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{{Short description|Smoke-like, fog-like air pollutions}}
{{Other uses}}
{{Use dmy dates|date=September 2020}}
[[File:Fanhe Town 10 day interval contrast.png|alt=A hazy cityscape to the right and a clear one to the left|thumb|Smog and a sunny day within a 10-day interval in [[Fanhe Town, Tieling|Fanhe]], China]]
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{{external media | width = 210px | float = right | headerimage= | audio1 = [https://www.sciencehistory.org/distillations/podcast/fighting-smog-in-los-angeles "Fighting Smog in Los Angeles"], ''Distillations'' Podcast, 2018 [[Science History Institute]]}}
'''Smog''', or '''smoke fog''', is a type of intense [[air pollution]]. The word "smog" was coined in the early 20th century, and is a [[portmanteau]] of the words ''[[smoke]]'' and ''[[fog]]''<ref>{{cite book|title=Globalistics and Globalization Studies: Global Transformations and Global Future|author=Olga Kornienko, Grinin L, Ilyin I, Herrmann P, Korotayev A|pages=220–225|url=https://hal-hprints.archives-ouvertes.fr/hprints-01794187/document|isbn=978-5-7057-5026-9|year=2016|place=Volgograd|publisher=Uchitel Publishing House|chapter=Social and Economic Background of Blending|chapter-url=https://www.socionauki.ru/upload/socionauki.ru/book/files/globalistics_and_globalization_studies_5_en/220-225.pdf}}</ref> to refer to smoky fog due to its opacity, and odor.<ref>{{cite book|title=A Social History of American Technology|last=Schwartz Cowan|first=Ruth|author-link=Ruth Schwartz Cowan |publisher=Oxford University Press|year=1997|isbn=978-0-19-504605-2}}{{page needed|date=October 2013}}</ref> The word was then intended to refer to what was sometimes known as [[pea soup fog]], a familiar and serious problem in [[London]] from the 19th century to the mid-20th century, where it was commonly known as a '''London particular''' or '''London fog'''. This kind of visible air pollution is composed of [[nitrogen oxide]]s, [[sulfur oxide]], [[ozone]], smoke and other [[Particulate matter|particulates]]. Man-made smog is derived from coal combustion emissions, vehicular emissions, industrial emissions, forest and agricultural fires and photochemical reactions of these emissions.
Smog is often categorized as being either [[summer smog]] or winter smog. Summer smog is primarily associated with the photochemical formation of ozone. During the summer season when the temperatures are warmer and there is more sunlight present, photochemical smog is the dominant type of smog formation. During the winter months when the temperatures are colder, and [[Inversion (meteorology)|atmospheric inversions]] are common, there is an increase in coal and other fossil fuel usage to heat homes and buildings. These combustion emissions, together with the lack of pollutant [[Atmospheric dispersion modeling|dispersion]] under inversions, characterize winter smog formation. Smog formation in general relies on both primary and secondary pollutants. Primary pollutants are emitted directly from a source, such as emissions of [[sulfur dioxide]] from coal combustion. Secondary pollutants, such as ozone, are formed when primary pollutants undergo chemical reactions in the atmosphere.
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== Etymology ==
Coinage of the term "smog" has been attributed to [[Henry Antoine Des Voeux]] in his 1905 paper, "Fog and Smoke" for a meeting of the [[Public Health Congress]]. The 26 July 1905 edition of the London newspaper ''Daily Graphic'' quoted Des Voeux, "He said it required no science to see that there was something produced in great cities which was not found in the country, and that was smoky fog, or what was known as 'smog'."<ref>{{cite book |url=http://www.psi.ch/ceg/PublicationsEN/Piazzesi,_PhD_thesis,_ETH_Zurich,_2006.pdf |first=Gaia |last=Piazzesi |year=2006 |title=The Catalytic Hydrolysis of Isocyanic Acid (HNCO) in the Urea-SCR Process |type=PhD Thesis |publisher=[[ETH Zurich]] |access-date=25 October 2013 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201131651/https://www.psi.ch/ceg/PublicationsEN/Piazzesi,_PhD_thesis,_ETH_Zurich,_2006.pdf |url-status=dead }}</ref>{{rp|1}}{{dead link|date=November 2022}} The following day the newspaper stated that "Dr. Des Voeux did a public service in coining a new word for the London fog."
However, the term appeared twenty-five years earlier than Voeux's paper, in the Santa Cruz & Monterey Illustrated Handbook published in 1880<ref>{{cite book|url=https://books.google.com/books?id=AcZBAQAAMAAJ&pg=PA8|first=Henry|last=Meyrick|year=1880|title=Santa Cruz & Monterey Illustrated Handbook|publisher=San Francisco News Publishing Co.|pages=7–8|quote=It is really not fog at all, but cloud of pure white mist, warmer and much less wetting than a "Scotch mist," and differing entirely from the true British fog, facetiously spelled "smog," because always colored and strongly impregnated with smoke, a mixture as unwholesome as it is unpleasant.}}</ref> and also appears in print in a column quoting from the book in the 3 July 1880, Santa Cruz Weekly Sentinel.<ref>{{cite news|url=https://cdnc.ucr.edu/?a=d&d=SCWS18800703.1.3&srpos=41&e=-------en--20--41-byDA-txt-txIN-smog-------1|newspaper=Santa Cruz Weekly Sentinel|title=The morning fog|date=3 July 1880|access-date=18 September 2019|page=3|quote=
==Anthropogenic causes==
===Coal===
Coal fire can emit significant clouds of smoke that contribute to the formation of winter smog. Coal fires can be used to heat individual buildings or to provide energy in a power-producing plant. Air pollution from this source has been reported in England since the [[Middle Ages]].<ref name="middleages3">{{cite web|url=http://www.environmentalgraffiti.com/offbeat-news/environmentalism-in-1306/725|title=Environmentalism in 1306|author=Chris|year=2007|publisher=By Environmental Graffiti|archive-url=https://web.archive.org/web/20080725090103/http://www.environmentalgraffiti.com/offbeat-news/environmentalism-in-1306/725|archive-date=25 July 2008|url-status=dead}}</ref><ref name="middleages22">{{cite web|url=http://scribol.com/art-and-design/green-design/environmentalism-in-1306/|title=Environmentalism in 1306|author=Karl|year=2008|publisher=By Environmental Graffiti|access-date=17 February 2017|archive-date=13 November 2019|archive-url=https://web.archive.org/web/20191113013723/https://scribol.com/art-and-design/green-design/environmentalism-in-1306/|url-status=dead}}</ref> London, in particular, was notorious up through the mid-20th century for its coal-caused smogs, which were nicknamed "[[Pea soup fog|pea-soupers]]". Air pollution of this type is still a problem in areas that generate significant smoke from burning coal. The emissions from coal combustion are one of the main causes of [[air pollution in China]].<ref>{{cite book|url=https://www.merics.org/en/merics-analysis/chinas-political-system/|title=China's Political System|editor-last=Heilmann|editor-first=Sebastian |publisher=Rowman & Littlefield|year=2017|page=360|archive-url=https://web.archive.org/web/20161011093650/http://www.merics.org/en/merics-analysis/chinas-political-system/|archive-date=11 October 2016|url-status=dead}}</ref> Especially during autumn and winter when coal-fired heating ramps up, the amount of produced smoke at times forces some Chinese cities to close down roads, schools or airports. One prominent example for this was China's Northeastern city of [[2013 Harbin smog|Harbin in 2013]].
