premature mortality due to air pollution in fast-growing tropical cities.<ref>{{Cite journal |last1=Vohra |first1=Karn |last2=Marais |first2=Eloise A. |last3=Bloss |first3=William J. |last4=Schwartz |first4=Joel |last5=Mickley |first5=Loretta J. |last6=Van Damme |first6=Martin |last7=Clarisse |first7=Lieven |last8=Coheur |first8=Pierre-F. |date=2022-04-08 |title=Rapid rise in premature mortality due to anthropogenic air pollution in fast-growing tropical cities from 2005 to 2018 |journal=Science Advances |language=en |volume=8 |issue=14 |article-number=eabm4435 |doi=10.1126/sciadv.abm4435 |pmid=35394832 |pmc=8993110 |bibcode=2022SciA....8M4435V |issn=2375-2548}}</ref> Indoor air pollution on the other hand is most common in rural areas, which may lack access to clean cooking fuels.{{sfn|World Health Organization|2016|pp=17-18}}
A map published in 2025 by Climate TRACE indicates that PM<sub>2.5</sub> (fine particles) and other toxins are released near the homes of about 1.6 billion people, about 900 million of whom are in the path of "super-emitting" facilities such as power plants, refineries, ports, and mines.<ref name=Guardian_20250924>{{cite news |last1=Harvey |first1=Fiona |title=Fossil fuel burning poses threat to health of 1.6bn people, data shows |url=https://www.theguardian.com/environment/2025/sep/24/fossil-fuel-burning-threat-health-16bn-people-data-shows |newspaper=The Guardian |date=24 September 2025 |archive-url=https://web.archive.org/web/20250924112040/https://www.theguardian.com/environment/2025/sep/24/fossil-fuel-burning-threat-health-16bn-people-data-shows |archive-date=24 September 2025 |url-status=live}}</ref>
== Health effects == {{Further|Environmental health}} thumb|The share of total deaths from indoor air pollution, 2017. Air pollution is an important risk factor for various diseases, such as COPD (a common lung disease), stroke, heart disease, lung cancer, and pneumonia. Indoor air pollution is also associated with cataract.<ref name='WHO_energy_health' /> According to the WHO, 99% of the world's population lives in areas with air pollution that exceeds WHO recommended levels.<ref>{{Cite web |title=Air pollution |url=https://www.who.int/health-topics/air-pollution#tab=tab_1 |url-status=live |archive-url=https://web.archive.org/web/20220519092143/https://www.who.int/health-topics/air-pollution#tab=tab_1 |archive-date=19 May 2022 |access-date=2025-05-02 |website=World Health Organization |language=en}}</ref> Even at very low levels (under the World Health Organization recommended levels), fine particulates can continue to cause harm.<ref name="HEI_2024_p7-8">{{Cite book |last1=Health Effects Institute |author-link1=Health Effects Institute |url=https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |title=State of Global Air Report 2024: A Special Report on Global Exposure to Air Pollution and its Health Impacts with a Focus on Children's Health. |last2=Institute for Health Metrics and Evaluation |author-link2=Institute for Health Metrics and Evaluation |last3=UNICEF |author-link3=UNICEF |date=2024 |publisher=Health Effects Institute |pages=7–8 |issn=2578-6873 |archive-date=3 July 2025 |access-date=23 July 2025 |archive-url=https://web.archive.org/web/20250703232128/https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |url-status=live }}</ref>
Pollutants strongly linked to ill health include particulate matter,<ref>{{Cite journal |last=Thompson |first=Jonathan E. |date=May 2018 |title=Airborne Particulate Matter: Human Exposure and Health Effects |url=https://journals.lww.com/joem/abstract/2018/05000/airborne_particulate_matter__human_exposure_and.2.aspx |journal=Journal of Occupational and Environmental Medicine |language=en-US |volume=60 |issue=5 |pages=392–423 |doi=10.1097/JOM.0000000000001277 |pmid=29334526 |bibcode=2018JOEM...60..392T |issn=1076-2752 |url-access=subscription |archive-date=30 April 2025 |access-date=2 May 2025 |archive-url=https://web.archive.org/web/20250430052123/https://journals.lww.com/joem/abstract/2018/05000/airborne_particulate_matter__human_exposure_and.2.aspx |url-status=live }}</ref> carbon monoxide,<ref>{{Cite journal |last1=Chen |first1=Tze-Ming |last2=Kuschner |first2=Ware G. |last3=Gokhale |first3=Janaki |last4=Shofer |first4=Scott |date=2007-04-01 |title=Outdoor Air Pollution: Nitrogen Dioxide, Sulfur Dioxide, and Carbon Monoxide Health Effects |url=https://www.sciencedirect.com/science/article/abs/pii/S0002962915325933 |journal=The American Journal of the Medical Sciences |volume=333 |issue=4 |pages=249–256 |doi=10.1097/MAJ.0b013e31803b900f |pmid=17435420 |issn=0002-9629 |url-access=subscription |archive-date=23 April 2024 |access-date=2 May 2025 |archive-url=https://web.archive.org/web/20240423082445/https://www.sciencedirect.com/science/article/abs/pii/S0002962915325933 |url-status=live }}</ref> nitrogen dioxide (NO<sub>2</sub>), ozone (O<sub>3</sub>),<ref>{{Cite web |last=American Lung Association |title=Ozone |url=https://www.lung.org/clean-air/outdoors/what-makes-air-unhealthy/ozone |access-date=2025-05-02 |website=www.lung.org |language=en |archive-date=5 May 2023 |archive-url=https://web.archive.org/web/20230505121336/https://www.lung.org/clean-air/outdoors/what-makes-air-unhealthy/ozone |url-status=live }}</ref> and sulfur dioxide (SO<sub>2</sub>). Fine particulates are especially damaging, as they can enter the bloodstream via the lungs and reach other organs.<ref>{{Cite web |last=US EPA |first=OAR |date=2016-04-26 |title=Health and Environmental Effects of Particulate Matter (PM) |url=https://www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm |access-date=2025-05-02 |website=www.epa.gov |language=en |archive-date=15 December 2019 |archive-url=https://web.archive.org/web/20191215135625/https://www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm |url-status=live }}</ref><ref>{{Cite journal |last=Schraufnagel |first=Dean E. |date=2020 |title=The health effects of ultrafine particles |journal=Experimental & Molecular Medicine |volume=52 |issue=3 |pages=311–317 |doi=10.1038/s12276-020-0403-3 |issn=2092-6413 |pmc=7156741 |pmid=32203102}}</ref> Air pollution causes disease by driving inflammation and oxidative stress, suppressing the immune system, and by damaging DNA.<ref name='WHO_energy_health' />
People living in poverty, babies, and older people are disproportionately affected by air pollution; pregnancy is also more risky when exposed to air pollution.<ref name="HEI_2024_p4">{{Cite book |last1=Health Effects Institute |author-link1=Health Effects Institute |url=https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |title=State of Global Air Report 2024: A Special Report on Global Exposure to Air Pollution and its Health Impacts with a Focus on Children's Health. |last2=Institute for Health Metrics and Evaluation |author-link2=Institute for Health Metrics and Evaluation |last3=UNICEF |author-link3=UNICEF |date=2024 |publisher=Health Effects Institute |page=4 |issn=2578-6873 |archive-date=3 July 2025 |access-date=23 July 2025 |archive-url=https://web.archive.org/web/20250703232128/https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |url-status=live }}</ref> Communities with a low socioeconomic status and minority groups are more vulnerable to pollution than more privileged communities.<ref name="Morello-Frosch 2011">{{cite journal |last1=Morello-Frosch |first1=Rachel |last2=Zuk |first2=Miriam |last3=Jerrett |first3=Michael |last4=Shamasunder |first4=Bhavna |last5=Kyle |first5=Amy D. |year=2011 |title=Understanding the Cumulative Impacts of Inequalities in Environmental Health: Implications for Policy |journal=Health Affairs |volume=30 |issue=5 |pages=879–87 |doi=10.1377/hlthaff.2011.0153 |pmid=21555471 |doi-access=free}}</ref> Lower-income groups might for instance have less access to healthcare.<ref name=":10" />
=== Mortality === thumb|Estimates of yearly deaths from air pollution range from 6.7 million to 8.8 million. In comparison, war caused 50,000 yearly deaths and terrorism 25,000. [[File:Death-rate-from-air-pollution-map 2021 IHME.svg|thumb|Deaths in 2021 from air pollution per 100,000 inhabitants (IHME).|alt=map showing low death rates in Europe and the Americas, and high death rates in South and South East Asia, and Africa]]Estimates of deaths due to air pollution vary.<ref>{{Cite journal |last=Roser |first=Max |date=2024-03-18 |title=Data review: how many people die from air pollution? |url=https://ourworldindata.org/data-review-air-pollution-deaths |journal=Our World in Data}}</ref> The 2024 Global Burden of Disease Study estimates that air pollution contributed to 8.1 million deaths in 2021, which is more than 1 in 8 deaths. Outdoor particulate pollution (PM<sub>2.5</sub>) was the largest cause of death (4.7 million), followed by indoor particulate pollution (3.1 million) and ozone (0.5 million).<ref name="HEI_2024_p3-4">{{Cite book |last1=Health Effects Institute |author-link1=Health Effects Institute |url=https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |title=State of Global Air Report 2024: A Special Report on Global Exposure to Air Pollution and its Health Impacts with a Focus on Children's Health. |last2=Institute for Health Metrics and Evaluation |author-link2=Institute for Health Metrics and Evaluation |last3=UNICEF |author-link3=UNICEF |date=2024 |publisher=Health Effects Institute |pages=3–4, 15 |issn=2578-6873 |archive-date=3 July 2025 |access-date=23 July 2025 |archive-url=https://web.archive.org/web/20250703232128/https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |url-status=live }}</ref>
The World Health Organization estimates that 6.7 million people die from air pollution each year, 4.2 million due to outdoor air pollution.<ref name="who2024">{{cite news |title=Ambient (outdoor) air pollution |date=24 October 2024 |url=https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health |access-date=15 January 2025 |publisher=World Health Organization |archive-date=8 October 2021 |archive-url=https://web.archive.org/web/20211008055940/https://www.who.int/news-room/fact-sheets/detail/ambient-%28outdoor%29-air-quality-and-health |url-status=live }}</ref> Roughly 68% of outdoor air pollution-related premature deaths were due to coronary heart disease and stroke, 14% due to COPD, and 14% due to lung infections (lower respiratory tract infections).<ref name="who2024" />
A study published in 2019 estimated that, for 2015, the number was about 8.8 million, with 5.5 million of these premature deaths due to air pollution from human sources.<ref>{{Cite journal |last1=Lelieveld |first1=J. |last2=Klingmüller |first2=K. |last3=Pozzer |first3=A. |last4=Burnett |first4=R. T. |last5=Haines |first5=A. |last6=Ramanathan |first6=V. |date=2019 |title=Effects of fossil fuel and total anthropogenic emission removal on public health and climate |journal=Proceedings of the National Academy of Sciences |language=en |volume=116 |issue=15 |pages=7192–7197 |bibcode=2019PNAS..116.7192L |doi=10.1073/pnas.1819989116 |issn=0027-8424 |pmc=6462052 |pmid=30910976 |doi-access=free}}</ref><ref name="2019-03-12-guardian" /> The global mean loss of life expectancy from air pollution in 2015 was 2.9 years, substantially more than, for example, 0.3 years from all forms of direct violence.<ref name="10.1093/cvr/cvaa025">{{cite journal |last1=Lelieveld |first1=Jos |last2=Pozzer |first2=Andrea |last3=Pöschl |first3=Ulrich |last4=Fnais |first4=Mohammed |last5=Haines |first5=Andy |last6=Münzel |first6=Thomas |title=Loss of life expectancy from air pollution compared to other risk factors: a worldwide perspective |journal=Cardiovascular Research |date=2020 |volume=116 |issue=11 |pages=1910–1917 |doi=10.1093/cvr/cvaa025 |pmid=32123898 |pmc=7449554 |issn=0008-6363}}</ref>
==== By region ==== Regional deaths due to air pollution depend not only on the regional exposure, but also on how large and how old the population is, and the health of people overall.<ref>{{Cite journal |last1=Yang |first1=Hui |last2=Huang |first2=Xinyuan |last3=Westervelt |first3=Daniel M. |last4=Horowitz |first4=Larry |last5=Peng |first5=Wei |date=2022-10-24 |title=Socio-demographic factors shaping the future global health burden from air pollution |url=https://www.nature.com/articles/s41893-022-00976-8 |journal=Nature Sustainability |language=en |volume=6 |issue=1 |pages=58–68 |doi=10.1038/s41893-022-00976-8 |bibcode=2022NatSu...6...58Y |issn=2398-9629 |archive-date=8 January 2025 |access-date=12 July 2025 |archive-url=https://web.archive.org/web/20250108212531/https://www.nature.com/articles/s41893-022-00976-8 |url-status=live }}</ref>
