Editing Ground-level ozone (section)

==Ozone and the climate==
Ground-level ozone is both naturally occurring and anthropogenically formed. It is the primary constituent of urban smog, forming naturally as a secondary pollutant through photochemical reactions involving nitrogen oxides and volatile organic compounds in the presence of bright sunshine with high temperatures.<ref>{{cite journal |last1=Ebi |first1=Kristie L. |last2=McGregor |first2=Glenn |title=Climate Change, Tropospheric Ozone, and Particulate Matter, and Health Impacts |date=2008-11-01 |journal=Environmental Health Perspectives |volume=116 |issue=11 |pages=1449–1455 |pmid=19057695 |doi=10.1289/ehp.11463 |pmc=2592262}}</ref>

Regardless of whether it occurs naturally or is anthropogenically formed, the change in ozone concentrations in the upper troposphere will:
* exert a considerable impact on global warming, because it is a key air pollutant and greenhouse gas, and
* impact the production of surface level ozone (contributing again to climate change).

As a result, photochemical smog pollution at the earth's surface, as well as stratospheric ozone depletion, have received a lot of attention in recent years. The disruptions in the "free troposphere" are likely to be the focus of the next cycle of scientific concern. In several parts of the northern hemisphere, tropospheric ozone levels have been rising.<ref>{{cite web |title=The Royal Society |website=royalsociety.org |url=https://royalsociety.org/~/media/royal_society_content/policy/publications/2008/7925.pdf |access-date=2022-03-31}}</ref> On various scales, this may have an impact on moisture levels, cloud volume and dispersion, precipitation, and atmospheric dynamics. A rising environment, on the other hand, favours ozone synthesis and accumulation in the atmosphere, owing to two physicochemical mechanisms. First, a warming climate alters humidity and wind conditions in some parts of the world, resulting in a reduction in the frequency of surface cyclones.<ref name="Ebi 1449–1455">{{cite journal |last1=Ebi |first1=Kristie L. |last2=McGregor |first2=Glenn |title=Climate Change, Tropospheric Ozone and Particulate Matter, and Health Impacts |date=2008-11-01 |journal=Environmental Health Perspectives |volume=116 |issue=11 |pages=1449–1455 |pmid=19057695 |doi=10.1289/ehp.11463 |pmc=2592262}}</ref>

===Climate change impacts on processes that affect ozone===
Changes in air temperature and water content affect the air's chemistry and the rates of chemical reactions that create and remove ozone. Many chemical reaction rates increase with temperature and lead to increased ozone production. Climate change projections show that rising temperatures and water vapour in the atmosphere will likely increase surface ozone in polluted areas like the eastern United States.<ref name="Ebi 1449–1455"/> In particular, the degradation of the pollutant [[peroxyacetyl nitrate]] (PAN), which is a significant reservoir species for long-range transport of ozone precursors, is accelerated by rising temperatures. As a result, as the temperature rises, the lifetime of PAN reduces, changing the long-range transport of ozone pollution. Second, the same {{CO2}} radiative forcing that causes global warming would chill the stratosphere. This cooling is projected to result in a relative rise in ozone depletion in the polar region, as well as an increase in the frequency of ozone holes.<ref>{{cite journal |last1=Mohnen |first1=V.A. |last2=Goldstein |first2=W. |last3=Wang |first3=W.-C. |title=Tropospheric Ozone and Climate Change |date=October 1993 |journal=Air & Waste |volume=43 |issue=10 |pages=1332–1334 |issn=1073-161X |doi=10.1080/1073161x.1993.10467207 |doi-access=free}}</ref>

Ozone depletion, on the other hand, is a radiative forcing of the climate system. Two opposite effects exist: Reduced ozone causes the stratosphere to absorb less solar radiation, cooling it while warming the troposphere; as a result, the stratosphere emits less long-wave radiation downward, cooling the troposphere. The IPCC believes that "measured stratospheric O3 losses over the past two decades have generated a negative forcing of the surface-troposphere system" of around 0.15 0.10 watts per square metre (W/m<sup>2</sup>).<ref>{{cite web |last1=Braconnot |first1=Pascale |last2=Gillett |first2=Nathan P. |last3=Luo |first3=Yong |last4=Marengo Orsini |first4=Jose A. |last5=Nicholls |first5=Neville |last6=Penner |first6=Joyce E. |last7=Stott |first7=Peter A. |title=Understanding and Attributing Climate Change |url=https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter9-1.pdf |url-status=live |archive-url=https://web.archive.org/web/20180508152907/http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter9.pdf |archive-date=2018-05-08}}</ref> Furthermore, rising air temperatures often improve ozone-forming processes, which has a repercussion on climate, as well.

Ozone production rises during [[heat wave]]s, because plants absorb less ozone. It is estimated that curtailed ozone absorption by plants could be responsible for the loss of 460 lives in the UK in the hot summer of 2006.<ref>{{cite news |title=It's not just the heat – it's the ozone: Study highlights hidden dangers |publisher=[[University of York]] |url=https://www.york.ac.uk/news-and-events/news/2013/research/heat-ozone/ |access-date=January 14, 2014}}</ref> A similar investigation to assess the joint effects of ozone and heat during the European heat waves in 2003, concluded that these appear to be additive.<ref>{{cite journal |author=Kosatsky T. |title=The 2003 European heat waves |date=July 2005 |journal=Eurosurveillance |volume=10 |issue=7 |pages=3–4 |pmid=29208081 |doi=10.2807/esm.10.07.00552-en |doi-access=free}}</ref>

In the Arctic, due to climate change, "the sea ice that lasts from one winter to the next [[Arctic sea ice decline|is decreasing]]. This has created a larger area of melted ice, and more ice that comes and goes with the seasons. This seasonal variation in ice ''could'' release more molecular chlorine into the atmosphere." "The level of molecular [[chlorine]] above Barrow was measured as high as 400 parts per trillion." "The ultimate source of the molecular chlorine is the sodium chloride in sea salt, most likely from the snow-covered ice pack. How the sea salt is transformed into molecular chlorine is unknown." The molecular chlorine reacts with UV radiation, producing highly reactive chlorine radicals that expedite the degradation of [[atmospheric methane|methane]] and tropospheric ozone, and oxidize [[mercury (element)|mercury]] into more toxic forms.<ref>{{cite news |title=High Levels of Molecular Chlorine Found in Arctic Atmosphere |date=January 13, 2014 |publisher=[[Georgia Tech]] News Center |url=https://news.gatech.edu/news/2014/01/13/high-levels-molecular-chlorine-found-arctic-atmosphere}}</ref><ref>{{cite journal |author=Jin Liao |display-authors=etal |title=High levels of molecular chlorine in the Arctic atmosphere |date=January 12, 2014 |journal=[[Nature Geoscience]] |volume=7 |issue=2 |pages=91–94 |bibcode=2014NatGe...7...91L |doi=10.1038/ngeo2046 |url=https://www.nature.com/articles/ngeo2046|url-access=subscription }}</ref>