===Transportation emissions===
Traffic emissions – such as from [[truck]]s, [[bus]]es, and [[automobile]]s – also contribute to the formation of smog.<ref>{{cite web|url=http://www.transact.org/report.asp?id=227|title=Clearing the Air|date=19 August 2003|publisher=The Surface Transportation Policy Project|archive-url=https://web.archive.org/web/20070208230135/http://www.transact.org/report.asp?id=227|archive-date=8 February 2007|url-status=dead|access-date=26 April 2007}}</ref> Airborne [[by-product]]s from vehicle [[exhaust system]]s and [https://lhkinsights.com/technology/car-air-conditioner-blowing-white-mist/ air conditioning] cause [[air pollution]] and are a major ingredient in the creation of smog in some large cities.<ref>{{cite press release|title=EPA Tools Available as Summer Smog Season Starts|date=30 April 2008|publisher=United States Environmental Protection Agency|location=Boston, Massachusetts|url=http://yosemite.epa.gov/opa/admpress.nsf/6427a6b7538955c585257359003f0230/228d9bf38da42f7c8525743b006db951!OpenDocument&Start=1&Count=5&Expand=1}}</ref><ref>{{cite web|url=http://www.sierraclub.org/sprawl/report01/carsandtrucks.asp|title=Sprawl Report 2001: Measuring Vehicle Contribution to Smog|year=2001|publisher=Sierra Club|access-date=25 October 2013|archive-date=15 November 2001|archive-url=https://web.archive.org/web/20011115044348/http://www.sierraclub.org/sprawl/report01/carsandtrucks.asp|url-status=dead}}</ref><ref>{{cite web|url=http://library.thinkquest.org/26026/Environmental_Problems/smog_-_causes.html|title=Smog – Causes|work=The Environment: A Global Challenge|access-date=25 October 2013|archive-date=19 January 2001|archive-url=https://web.archive.org/web/20010119154200/http://library.thinkquest.org/26026/Environmental_Problems/smog_-_causes.html|url-status=dead}}</ref><ref name=epa>{{Cite report|date=July 1999|title=Smog — Who Does It Hurt? What You Need to Know About Ozone and Your Health (EPA-452/K-99-001)|url=http://www.epa.gov/air/ozonepollution/pdfs/smog.pdf|publisher=United States Environmental Protection Agency|archive-url=https://web.archive.org/web/20080328164916/http://www.epa.gov/air/ozonepollution/pdfs/smog.pdf|archive-date=28 March 2008}}</ref>
The major culprits from transportation sources are [[carbon monoxide]] (CO),<ref>{{cite web|url=http://www.epa.gov/cgi-bin/broker?_service=data&_debug=0&_program=dataprog.national_1.sas&polchoice=CO|title=State and County Emission Summaries: Carbon Monoxide|date=25 October 2013|work=Air Emission Sources|publisher=United States Environmental Protection Agency}}</ref><ref name="queensland2">{{cite web|url=http://www.tmr.qld.gov.au/Community-and-environment/Environmental-management/How-you-can-make-a-difference/Motor-vehicle-pollution.aspx|title=Motor vehicle pollution|date=4 April 2013|publisher=Queensland Government|access-date=25 October 2013|archive-date=5 December 2019|archive-url=https://web.archive.org/web/20191205161028/https://www.tmr.qld.gov.au/Community-and-environment/Environmental-management/How-you-can-make-a-difference/Motor-vehicle-pollution.aspx|url-status=dead}}</ref> [[nitrogen oxides]] ([[Nitric oxide|NO]] and [[NO2|NO<sub>2</sub>]]),<ref name="epa-no22">{{cite web|url=http://www.epa.gov/air/nitrogenoxides/health.html|title=Health|date=14 February 2013|work=Nitrogen Dioxide|publisher=United States Environmental Protection Agency}}</ref><ref>{{cite web|url=http://www.epa.gov/air/noxfacts.pdf|title=The Regional Transport of Ozone: New EPA Rulemaking on Nitrogen Oxide Emissions (EPA-456/F-98-006)|date=September 1998|publisher=United States Environmental Protection Agency}}</ref><ref name="EPA_NOx2">{{cite web|url=http://www.epa.gov/cgi-bin/broker?_service=data&_debug=0&_program=dataprog.national_1.sas&polchoice=NOX|title=State and County Emission Summaries: Nitrogen Oxides|date=25 October 2013|work=Air emission sources|publisher=United States Environmental Protection Agency}}</ref> volatile organic compounds,<ref name="queensland2" /><ref name="epa-no22" /> and [[hydrocarbons]] (hydrocarbons are the main component of [[petroleum fuels]] such as [[gasoline]] and [[diesel fuel]]).<ref name="queensland2" /> Transportation emissions also include [[sulfur dioxides]] and particulate matter but in much smaller quantities than the pollutants mentioned previously. The nitrogen oxides and volatile organic compounds can undergo a series of chemical reactions with sunlight, heat, [[ammonia]], moisture, and other compounds to form the noxious vapors, [[ground level ozone]], and particles that comprise smog.<ref name="queensland2" /><ref name="epa-no22" />
== Photochemical smog ==
[[File:Photochemical_smog_formation.png|thumb|The photochemical smog formation diagram. (Based on U 6.3.3 in mrgsciences.com<ref>{{Cite web|url=https://www.mrgscience.com/ess-topic-63-photochemical-smog.html|title=ESS Topic Smog|website=Amazing World of Science With Mr. Green|language=en|access-date=19 September 2019}}</ref>)]]
Photochemical smog, often referred to as "summer smog", is the chemical reaction of sunlight, [[nitrogen oxides]] and [[volatile organic compound]]s in the atmosphere, which leaves [[Atmospheric particulate matter|airborne particles]] and [[Tropospheric ozone|ground-level ozone]].<ref>{{Cite
[[File:PLANE (SUPPLIED BY NASA) USES SPACE TECHNIQUES IN SMOG RESEARCH. SCIENTISTS FROM STATEWIDE AIR - NARA - 542670.jpg|thumb|right|Airplane used to collect airborne hydrocarbons, May 1972]]
The composition and chemical reactions involved in photochemical smog were not understood until the 1950s. In 1948, flavor chemist [[Arie Jan Haagen-Smit|Arie Haagen-Smit]] adapted some of his equipment to collect chemicals from polluted air, and identified ozone as a component of Los Angeles smog. Haagen-Smit went on to discover that nitrogen oxides from automotive exhausts and gaseous hydrocarbons from cars and oil refineries, exposed to sunlight, were key ingredients in the formation of ozone and photochemical smog.<ref name="hundred2">{{cite book|url=https://books.google.com/books?id=edtL_hIi8M0C&pg=PA219|title=Arnold O. Beckman : one hundred years of excellence|author-last1=Thackray|author-first1=Arnold|author-last2=Myers Jr.|author-first2=Minor|publisher=Chemical Heritage Foundation|year=2000|isbn=978-0-941901-23-9|location=Philadelphia, Pa.|name-list-style=amp}}</ref>{{rp|219–224}}<ref name="Gardner2">{{cite web|url=http://www.englishnotes4all.com/|title=
=== Formation and reactions ===
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(7) <chem>NO2 + OH{.} + M -> HNO3 + M</chem>
This reaction removes NO<sub>2</sub> which limits the amount of O<sub>3</sub> that can be produced from its photolysis (reaction 4). HNO<sub>3</sub>, nitric acid, is a sticky compound that can easily be removed onto surfaces (dry deposition) or dissolved in water and be rained out (wet deposition). Both ways are common in the atmosphere and can efficiently remove radicals and nitrogen dioxide.
