Editing Smog (section)

==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 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> and volatile organic compounds<ref name="queensland2" /><ref name="epa-no22" /> including [[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" />