In some countries, more than 20% of deaths are attributed to air pollution (e.g. China, Nepal, Bangladesh, Laos, and North Korea). In South America, about 4% of deaths are from air pollution, while in countries such as Australia, Canada, and the US, this number is under 3%.<ref>{{Cite journal |last1=Ritchie |first1=Hannah |last2=Roser |first2=Max |date=February 2024 |title=Air Pollution |url=https://ourworldindata.org/air-pollution |journal=Our World in Data |language=en |access-date=19 January 2024 |archive-date=17 January 2024 |archive-url=https://web.archive.org/web/20240117143952/https://ourworldindata.org/air-pollution |url-status=live }}</ref>
In absolute number, India and China have the higher number of deaths from air pollution. In India, it contributed to 2.1 million deaths in 2021, whereas China saw 2.4 million deaths.<ref>{{Cite web |date=20 May 2024 |title=Deaths from air pollution |url=https://ourworldindata.org/grapher/air-pollution-deaths-country |archive-url=https://web.archive.org/web/20250114131817/https://ourworldindata.org/grapher/air-pollution-deaths-country |archive-date=14 January 2025 |access-date=2025-01-19 |website=Our World in Data |language=en |url-status=live }}</ref> Annual premature European deaths from air pollution are estimated at 416,000<ref>{{Cite web |date=2024-12-10 |title=Harm to human health from air pollution in Europe: burden of disease status, 2024 |url=https://www.eea.europa.eu/en/analysis/publications/harm-to-human-health-from-air-pollution-2024 |access-date=2025-02-15 |website=www.eea.europa.eu |language=en |archive-date=1 March 2025 |archive-url=https://web.archive.org/web/20250301150928/https://www.eea.europa.eu/en/analysis/publications/harm-to-human-health-from-air-pollution-2024 |url-status=live }}</ref> to 800,000.<ref name="2019-03-12-guardian">{{cite news |last=Carrington |first=Damian |date=12 March 2019 |title=Air pollution deaths are double previous estimates, finds research |url=https://www.theguardian.com/environment/2019/mar/12/air-pollution-deaths-are-double-previous-estimates-finds-research |access-date=12 March 2019 |work=The Guardian |archive-date=4 February 2020 |archive-url=https://web.archive.org/web/20200204144617/https://www.theguardian.com/environment/2019/mar/12/air-pollution-deaths-are-double-previous-estimates-finds-research |url-status=live }}</ref> The UK saw some 17,000 deaths in 2021 due to air pollution and the US saw 64,000. Nigeria, Indonesia and Pakistan each saw over 200,000 deaths resulting from air pollution.<ref>{{Cite web |title=Explore the Data {{!}} State of Global Air |url=https://www.stateofglobalair.org/data |access-date=2025-02-15 |website=www.stateofglobalair.org |archive-date=19 February 2025 |archive-url=https://web.archive.org/web/20250219230303/https://www.stateofglobalair.org/data |url-status=live }}</ref>
==== By source ==== {{Further|#Sources}} thumb |Though the rate of exposure to ground-level ozone ("smog") and small-particulate matter ("soot") has been declining, in 2026, nearly half of people in the US under age{{nbsp}}18 live in an area receiving a failing grade for at least one measure of air pollution.<ref name=WashPost_20260422>American Lung Association ''State of the Air 2026'' as presented by {{cite news |last1=Dennis |first1=Brady |last2=Noll |first2=Ben |title=More Americans are exposed to polluted air in the United States. See where. |url=https://www.washingtonpost.com/climate-environment/2026/04/22/unhealthy-air-pollution-report/ |work=The Washington Post |date=22 April 2026}}</ref> {{multiple image | total_width = 250 | image1 = 2021 Death rates, by energy source.svg | caption1 = Deaths caused by accidents and air pollution from fossil fuel use in power plants exceed those caused by production of renewable energy.<ref name=OWID_SafestEnergy_2021>{{cite journal |last1=Ritchie |first1=Hannah |author1-link=Hannah Ritchie |last2=Roser |first2=Max |author2-link=Max Roser |title=What are the safest and cleanest sources of energy? |url=https://ourworldindata.org/safest-sources-of-energy |journal=Our World in Data |archive-url=https://web.archive.org/web/20240115112316/https://ourworldindata.org/safest-sources-of-energy |archive-date=15 January 2024 |date=2021 |url-status=live }} Data sources: Markandya & Wilkinson (2007); UNSCEAR (2008; 2018); Sovacool et al. (2016); IPCC AR5 (2014); Pehl et al. (2017); Ember Energy (2021).</ref> }}
The burning of fossil fuels is the largest source of air pollution deaths.<ref name="10.1016/j.envres.2021.110754">{{cite journal |last1=Vohra |first1=Karn |last2=Vodonos |first2=Alina |last3=Schwartz |first3=Joel |last4=Marais |first4=Eloise A. |last5=Sulprizio |first5=Melissa P. |last6=Mickley |first6=Loretta J. |date=2021 |title=Global mortality from outdoor fine particle pollution generated by fossil fuel combustion: Results from GEOS-Chem |url=https://www.sciencedirect.com/science/article/abs/pii/S0013935121000487 |journal=Environmental Research |language=en |volume=195 |article-number=110754 |bibcode=2021ER....19510754V |doi=10.1016/j.envres.2021.110754 |issn=0013-9351 |pmid=33577774 |s2cid=231909881 |access-date=5 March 2021 |archive-date=4 March 2021 |archive-url=https://web.archive.org/web/20210304112341/https://www.sciencedirect.com/science/article/abs/pii/S0013935121000487 |url-status=live }}</ref> There are estimated 4.5 million annual premature deaths worldwide due to pollutants released by high-emission power stations and vehicle exhausts.<ref>{{Cite book |last1=Farrow |first1=Aidan |url=https://www.greenpeace.org/static/planet4-southeastasia-stateless/2020/02/21b480fa-toxic-air-report-110220.pdf |title=Toxic air: The price of fossil fuels |last2=Miller |first2=Kathryn A |last3=Myllyvirta |first3=Lauri |date=February 2020 |publisher=Greenpeace Southeast Asia |location=Seoul |archive-date=11 September 2024 |access-date=16 August 2024 |archive-url=https://web.archive.org/web/20240911114830/https://www.greenpeace.org/static/planet4-southeastasia-stateless/2020/02/21b480fa-toxic-air-report-110220.pdf |url-status=live }}</ref> PM<sub>2.5</sub> formed from emissions from coal-fired power plants could be more harmful than other types of fine particulate matter.<ref name="science2023mortality">{{cite journal |last1=Henneman |first1=Lucas |last2=Choirat |first2=Christine |last3=Dedoussi |first3=Irene |last4=Dominici |first4=Francesca |last5=Roberts |first5=Jessica |last6=Zigler |first6=Corwin |date=2023 |title=Mortality risk from United States coal electricity generation |journal=Science |volume=382 |issue=6673 |pages=941–946 |bibcode=2023Sci...382..941H |doi=10.1126/science.adf4915 |pmc=10870829 |pmid=37995235}}</ref>
The World Health Organization (WHO) estimates that cooking-related pollution causes 3.8 million annual deaths.<ref>{{Cite web |date=8 May 2018 |title=Household air pollution and health: fact sheet |url=https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health |access-date=2020-11-21 |publisher=World Health Organization |language=en |archive-date=12 November 2021 |archive-url=https://web.archive.org/web/20211112161107/https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health |url-status=live }}</ref> The Global Burden of Disease study estimated the number of deaths in 2021 at 3.1 million.<ref>{{cite journal |last1=Ritchie |first1=Hannah |author1-link=Hannah Ritchie |last2=Roser |first2=Max |author2-link=Max Roser |date=2024 |title=Access to Energy |url=https://ourworldindata.org/indoor-air-pollution#indoor-air-pollution-is-one-of-the-leading-risk-factors-for-premature-death |journal=Our World in Data |access-date=1 April 2021 |quote= |archive-date=1 November 2021 |archive-url=https://web.archive.org/web/20211101224356/https://ourworldindata.org/indoor-air-pollution#indoor-air-pollution-is-one-of-the-leading-risk-factors-for-premature-death |url-status=live }}</ref>
=== Cardiovascular disease ===
There is strong evidence that air pollution increases the risk of cardiovascular disease, including stroke, high blood pressure, and coronary heart disease.<ref name="de BontJaganathanDahlquist2022">{{cite journal |last1=de Bont |first1=Jeroen |last2=Jaganathan |first2=Suganthi |last3=Dahlquist |first3=Marcus |last4=Persson |first4=Åsa |last5=Stafoggia |first5=Massimo |last6=Ljungman |first6=Petter |date=8 March 2022 |title=Ambient air pollution and cardiovascular diseases: An umbrella review of systematic reviews and meta-analyses |url= |journal=Journal of Internal Medicine |volume=291 |issue=6 |pages=779–800 |doi=10.1111/joim.13467 |issn=0954-6820 |eissn=1365-2796 |pmc=9310863 |pmid=35138681}}</ref> According to the Global Burden of Disease Study, air pollution is responsible for 27% of deaths from strokes worldwide and 28% of coronary heart disease.<ref name="HEI_2024_p27">{{Cite book |last1=Health Effects Institute |author-link1=Health Effects Institute |url=https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |title=State of Global Air Report 2024: A Special Report on Global Exposure to Air Pollution and its Health Impacts with a Focus on Children's Health. |last2=Institute for Health Metrics and Evaluation |author-link2=Institute for Health Metrics and Evaluation |last3=UNICEF |author-link3=UNICEF |date=2024 |publisher=Health Effects Institute |page=27 |issn=2578-6873}}</ref> The risks are highest in regions with higher air pollution (e.g. Asia), for elderly and for people who are overweight.<ref name="de BontJaganathanDahlquist2022" />
Air pollution is a leading risk factor for stroke, particularly in developing countries where pollutant levels are highest.<ref name="HEI_2024_p27" /> A systematic analysis of 17 different risk factors in 188 countries found air pollution is associated with nearly one in three strokes (29%) worldwide (34% of strokes in developing countries versus 10% in developed countries).<ref name="Mayor2016">{{cite journal |last1=Mayor |first1=Susan |date=12 June 2016 |title=Air pollution is a leading risk factor for stroke, global study shows |url= |journal=BMJ |volume=353 |article-number=i3272 |doi=10.1136/bmj.i3272 |eissn=1756-1833 |pmid=27298274}}</ref><ref name="FeiginRothNaghavi2016">{{cite journal | last1 = Feigin | first1 = Valery L | last2 = Roth | first2 = Gregory A | last3 = Naghavi | first3 = Mohsen | last4 = Parmar | first4 = Priya | last5 = Krishnamurthi | first5 = Rita | last6 = Chugh | first6 = Sumeet | last7 = Mensah | first7 = George A | last8 = Norrving | first8 = Bo | last9 = Shiue | first9 = Ivy | last10 = Ng | first10 = Marie | last11 = Estep | first11 = Kara | last12 = Cercy | first12 = Kelly | last13 = Murray | first13 = Christopher J L | last14 = Forouzanfar | first14 = Mohammad H | title = Global burden of stroke and risk factors in 188 countries, during 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013 | journal = The Lancet Neurology | date = August 2016 | volume = 15 | issue = 9 | pages = 913–924 | issn = 1474-4422 | doi = 10.1016/S1474-4422(16)30073-4 | pmid = 27291521 | hdl = 10292/14061 | url = | hdl-access = free }}</ref> The mechanisms linking air pollution to increased cardiovascular mortality are not fully understood, but likely include systemic inflammation and oxidative stress.<ref>{{Cite journal |last1=Montone |first1=Rocco A. |last2=Rinaldi |first2=Riccardo |last3=Bonanni |first3=Alice |last4=Severino |first4=Anna |last5=Pedicino |first5=Daniela |last6=Crea |first6=Filippo |last7=Liuzzo |first7=Giovanna |date=2023 |title=Impact of air pollution on ischemic heart disease: Evidence, mechanisms, clinical perspectives |journal=Atherosclerosis |language=en |volume=366 |pages=22–31 |doi=10.1016/j.atherosclerosis.2023.01.013|pmid=36696748 |doi-access=free }}</ref>
=== Lung disease === Air pollution is associated with increased development, hospitalization, mortality, and COPD (chronic obstructive pulmonary disease).<ref name=":22">{{Cite journal |last1=Sin |first1=Don D. |last2=Doiron |first2=Dany |last3=Agusti |first3=Alvar |last4=Anzueto |first4=Antonio |last5=Barnes |first5=Peter J. |last6=Celli |first6=Bartolome R. |last7=Criner |first7=Gerard J. |last8=Halpin |first8=David |last9=Han |first9=MeiLan K. |last10=Martinez |first10=Fernando J. |last11=Montes de Oca |first11=Maria |last12=Papi |first12=Alberto |last13=Pavord |first13=Ian |last14=Roche |first14=Nicolas |last15=Singh |first15=Dave |date=2023 |title=Air pollution and COPD: GOLD 2023 committee report |url=https://publications.ersnet.org/content/erj/61/5/2202469 |journal=European Respiratory Journal |language=en |volume=61 |issue=5 |page=2202469 |doi=10.1183/13993003.02469-2022 |pmid=36958741 |issn=0903-1936|url-access=subscription }}</ref> COPD is a common disease which causes restricted airflow and breathing difficulties, and is the fourth-largest cause of death globally.<ref>{{Cite web |title=Chronic obstructive pulmonary disease (COPD) |url=https://www.who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-(copd) |access-date=2025-02-13 |publisher=World Health Organization |archive-date=21 April 2020 |archive-url=https://web.archive.org/web/20200421005735/https://www.who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-(copd) |url-status=live }}</ref> Nearly half of global COPD deaths are due to air pollution.<ref name="HEI_2024_p27" /> Fine particles (PM<sub>2.5</sub>) and NO<sub>2</sub> are associated with increased risk of developing COPD.<ref>{{Cite journal |last1=Holtjer |first1=Judith C.S. |last2=Bloemsma |first2=Lizan D. |last3=Beijers |first3=Rosanne J.H.C.G. |last4=Cornelissen |first4=Merel E.B. |last5=Hilvering |first5=Bart |last6=Houweling |first6=Laura |last7=Vermeulen |first7=Roel C.H. |last8=Downward |first8=George S. |last9=Maitland-Van der Zee |first9=Anke-Hilse |date=2023 |title=Identifying risk factors for COPD and adult-onset asthma: an umbrella review |journal=European Respiratory Review |language=en |volume=32 |issue=168 |page=230009 |doi=10.1183/16000617.0009-2023 |issn=0905-9180 |pmc=10155046 |pmid=37137510}}</ref> In children, air pollution can hinder lung development, which may increase their susceptibility to COPD later in life.<ref name=":22" />