[[File:Lightmatter_Golden_gate_bridge.jpg|center|thumb|600x600px|The presence of smog in [[California]] is shown near the [[Golden Gate Bridge]]. The brown coloration is due to the NO<sub>2</sub> formed from photochemical smog reactions.<nowiki/>]]
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Modern studies continue to find links between mortality and the presence of smog. One study, published in [[Nature magazine]], found that smog episodes in the city of Jinan, a large city in eastern China, during 2011–15, were associated with a 5.87% (95% CI 0.16–11.58%) increase in the rate of overall mortality. This study highlights the effect of exposure to air pollution on the rate of mortality in China.<ref>Ambient air pollution, smog episodes and mortality in Jinan, China: Jun Zhang, Yao Liu, Liang-liang Cui, Shou-qin Liu, Xi-xiang Yin & Huai-chen Li
Scientific Reports 7, Article number: 11209 (2017)
doi:10.1038/s41598-017-11338-2</ref> A similar study in
===Levels of unhealthy exposure===
The [[United States Environmental Protection Agency|U.S. EPA]] has developed an [[air quality index]] to help explain air pollution levels to the general public. 8 hour average ozone concentrations of 85 to 104 [[parts per notation|ppbv]] are described as "Unhealthy for Sensitive Groups", 105 ppbv to 124 ppbv as "unhealthy" and 125 ppb to 404 ppb as "very unhealthy".<ref name=epa/> The "very unhealthy" range for some other pollutants are: 355 μg m<sup>−3</sup> – 424 μg m<sup>−3</sup> for [[PM10]]; 15.5 ppm – 30.4ppm for CO and 0.65 ppm – 1.24 ppm for NO<sub>2</sub>.<ref>{{Cite journal | url = http://www.epa.gov/ttn/oarpg/t1/memoranda/rg701.pdf | title = Guidelines for the Reporting of Daily Air Quality – the Air Quality Index (AQI) | date = May 2006 | publisher = United States Environmental Protection Agency, Office of Air Quality Planning and Standards | issue = EPA-454/B-06-001 }}</ref>
===Premature deaths due to cancer and respiratory disease===
In 2016, the [[Ontario Medical Association]] announced that smog is responsible for an estimated 9,500 premature deaths in the province each year.<ref>{{cite web|url=http://wheels.ca/reviews/article/256058 |publisher=Wheels.ca |title=$3.83 to power hybrid plug-in for 6 days |first=Tyler |last=Hamilton |date=9 June 2016 |url-status=dead |archive-url=https://web.archive.org/web/20100818225927/http://www.wheels.ca/reviews/article/256058 |archive-date=18 August 2010 }}</ref>
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===Risk of certain birth defects===
A study examining 806 women who had babies with birth defects between 1997 and 2006, and 849 women who had healthy babies, found that smog in the [[San Joaquin Valley]] area of [[California]] was linked to two types of [[neural tube defect]]s: [[spina bifida]] (a condition involving, among other manifestations, certain malformations of the [[spinal column]]), and [[anencephaly]] (the underdevelopment or absence of part or all of the brain, which if not fatal usually results in profound impairment).<ref>{{cite journal |pmid=23045474 |year=2012 |last1=Padula |first1=AM |last2=Mortimer |first2=K |last3=Hubbard |first3=A |last4=Lurmann |first4=F |last5=Jerrett |first5=M |last6=Tager |first6=IB |title=Exposure to traffic-related air pollution during pregnancy and term low birth weight: Estimation of causal associations in a semiparametric model |volume=176 |issue=9 |pages=815–24 |doi=10.1093/aje/kws148 |pmc=3571254 |journal=American Journal of Epidemiology}}</ref> An emerging cohort study in China linked early-life smog exposure to an increased risk for adverse pregnancy outcomes, in particular oxidative stress.<ref>{{Cite journal|last1=Song|first1=Jing|last2=Chen|first2=Yi|last3=Wei|first3=Ling|last4=Ma|first4=Ying|last5=Tian|first5=Ning|last6=Huang|first6=Shi Yun|last7=Dai|first7=Yin Mei|last8=Zhao|first8=Li Hong|last9=Kong|first9=Yuan Yuan|date=2017-09-03|title=Early-life exposure to air pollutants and adverse pregnancy outcomes: protocol for a prospective cohort study in Beijing|journal=BMJ Open|volume=7|issue=9|pages=e015895|doi=10.1136/bmjopen-2017-015895|issn=2044-6055|pmc=5588991|pmid=28871018}}</ref>
===Low birth weight===
According to a study published in [[The Lancet]], even a very small (5 μg) change in [[PM2.5]] exposure was associated with an increase (18%) in risk of a low birth weight at delivery, and this relationship held even below the current accepted safe levels.<ref>{{cite journal |doi=10.1016/S2213-2600(13)70192-9 |pmid=24429273 |title=Ambient air pollution and low birthweight: A European cohort study (ESCAPE) |year=2013 |last1=Pedersen |first1=Marie |last2=Giorgis-Allemand |first2=Lise |last3=Bernard |first3=Claire |last4=Aguilera |first4=Inmaculada |last5=Andersen |first5=Anne-Marie Nybo |last6=Ballester |first6=Ferran |last7=Beelen |first7=Rob M J |last8=Chatzi |first8=Leda |last9=Cirach |first9=Marta |last10=Danileviciute |first10=Asta |last11=Dedele |first11=Audrius |last12=Eijsden |first12=Manon van |last13=Estarlich |first13=Marisa |last14=Fernández-Somoano |first14=Ana |last15=Fernández |first15=Mariana F |last16=Forastiere |first16=Francesco |last17=Gehring |first17=Ulrike |last18=Grazuleviciene |first18=Regina |last19=Gruzieva |first19=Olena |last20=Heude |first20=Barbara |last21=Hoek |first21=Gerard |last22=Hoogh |first22=Kees de |last23=Van Den Hooven |first23=Edith H |last24=Håberg |first24=Siri E |last25=Jaddoe |first25=Vincent W V |last26=Klümper |first26=Claudia |last27=Korek |first27=Michal |last28=Krämer |first28=Ursula |last29=Lerchundi |first29=Aitana |last30=Lepeule |first30=Johanna |journal=The Lancet Respiratory Medicine |volume=1 |issue=9 |pages=695–704 |display-authors=5|arxiv=0706.4406 }}</ref>
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Smog can form in almost any climate where industries or cities release large amounts of [[air pollution]], such as smoke or gases. However, it is worse during periods of warmer, sunnier weather when the upper air is warm enough to inhibit vertical circulation. It is especially prevalent in geologic basins encircled by hills or mountains. It often stays for an extended period of time over densely populated cities or urban areas and can build up to dangerous levels.
===
According to the Canadian Science Smog Assessment published in 2012, smog is responsible for detrimental effects on human and ecosystem health, as well as socioeconomic well-being across the country. It was estimated that the province of [[Ontario]] sustains $201 million in damages annually for selected crops, and an estimated tourism revenue degradation of $7.5 million in [[Vancouver]] and $1.32 million in The [[Fraser Valley]] due to decreased visibility. [[Air pollution in British Columbia]] is of particular concern, especially in the Fraser Valley, because of a meteorological effect called [[Inversion (meteorology)|inversion]] which decreases air dispersion and leads to smog concentration.<ref>{{cite book▼
▲=== Delhi, India ===
{{See also|Environmental issues in Delhi}}
[[File: Aerial view of Air Pollution in North India, Agriculture Fires, November 2013.jpg|300px|thumb|During the autumn and spring months, some 500 million tons of [[stubble burning|rice and wheat crop residues are burnt]], and [[western disturbances|winds blow from India's north and northwest towards east]].<ref>Badarinath, K. V. S., Kumar Kharol, S., & Rani Sharma, A. (2009), Long-range transport of aerosols from agriculture crop residue burning in Indo-Gangetic Plains—a study using LIDAR, ground measurements and satellite data. Journal of Atmospheric and Solar-Terrestrial Physics, 71(1), 112–120</ref><ref>Sharma, A. R., Kharol, S. K., Badarinath, K. V. S., & Singh, D. (2010), Impact of agriculture crop residue burning on atmospheric aerosol loading—a study over Punjab State, India. Annales Geophysicae, 28(2), pp 367–379</ref><ref>{{cite journal|first1=Tina|last1=Adler|title=Respiratory Health: Measuring the Health Effects of Crop Burning|journal=Environmental Health Perspectives|date=November 2010|volume=118|issue=11|page=A475|doi=10.1289/ehp.118-a475|pmc=2974718|pmid=21465742}}</ref> This aerial view shows India's annual crop burning, resulting in smoke and air pollution over Delhi and adjoining areas.]]
