Editing Megacity (section)

===Air pollution===
[[File:Shanghai Smog.JPG|thumb|Air pollution in [[Shanghai]], China]]
[[Air pollution]] is the introduction into the [[Earth's atmosphere|atmosphere]] of [[chemical]]s, [[Atmospheric particulate matter|particulate matter]], or [[biotic material|biological materials]] that cause harm or discomfort to humans or other living organisms, or damages the [[natural environment]].<ref>{{cite journal |last1=Decker |first1=Ethan H. |last2=Elliott |first2=Scott |last3=Smith |first3=Felisa A. |title=Megacities and the Environment |journal=[[The Scientific World Journal]] |date=2002 |volume=2 |pages=374–386 |doi=10.1100/tsw.2002.103|pmid=12806023 |pmc=6009397 |doi-access=free }}</ref><ref>{{cite journal |last1=Folberth |first1=Gerd A. |last2=Butler |first2=Timothy M. |last3=Collins |first3=William J. |last4=Rumbold |first4=Steven T. |title=Megacities and climate change – A brief overview |journal=[[Environmental Pollution (journal)|Environmental Pollution]] |date=2015 |volume=203 |pages=235–242 |doi=10.1016/j.envpol.2014.09.004 |pmid=25300966 |doi-access=free|bibcode=2015EPoll.203..235F }}</ref> This issue is particularly prevalent in developing nations. As part of the Global Environment Monitoring System, [[WHO]] and [[UNEP]] established an air pollution monitoring network that oversees 50 cities.<ref>{{Cite journal |last1=Mage |first1=David |last2=Ozolins |first2=Guntis |last3=Peterson |first3=Peter |last4=Webster |first4=Anthony |last5=Orthofer |first5=Rudi |last6=Vandeweerd |first6=Veerle |last7=Gwynne |first7=Michael |date=1996-03-01 |title=Urban air pollution in megacities of the world |url=https://linkinghub.elsevier.com/retrieve/pii/1352231095002197 |journal=Atmospheric Environment |series=Supercities: Environment Quality and Sustainable Development |volume=30 |issue=5 |pages=681–686 |doi=10.1016/1352-2310(95)00219-7 |bibcode=1996AtmEn..30..681M |issn=1352-2310}}</ref> Many urban areas have significant problems with [[smog]], a type of [[air pollution]] derived from [[Motor vehicle emissions|vehicle emissions]] from [[internal combustion engine]]s and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form [[photochemical smog]].<ref name=":0" />