Air pollution is further associated with increased risk of asthma and worsening of symptoms, and this effect seems stronger in children.<ref>{{Cite journal |last1=Zhou |first1=Xiaoying |last2=Sampath |first2=Vanitha |last3=Nadeau |first3=Kari C. |date=2024 |title=Effect of air pollution on asthma |url=https://www.annallergy.org/article/S1081-1206(24)00018-8/fulltext |journal=Annals of Allergy, Asthma & Immunology |language=English |volume=132 |issue=4 |pages=426–432 |doi=10.1016/j.anai.2024.01.017 |pmid=38253122 |pmc=10990824 |issn=1081-1206 |archive-date=12 February 2024 |access-date=13 February 2025 |archive-url=https://web.archive.org/web/20240212014253/https://www.annallergy.org/article/S1081-1206(24)00018-8/fulltext |url-status=live }}</ref> For adults, fine particles (PM<sub>2.5</sub>) or NO<sub>2</sub> seem linked to asthma onset too.<ref>{{Cite journal |last1=Lee |first1=Spencer |last2=Tian |first2=Derek |last3=He |first3=Rose |last4=Cragg |first4=Jacquelyn J |last5=Carlsten |first5=Chris |last6=Giang |first6=Amanda |last7=Gill |first7=Prubjot K |last8=Johnson |first8=Kate M |last9=Brigham |first9=Emily |date=2024 |title=Ambient air pollution exposure and adult asthma incidence: a systematic review and meta-analysis |journal=The Lancet Planetary Health |language=en |volume=8 |issue=12 |pages=e1065–e1078 |doi=10.1016/S2542-5196(24)00279-1|pmid=39674196 |doi-access=free }}</ref> Short-term exposure to ozone makes asthma worse in children.<ref name="HEI_2024_p18">{{Cite book |last1=Health Effects Institute |author-link1=Health Effects Institute |url=https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |title=State of Global Air Report 2024: A Special Report on Global Exposure to Air Pollution and its Health Impacts with a Focus on Children's Health. |last2=Institute for Health Metrics and Evaluation |author-link2=Institute for Health Metrics and Evaluation |last3=UNICEF |author-link3=UNICEF |date=2024 |publisher=Health Effects Institute |page=18|issn=2578-6873}}</ref> There is limited evidence on (almost) fatal asthma attacks in children: ground-level ozone and PM<sub>2.5</sub> seem to increase its risk.<ref>{{Cite journal |last1=Varghese |first1=Deepa |last2=Ferris |first2=Kathryn |last3=Lee |first3=Bohee |last4=Grigg |first4=Jonathan |last5=Pinnock |first5=Hilary |last6=Cunningham |first6=Steve |date=2024 |title=Outdoor air pollution and near-fatal/fatal asthma attacks in children: A systematic review |url=https://onlinelibrary.wiley.com/doi/10.1002/ppul.26932 |journal=Pediatric Pulmonology |language=en |volume=59 |issue=5 |pages=1196–1206 |doi=10.1002/ppul.26932 |pmid=38477643 |issn=8755-6863 |archive-date=21 March 2024 |access-date=13 February 2025 |archive-url=https://web.archive.org/web/20240321135510/https://onlinelibrary.wiley.com/doi/10.1002/ppul.26932 |url-status=live |hdl=20.500.11820/61941359-4c08-4f9b-b470-c5523ba06646 |hdl-access=free }}</ref>
=== Cancer === thumb|upright|Dark factory-emitted clouds obscuring the Clark Avenue Bridge in Cleveland, Ohio in July 1973.|alt=Dark factory clouds obscure the Clark Avenue Bridge in Cleveland, Ohio, July 1973.
About 265,000 lung cancer deaths were attributed globally in 2019 to exposure to fine particulate matter (PM<sub>2.5</sub>) suspended in the air.<ref name=":12">{{Cite journal |last1=Berg |first1=Christine D. |last2=Schiller |first2=Joan H. |last3=Boffetta |first3=Paolo |last4=Cai |first4=Jing |last5=Connolly |first5=Casey |last6=Kerpel-Fronius |first6=Anna |last7=Kitts |first7=Andrea Borondy |last8=Lam |first8=David C. L. |last9=Mohan |first9=Anant |last10=Myers |first10=Renelle |last11=Suri |first11=Tejas |last12=Tammemagi |first12=Martin C. |last13=Yang |first13=Dawei |last14=Lam |first14=Stephen |date=2023 |title=Air Pollution and Lung Cancer: A Review by International Association for the Study of Lung Cancer Early Detection and Screening Committee |journal=Journal of Thoracic Oncology |language=English |volume=18 |issue=10 |pages=1277–1289 |doi=10.1016/j.jtho.2023.05.024 |issn=1556-0864 |pmid=37277094|doi-access=free }}</ref> Exposure to indoor air pollution, including radon, caused another 170,000 lung cancer deaths.<ref name=":12" /> Lung cancer was also more common among people exposed to NO<sub>2</sub> and black carbon.<ref>{{Cite journal |last1=Karimi |first1=Behrooz |last2=Samadi |first2=Sadegh |date=2024 |title=Long-term exposure to air pollution on cardio-respiratory, and lung cancer mortality: a systematic review and meta-analysis |journal=Journal of Environmental Health Science & Engineering |volume=22 |issue=1 |pages=75–95 |doi=10.1007/s40201-024-00900-6 |issn=2052-336X |pmid=38887768|pmc=11180069 |bibcode=2024JEHSE..22...75K }}</ref>
Outdoor air pollution may increase risk of other types of cancer too, but the evidence is not as clear as for lung cancer.<ref name=":11">{{Cite journal |last1=Turner |first1=Michelle C. |last2=Andersen |first2=Zorana J. |last3=Baccarelli |first3=Andrea |last4=Diver |first4=W. Ryan |last5=Gapstur |first5=Susan M. |last6=Pope |first6=C. Arden |last7=Prada |first7=Diddier |last8=Samet |first8=Jonathan |last9=Thurston |first9=George |last10=Cohen |first10=Aaron |date=2020 |title=Outdoor air pollution and cancer: An overview of the current evidence and public health recommendations |journal=CA: A Cancer Journal for Clinicians |volume=70 |issue=6 |pages=460–479 |doi=10.3322/caac.21632 |issn=1542-4863 |pmc=7904962 |pmid=32964460}}</ref> For example, there may be a relationship between kidney cancer and PM<sub>2.5</sub> and NO<sub>2</sub> levels.<ref>{{Cite journal |last1=Dahman |first1=Lina |last2=Gauthier |first2=Victoria |last3=Camier |first3=Aurore |last4=Bigna |first4=Jean Joel |last5=Glowacki |first5=François |last6=Amouyel |first6=Philippe |last7=Dauchet |first7=Luc |last8=Hamroun |first8=Aghiles |date=2024 |title=Air pollution and kidney cancer risk: a systematic review and meta-analysis |journal=Journal of Nephrology |volume=37 |issue=7 |pages=1779–1790 |doi=10.1007/s40620-024-01984-x |issn=1724-6059 |pmid=38913266|pmc=11519201 }}</ref> Household air pollution – from cooking with solid fuels, but also from radon in building material – has been associated with cervical, oral, and esophageal cancer.<ref name=":11" />
=== Pregnancy and children === Stillbirths, miscarriages, and birth defects are all more likely when the mother is exposed to air pollution during pregnancy.<ref name="HEI_2024_p21-23" /> Exposure to air pollution also raises the chance that a baby has a low birth weight. The impacts might be due to pollutants directly impacting the placenta or fetus, or indirectly via the mother's health (as air pollution can cause systemic inflammation and oxidative stress).<ref name="HEI_2024_p21-23" />
Over a third of preterm births were associated with air pollution in 2021 globally. It causes more than half a million newborn deaths, a quarter of overall deaths.<ref name="HEI_2024_p21-23" /> The source of PM<sub>2.5</sub> differs greatly by region. In South and East Asia, pregnant women are frequently exposed to indoor air pollution because of wood and other biomass fuels being used for cooking, which are responsible for more than 80% of regional pollution. In the Middle East, North Africa, and West sub-Saharan Africa, fine PM comes from natural sources, such as dust storms.<ref name=":0">{{Cite journal |last1=Malley |first1=Christopher S. |last2=Kuylenstierna |first2=Johan C. I. |last3=Vallack |first3=Harry W. |last4=Henze |first4=Daven K. |last5=Blencowe |first5=Hannah |last6=Ashmore |first6=Mike R. |date=2017 |title=Preterm birth associated with maternal fine particulate matter exposure: A global, regional and national assessment |url=http://eprints.whiterose.ac.uk/112553/1/Malley_2017_Environment_International.pdf |journal=Environment International |volume=101 |pages=173–82 |bibcode=2017EnInt.101..173M |doi=10.1016/j.envint.2017.01.023 |issn=1873-6750 |pmid=28196630 |doi-access=free |archive-date=25 April 2022 |access-date=27 August 2019 |archive-url=https://web.archive.org/web/20220425080352/https://eprints.whiterose.ac.uk/112553/1/Malley_2017_Environment_International.pdf |url-status=live }}</ref>
For data including older children, polluted air resulted in the death of over 700,000 children in 2021 (709,000 under 5 years of age and 16,600 aged 5–14 years).<ref name="HEI_2024_p21-23">{{Cite book |last1=Health Effects Institute |author-link1=Health Effects Institute |url=https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |title=State of Global Air Report 2024: A Special Report on Global Exposure to Air Pollution and its Health Impacts with a Focus on Children's Health. |last2=Institute for Health Metrics and Evaluation |author-link2=Institute for Health Metrics and Evaluation |last3=UNICEF |author-link3=UNICEF |date=2024 |publisher=Health Effects Institute |pages=21–23 |issn=2578-6873 |archive-date=3 July 2025 |access-date=23 July 2025 |archive-url=https://web.archive.org/web/20250703232128/https://www.stateofglobalair.org/sites/default/files/documents/2024-06/soga-2024-report_0.pdf |url-status=live }}</ref> Children in low- or middle-income countries are exposed to higher levels of fine particulate matter than those in high income countries.<ref name=":8">{{Cite book |url=https://www.who.int/publications/i/item/air-pollution-and-child-health |title=Air pollution and child health: prescribing clean air. Summary. |date=2018 |publisher=World Health Organization |location=Geneva |pages=2–6 |archive-date=16 September 2024 |access-date=26 August 2024 |archive-url=https://web.archive.org/web/20240916165913/https://www.who.int/publications/i/item/air-pollution-and-child-health |url-status=live }}</ref> Further health effects of air pollution on children include asthma, pneumonia, and lower respiratory tract infections.<ref name=":9">{{Cite book |last1=Gordon |first1=Bruce |url=https://www.who.int/publications/i/item/9241591560 |title=Inheriting the World: The Atlas of Children's Health and the Environment |last2=Mackay |first2=Richard |last3=Rehfuess |first3=Eva |date=2004 |publisher=World Health Organization |chapter=Polluted Cities: The Air Children Breathe}}</ref> There is possibly a link between exposure to air pollution during pregnancy and after birth and autism in children.<ref>{{Cite journal |last1=Dutheil |first1=Frédéric |last2=Comptour |first2=Aurélie |last3=Morlon |first3=Roxane |last4=Mermillod |first4=Martial |last5=Pereira |first5=Bruno |last6=Baker |first6=Julien S. |last7=Charkhabi |first7=Morteza |last8=Clinchamps |first8=Maëlys |last9=Bourdel |first9=Nicolas |date=2021 |title=Autism spectrum disorder and air pollution: A systematic review and meta-analysis |url=https://linkinghub.elsevier.com/retrieve/pii/S0269749121004383 |journal=Environmental Pollution |language=en |volume=278 |article-number=116856 |doi=10.1016/j.envpol.2021.116856 |pmid=33714060 |bibcode=2021EPoll.27816856D |archive-date=22 January 2025 |access-date=18 January 2025 |archive-url=https://web.archive.org/web/20250122222308/https://linkinghub.elsevier.com/retrieve/pii/S0269749121004383 |url-status=live }}</ref><ref>{{Cite journal |last1=Kang |first1=Ni |last2=Sargsyan |first2=Suzan |last3=Chough |first3=Ino |last4=Petrick |first4=Lauren |last5=Liao |first5=Jiawen |last6=Chen |first6=Wu |last7=Pavlovic |first7=Nathan |last8=Lurmann |first8=Frederick W. |last9=Martinez |first9=Mayra P. |last10=McConnell |first10=Rob |last11=Xiang |first11=Anny H. |last12=Chen |first12=Zhanghua |date=2024 |title=Dysregulated metabolic pathways associated with air pollution exposure and the risk of autism: Evidence from epidemiological studies |journal=Environmental Pollution |volume=361 |article-number=124729 |doi=10.1016/j.envpol.2024.124729 |pmid=39147228 |pmc=11902886 |issn=0269-7491}}</ref>