For the past few years, cities in northern [[India]] have been covered in a thick layer of [[winter]] smog. The situation has turned quite drastic in the
▲For the past few years, cities in northern [[India]] have been covered in a thick layer of [[winter]] smog. The situation has turned quite drastic in the National Capital, [[Delhi]]. This smog is caused by the collection of [[Particulate matter|Particulate Matter]] (a very fine type of dust and toxic gases) in the air due to stagnant movement of air during winters.<ref>{{Cite news|url=https://www.honeywellsmarthomes.com/blog/causes-of-smog-and-how-to-protect/|title=Causes of Smog {{!}} How to Protect Yourself from Smog - Honeywell Blog|date=26 November 2017|work=Official Blog Updates - Honeywell Air Purifiers|access-date=7 March 2018|language=en-US}}</ref>
Delhi is the most polluted<ref>{{cite news|url=http://www.hindustantimes.com/india-news/delhi-has-dirtiest-air-china-data-foggy-who/article1-1216605.aspx |archive-url=https://web.archive.org/web/20140508004750/http://www.hindustantimes.com/india-news/delhi-has-dirtiest-air-china-data-foggy-who/article1-1216605.aspx |url-status=dead |archive-date=8 May 2014 |title=Delhi is most polluted city in world, Beijing much better: WHO study |work=Hindustan Times|access-date=8 May 2014}}</ref> city in the world and according to one estimate, air pollution causes the death of about 10,500 people in Delhi every year.<ref name="TimePollution">{{cite magazine|url=http://world.time.com/2014/02/10/smog-in-new-delhi/ |archive-url=https://web.archive.org/web/20140302085642/http://world.time.com/2014/02/10/smog-in-new-delhi/ |url-status=dead |archive-date=2 March 2014 |title=Delhi's Air Has Become a Lethal Hazard and Nobody Seems to Know What to Do About It |magazine=Time magazine |access-date=10 February 2014}}</ref><ref name="VOAPollution">{{cite web |url=http://www.voanews.com/content/indias-air-pollution-triggers-comparisons-with-china/1855331.html |title=India's Air Pollution Triggers Comparisons with China |publisher=Voice of America |access-date=20 February 2014 |archive-url=https://web.archive.org/web/20140221104928/http://www.voanews.com/content/indias-air-pollution-triggers-comparisons-with-china/1855331.html |archive-date=21 February 2014 |url-status=dead }}</ref><ref name="EconomistPollution">{{cite news|url=https://www.economist.com/blogs/banyan/2012/11/air-pollution-india |title=A Delhi particular |newspaper=The Economist|access-date=6 November 2012}}</ref> During 2013–14, peak levels of fine [[Particle|particulate]] matter (PM) in Delhi increased by about 44%, primarily due to high vehicular and industrial emissions, construction work and crop burning in adjoining states.<ref name="TimePollution" /><ref name="WSJPollution">{{cite news|url=https://blogs.wsj.com/indiarealtime/2014/02/15/how-crop-burning-affects-delhis-air-pollution/ |title=How Crop Burning Affects Delhi's Air |newspaper=Wall Street Journal |access-date=15 February 2014}}</ref><ref name=Gardiner>{{cite news|last=Harris|first=Gardiner|title=Beijing's Bad Air Would Be Step Up for Smoggy Delhi|url=https://www.nytimes.com/2014/01/26/world/asia/beijings-air-would-be-step-up-for-smoggy-delhi.html?emc=edit_tnt_20140126&tntemail0=y|access-date=27 January 2014|newspaper=New York Times|date=25 January 2014}}</ref><ref>{{cite news|last=Bearak|first=Max|title=Desperate for Clean Air, Delhi Residents Experiment with Solutions|url=http://india.blogs.nytimes.com/2014/02/07/desperate-for-clean-air-delhi-residents-experiment-with-solutions/?emc=edit_tnt_20140208&tntemail0=y|access-date=8 February 2014|newspaper=New York Times|date=7 February 2014}}</ref> Delhi has the highest level of the airborne particulate matter, [[PM2.5]] considered most harmful to health, with 153 micrograms.<ref>{{cite news|author=Madison Park|title=Top 20 most polluted cities in the world|url=http://www.cnn.com/2014/05/08/world/asia/india-pollution-who/index.htm|publisher=CNN|date=8 May 2014}}</ref> Rising air pollution level has significantly increased lung-related ailments (especially asthma and lung cancer) among Delhi's children and women.<ref name="TodayPollution">{{cite magazine|url=http://indiatoday.intoday.in/story/pollution-in-delhi-cng-children-in-delhi/1/344904.html |title=Children in Delhi have lungs of chain-smokers! |magazine=India Today |access-date=22 February 2014}}</ref><ref name="DNAPollution">{{cite web|url=http://www.dnaindia.com/health/report-pollution-increasing-lung-cancer-in-indian-women-1959054 |title=Pollution increasing lung cancer in Indian women |publisher=DNA |access-date=3 February 2014|date=3 February 2014 }}</ref> The dense smog in Delhi during winter season results in major air and rail traffic disruptions every year.<ref name="ReutersPollution">{{cite news |url=http://in.reuters.com/article/india-delhi-winter-smog-idINDEE9BH0D420131218 |title=Delhi blanketed in thick smog, transport disrupted |work=Reuters |access-date=18 December 2013 |date=18 December 2013 |archive-date=20 December 2013 |archive-url=https://web.archive.org/web/20131220012916/http://in.reuters.com/article/2013/12/18/india-delhi-winter-smog-idINDEE9BH0D420131218 |url-status=dead }}</ref> According to Indian meteorologists, the average maximum temperature in Delhi during winters has declined notably since 1998 due to rising air pollution.<ref>{{Cite news|url=https://timesofindia.indiatimes.com/city/delhi/January-days-getting-colder-tied-to-rise-in-pollution/articleshow/29429495.cms|title=January days getting colder, tied to rise in pollution |website=The Times of India|date=27 January 2014 }}</ref>
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However, according to several authors, most of these gains have been lost, especially due to [[stubble burning]], rise in market share of [[diesel exhaust|diesel cars]] and a considerable decline in bus ridership.<ref name="kumari">{{cite journal |author1=R. Kumari |author2=A.K. Attri |author3=L. Int Panis |author4=B.R. Gurjar | title = Emission estimates of Particulate Matter and Heavy Metals from Mobile sources in Delhi (India)| journal = J. Environ. Science & Engg.| volume = 55 | issue = 2 | pages = 127–142 |date=April 2013 |url=https://www.researchgate.net/publication/259827470}}</ref><ref name="Pollution">{{cite web|url=http://cseindia.org/node/835 |title=What is the status of air pollution in Delhi? |publisher=CSE, India |access-date=2 March 2014}}</ref> According to CUE and System of Air Quality Weather Forecasting and Research (SAFER), burning of agricultural waste in nearby Punjab, Haryana and Uttar Pradesh regions results in severe intensification of smog over Delhi.<ref name="Antipollution">{{cite news|url=http://articles.economictimes.indiatimes.com/2014-11-06/news/55835957_1_pm-2-5-level-air-quality-weather-forecasting-pollution-levels |title=Delhi's air quality deteriorating due to burning of agriculture waste |newspaper=Economic Times }}</ref><ref name="CSE2Pollution">{{cite magazine|url=http://indiatoday.intoday.in/story/smog-delhi-winter-low-wind-speed-emissions/1/398601.html |title=Thick blanket of smog envelopes Delhi, northern India |magazine=India Today }}</ref> The state government of adjoining Uttar Pradesh is considering imposing a ban on crop burning to reduce pollution in Delhi NCR and an environmental panel has appealed to India's Supreme Court to impose a 30% cess on diesel cars.<ref>{{Cite web|url=http://timesofindia.indiatimes.com/city/noida/Straw-burning-ban-soon-to-reduce-smog-in-NCR/articleshow/2835975.cms|title=Straw burning ban soon to reduce smog in NRC, Times of India, 4 January 2014|website=[[The Times of India]]}}</ref><ref>{{Cite news|url=https://timesofindia.indiatimes.com/home/environment/pollution/Impose-30-cess-on-diesel-cars-panel-tells-Supreme-Court/articleshow/30180391.cms|title=Impose 30% cess on diesel cars, panel tells Supreme Court - Times of India|website=The Times of India|date=11 February 2014 }}</ref>
===
{{main|Beijing#Air quality}}
Joint research between American and Chinese researchers in 2006 concluded that much of
In December 2005, schools and public offices
====
In the late 1990s, massive immigration to [[Ulaanbaatar]] from the countryside began. An estimated 150,000 households, mainly living in traditional Mongolian [[Yurt|gers]] on the outskirts of Ulaanbaatar, burn wood and coal (some poor families burn even car tires and trash) to heat themselves during the harsh winter, which lasts from October to April, since these outskirts are not connected to the city's central heating system. A temporary solution to decrease smog was proposed in the form of stoves with improved efficiency, although with no visible results.
