Editing Smog (section)

===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" />