Many of these relationships could previously only be described as correlations, as study designs that demonstrate causation are difficult or impossible to conduct in environmental medicine. This would require a randomized controlled trial. Scientists at BIPS in Bremen were able to demonstrate a causal relationship for at least some health problems (e.g. diabetes and high blood pressure) using a special study design.<ref>{{Cite web |date=2025-10-09 |title=Clean air protects children from high blood pressure and elevated diabetes markers |url=https://www.bips-institut.de/en/media/press/single-view/saubere-luft-schuetzt-kinder-vor-hohem-blutdruck-und-erhoehten-diabetes-markern.html |access-date=2025-11-05 |website=www.bips-institut.de |language=en-GB}}</ref>
=== Brain health === {{see also|Brain health and pollution}}
Air pollution is linked to various diseases of the brain.<ref>{{Cite journal |last1=Huang |first1=Xinmei |last2=Steinmetz |first2=Jaimie |last3=Marsh |first3=Elizabeth K. |last4=Aravkin |first4=Aleksandr Y. |last5=Ashbaugh |first5=Charlie |last6=Murray |first6=Christopher J. L. |last7=Yang |first7=Fanghan |last8=Ji |first8=John S. |last9=Zheng |first9=Peng |last10=Sorensen |first10=Reed J. D. |last11=Wozniak |first11=Sarah |last12=Hay |first12=Simon I. |last13=McLaughlin |first13=Susan A. |last14=Garcia |first14=Vanessa |last15=Brauer |first15=Michael |date=May 2025 |title=A systematic review with a Burden of Proof meta-analysis of health effects of long-term ambient fine particulate matter (PM2.5) exposure on dementia |journal=Nature Aging |language=en |volume=5 |issue=5 |pages=897–908 |doi=10.1038/s43587-025-00844-y |issn=2662-8465 |pmc=12092285 |pmid=40119171}}</ref> It increases the risk of dementia.<ref>{{Cite journal |last1=Livingston |first1=Gill |last2=Huntley |first2=Jonathan |last3=Liu |first3=Kathy Y. |last4=Costafreda |first4=Sergi G. |last5=Selbæk |first5=Geir |last6=Alladi |first6=Suvarna |last7=Ames |first7=David |last8=Banerjee |first8=Sube |last9=Burns |first9=Alistair |last10=Brayne |first10=Carol |last11=Fox |first11=Nick C. |last12=Ferri |first12=Cleusa P. |last13=Gitlin |first13=Laura N. |last14=Howard |first14=Robert |last15=Kales |first15=Helen C. |date=2024-08-10 |title=Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission |url=https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(24)01296-0/abstract |journal=The Lancet |language=English |volume=404 |issue=10452 |pages=572–628 |doi=10.1016/S0140-6736(24)01296-0 |issn=0140-6736 |pmid=39096926 |bibcode=2024Lanc..404..572L |archive-date=6 August 2024 |access-date=22 July 2025 |archive-url=https://web.archive.org/web/20240806162628/https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(24)01296-0/abstract |url-status=live }}</ref><ref>{{Cite journal |last1=Best Rogowski |first1=Clare B |last2=Bredell |first2=Christiaan |last3=Shi |first3=Yan |last4=Tien-Smith |first4=Alexandra |last5=Szybka |first5=Magdalena |last6=Fung |first6=Kwan Wai |last7=Hong |first7=Lucy |last8=Phillips |first8=Veronica |last9=Jovanovic Andersen |first9=Zorana |last10=Sharp |first10=Stephen J |last11=Woodcock |first11=James |last12=Brayne |first12=Carol |last13=Navaratnam |first13=Annalan |last14=Khreis |first14=Haneen |date=July 2025 |title=Long-term air pollution exposure and incident dementia: a systematic review and meta-analysis |journal=The Lancet Planetary Health |language=en |volume=9 |issue=7 |page=101266 |doi=10.1016/S2542-5196(25)00118-4 |pmid=40716448 |doi-access=free }}</ref> Indoor air pollution exposure during childhood may negatively affect cognitive function and neurodevelopment.<ref>{{cite journal |last1=Julvez |first1=Jordi |last2=López-Vicente |first2=Mónica |last3=Warembourg |first3=Charline |last4=Maitre |first4=Lea |last5=Philippat |first5=Claire |last6=Gützkow |first6=Kristine B. |last7=Guxens |first7=Monica |last8=Evandt |first8=Jorunn |last9=Andrusaityte |first9=Sandra |last10=Burgaleta |first10=Miguel |last11=Casas |first11=Maribel |last12=Chatzi |first12=Leda |last13=de Castro |first13=Montserrat |last14=Donaire-González |first14=David |last15=Gražulevičienė |first15=Regina |last16=Hernandez-Ferrer |first16=Carles |last17=Heude |first17=Barbara |last18=Mceachan |first18=Rosie |last19=Mon-Williams |first19=Mark |last20=Nieuwenhuijsen |first20=Mark |last21=Robinson |first21=Oliver |last22=Sakhi |first22=Amrit K. |last23=Sebastian-Galles |first23=Nuria |last24=Slama |first24=Remy |last25=Sunyer |first25=Jordi |last26=Tamayo-Uria |first26=Ibon |last27=Thomsen |first27=Cathrine |last28=Urquiza |first28=Jose |last29=Vafeiadi |first29=Marina |last30=Wright |first30=John |last31=Basagaña |first31=Xavier |last32=Vrijheid |first32=Martine |title=Early life multiple exposures and child cognitive function: A multi-centric birth cohort study in six European countries |journal=Environmental Pollution |date=1 September 2021 |volume=284 |article-number=117404 |doi=10.1016/j.envpol.2021.117404 |pmid=34077897 |pmc=8287594 |bibcode=2021EPoll.28417404J |language=en |issn=0269-7491}}</ref><ref name="10.1016/j.pharmthera.2020.107523">{{cite journal |last1=Costa |first1=Lucio G. |last2=Cole |first2=Toby B. |last3=Dao |first3=Khoi |last4=Chang |first4=Yu-Chi |last5=Coburn |first5=Jacki |last6=Garrick |first6=Jacqueline M. |date=2020 |title=Effects of air pollution on the nervous system and its possible role in neurodevelopmental and neurodegenerative disorders |journal=Pharmacology & Therapeutics |volume=210 |article-number=107523 |doi=10.1016/j.pharmthera.2020.107523 |issn=1879-016X |pmc=7245732 |pmid=32165138}}</ref> Prenatal exposure may also affect neurodevelopment.<ref>{{cite journal |last1=Volk |first1=Heather E. |last2=Perera |first2=Frederica |last3=Braun |first3=Joseph M. |last4=Kingsley |first4=Samantha L. |last5=Gray |first5=Kimberly |last6=Buckley |first6=Jessie |last7=Clougherty |first7=Jane E. |last8=Croen |first8=Lisa A. |last9=Eskenazi |first9=Brenda |last10=Herting |first10=Megan |last11=Just |first11=Allan C. |last12=Kloog |first12=Itai |last13=Margolis |first13=Amy |last14=McClure |first14=Leslie A. |last15=Miller |first15=Rachel |last16=Levine |first16=Sarah |last17=Wright |first17=Rosalind |title=Prenatal air pollution exposure and neurodevelopment: A review and blueprint for a harmonized approach within ECHO |journal=Environmental Research |date=2021 |volume=196 |article-number=110320 |doi=10.1016/j.envres.2020.110320 |pmid=33098817 |pmc=8060371 |bibcode=2021ER....19610320V |language=en |issn=0013-9351}}</ref><ref>{{cite journal |last1=Shang |first1=Li |last2=Yang |first2=Liren |last3=Yang |first3=Wenfang |last4=Huang |first4=Liyan |last5=Qi |first5=Cuifang |last6=Yang |first6=Zixuan |last7=Fu |first7=Zhuxuan |last8=Chung |first8=Mei Chun |title=Effects of prenatal exposure to NO<sub>2</sub> on children's neurodevelopment: a systematic review and meta-analysis |journal=Environmental Science and Pollution Research |date=2020 |volume=27 |issue=20 |pages=24786–24798 |doi=10.1007/s11356-020-08832-y |pmc=7329770 |pmid=32356052 |bibcode=2020ESPR...2724786S |s2cid=216650267 |language=en |issn=1614-7499}}</ref> Exposure to air pollution may contribute to neurodegenerative diseases such as Parkinson's disease.<ref name="10.1016/j.pharmthera.2020.107523" />
Exposure to air pollution may also drive mental health issues, such as depression and anxiety.<ref>{{Cite journal |last1=Cao |first1=Tingting |last2=Tian |first2=Meichen |last3=Hu |first3=Han |last4=Yu |first4=Qingqing |last5=You |first5=Jing |last6=Yang |first6=Yishu |last7=An |first7=Zhen |last8=Song |first8=Jie |last9=Zhang |first9=Guofu |last10=Zhang |first10=Guicheng |last11=Wu |first11=Weidong |last12=Wu |first12=Hui |date=2024-03-01 |title=The relationship between air pollution and depression and anxiety disorders – A systematic evaluation and meta-analysis of a cohort-based study |url=https://journals.sagepub.com/doi/10.1177/00207640231197941?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed |journal=International Journal of Social Psychiatry |language=en |volume=70 |issue=2 |pages=241–270 |doi=10.1177/00207640231197941 |pmid=37753871 |issn=0020-7640|url-access=subscription }}</ref> In particular, air pollution from the use of solid fuels was associated with a higher depression risk.<ref>{{Cite journal |last1=Zhang |first1=Xiaona |last2=Ding |first2=Linlin |last3=Yang |first3=Fen |last4=Qiao |first4=Guiyuan |last5=Gao |first5=Xiaolian |last6=Xiong |first6=Zhenfang |last7=Zhu |first7=Xinhong |date=2024 |title=Association between indoor air pollution and depression: a systematic review and meta-analysis of cohort studies |journal=BMJ Open |volume=14 |issue=5 |article-number=e075105 |doi=10.1136/bmjopen-2023-075105 |doi-access=free|issn=2044-6055 |pmid=38719299|pmc=11086541 }}</ref> Depression risk and suicide was more strongly linked to finer particulate matter (PM<sub>2.5</sub>), compared to coarser particles (PM<sub>10</sub>). The association was strongest for people over the age of 65.<ref>{{Cite journal |last1=Liu |first1=Qisijing |last2=Wang |first2=Wanzhou |last3=Gu |first3=Xuelin |last4=Deng |first4=Furong |last5=Wang |first5=Xueqin |last6=Lin |first6=Hualiang |last7=Guo |first7=Xinbiao |last8=Wu |first8=Shaowei |date=2021 |title=Association between particulate matter air pollution and risk of depression and suicide: a systematic review and meta-analysis |journal=Environmental Science and Pollution Research International |volume=28 |issue=8 |pages=9029–9049 |doi=10.1007/s11356-021-12357-3 |issn=1614-7499 |pmid=33481201|bibcode=2021ESPR...28.9029L }}</ref>
Problems with thinking (cognitive issues) are also associated with air pollution. In people over the age of 40, both NO<sub>x</sub> and PM<sub>2.5</sub> have been linked to general cognitive problems. PM<sub>2.5</sub> was also associated with reduced verbal fluency (for instance, number of animals one can list in a minute) and worse executive functions (like attention and working memory). Similarly, children tended to fare worse in tests involving working memory when there was NO<sub>x</sub>, PM<sub>2.5</sub>, or PM<sub>10</sub> pollution.<ref>{{Cite journal |last1=Thompson |first1=Rhiannon |last2=Smith |first2=Rachel B. |last3=Karim |first3=Yasmin Bou |last4=Shen |first4=Chen |last5=Drummond |first5=Kayleigh |last6=Teng |first6=Chloe |last7=Toledano |first7=Mireille B. |date=2023 |title=Air pollution and human cognition: A systematic review and meta-analysis |url=https://linkinghub.elsevier.com/retrieve/pii/S004896972207334X |journal=Science of the Total Environment |volume=859 |issue=Pt 2 |article-number=160234 |doi=10.1016/j.scitotenv.2022.160234 |pmid=36427724 |bibcode=2023ScTEn.85960234T |hdl=10044/1/101759 |issn=0048-9697 |hdl-access=free |archive-date=28 February 2025 |access-date=30 January 2025 |archive-url=https://web.archive.org/web/20250228015633/https://linkinghub.elsevier.com/retrieve/pii/S004896972207334X |url-status=live }}</ref>
=== Physical activity === The health benefits of physical exercise may be modulated by air quality. A 2025 cross-national study involving 1.5 million adults demonstrated that high levels of ambient fine particulate matter (PM <sub>2.5</sub> μg/m³) can significantly diminish the protective effects of leisure-time physical activity against all-cause and cause-specific mortality.<ref name="ku">{{cite journal |vauthors=Ku PW, Steptoe A, Hamer M, et al.|title=Does ambient PM2.5 reduce the protective association of leisure-time physical activity with mortality? A systematic review, meta-analysis, and individual-level pooled analysis of cohort studies involving 1.5 million adults |journal=BMC Medicine |volume=23 |issue=1 |pages=647 |date=November 2025 |pmid=41310726 |pmc=12661664 |doi=10.1186/s12916-025-04496-y|doi-access=free}}</ref>
The study identified a critical threshold of 25 μg/m³ exposure; below this annual average concentration, regular exercise reduced all-cause mortality by approximately 30%. However, this benefit was halved (to 12–15%) when concentrations exceeded 25 μg/m³ exposure.<ref name=ku/>
== Social and environmental impacts ==
=== Acid rain === thumb|Monument damaged by acid rain.|alt=Statue with a nose eroded away [[File:Acid rain woods1.JPG|thumb|Effects of acid rain in the Jizera Mountains, Czech Republic.|alt=dead tree trunks which have lost all their leafs]] Naturally, water in the atmosphere is slightly acidic. Some pollutants can form strong acids, making rainwater much more acidic. Key acids that cause acid rain are nitric acid (HNO<sub>3</sub>), sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) and hydrochloric acid (HCl). HCl comes from coal combustion. H<sub>2</sub>SO<sub>4</sub> forms from SO<sub>2</sub>, which comes from the burning of coal and oil and from some industrial processes like smelting. HNO<sub>3</sub> forms from NO<sub>2</sub>, which is formed during high-temperature combustion. The term acid rain not only refers to rain, but also to pollution from hail, fog, and snow.<ref name=Seigneur_acid_rain>{{Citation |title=Environmental Impacts |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |pages=306–308 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/air-pollution/environmental-impacts/8F47851775A4681857CEB599B3C32DF5 |access-date=2025-06-04 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.013 |isbn=978-1-108-48163-2|url-access=subscription }}</ref>