Coal-fired ger stoves release high levels of ash and other particulate matter (PM). When inhaled, these particles can settle in the lungs and respiratory tract and cause health problems. At two to 10 times above Mongolian and international air quality standards, Ulaanbaatar's PM rates are among the worst in the world, according to a December 2009 World Bank report. The Asian Development Bank (ADB) estimates that health costs related to this air pollution account for as much as 4 percent of Mongolia's GDP.<ref>{{cite news | url = http://www.eurasianet.org/departments/news/articles/eav032310e.shtml | title = Mongolia: Ulaanbaatar Grapples with Smog Problem | date = 22 March 2010 | first = Andrew | last = Cullen | publisher = EurasiaNet.org | access-date = 1 October 2012 | archive-url = https://web.archive.org/web/20120828095515/http://www.eurasianet.org/departments/news/articles/eav032310e.shtml | archive-date = 28 August 2012 | url-status = dead }}</ref>▼
==== Southeast Asia ====▼
{{See also|Asian brown cloud|haze}}▼
[[Image:Downtown Core, Singapore, Oct 06.JPG|thumb|left|[[Singapore]]'s [[Downtown Core]] on 7 October 2006, when it was affected by [[wildfire|forest fires]] in [[Sumatra]], [[Indonesia]]]]▼
Smog is a regular problem in [[Southeast Asia]] caused by [[wildfire|land and forest fires]] in [[Indonesia]], especially [[Sumatra]] and [[Kalimantan]], although the term [[haze]] is preferred in describing the problem. Farmers and plantation owners are usually responsible for the fires, which they use to clear tracts of land for further plantings. Those fires mainly affect [[Brunei]], [[Indonesia]], [[Philippines]], [[Malaysia]], [[Singapore]] and [[Thailand]], and occasionally [[Guam]] and [[Saipan]].<ref>{{cite news|url=http://www.saipantribune.com/newsstory.aspx?cat=1&newsID=61706 |date=5 October 2006 |title=Indon haze spreads to NMI |first=Ferdie |last=de la Torre |work=Saigpan Tribune |url-status=dead |archive-url=https://web.archive.org/web/20070218044848/http://www.saipantribune.com/newsstory.aspx?cat=1&newsID=61706 |archive-date=18 February 2007 }}</ref><ref>{{cite news | url = http://www.sun2surf.com/article.cfm?id=15717 | title = 15 areas with unhealthy air (updated) | first = S.Tamarai | last = Chelvi | location = Petaling Jaya | publisher = Sun Media Corporation Sdn. Bhd. | archive-url = https://web.archive.org/web/20090110073337/http://www.sun2surf.com/article.cfm?id=15717 | archive-date = 10 January 2009}}</ref> The economic losses of the fires in 1997 have been estimated at more than US$9 billion.<ref>{{cite web | url = http://haze.asean.org/?wpfb_dl=12 | date = 28 June 2007 | title = Combating Haze in ASEAN: Frequently Asked Questions | author = ASEAN Secretariat, Jl. | publisher = ASEAN Haze Action Online | access-date = 25 October 2013 | archive-date = 29 October 2013 | archive-url = https://web.archive.org/web/20131029195409/http://haze.asean.org/?wpfb_dl=12 | url-status = dead }}</ref> This includes damages in agriculture production, destruction of forest lands, health, transportation, tourism, and other economic endeavours. Not included are social, environmental, and psychological problems and long-term health effects. The [[2006 Southeast Asian haze|second-latest bout of haze]] to occur in [[Malaysia]], [[Singapore]] and the [[Malacca Straits]] is in October 2006, and was caused by smoke from fires in [[Indonesia]] being blown across the Straits of Malacca by south-westerly winds. A similar haze has occurred in June 2013, with the PSI setting a [[Pollutant Standards Index#PSI in Singapore|new record]] in Singapore on 21 June at 12pm with a reading of 401, which is in the "Hazardous" range.<ref>{{cite news|url=http://www.channelnewsasia.com/news/singapore/psi-hits-new-all-time/719496.html |archive-url=https://web.archive.org/web/20130624015317/http://www.channelnewsasia.com/news/singapore/psi-hits-new-all-time/719496.html |archive-date=24 June 2013 |title=Singapore: PSI hits new all-time high of 401 on Friday |publisher=Channel NewsAsia |date=21 June 2013 |url-status=dead }}</ref>▼
The [[Association of Southeast Asian Nations]] (ASEAN) reacted. In 2002, the [[ASEAN Agreement on Transboundary Haze Pollution|Agreement on Transboundary Haze Pollution]] was signed between all ASEAN nations.<ref>{{cite web | url = http://haze.asean.org/?page_id=185 | title = ASEAN Agreement on Transboundary Haze Pollution | author = ASEAN Secretariat, Jl. | publisher = ASEAN Haze Action Online | access-date = 31 January 2019 | archive-url = https://web.archive.org/web/20150910063035/http://haze.asean.org/?page_id=185 | archive-date = 10 September 2015 | url-status = dead }}</ref> ASEAN formed a Regional Haze Action Plan (RHAP) and established a co-ordination and support unit (CSU).<ref>{{cite web | url = http://haze.asean.org/?page_id=244 | title = About Us | author = ASEAN Secretariat, Jl. | publisher = ASEAN Haze Action Online | access-date = 31 January 2019 | archive-url = https://web.archive.org/web/20150912134926/http://haze.asean.org/?page_id=244 | archive-date = 12 September 2015 | url-status = dead }}</ref> RHAP, with the help of [[Canada]], established a monitoring and warning system for forest/vegetation fires and implemented a Fire Danger Rating System (FDRS). The Malaysian Meteorological Department (MMD) has issued a daily rating of fire danger since September 2003.<ref>{{cite web | url = http://www.met.gov.my/index.php?option=com_content&task=view&id=4749&Itemid=1157 | title = Fire Danger Rating System (FDRS) for Southeast Asia | author = Malaysian Meteorological Department | publisher = Ministry of Science, Technology, and Innovation (MOSTI), Malaysia | access-date = 25 October 2013 | url-status = dead | archive-url = https://web.archive.org/web/20131029192243/http://www.met.gov.my/index.php?option=com_content&task=view&id=4749&Itemid=1157 | archive-date = 29 October 2013 }}</ref> Indonesia has been ineffective at enforcing legal policies on errant farmers.{{citation needed | date = October 2013}}▼
==== Pakistan ====
Since the start of the winter season, heavy smog loaded with pollutants covered major parts of [[Punjab, Pakistan|Punjab]], especially the city of [[Lahore]],<ref>{{Cite web|url=https://scroll.in/article/856628/smoke-signal-winter-smog-is-a-reminder-india-and-pakistan-need-to-talk-about-more-than-geopolitics|title=Smoke signal: Winter smog is a reminder India and Pakistan need to talk about more than geopolitics|website=Scroll.in|date=5 November 2017 }}</ref> causing breathing problems and disrupting normal traffic.<ref>{{Cite news|url=http://www.foxnews.com/world/2016/11/05/polluted-smog-covers-pakistan-city-lahore.html|title=Polluted smog covers Pakistan's city of Lahore|date=5 November 2016|newspaper=Fox News|language=en-US|access-date=6 November 2016}}</ref> A recent study from 2022 shows that the primary cause of pollution in Lahore is from traffic-related PM (both exhausts and non exhaust sources)<ref>{{Cite journal|url=https://www.repository.cam.ac.uk/bitstreams/9fab52d7-4aac-4adf-ab2a-28ad0da46cc7/download|title=Biomagnetic Characterization of Air Pollution Particulates in Lahore, Pakistan|last=Sheikh|first=Hassan Aftab|journal=Geochemistry, Geophysics, Geosystems |date=18 January 2022|volume=23 |issue=2 |doi=10.1029/2021GC010293 |bibcode=2022GGG....2310293S |s2cid=245135298 }}</ref>▼