Acid rain caused substantial damage in the 1970s, including lake acidification and forest diebacks in Northern Europe. Due to the changed acidity in water bodies and soils, essential nutrients such as magnesium and calcium became soluble and could be washed away. Other elements, such as aluminium, which were toxic to vegetation, became available for the roots to absorb. Acid rain also impacts buildings and statues made of specific stones (e.g. marble, calcite or freestone), as the stone reacts chemically with the acid in the water and erodes.<ref name=Seigneur_acid_rain />
=== Water and soil pollution === Air pollution can settle (deposit) on the soil or in water, causing various problems. For instance, ammonia and nitric acid in the air can contribute to nutrient pollution in water, a process called eutrophication. At first, the extra nutrients help plants grow, but dense plant growth blocks sunlight from reaching the bottom. Plants in the lower layers then die, and with fewer plants producing oxygen, the oxygen level drops. This harms organisms that need oxygen to live,<ref>{{Citation |title=Environmental Impacts |date=2019 |work=Air Pollution: Concepts, Theory, and Applications |pages=308–309 |editor-last=Seigneur |editor-first=Christian |url=https://www.cambridge.org/core/books/air-pollution/environmental-impacts/8F47851775A4681857CEB599B3C32DF5 |access-date=2025-06-04 |place=Cambridge |publisher=Cambridge University Press |doi=10.1017/9781108674614.013 |isbn=978-1-108-48163-2|url-access=subscription }}</ref> and can lead to the loss of sensitive species.<ref>{{Cite web |date=29 November 2018 |title=Eutrophication of terrestrial ecosystems due to air pollution |url=https://www.eea.europa.eu/airs/2018/natural-capital/eutrophication-of-terrestrial-ecosystems |access-date=2025-07-12 |website=European Environment Agency |language=en |archive-date=21 June 2025 |archive-url=https://web.archive.org/web/20250621115307/https://www.eea.europa.eu/airs/2018/natural-capital/eutrophication-of-terrestrial-ecosystems/ |url-status=live }}</ref>
=== Agricultural effects === Various studies have estimated the impacts of air pollution on agriculture, especially ozone. Ozone acts as an oxidant and reduces photosynthesis. One study estimated that for a 1% increase in ozone concentrations, there would be a global economic loss of $10 billion each year. For PM<sub>2.5</sub>, a 1% increase in pollution levels would lead to about $5 billion in losses, especially in colder climates.<ref name="Dong2023">{{cite journal|title=Air pollution as a substantial threat to the improvement of agricultural total factor productivity: Global evidence|last1=Dong|first1=Daxin|last2=Wang|first2=Jiaxin|journal=Environment International|volume=173|date=2023|article-number=107842 |doi=10.1016/j.envint.2023.107842|pmid=36863165 |bibcode=2023EnInt.17307842D |doi-access=free}}</ref> After air pollutants enter the agricultural environment, they not only directly affect agricultural production and quality, but also enter agricultural waters and soil.<ref>{{Cite journal |last1=Li |first1=Houjian |last2=Tang |first2=Mengqian |last3=Cao |first3=Andi |last4=Guo |first4=Lili |date=2022 |title=Assessing the relationship between air pollution, agricultural insurance, and agricultural green total factor productivity: evidence from China |url=https://link.springer.com/10.1007/s11356-022-21287-7 |journal=Environmental Science and Pollution Research |language=en |volume=29 |issue=52 |pages=78381–78395 |doi=10.1007/s11356-022-21287-7 |pmid=35689771 |bibcode=2022ESPR...2978381L |s2cid=249551277 |issn=0944-1344 |url-access=subscription |archive-date=7 December 2022 |access-date=20 November 2022 |archive-url=https://web.archive.org/web/20221207040939/https://link.springer.com/article/10.1007/s11356-022-21287-7 |url-status=live }}</ref> Air pollution further decreases the productivity of laborers via health impacts.<ref name="Dong2023" />
The COVID-19 lockdowns created a natural experiment to examine the links between air quality and agricultural output. In India, the lockdown improved air quality, which enhanced surface greenness and photosynthetic activity. Both forests and crops saw positive effects; the improvement was most pronounced for crops.<ref>{{Cite journal |last1=Kashyap |first1=Rahul |last2=Kuttippurath |first2=J. |last3=Patel |first3=V. K. |date=2023 |title=Improved air quality leads to enhanced vegetation growth during the COVID–19 lockdown in India |journal=Applied Geography |language=en |volume=151 |article-number=102869 |doi=10.1016/j.apgeog.2022.102869 |pmid=36619606 |pmc=9805897 |bibcode=2023AppGe.15102869K |s2cid=255439854 |issn=0143-6228}}</ref>
=== Economic effects === Air pollution has a strong impact on the economy via its health effects – such as reduced productivity at work and the costs of healthcare – and its effects on crop yield. It also affects tourism, biodiversity, forestry, and water quality. Tourism may be negatively affected due to decreased visibility and damage to cultural heritage.<ref>{{Cite book |last=OECD |url=https://www.oecd.org/content/dam/oecd/en/publications/reports/2016/06/the-economic-consequences-of-outdoor-air-pollution_g1g68583/9789264257474-en.pdf |title=The Economic Consequences of Outdoor Air Pollution |publisher=OECD Publishing |year=2016 |location=Paris |page=22 |doi=10.1787/9789264257474-en|isbn=978-92-64-25746-7 }}</ref> People may be more prone to accidents due to air pollution. Increased NO<sub>2</sub> levels are for instance linked to construction site accidents.<ref name="Lavy Rachkovski Yoresh 2022 p.">{{cite report |url=https://www.nber.org/papers/w30715 |title=Heads Up: Does Air Pollution Cause Workplace Accidents? |last1=Lavy |first1=Victor |last2=Rachkovski |first2=Genia |last3=Yoresh |first3=Omry |year=2022 |publisher=National Bureau of Economic Research |doi=10.3386/w30715 |page= |publication-place=Cambridge, MA |archive-date=5 October 2023 |access-date=15 September 2023 |archive-url=https://web.archive.org/web/20231005195843/https://www.nber.org/papers/w30715 |url-status=live |doi-access=free }}</ref>
In terms of the welfare cost on human health (non-market costs), a World Bank study found that PM<sub>2.5</sub> pollution in 2019 cost the world economy over $8 trillion, over 6% of global GDP. In India and China, the loss of GDP was over 10%. About 85% of this loss globally came from the loss of life, the rest from increased ill health.<ref name=":15">{{Cite book |last=World Bank |url=https://documents1.worldbank.org/curated/en/455211643691938459/pdf/The-Global-Health-Cost-of-PM-2-5-Air-Pollution-A-Case-for-Action-Beyond-2021.pdf |title=The Global Health Cost of PM2.5 Air Pollution: A Case for Action Beyond 2021 |date=2022-04-12 |publisher=The World Bank |isbn=978-1-4648-1816-5 |language=en |doi=10.1596/978-1-4648-1816-5 |hdl=10986/36501 |archive-date=24 January 2025 |access-date=11 April 2025 |archive-url=https://web.archive.org/web/20250124140007/https://documents1.worldbank.org/curated/en/455211643691938459/pdf/The-Global-Health-Cost-of-PM-2-5-Air-Pollution-A-Case-for-Action-Beyond-2021.pdf |url-status=live }}</ref>{{Rp|page=|pages=23–24}} The costs of lives lost are calculated using the Value of Statistical Life, a number that tries to estimate how much people would be willing to pay to reduce their risk of dying.<ref name=":15" />{{Rp|page=xiii|pages=}} This number differs by country and is difficult to estimate for low- and middle-income countries.<ref>{{Cite journal |last1=Wang |first1=Siyuan |last2=Song |first2=Rong |last3=Xu |first3=Zhiwei |last4=Chen |first4=Mingsheng |last5=Di Tanna |first5=Gian Luca |last6=Downey |first6=Laura |last7=Jan |first7=Stephen |last8=Si |first8=Lei |date=2024 |title=The costs, health and economic impact of air pollution control strategies: a systematic review |journal=Global Health Research and Policy |language=en |volume=9 |issue=1 |page=30 |doi=10.1186/s41256-024-00373-y |issn=2397-0642 |pmc=11337783 |pmid=39164785 |doi-access=free}}</ref>
The direct market impacts on productivity loss, healthcare use, and crop losses were estimated to rise to 1% of GDP by 2060, according to the OECD. The Caspian region and China would see the largest impact.<ref>{{Cite book |last=OECD |url=https://www.oecd.org/content/dam/oecd/en/publications/reports/2016/06/the-economic-consequences-of-outdoor-air-pollution_g1g68583/9789264257474-en.pdf |title=The Economic Consequences of Outdoor Air Pollution |publisher=OECD Publishing |year=2016 |location=Paris |pages=14–15 |doi=10.1787/9789264257474-en |isbn=978-92-64-25746-7 |archive-date=10 May 2025 |access-date=11 April 2025 |archive-url=https://web.archive.org/web/20250510190842/https://www.oecd.org/content/dam/oecd/en/publications/reports/2016/06/the-economic-consequences-of-outdoor-air-pollution_g1g68583/9789264257474-en.pdf |url-status=live }}</ref> Air pollution also has an impact on energy production, as it reduces the amount of sunlight that reaches solar panels. It also causes the panels to become dirty, further reducing their energy output.<ref>{{Cite journal |last1=Song |first1=Zhe |last2=Liu |first2=Jia |last3=Yang |first3=Hongxing |date=2021 |title=Air pollution and soiling implications for solar photovoltaic power generation: A comprehensive review |url=https://www.sciencedirect.com/science/article/abs/pii/S030626192100667X |journal=Applied Energy |volume=298 |article-number=117247 |doi=10.1016/j.apenergy.2021.117247 |bibcode=2021ApEn..29817247S |hdl=10397/102795 |issn=0306-2619 |hdl-access=free |archive-date=5 December 2024 |access-date=21 April 2025 |archive-url=https://web.archive.org/web/20241205145043/https://www.sciencedirect.com/science/article/abs/pii/S030626192100667X |url-status=live }}</ref>
== History of air pollution == Mummified remains of people in Peru, Egypt and Britain show that ancient people in these regions suffered from blackening of the lungs caused by open fires in poorly ventilated homes. Recorded complaints of air pollution go back to the Greek and Roman period. Outdoor air pollution became a problem with the rise of cities, caused by household smoke and by early industrial activities (such as smelting and mining). In particular, lead levels, found in Arctic ice cores, were about ten times higher in the Roman period than in the period before.<ref>{{Citation |last=Mosley |first=Stephen |title=Environmental History of Air Pollution and Protection |date=2014 |work=The Basic Environmental History |volume=4 |pages=144–148 |editor-last=Agnoletti |editor-first=Mauro |url=https://link.springer.com/chapter/10.1007/978-3-319-09180-8_5 |access-date=2025-03-29 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-09180-8_5 |isbn=978-3-319-09179-2 |editor2-last=Neri Serneri |editor2-first=Simone|url-access=subscription }}</ref> ===Industrial Revolution=== During the Industrial Revolution, outdoor air pollution started to rise strongly, mostly due to the large-scale burning of coal. This occurred first in Britain, then in the rest of Northern Europe and the United States. By the 19th century, buildings around industrial plants started to blacken, while plants and trees in public parks started to wither. Smoke-induced fogs reduced the amount of sunlight city-dwellers got, contributing to cases of rickets, a childhood disease caused by lack of sunlight and poor diet.<ref name=":14">{{Citation |last=Mosley |first=Stephen |title=Environmental History of Air Pollution and Protection |date=2014 |work=The Basic Environmental History |volume=4 |pages=148–156 |editor-last=Agnoletti |editor-first=Mauro |url=https://link.springer.com/chapter/10.1007/978-3-319-09180-8_5 |access-date=2025-03-29 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-09180-8_5 |isbn=978-3-319-09179-2 |editor2-last=Neri Serneri |editor2-first=Simone |url-access=subscription |archive-date=29 March 2025 |archive-url=https://web.archive.org/web/20250329093617/https://link.springer.com/chapter/10.1007/978-3-319-09180-8_5 |url-status=live }}</ref>
However, the business and political leadership of the industrial cities were enthusiastic backers of the industry: heavy black smoke meant prosperity, high profits, and high wages.<ref>Stephen Mosley, "Selling the smokeless city: advertising images and smoke abatement in urban-industrial Britain, circa 1840–1960." ''History and Technology'' 32.2 (2016): 201-211 [https://eprints.leedsbeckett.ac.uk/id/eprint/2935/1/Mosley%20History%20and%20Technology%20paper.docx online] {{Webarchive|url=https://web.archive.org/web/20250701183646/https://eprints.leedsbeckett.ac.uk/id/eprint/2935/1/Mosley%20History%20and%20Technology%20paper.docx |date=1 July 2025 }}.</ref> alt=See caption|thumb|Poster in the Soviet Union praising "The smoke of chimneys is the breath of Soviet Russia."
===Miasma theory=== The miasma theory was a prominent idea in the 18th and 19th centuries that gave a false explanation of how deadly epidemics like cholera, yellow fever, and malaria ("bad air") originated and spread. It said that illnesses were caused by breathing in a mysterious "miasma," a harmful vapor that arose from decaying organic matter. Epidemics often came in the summer because that is when people spent more time outside. The theory motivated an enormous emphasis on public sanitation in major cities to remove smelly pollution, especially human and animal excrement, from streets and back alleys. The theory collapsed when physicians accepted the new germ theory of disease in the late 19th century. Germs coughed up by an infected person or spread by certain types of mosquitoes or hookworms were the real reason people caught an infectious disease.<ref> John Duffy, ''The Sanitarians: A History of American Public Health'' (1990) pp.67-77, 129. </ref>
===Anti-smoke action and modern protections=== In the 1830s, anti-smoke groups emerged in Britain, followed by groups in the United States in the 1880s. Legislation against pollution was weak however, as it was seen to conflict with industrial interests. During the interwar period of 1920s and 1930s, a move from coal to gas and oil meant there was less air pollution, but this trend reversed when World War II broke out.<ref name=":14" /> The United Kingdom suffered its worst air pollution during the 1952 Great Smog of London, with some 12,000 deaths, which led to the Clean Air Act 1956.<ref name="EHP_112_1">{{cite journal |last1=Bell |first1=Michelle L. |last2=Davis |first2=Devra L. |last3=Fletcher |first3=Tony |date=2004 |title=A Retrospective Assessment of Mortality from the London Smog Episode of 1952: The Role of Influenza and Pollution |journal=Environ Health Perspect |volume=112 |issue=1 |pages=6–8 |bibcode=2004EnvHP.112....6B |doi=10.1289/ehp.6539 |pmc=1241789 |pmid=14698923 |s2cid=13045119}}</ref> The 1948 Donora smog in the US, killing 20 people, prompted the US to start regulating air pollution.<ref name=":14" /><ref>{{cite book |last=Davis |first=Devra |url=https://archive.org/details/whensmokeranlike00davi |title=When Smoke Ran Like Water: Tales of Environmental Deception and the Battle Against Pollution |publisher=Basic Books |year=2002 |isbn=978-0-465-01521-4 |url-access=registration}}</ref> Japan followed in 1960, but other heavily polluted regions, such as the Soviet Union and China, did not implement effective regulation.<ref name=":14" />
Technological disasters have caused severe problems with air pollution. The world's worst pollution disaster was the 1984 Bhopal Disaster in India. Leaked industrial vapours from the Union Carbide factory (later bought by the Dow Chemical Company), killed at least 20,000 people and affected about 600,000.<ref name="Mosley54">{{Citation |last=Silei |first=Gianni |title=Environmental History of Air Pollution and Protection |date=2014 |work=The Basic Environmental History |volume=4 |pages=248–249 |editor-last=Agnoletti |editor-first=Mauro |url=https://link.springer.com/chapter/10.1007/978-3-319-09180-8_8 |access-date=2025-03-29 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-09180-8_8 |isbn=978-3-319-09179-2 |editor2-last=Neri Serneri |editor2-first=Simone |url-access=subscription |archive-date=2 June 2018 |archive-url=https://web.archive.org/web/20180602071606/https://link.springer.com/chapter/10.1007%2F978-3-319-09180-8_8 |url-status=live }}</ref>
In the 1950s, smog in developed countries was regulated, but other pollutants were not. Acid rain, caused by sulfur dioxide, became a major issue as it spread across borders. In the 1990s, for instance, Japan experienced acid rain from Chinese and Korean industry. International cooperation was needed to curb acid rain, and various coalitions were started. In 1975, it was discovered that certain chemicals caused a hole in the ozone layer; thanks to successful international negotiations, these chemicals were banned worldwide. There has been far less success in combatting climate change, and greenhouse gas emissions, mostly from fossil fuels, continue to rise.<ref name='Raiser2020'>{{Cite journal |last1=Raiser |first1=Kilian |last2=Kornek |first2=Ulrike |last3=Flachsland |first3=Christian |last4=Lamb |first4=William F |date=2020 |title=Is the Paris Agreement effective? A systematic map of the evidence |journal=Environmental Research Letters |volume=15 |issue=8 |page=083006 |bibcode=2020ERL....15h3006R |doi=10.1088/1748-9326/ab865c |issn=1748-9326 |doi-access=free }}</ref>
== Measurement and monitoring ==
=== Monitoring === {{Further|Air pollution measurement| Environmental monitoring}}[[File:New Delhi Met Office, India 02.jpg|thumb|Air quality monitoring, New Delhi, India.|alt=Display showing poor air quality for PM2.5 and PM10]]Air pollution can be monitored using different techniques. For instance, satellites and remote sensing are used to track PM, NO<sub>2,</sub> and ozone.<ref>{{Cite web |title=Air Quality from Space |url=https://airquality.gsfc.nasa.gov/ |access-date=2025-02-23 |website=airquality.gsfc.nasa.gov |archive-date=22 February 2025 |archive-url=https://web.archive.org/web/20250222112805/https://airquality.gsfc.nasa.gov/ |url-status=live }}</ref> Many regions have a network of monitoring stations, with good coverage in India, China, Europe, and the US. Poor coverage exists however for a number of highly polluted countries, such as Chad and Iran. The density of measurements is improving as there are more low-cost techniques to measure air pollution.<ref>{{Cite report |url=https://www.iqair.com/dl/2023_World_Air_Quality_Report.pdf |title=2023 World Air Quality Report |last=IQAir |author-link=IQAir |date=2024 |page=11}}</ref> Low-cost monitors can also be used for indoor air quality monitoring.<ref>{{Cite web |last=US EPA |date=2019-09-16 |title=Low–Cost Air Pollution Monitors and Indoor Air Quality |url=https://www.epa.gov/indoor-air-quality-iaq/low-cost-air-pollution-monitors-and-indoor-air-quality |access-date=2025-02-23 |website=www.epa.gov |language=en |archive-date=22 February 2025 |archive-url=https://web.archive.org/web/20250222221811/https://www.epa.gov/indoor-air-quality-iaq/low-cost-air-pollution-monitors-and-indoor-air-quality |url-status=live }}</ref> Finally, air quality sensors can be incorporated into drones to measure air pollution higher up in the air.<ref>{{Cite web |title=Monitoring ambient air: choosing a monitoring technique and method |url=https://www.gov.uk/guidance/monitoring-ambient-air-choosing-a-monitoring-technique-and-method |access-date=2025-02-23 |website=GOV.UK |language=en |archive-date=23 November 2024 |archive-url=https://web.archive.org/web/20241123014515/https://www.gov.uk/guidance/monitoring-ambient-air-choosing-a-monitoring-technique-and-method |url-status=live }}</ref> Some websites attempt to map air pollution levels using available data.<ref>{{cite web |title=World Air Map: Live air quality everywhere in the world |url=https://air.plumelabs.com/en/ |access-date=20 December 2021 |website=Plume Labs Air Report |archive-date=30 December 2021 |archive-url=https://web.archive.org/web/20211230101754/https://air.plumelabs.com/en/ |url-status=live }}</ref><ref>{{cite web |title=Live Animated Air Quality Map (AQI, PM2.5...) {{!}} AirVisual |url=https://www.iqair.com/air-quality-map |access-date=27 January 2022 |publisher=IQAir |archive-date=27 January 2022 |archive-url=https://web.archive.org/web/20220127163131/https://www.iqair.com/air-quality-map |url-status=live }}</ref>
Air quality indexes (AQIs) offer a simple way to communicate changes in air quality and associated health risks to a wide audience. An AQI is essentially a health protection tool people can use to help reduce their short-term exposure to air pollution by adjusting activity levels during increased levels of air pollution. These indexes can indicate when air quality is good, when it is dangerous for sensitive groups (e.g. children with asthma) and when it is a general hazard.<ref>{{Cite book |last=Vallero |first=Daniel A. |title=Fundamentals of Air Pollution |date=2014 |publisher=Academic Press |isbn=978-0-12-401733-7|edition=5th|pages=777–779}}</ref>
=== Modelling and inventories === {{Main|Air quality modeling}}
[[File:Portrait of Global Aerosols.jpeg|alt=High resolution map showing wildfire smoke and desert dust over Africa and the Atlantic, sea salt particles in cyclones over the world ocean and sulphate particle pollution from industrial sites over Europe, North America and China|thumb|Map of simulated particle pollution. Wildfire smoke is in green, desert dust is in orange, light blue is sea salt, and white shows sulfate particle pollution.]] When direct data is unavailable or when projecting future air pollutant levels, estimates can be derived using models or emission factors.<ref>{{Cite book |last=Vallero |first=Daniel A. |title=Fundamentals of Air Pollution |date=2014 |publisher=Academic Press |isbn=978-0-12-401733-7|edition=5th|pages=704, 822}}</ref> Air pollutant emission factors are typical values that link the amount of a pollutant released into the air to a related activity. This could for instance be the typical amount of particulate matter released from a coal-power station.<ref>{{Cite web |last=Environment and Climate Change Canada |title=Air pollutant emissions |url=https://www.canada.ca/en/environment-climate-change/services/environmental-indicators/air-pollutant-emissions.html |access-date=2022-06-07 |website=Canada.ca |date=14 June 2010 |archive-date=3 September 2022 |archive-url=https://web.archive.org/web/20220903174228/https://www.canada.ca/en/environment-climate-change/services/environmental-indicators/air-pollutant-emissions.html |url-status=live }}</ref> The United States Environmental Protection Agency has published a compilation of air pollutant emission factors for a wide range of industrial sources,<ref>{{cite web |title=AP 42, Volume I |url=http://www.epa.gov/ttn/chief/ap42/index.html |archive-url=https://web.archive.org/web/20100924132127/http://www.epa.gov/ttn/chief/ap42/index.html |archive-date=24 September 2010 |access-date=29 August 2010 |website=US Environmental Protection Agency}}</ref> as did the European Environment Agency.<ref>{{cite web |date=19 June 2009 |title=EMEP/EEA air pollutant emission inventory guidebook—2009 |url=http://www.eea.europa.eu/publications/emep-eea-emission-inventory-guidebook-2009 |access-date=11 December 2012 |website=Eea.europa.eu |publisher=European Environment Agency |archive-date=14 January 2013 |archive-url=https://web.archive.org/web/20130114012635/http://www.eea.europa.eu/publications/emep-eea-emission-inventory-guidebook-2009 |url-status=live }}</ref>
Air quality models use meteorological and emissions data to simulate how pollutants disperse and react in the atmosphere. Regulatory agencies use them to assess whether a new source of air pollution would exceed acceptable pollution levels, for permitting purposes. They can also be used to predict future pollution levels under different policy scenarios.<ref>{{Cite web |last=US EPA |date=2016-07-14 |title=Air Quality Models |url=https://www.epa.gov/scram/air-quality-models |access-date=2025-04-19 |website=www.epa.gov |language=en |archive-date=5 April 2025 |archive-url=https://web.archive.org/web/20250405090441/https://www.epa.gov/scram/air-quality-models |url-status=live }}</ref> There are models for local pollution, but also for cross-boundary pollution.<ref>{{Cite web |date=2016 |title=Air Pollution Modelling |url=https://www.apis.ac.uk/air-pollution-modelling |access-date=2025-04-19 |website= |publisher=Air Pollution Information System |archive-date=26 April 2025 |archive-url=https://web.archive.org/web/20250426045933/https://www.apis.ac.uk/air-pollution-modelling |url-status=live }}</ref>
== Pollution reduction by sector ==
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)<ref>{{cite journal |last1=Camahan |first1=James V. |last2=Thurston |first2=Deborah L. |author2-link=Deborah Thurston |title=Trade-off Modeling for Product and Manufacturing Process Design for the Environment |journal=Journal of Industrial Ecology |date=1998 |volume=2 |issue=1 |pages=79–92 |doi=10.1162/jiec.1998.2.1.79 |bibcode=1998JInEc...2...79C |s2cid=154730593 |language=en |issn=1530-9290}}</ref> as well as efforts towards renewable energy transitions.<ref>{{cite journal |last1=Jacobson |first1=Mark Z. |last2=von Krauland |first2=Anna-Katharina |last3=Coughlin |first3=Stephen J. |last4=Palmer |first4=Frances C. |last5=Smith |first5=Miles M. |title=Zero air pollution and zero carbon from all energy at low cost and without blackouts in variable weather throughout the U.S. with 100% wind-water-solar and storage |journal=Renewable Energy |date=2022 |volume=184 |pages=430–442 |doi=10.1016/j.renene.2021.11.067 |bibcode=2022REne..184..430J |s2cid=244820608 |language=en |issn=0960-1481 |url=https://www.sciencedirect.com/science/article/abs/pii/S0960148121016499 |url-access=subscription |archive-date=18 January 2022 |access-date=27 January 2022 |archive-url=https://web.archive.org/web/20220118182656/https://www.sciencedirect.com/science/article/abs/pii/S0960148121016499 |url-status=live }}</ref><ref>{{cite journal |last1=Gielen |first1=Dolf |last2=Boshell |first2=Francisco |last3=Saygin |first3=Deger |last4=Bazilian |first4=Morgan D. |last5=Wagner |first5=Nicholas |last6=Gorini |first6=Ricardo |title=The role of renewable energy in the global energy transformation |journal=Energy Strategy Reviews |date=2019 |volume=24 |pages=38–50 |doi=10.1016/j.esr.2019.01.006 |bibcode=2019EneSR..24...38G |s2cid=135283552 |language=en |issn=2211-467X|doi-access=free }}</ref>