Doctors advised residents to stay indoors and wear facemasks outside.<ref>{{Cite news|url=http://www.dawn.com/news/1159190|title=Lahore smog: It's not a natural phenomenon|last=Khan|first=Rina Saeed|date=24 January 2015|newspaper=dawn.com|access-date=6 November 2016}}</ref>▼
====London====
[[Image:LondonSmog.jpg|thumbnail|right|[[Victorian era|Victorian]] [[London]] was notorious for its thick smogs, or "[[Pea soup fog|pea-soupers]]", a fact that is often recreated (as here) to add an air of mystery to a period [[costume drama]]]]
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The cities of Glasgow and Edinburgh, in Scotland, suffered smoke-laden fogs in 1909. Des Voeux, commonly credited with creating the "smog" moniker, presented a paper in 1911 to the Manchester Conference of the Smoke Abatement League of Great Britain about the fogs and resulting deaths.<ref>{{cite web | url = http://www.grida.no/geo/GEO/Geo-3-010.htm | title = The Great Smog Of 1952 | publisher = The Met Office | url-status = dead | archive-url = https://web.archive.org/web/20131029194334/http://www.grida.no/geo/GEO/Geo-3-010.htm | archive-date = 29 October 2013 }}</ref>
One [[Birmingham]] resident described near black-out conditions in the 1900s before the Clean Air Act, with visibility so poor that cyclists had to dismount and walk
On 29 April 2015, the [[UK Supreme Court]] ruled that the government must take immediate action to cut air pollution,<ref>{{cite news|url=https://www.bbc.co.uk/news/science-environment-32512152 |title=Court orders UK to cut NO2 air pollution |work=BBC News |publisher=BBC |date=29 April 2015 |access-date=29 April 2015}}</ref> following a case brought by environmental lawyers at ClientEarth.<ref>{{cite news|url=http://www.clientearth.org/news/press-releases/uk-supreme-court-orders-government-to-take-immediate-action-on-air-pollution-2843 |title=UK Supreme Court orders Government to take "immediate action" on air pollution |publisher=ClientEarth |date=29 April 2015 |access-date=29 April 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150505041213/http://www.clientearth.org/news/press-releases/uk-supreme-court-orders-government-to-take-immediate-action-on-air-pollution-2843 |archive-date=5 May 2015 }}</ref>
===
==== Mexico ====
[[File:AerialViewMexicoCity.jpg|thumb|Situated in a valley, and relying heavily on automobiles, Mexico City often suffers from poor air quality.]]
Due to its location in a highland "bowl", cold air sinks down onto the urban area of [[Mexico City]], trapping industrial and vehicle pollution underneath, and turning it into the most infamously smog-plagued city of Latin America. Within one generation, the city has changed from being known for some of the cleanest air of the world into one with some of the worst pollution, with pollutants like [[nitrogen dioxide]] being double or even triple international standards.<ref>[http://biophysics.sbg.ac.at/mexico/air.htm SBC.ac.at] {{Webarchive|url=https://web.archive.org/web/20110914131727/http://biophysics.sbg.ac.at/mexico/air.htm |date=14 September 2011 }}, Air pollution in Mexico City, [[University of Salzburg]]</ref>
[[File:AerialViewPhotochemicalSmogMexicoCity 2.jpg|thumb|Photochemical smog over Mexico City, December 2010]]
===
Similar to Mexico City, the air pollution of the [[Santiago]] valley in Chile, located between the [[Andes]] and the [[Chilean Coast Range]], turn it into the most infamously smog-plagued city of South America. Other aggravates of the situation reside in its high latitude (31 degrees South) and dry weather during most of the year.
===
==== Canada ====
▲According to the Canadian Science Smog Assessment published in 2012, smog is responsible for detrimental effects on human and ecosystem health, as well as socioeconomic well-being across the country. It was estimated that the province of [[Ontario]] sustains $201 million in damages annually for selected crops, and an estimated tourism revenue degradation of $7.5 million in [[Vancouver]] and $1.32 million in The [[Fraser Valley]] due to decreased visibility. [[Air pollution in British Columbia]] is of particular concern, especially in the Fraser Valley, because of a meteorological effect called [[Inversion (meteorology)|inversion]] which decreases air dispersion and leads to smog concentration.<ref>{{cite book |last1 = Environment Canada |last2 = Health Canada |author-link = Environment and Climate Change Canada |author2-link = Health Canada |title = Canadian Smog Science Assessment – Highlights and Key Messages |publisher = Environment Canada |date = 2011 |location = Ottawa |pages = 57 |url = http://www.ec.gc.ca/Publications/AD024B6B-A18B-408D-ACA2-59B1B4E04863/CanadianSmogScienceAssessmentHighlightsAndKeyMessages.pdf |isbn = 978-1-100-19064-8 |access-date = 18 March 2017 |archive-url = https://web.archive.org/web/20160804082323/http://www.ec.gc.ca/Publications/AD024B6B-A18B-408D-ACA2-59B1B4E04863/CanadianSmogScienceAssessmentHighlightsAndKeyMessages.pdf |archive-date = 4 August 2016 |url-status = dead}}</ref>
==== United States ====
▲In December 2005, schools and public offices had to close in [[Tehran]] and 1,600 people were taken to hospital, in a severe smog blamed largely on unfiltered car exhaust.<ref>{{cite news |url=http://news.bbc.co.uk/1/hi/world/middle_east/4516430.stm |title=Hundreds treated over Tehran smog |work=[[BBC]] News |date=10 December 2005 |access-date=3 August 2006}}</ref>
▲=== United States ===
[[Image:Upstatenysmog.jpg|thumb|right|A [[NASA]] astronaut's photograph of a smog layer over central [[New York (state)|New York]]]]
[[Image:LAcityhalllookingsouth8.JPG|thumb|right|View of smog south from [[Los Angeles City Hall]], September 2011]]
[[Image:US Counties Designated Non-attainment according to EPA NAAQS.jpg|thumb|right|Counties in the United States where one or more [[National Ambient Air Quality Standards]] are not met, as of October 2015]]