=== Industry and waste === [[File:Thermal-oxidizer-rto.jpg|thumb|Thermal oxidisers are air pollution abatement options for hazardous air pollutants (HAPs), volatile organic compounds (VOCs), and odorous emissions.|alt=a smokestack attached to a metal box]] Various pollution control technologies and strategies are available to reduce air pollution. For instance, industrial plants can install scrubbers, such as flue-gas desulfurization or catalysts to remove NO<sub>x</sub>. In the power sector, a very effective means to reduce air pollution is the transition to renewable energy (e.g. solar and wind energy) or nuclear power.<ref name=":2">{{Cite journal |last1=Amann |first1=Markus |last2=Kiesewetter |first2=Gregor |last3=Schöpp |first3=Wolfgang |last4=Klimont |first4=Zbigniew |last5=Winiwarter |first5=Wilfried |last6=Cofala |first6=Janusz |last7=Rafaj |first7=Peter |last8=Höglund-Isaksson |first8=Lena |last9=Gomez-Sabriana |first9=Adriana |last10=Heyes |first10=Chris |last11=Purohit |first11=Pallav |last12=Borken-Kleefeld |first12=Jens |last13=Wagner |first13=Fabian |last14=Sander |first14=Robert |last15=Fagerli |first15=Hilde |date=2020 |title=Reducing global air pollution: the scope for further policy interventions |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=378 |issue=2183 |article-number=20190331 |bibcode=2020RSPTA.37890331A |doi=10.1098/rsta.2019.0331 |pmc=7536039 |pmid=32981437}}</ref> Switching from coal-fired power plants to fossil gas reduces air pollution, but does not eliminate it.<ref>{{Cite journal |last=Burney |first=Jennifer A. |date=2020-01-06 |title=The downstream air pollution impacts of the transition from coal to natural gas in the United States |url=https://www.nature.com/articles/s41893-019-0453-5 |journal=Nature Sustainability |language=en |volume=3 |issue=2 |pages=152–160 |doi=10.1038/s41893-019-0453-5 |bibcode=2020NatSu...3..152B |issn=2398-9629|url-access=subscription }}</ref>
A growing number of countries regulate waste, through national or city-wide waste management systems, opening managed landfills, landfill gas capture (for electricity production), and waste separation.{{sfn|United Nations Environmental Programme|2021|pp=37–39}} In agriculture, air pollution can be minimized by not overusing fertilizers and by not feeding excess protein to livestock.<ref name=":2" />
{{Clear}}
=== Transport === {{Further|Sustainable transport}} [[File:Electric Rickshaws.jpg|thumb|Electric rickshaws in Nepal.|alt=a row of electric rickshaws with a couple of people inside]] [[File:Alicante Tram 5.jpg|thumb|Tram in Alicante, Spain.|alt=see caption]] The avoid-shift-improve framework groups efforts to cut pollution from vehicles into reducing travel, shifting to sustainable transport, and improving vehicle technology.<ref name=":4">{{Cite journal |last1=Leroutier |first1=Marion |last2=Quirion |first2=Philippe |date=2023 |title=Tackling Car Emissions in Urban Areas: Shift, Avoid, Improve |url=https://linkinghub.elsevier.com/retrieve/pii/S0921800923002148 |journal=Ecological Economics |volume=213 |article-number=107951 |doi=10.1016/j.ecolecon.2023.107951 |bibcode=2023EcoEc.21307951L |issn=0921-8009 |archive-date=26 March 2025 |access-date=28 February 2025 |archive-url=https://web.archive.org/web/20250326061144/https://linkinghub.elsevier.com/retrieve/pii/S0921800923002148 |url-status=live }}</ref> Reducing motor vehicle travel can curb pollution. One strategy is to build compact cities, so that amenities are close by and cars are not needed.{{sfn|Ringenson|Kramers|2021|p=218}} Motor traffic can be reduced by creating more walkable cities and by investing in cycling infrastructure.<ref>{{Cite web |title=Blue skies and healthy lives: How active travel is transforming our cities |url=https://www.c40.org/news/how-active-travel-is-transforming-cities/ |access-date=2025-01-10 |website=C40 Cities |language=en-GB |archive-date=10 January 2025 |archive-url=https://web.archive.org/web/20250110211452/https://www.c40.org/news/how-active-travel-is-transforming-cities/ |url-status=live }}</ref> Working from home is another way of avoiding motorized traffic.<ref name=":4" />
Traffic can be shifted to cleaner modes of transport by increasing use of public transport,<ref>{{cite journal |last1=Landrigan |first1=Philip J. |date=1 January 2017 |title=Air pollution and health |journal=The Lancet Public Health |language=English |volume=2 |issue=1 |pages=e4–e5 |doi=10.1016/S2468-2667(16)30023-8 |issn=2468-2667 |pmid=29249479|doi-access=free }}</ref> for instance through higher parking fees or offering free public transport. Tackling congestion, which increases fuel usage, with congestion charging, also shifts people to use cleaner modes of transport. Finally, road vehicles can be improved from increased fuel efficiency, improved quality of fuels, emission standards, and conversion to electric vehicles.<ref>{{Cite journal |last1=Jonidi Jafari |first1=Ahmad |last2=Charkhloo |first2=Esmail |last3=Pasalari |first3=Hasan |date=2021 |title=Urban air pollution control policies and strategies: a systematic review |journal=Journal of Environmental Health Science and Engineering |language=en |volume=19 |issue=2 |pages=1911–1940 |doi=10.1007/s40201-021-00744-4 |issn=2052-336X |pmc=8617239 |pmid=34900316|bibcode=2021JEHSE..19.1911J }}</ref> For example, buses in New Delhi, India, switched to compressed natural gas after 2000, to reduce the city's thick pea soup smog.<ref name=":9" /><ref>{{Cite journal |last1=Krelling |first1=Christian |last2=Badami |first2=Madhav G. |date=2022 |title=Cost-effectiveness analysis of compressed natural gas implementation in the public bus transit fleet in Delhi, India |url=https://www.sciencedirect.com/science/article/abs/pii/S0967070X21002973 |journal=Transport Policy |volume=115 |pages=49–61 |doi=10.1016/j.tranpol.2021.10.019 |issn=0967-070X |url-access=subscription |archive-date=10 December 2024 |access-date=26 August 2024 |archive-url=https://web.archive.org/web/20241210052840/https://www.sciencedirect.com/science/article/abs/pii/S0967070X21002973 |url-status=live }}</ref>
In 2006, Lawrence D. Frank and his co-authors published a study with over 1,930 citations: ''Many Pathways from Land Use to Health.''<ref>{{Cite web |title=Lawrence Frank |url=https://scholar.google.com/citations?user=sF_AKKQAAAAJ&hl=en |access-date=2026-02-08 |website=scholar.google.com}}</ref> The authors demonstrated that a 5% increase in walkability was associated with many benefits, including a 6.5% reduction in vehicle miles driven, a 5.6% reduction in grams of nitrogen oxides emissions, and a 5.5% emission reduction of volatile organic compounds (VOCs).<ref>{{Cite journal |last=Frank |first=Lawrence D. |last2=Sallis |first2=James F. |last3=Conway |first3=Terry L. |last4=Chapman |first4=James E. |last5=Saelens |first5=Brian E. |last6=Bachman |first6=William |date=2006-03-31 |title=Many Pathways from Land Use to Health: Associations between Neighborhood Walkability and Active Transportation, Body Mass Index, and Air Quality |url=https://www.tandfonline.com/doi/full/10.1080/01944360608976725 |journal=Journal of the American Planning Association |language=en |volume=72 |issue=1 |pages=75–87 |doi=10.1080/01944360608976725 |issn=0194-4363|url-access=subscription }}</ref>
=== Cooking, lighting and heating === [[File:Solar_Cooker_Phuktar_Gompa_Zanskar_Oct22_A7C_04476.jpg|thumb|A kettle heated by a solar cooker at the Phugtal Monastery in Ladakh, India.|alt=a parabolic mirror concentrates heat into a placeholder for kettles and pans.]] Various technologies are available for clean cooking, to replace traditional biomass stoves or three-stone fires. For example, a switch to cooking with biogas, bioethanol, electricity, natural gas, or LPG (liquified petroleum gas) significantly reduces air pollution. Improved cook stoves, which use biomass more efficiently, improve air quality less, but can be an intermediate solution if clean cook stoves or their fuels are not available. These clean cooking devices, including those run on fossil fuels, usually have a smaller climate impact than traditional biomass stoves.<ref>{{cite book|author=International Energy Agency, African Development Bank Group|title=A Vision for Clean Cooking Access for All|date=2023|url=https://iea.blob.core.windows.net/assets/f63eebbc-a3df-4542-b2fb-364dd66a2199/AVisionforCleanCookingAccessforAll.pdf|pages=19, 21|archive-date=3 June 2025|access-date=23 April 2025|archive-url=https://web.archive.org/web/20250603005202/https://iea.blob.core.windows.net/assets/f63eebbc-a3df-4542-b2fb-364dd66a2199/AVisionforCleanCookingAccessforAll.pdf|url-status=live}}</ref>
Kerosene for lighting can be replaced with efficient LED lights, for instance, solar-powered LED lights.{{sfn|World Health Organization|2016|p=52}} Combustion of fossil fuels for space heating can be replaced by the use of electricity in heat pumps.<ref>{{Cite web |date=2024-11-13 |title=Air pollution from heating and cooling: stepping up clean energy use urgently needed - European Commission |url=https://joint-research-centre.ec.europa.eu/jrc-news-and-updates/air-pollution-heating-and-cooling-stepping-clean-energy-use-urgently-needed-2025-01-07_en |access-date=2025-01-10 |website=joint-research-centre.ec.europa.eu |language=en |archive-date=8 January 2025 |archive-url=https://web.archive.org/web/20250108112007/https://joint-research-centre.ec.europa.eu/jrc-news-and-updates/air-pollution-heating-and-cooling-stepping-clean-energy-use-urgently-needed-2025-01-07_en |url-status=live }}</ref> Ventilation improves indoor air quality, but leads to outdoor air pollution, which can in turn reduce local indoor air quality.{{sfn|World Health Organization|2016|p=18}}
== Policy and regulation == === Laws and regulations ===
{{Main|Air quality law|Emission standard}}
[[File:"When the smoke came", air pollution in Shanghai.jpg|alt=Cityscape in a dense smog|thumb|Air pollution in Shanghai, China, in 2013. China launched a "war against pollution" in 2014, which drastically lowered particle pollution levels across the country.<ref>{{Cite web |title=AQLI Policy Impacts—China: National Air Quality Action Plan (2014) |url=https://aqli.epic.uchicago.edu/policy-impacts/china-national-air-quality-action-plan-2014/ |access-date=2025-05-24 |website=AQLI |language=en |archive-date=24 May 2025 |archive-url=https://web.archive.org/web/20250524164152/https://aqli.epic.uchicago.edu/policy-impacts/china-national-air-quality-action-plan-2014/ |url-status=live }}</ref>]] Although a majority of countries have air pollution laws, 43% of countries lack a legal definition of air pollution, 34% lack outdoor air quality standards, and just 31% have laws for tackling pollution originating from outside their borders. Few countries have limits that are as strict as the World Health Organization's recommendations.<ref name="unep2021">{{cite book |url=https://www.unep.org/resources/report/regulating-air-quality-first-global-assessment-air-pollution-legislation |title=Regulating Air Quality: The First Global Assessment of Air Pollution Legislation |date=2021 |publisher=United Nations Environment Programme |isbn=978-92-807-3872-8 |location=Nairobi, Kenya |pages=7, 41, 46, 56 |access-date=10 April 2024 |archive-date=7 May 2024 |archive-url=https://web.archive.org/web/20240507042552/https://www.unep.org/resources/report/regulating-air-quality-first-global-assessment-air-pollution-legislation |url-status=live }}</ref>