Smog was brought to the attention of the general U.S. public in 1933 with the publication of the book "Stop That Smoke", by Henry Obermeyer, a New York public utility official, in which he pointed out the effect on human life and even the destruction of {{convert|3000|acre|km2}} of a farmer's spinach crop.<ref>{{Cite web|url=https://books.google.com/books?id=6CcDAAAAMBAJ&q=motor+gun+boat&pg=PA29|title=Popular Science|date=10 October 1933|publisher=Bonnier Corporation|via=Google Books}}</ref> Since then, the [[United States Environmental Protection Agency]] has designated over 300 U.S. counties to be non-attainment areas for one or more pollutants tracked as part of the [[National Ambient Air Quality Standards]].<ref>[http://www.epa.gov/oar/oaqps/greenbk/ EPA.gov<!-- Bot generated title -->], The Green Book Nonattainment Areas, Green Book |</ref> These areas are largely clustered around large metropolitan areas, with the largest contiguous non-attainment zones in California and the Northeast. Various U.S. and Canadian government agencies collaborate to produce real-time air quality maps and [[Air pollution forecasting|forecasts]].<ref>{{cite web | url = http://www.airnow.gov/index.cfm?action=topics.about_airnow | title = About AIRNow | date = 6 May 2013 | publisher = AIRNow | access-date = 25 October 2013 | archive-url = https://web.archive.org/web/20131029190708/http://www.airnow.gov/index.cfm?action=topics.about_airnow | archive-date = 29 October 2013 | url-status = dead }}</ref> To combat smog conditions, localities may declare "smog alert" days, such as in the [[Spare the Air program]] in the [[San Francisco Bay Area]]. By 1970, Congress enacted the Clean Air Act to regulate air pollutant emissions.<ref>{{Cite web |last=US EPA |first=OP |date=2013-02-22 |title=Summary of the Clean Air Act |url=https://www.epa.gov/laws-regulations/summary-clean-air-act |access-date=2022-03-13 |website=www.epa.gov |language=en}}</ref>
In the United States, smog pollution kills 24,000 Americans every year. The U.S. is among the dirtier countries in terms of smog, ranked 123 out of 195 countries measured, where 1 is cleanest and 195 is most smog polluted.<ref>Associated Press, 5 June 2019, [https://www.apnews.com/a2e7024d43c9409087ec8d5245534092 "AP Fact Check: Trump Didn't Set Records on Clean Air in US"]</ref>
====={{anchor|LA}}Los Angeles and the San Joaquin Valley=====
Because of their locations in low basins surrounded by mountains, [[Los Angeles]] and the [[San Joaquin Valley]] are notorious for their smog. Heavy automobile traffic, combined with the additional effects of the [[San Francisco Bay]] and Los Angeles/[[Long Beach, California|Long Beach]] port complexes, frequently contribute to further air pollution.
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Los Angeles was one of the best-known cities suffering from transportation smog for much of the 20th century, so much so that it was sometimes said that ''Los Angeles'' was a synonym for ''smog.''<ref>{{cite book|title=The Economics and Politics of the Slowdown in Regulatory Reform|author=Roger G. Noll|year=1999}}</ref> In 1970, when the Clean Air Act was passed, Los Angeles was the most polluted basin in the country, and California was unable to create a State Implementation Plan that would enable it to meet the new air quality standards.<ref>"Early Implementation of the Clean Air Act of 1970 in California." EPA Alumni Association. [http://www.epaalumni.org/history/video/interview.cfm?id=38 Video], [https://www.epaalumni.org/userdata/pdf/2B9E3C6816EC9466.pdf#page=1 Transcript] (see p6). 12 July 2016.</ref> However, ensuing strict regulations by state and federal government agencies overseeing this problem (such as the [[California Air Resources Board]] and the [[United States Environmental Protection Agency]]), including tight restrictions on allowed emissions levels for all new cars sold in California and mandatory regular emission tests of older vehicles, resulted in significant improvements in air quality.<ref>{{Cite web|last=US EPA|first=OAR|date=2016-05-05|title=Vehicle Emissions California Waivers and Authorizations|url=https://www.epa.gov/state-and-local-transportation/vehicle-emissions-california-waivers-and-authorizations|access-date=2020-11-26|website=US EPA|language=en}}</ref> For example, air concentrations of volatile organic compounds declined by a factor of 50 between 1962 and 2012.<ref>{{Cite web|url=https://csl.noaa.gov/news/2012/119_0809.html|title=NOAA CSL: 2012 News & Events: 50-year decline in some Los Angeles vehicle-related pollutants|first=NOAA Chemical Sciences|last=Laboratory (CSL)|website=csl.noaa.gov}}</ref> Concentrations of air pollutants such as nitrous oxides and ozone declined by 70% to 80% over the same period of time.<ref>{{cite web|url=http://hbsciu.com/2015/02/15/is-clean-air-worth-the-cost-a-case-study-for-developing-megacities-2/|title=Is clean air worth the cost? A case study for developing megacities|date=15 February 2015}}</ref>
===== Major incidents in the U.S. =====
* 26 July 1943, [[Los Angeles, California]]: A smog so sudden and severe that "Los Angeles residents believe the Japanese are attacking them with chemical warfare."<ref>{{cite magazine | date = 2010 | url = https://www.wired.com/2010/07/0726la-first-big-smog/ | title = July 26, 1943: L.A. Gets First Big Smog | author = Jess McNally | magazine = Wired}}</ref><ref>{{cite book |last=Buntin |first=John |title=L.A. Noir: The Struggle for the Soul of America's Most Seductive City |url=https://books.google.com/books?id=PIHClVp5F4AC |access-date=12 October 2014 |year=2009 |publisher=Harmony Books |location=New York |isbn=9780307352071 |oclc=431334523 |page=108}}</ref>
* [[1948 Donora smog|30-31 October 1948]], [[Donora, Pennsylvania]]: 20 died, 600 hospitalized, thousands more stricken. Lawsuits were not settled until 1951.<ref name="autogenerated2">{{cite web | date = 1948 | url = http://www.radford.edu/~wkovarik/envhist/7forties.html | title = World War II and the Postwar Years | publisher = Environmental History Timeline | url-status = dead | archive-url = https://web.archive.org/web/20110205085302/http://www.radford.edu/~wkovarik/envhist/7forties.html | archive-date = 5 February 2011 }}</ref>
* [[1966 New York City smog|24 November 1966]], [[New York City, New York]]: Smog kills at least 169<ref>{{cite news|url=https://www.washingtonpost.com/blogs/capital-weather-gang/post/the-killer-london-smog-event-of-december-1952-a-reminder-of-deadly-smog-events-in-us/2012/12/19/452c66bc-498e-11e2-b6f0-e851e741d196_blog.html |title=The Killer London Smog Event of December 1952: A Reminder of Deadly Smog Events in the US |last=Tracton |first=Steve |newspaper=The Washington Post |date=20 December 2012 |access-date=25 February 2015}}</ref> people.
▲In the late 1990s, massive immigration to [[Ulaanbaatar]] from the countryside began. An estimated 150,000 households, mainly living in traditional Mongolian [[Yurt|gers]] on the outskirts of Ulaanbaatar, burn wood and coal (some poor families burn even car tires and trash) to heat themselves during the harsh winter, which lasts from October to April, since these outskirts are not connected to the city's central heating system. A temporary solution to decrease smog was proposed in the form of stoves with improved efficiency, although with no visible results.