Some air pollution laws include specific air quality standards, such as the U.S. National Ambient Air Quality Standards and E.U. Air Quality Directive,<ref>{{Cite web |url=http://ec.europa.eu/environment/air/quality/legislation/directive.htm |archive-url=https://web.archive.org/web/20110511090225/http://ec.europa.eu/environment/air/quality/legislation/directive.htm |archive-date=2011-05-11 |title=European Commission - Environment - Air - Air quality |date=11 May 2011 |author=European Commission}}</ref> which specify maximum atmospheric concentrations for specific pollutants. Other examples of air quality laws around the world include the Clean Air Act in Britain, the US Clean Air Act, and the TA Luft in Germany.<ref>{{Cite web |title=German TA-Luft is guaranteed by us |url=https://www.centrotherm-cs.de/en/innovation/news-journal/detail/?cHash=2f8c3c73736a8bfee683c94544e0d805&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Bnews%5D=9 |access-date=2022-02-27 |website=centrotherm clean solutions |language=en-US |archive-date=29 June 2022 |archive-url=https://web.archive.org/web/20220629162917/https://www.centrotherm-cs.de/en/innovation/news-journal/detail/?cHash=2f8c3c73736a8bfee683c94544e0d805&tx_news_pi1%5Baction%5D=detail&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Bnews%5D=9 }}</ref> Air pollution laws might also put limits on the {{em|emissions}} of air pollutants, e.g. from vehicles.<ref name="unep2021_p42">{{cite book |url=https://www.unep.org/resources/report/regulating-air-quality-first-global-assessment-air-pollution-legislation |title=Regulating Air Quality: The First Global Assessment of Air Pollution Legislation |date=2021 |publisher=United Nations Environment Programme |isbn=978-92-807-3872-8 |location=Nairobi, Kenya |page=42 |access-date=10 April 2024 |archive-date=7 May 2024 |archive-url=https://web.archive.org/web/20240507042552/https://www.unep.org/resources/report/regulating-air-quality-first-global-assessment-air-pollution-legislation |url-status=live }}</ref>
The World Health Organization's Global Air Quality Guidelines encourage improvements in a similar way to national standards, but are "recommendations" and "good practice" rather than mandatory targets that countries must achieve.<ref name="who-guidelines">{{cite web |title=WHO Global Air Quality Guidelines |url=https://www.who.int/news-room/questions-and-answers/item/who-global-air-quality-guidelines |publisher=World Health Organization |access-date=17 January 2025 |archive-date=31 December 2024 |archive-url=https://web.archive.org/web/20241231062754/https://www.who.int/news-room/questions-and-answers/item/who-global-air-quality-guidelines |url-status=live }}</ref>
Some air pollution action has been successful at the international level, such as the Montreal Protocol,<ref name=":20">{{Cite web |last=UNEP |date=2018-10-29 |title=About Montreal Protocol |url=http://www.unep.org/ozonaction/who-we-are/about-montreal-protocol |access-date=2022-06-07 |website=Ozonaction |archive-date=5 December 2022 |archive-url=https://web.archive.org/web/20221205183623/https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol |url-status=live }}</ref> which phased out harmful ozone-depleting chemicals. It was ratified worldwide. On the other hand, international action on climate change, has been less successful.<ref name=":21">{{Cite web |title=Global Climate Agreements: Successes and Failures |url=https://www.cfr.org/backgrounder/paris-global-climate-change-agreements |access-date=2022-06-07 |website=Council on Foreign Relations |archive-date=12 June 2021 |archive-url=https://web.archive.org/web/20210612023125/https://www.cfr.org/backgrounder/paris-global-climate-change-agreements |url-status=live }}</ref> The 1997 Kyoto Protocol introduced modest reduction targets for some countries but lacked strong enforcement,<ref name="Mosley86">{{Citation |last=Mosley |first=Stephen |title=Technological Hazards, Disasters and Accidents |date=2014 |work=The Basic Environmental History |volume=4 |pages=156–165 |editor-last=Agnoletti |editor-first=Mauro |url=https://link.springer.com/chapter/10.1007/978-3-319-09180-8_5 |access-date=2025-03-29 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-09180-8_5 |isbn=978-3-319-09179-2 |editor2-last=Neri Serneri |editor2-first=Simone |url-access=subscription |archive-date=29 March 2025 |archive-url=https://web.archive.org/web/20250329093617/https://link.springer.com/chapter/10.1007/978-3-319-09180-8_5 |url-status=live }}</ref> while the 2015 Paris Agreement set no binding limits, instead encouraging all countries to raise their ambition over time.<ref name='Raiser2020' />
=== Clean air as a human right === In 2022, the UN General Assembly passed a resolution recognizing the right to a clean, healthy, and sustainable environment as a human right. The resolution is not legally binding. This resolution followed the declaration from the UN Human Rights Council published earlier that year.<ref>{{Cite web |date=2022-07-28 |title=In historic move, UN declares healthy environment a human right |url=https://www.unep.org/news-and-stories/story/historic-move-un-declares-healthy-environment-human-right |access-date=2025-02-12 |website=www.unep.org |language=en |archive-date=19 February 2025 |archive-url=https://web.archive.org/web/20250219055722/https://www.unep.org/news-and-stories/story/historic-move-un-declares-healthy-environment-human-right |url-status=live }}</ref>
While many countries have air pollution laws, they differ in how they can be enforced via litigation. In the European Union, individual countries, including France, have been fined by the EU for not complying with air quality rules. The revised Ambient Air Quality Directive also makes it possible for individuals in the EU to seek compensation.<ref>{{Cite web |date=2020-10-30 |title=Air quality: Commission decides to refer France to the Court over failure to meet its obligation to protect citizens against poor air quality |url=https://ec.europa.eu/commission/presscorner/detail/en/ip_20_1880 |access-date=2025-02-12 |website=European Commission |archive-date=16 June 2024 |archive-url=https://web.archive.org/web/20240616122155/https://ec.europa.eu/commission/presscorner/detail/en/IP_20_1880 |url-status=live }}</ref> While China allows litigation on environmental grounds, it is rare as it is seen as risky.<ref>{{Cite web |last=Kurushina |first=Daria |date=2024-07-09 |title=Climate litigation can power China's low-carbon transition |url=https://dialogue.earth/en/justice/climate-litigation-can-power-chinas-low-carbon-transition/ |access-date=2025-05-24 |website=Dialogue Earth |language=en |archive-date=18 April 2025 |archive-url=https://web.archive.org/web/20250418063231/https://dialogue.earth/en/justice/climate-litigation-can-power-chinas-low-carbon-transition/ |url-status=live }}</ref> In Chile, the right to a healthy environment is part of the constitution, and the Supreme Court found that the government has to act to provide clear air because of this.<ref>{{Cite journal |last1=Tigre |first1=Maria Antonia |last2=Urzola |first2=Natalia |last3=Goodman |first3=Alexandra |date=2023 |title=Climate litigation in Latin America: is the region quietly leading a revolution? |url=https://www.elgaronline.com/view/journals/jhre/14/1/article-p67.xml?tab_body=pdf |journal=Journal of Human Rights and the Environment |language=en |volume=14 |issue=1 |pages=67–93 |doi=10.4337/jhre.2023.01.04 |bibcode=2023JHRE...14...67T |issn=1759-7188 |url-access=subscription |archive-date=1 November 2024 |access-date=24 May 2025 |archive-url=https://web.archive.org/web/20241101134616/https://www.elgaronline.com/view/journals/jhre/14/1/article-p67.xml?tab_body=pdf |url-status=live }}</ref>
== See also == {{Div col}} * Air stagnation * Atmospheric chemistry * Global Atmosphere Watch * Global dimming * List of smogs by death toll * Sustainable energy {{Div col end}} {{Clear}}
== References == {{Reflist}} === Cited sources === {{refbegin|30em}} * {{cite book |last1=Amato |first1=Fulvio |url=https://books.google.com/books?id=hSk0DwAAQBAJ |title=Non-Exhaust Emissions: An Urban Air Quality Problem for Public Health; Impact and Mitigation Measures |date=2018 |publisher=Academic Press |isbn=978-0-12-811770-5 |location=London, UK |access-date=17 January 2025 }} * {{cite book |last1=Cook |first1=E |last2=Velis |first2=Costas |url=https://eprints.whiterose.ac.uk/169766/6/GRoSEEL_LR.pdf |title=Global Review on Safer End of Engineered Life |publisher=Engineering X (founded by the Royal Academy of Engineering and the Lloyd's Register Foundation) |year=2020 |archive-date=23 March 2025 |access-date=23 March 2025 |archive-url=https://web.archive.org/web/20250323132902/https://eprints.whiterose.ac.uk/169766/6/GRoSEEL_LR.pdf |url-status=live }} * {{Cite book |title=Indoor air pollution |date=2019 |publisher=Royal Society of Chemistry |isbn=978-1-78801-617-9 |editor-last=Harrison |editor-first=Roy M. |series=Issues in environmental science and technology |location=London |editor-last2=Hester |editor-first2=Ronald E.}} * {{Cite book |last=Hill |first=Marquita K. |title=Understanding environmental pollution |date=2020 |publisher=Cambridge University Press |isbn=978-1-108-42308-3 |edition=Fourth |location=Cambridge, United Kingdom ; New York, NY}} * {{Cite book |last1=Pearson |first1=John K. |last2=Derwent |first2=Richard G. |url=https://www.taylorfrancis.com/books/9781003293132 |title=Air Pollution and Climate Change: The Basics |year=2022 |publisher=Routledge |isbn=978-1-003-29313-2 |edition=1 |location=London |pages=1, 6 |language=en |doi=10.4324/9781003293132 }} * {{cite book |last1=Ringenson |first1=Tina |chapter=Mobility as a Service and the Avoid-Shift-Improve Approach |date=2021 |title=Progress in IS |page=218 |location=Cham |publisher=Springer International |isbn=978-3-030-88062-0 |last2=Kramers |first2=Anna|doi=10.1007/978-3-030-88063-7_14 }} * {{Cite book| chapter=Cost-Effective Technologies Used to Curb Air Pollution |last1=Singh|first1=Ravi Prakash|last2=Singh|first2=Saumya| title=Air Pollution: Sources, Impacts and Controls |date=2019 |publisher=CAB International |isbn=978-1-78639-391-3 |editor-last=Saxena |editor-first=Pallavi |location=Boston |editor-last2=Nāīka |editor-first2=Vaiśālī}} * {{Cite book |last=United Nations Environmental Programme |url=https://www.unep.org/resources/report/actions-air-quality-global-summary-policies-and-programmes-reduce-air-pollution |title=Actions on Air Quality: A Global Summary of Policies and Programmes to Reduce Air Pollution |date=2021 |isbn=978-92-807-3880-3 |archive-date=1 March 2025 |access-date=1 March 2025 |archive-url=https://web.archive.org/web/20250301095456/https://www.unep.org/resources/report/actions-air-quality-global-summary-policies-and-programmes-reduce-air-pollution |url-status=live }} * {{Cite book |url=https://iris.who.int/bitstream/handle/10665/204717/9789241565233_eng.pdf |title=Burning opportunity: clean household energy for health, sustainable development, and wellbeing of women and children |publisher=World Health Organization |year=2016 |location=Geneva, Switzerland |archive-url=https://web.archive.org/web/20171124101534/http://www.who.int/airpollution/publications/burning-opportunities/en/ |archive-date=November 24, 2017 |url-status=live |ref={{sfnref|World Health Organization|2016}} }} {{refend}}
== Further reading == {{Library resources box |by=no |onlinebooks=no |others=yes lcheading=Air – Pollution}} * {{cite book |last1=Corton |first1=Christine |title=London Fog: The Biography |date=2015 |publisher=Harvard University Press |isbn=978-0-674-08835-1 |url=https://books.google.com/books?id=uipUCwAAQBAJ |access-date=8 January 2025}} * {{cite journal |last1=Fowler |first1=David|author1-link=David Fowler (physicist) |last2=Brimblecombe |first2=Peter |last3=Burrows |first3=John |last4=Heal |first4=Mathew |last5=Grennfelt |first5=Peringe |last6=Stevenson|first6=David|first7=Alan|last7=Jowett|first8=Eiko|last8=Nemitz|first9=Mhairi|last9=Coyle|first10=Xuejun|last10=Liu|first11=Yunhua|last11=Chang|first12=Gary|last12=Fuller|first13=Mark|last13=Sutton|first14=Zbigniew|last14=Klimont|first15=Mike|last15=Unsworth|first16=Massimo|last16=Vieno|title=A chronology of global air quality |journal=Phil. Trans. R. Soc. A |date=2020 |volume=378 |issue=2183 |doi=10.1098/rsta.2019.0314 |pmid=32981430|pmc=7536029 |bibcode=2020RSPTA.37890314F }} * {{cite book |last1=Gonzalez |first1=George |title=The Politics of Air Pollution: Urban Growth, Ecological Modernization, and Symbolic Inclusion |date=2012 |publisher=State University of New York Press |location=New York |isbn=978-0-7914-8386-2 |url=https://books.google.com/books?id=ofxc2dMtEBAC |access-date=8 January 2025}} * {{cite book | first1 = Chris |last1=Woodford|author1-link=Chris Woodford (author) | date = 2021 | title = Breathless: Why Air Pollution Matters – and How it Affects You | publisher = Icon Books | pages = | isbn = 978-1-78578-710-2 | url = https://books.google.com/books?id=0lEXEAAAQBAJ|access-date=8 January 2025}}
== External links == {{Commons}} {{Wikivoyage|3=travel information}} * [https://www.who.int/data/gho/data/themes/air-pollution/who-air-quality-database WHO Ambient Air quality database] * [http://aqicn.org/map/world/ Global real-time air quality index map] * [https://www.airnow.gov/aqi/ Air Quality Index (AQI) Basics and Calculator] * [https://ec.europa.eu/environment/air/quality/index.htm European Commission > Environment > Air > Air Quality] * [https://www.epa.gov/haps Hazardous air pollutants] at EPA.gov
{{Pollution}} {{World topic|prefix=Air pollution in|title=Air pollution in the world|noredlinks=yes}} {{Asia Pollution|state=collapsed}} {{Environmental science}} {{Public health}} {{Natural resources}} {{Authority control}}
{{DEFAULTSORT:Air Pollution}} Category:Air pollution Category:Articles containing video clips Category:Climate forcing Category:Pollution Category:Global environmental issues Category:Human impact on the environment