▲Coal-fired ger stoves release high levels of ash and other particulate matter (PM). When inhaled, these particles can settle in the lungs and respiratory tract and cause health problems. At two to 10 times above Mongolian and international air quality standards, Ulaanbaatar's PM rates are among the worst in the world, according to a December 2009 World Bank report. The Asian Development Bank (ADB) estimates that health costs related to this air pollution account for as much as 4 percent of Mongolia's GDP.<ref>{{cite news | url = http://www.eurasianet.org/departments/news/articles/eav032310e.shtml | title = Mongolia: Ulaanbaatar Grapples with Smog Problem | date = 22 March 2010 | first = Andrew | last = Cullen | publisher = EurasiaNet.org | access-date = 1 October 2012 | archive-url = https://web.archive.org/web/20120828095515/http://www.eurasianet.org/departments/news/articles/eav032310e.shtml | archive-date = 28 August 2012 | url-status = dead }}</ref>
▲=== Southeast Asia ===
▲{{See also|Asian brown cloud|haze}}
▲[[Image:Downtown Core, Singapore, Oct 06.JPG|thumb|left|[[Singapore]]'s [[Downtown Core]] on 7 October 2006, when it was affected by [[wildfire|forest fires]] in [[Sumatra]], [[Indonesia]]]]
▲Smog is a regular problem in [[Southeast Asia]] caused by [[wildfire|land and forest fires]] in [[Indonesia]], especially [[Sumatra]] and [[Kalimantan]], although the term [[haze]] is preferred in describing the problem. Farmers and plantation owners are usually responsible for the fires, which they use to clear tracts of land for further plantings. Those fires mainly affect [[Brunei]], [[Indonesia]], [[Philippines]], [[Malaysia]], [[Singapore]] and [[Thailand]], and occasionally [[Guam]] and [[Saipan]].<ref>{{cite news|url=http://www.saipantribune.com/newsstory.aspx?cat=1&newsID=61706 |date=5 October 2006 |title=Indon haze spreads to NMI |first=Ferdie |last=de la Torre |work=Saigpan Tribune |url-status=dead |archive-url=https://web.archive.org/web/20070218044848/http://www.saipantribune.com/newsstory.aspx?cat=1&newsID=61706 |archive-date=18 February 2007 }}</ref><ref>{{cite news | url = http://www.sun2surf.com/article.cfm?id=15717 | title = 15 areas with unhealthy air (updated) | first = S.Tamarai | last = Chelvi | location = Petaling Jaya | publisher = Sun Media Corporation Sdn. Bhd. | archive-url = https://web.archive.org/web/20090110073337/http://www.sun2surf.com/article.cfm?id=15717 | archive-date = 10 January 2009}}</ref> The economic losses of the fires in 1997 have been estimated at more than US$9 billion.<ref>{{cite web | url = http://haze.asean.org/?wpfb_dl=12 | date = 28 June 2007 | title = Combating Haze in ASEAN: Frequently Asked Questions | author = ASEAN Secretariat, Jl. | publisher = ASEAN Haze Action Online | access-date = 25 October 2013 | archive-date = 29 October 2013 | archive-url = https://web.archive.org/web/20131029195409/http://haze.asean.org/?wpfb_dl=12 | url-status = dead }}</ref> This includes damages in agriculture production, destruction of forest lands, health, transportation, tourism, and other economic endeavours. Not included are social, environmental, and psychological problems and long-term health effects. The [[2006 Southeast Asian haze|second-latest bout of haze]] to occur in [[Malaysia]], [[Singapore]] and the [[Malacca Straits]] is in October 2006, and was caused by smoke from fires in [[Indonesia]] being blown across the Straits of Malacca by south-westerly winds. A similar haze has occurred in June 2013, with the PSI setting a [[Pollutant Standards Index#PSI in Singapore|new record]] in Singapore on 21 June at 12pm with a reading of 401, which is in the "Hazardous" range.<ref>{{cite news|url=http://www.channelnewsasia.com/news/singapore/psi-hits-new-all-time/719496.html |archive-url=https://web.archive.org/web/20130624015317/http://www.channelnewsasia.com/news/singapore/psi-hits-new-all-time/719496.html |archive-date=24 June 2013 |title=Singapore: PSI hits new all-time high of 401 on Friday |publisher=Channel NewsAsia |date=21 June 2013 |url-status=dead }}</ref>
▲The [[Association of Southeast Asian Nations]] (ASEAN) reacted. In 2002, the [[ASEAN Agreement on Transboundary Haze Pollution|Agreement on Transboundary Haze Pollution]] was signed between all ASEAN nations.<ref>{{cite web | url = http://haze.asean.org/?page_id=185 | title = ASEAN Agreement on Transboundary Haze Pollution | author = ASEAN Secretariat, Jl. | publisher = ASEAN Haze Action Online | access-date = 31 January 2019 | archive-url = https://web.archive.org/web/20150910063035/http://haze.asean.org/?page_id=185 | archive-date = 10 September 2015 | url-status = dead }}</ref> ASEAN formed a Regional Haze Action Plan (RHAP) and established a co-ordination and support unit (CSU).<ref>{{cite web | url = http://haze.asean.org/?page_id=244 | title = About Us | author = ASEAN Secretariat, Jl. | publisher = ASEAN Haze Action Online | access-date = 31 January 2019 | archive-url = https://web.archive.org/web/20150912134926/http://haze.asean.org/?page_id=244 | archive-date = 12 September 2015 | url-status = dead }}</ref> RHAP, with the help of [[Canada]], established a monitoring and warning system for forest/vegetation fires and implemented a Fire Danger Rating System (FDRS). The Malaysian Meteorological Department (MMD) has issued a daily rating of fire danger since September 2003.<ref>{{cite web | url = http://www.met.gov.my/index.php?option=com_content&task=view&id=4749&Itemid=1157 | title = Fire Danger Rating System (FDRS) for Southeast Asia | author = Malaysian Meteorological Department | publisher = Ministry of Science, Technology, and Innovation (MOSTI), Malaysia | access-date = 25 October 2013 | url-status = dead | archive-url = https://web.archive.org/web/20131029192243/http://www.met.gov.my/index.php?option=com_content&task=view&id=4749&Itemid=1157 | archive-date = 29 October 2013 }}</ref> Indonesia has been ineffective at enforcing legal policies on errant farmers.{{citation needed | date = October 2013}}
▲=== Pakistan ===
▲Since the start of the winter season, heavy smog loaded with pollutants covered major parts of [[Punjab, Pakistan|Punjab]], especially the city of [[Lahore]],<ref>{{Cite web|url=https://scroll.in/article/856628/smoke-signal-winter-smog-is-a-reminder-india-and-pakistan-need-to-talk-about-more-than-geopolitics|title=Smoke signal: Winter smog is a reminder India and Pakistan need to talk about more than geopolitics|website=Scroll.in|date=5 November 2017 }}</ref> causing breathing problems and disrupting normal traffic.<ref>{{Cite news|url=http://www.foxnews.com/world/2016/11/05/polluted-smog-covers-pakistan-city-lahore.html|title=Polluted smog covers Pakistan's city of Lahore|date=5 November 2016|newspaper=Fox News|language=en-US|access-date=6 November 2016}}</ref> A recent study from 2022 shows that the primary cause of pollution in Lahore is from traffic-related PM (both exhausts and non exhaust sources)<ref>{{Cite journal|url=https://www.repository.cam.ac.uk/bitstreams/9fab52d7-4aac-4adf-ab2a-28ad0da46cc7/download|title=Biomagnetic Characterization of Air Pollution Particulates in Lahore, Pakistan|last=Sheikh|first=Hassan Aftab|journal=Geochemistry, Geophysics, Geosystems |date=18 January 2022|volume=23 |issue=2 |doi=10.1029/2021GC010293 |bibcode=2022GGG....2310293S |s2cid=245135298 }}</ref>
▲Doctors advised residents to stay indoors and wear facemasks outside.<ref>{{Cite news|url=http://www.dawn.com/news/1159190|title=Lahore smog: It's not a natural phenomenon|last=Khan|first=Rina Saeed|date=24 January 2015|newspaper=dawn.com|access-date=6 November 2016}}</ref>
== Pollution index ==
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