Editing Ground-level ozone (section)

{{Short description|Constituent gas of the troposphere}}
[[File:TOR.Seasonal.Global.CLIM.jpeg|thumb|Seasonal average vertical columns of tropospheric ozone in [[Dobson unit]]s over the period 1979 to 2000. In June to August, photochemical ozone production causes very high concentrations over the East Coast of the US and China.]]

'''Ground-level ozone''' ('''{{O3}}'''), also known as '''surface-level ozone''' and '''tropospheric ozone''', is a [[trace gas]] in the [[troposphere]] (the lowest level of the [[atmosphere of Earth|Earth's atmosphere]]), with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas.<ref name=":6">{{cite book |title=Chemistry of The Natural Atmosphere |last=Warneck |first=Peter |publisher=Academic Press |year=1999 |isbn=9780080529066}}</ref><ref name=":32">{{cite web |title=8.2 Tropospheric ozone |website=elte.prompt.hu |url=http://elte.prompt.hu/sites/default/files/tananyagok/AtmosphericChemistry/ch08s02.html |access-date=2018-11-12}}</ref> Ozone is also an important constituent of the [[stratosphere]], where the [[ozone layer]] (2 to 8 parts per million ozone) exists which is located between 10 and 50 kilometers above the Earth's surface.<ref>{{cite web |title=What is Stratospheric Ozone?- Defra, UK |last=Department for Environment |first=Food and Rural Affairs (Defra) webmaster@defra gsi gov uk |website=uk-air.defra.gov.uk |url=https://uk-air.defra.gov.uk/research/ozone-uv/ozone-concerns |access-date=2019-10-26}}</ref> The [[troposphere]] extends from the ground up to a variable height of approximately 14 kilometers above [[sea level]]. Ozone is least concentrated in the ground layer (or [[planetary boundary layer]]) of the troposphere.

Ground-level or tropospheric ozone is created by chemical reactions between [[NOx]] gases (oxides of nitrogen produced by combustion) and [[volatile organic compound]]s (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, with a maximum concentration at the [[tropopause]].<ref name=":0">{{cite web |title=Nasa Ozone Watch: Ozone facts |website=ozonewatch.gsfc.nasa.gov |url=https://ozonewatch.gsfc.nasa.gov/facts/SH.html |access-date=2018-11-12}}</ref> About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere.<ref>{{cite book |last=Fahey, David W. |title=Twenty questions and answers about the ozone layer 2010 update: scientific assessment of ozone depletion 2010 |date=2011 |publisher=World Meteorological Organisation |others=Hegglin, Michaela I., United States. National Oceanic and Atmospheric Administration., United States. National Aeronautics and Space Administration., United Nations Environment Programme., World Meteorological Organization., European Commission. |isbn=978-9966-7319-4-4 |location=Geneva, Switzerland |oclc=770711102 |url=https://www2.atmos.umd.edu/~rjs/class/spr2017/readings/WMO_Ozone_2010_QAs_lecture02.pdf}}</ref> Although ground-level ozone is less concentrated than stratospheric ozone, it is of concern because of its [[#Health effects|health effects]].<ref name=":42">{{cite web |title=Ozone in the Troposphere |publisher=UCAR Center for Science Education |website=scied.ucar.edu |url=https://scied.ucar.edu/learning-zone/air-quality/ozone-troposphere |access-date=2018-11-12}}</ref> Ozone in the troposphere is a [[greenhouse gas]], and as such contribute to [[global warming#Greenhouse gases|global warming]].<ref name=":0" /><ref name=":42" /> It is the third most important greenhouse gas after {{CO2}} and {{CH4}}, as indicated by estimates of its [[radiative forcing]].<ref>{{cite journal |last=Skeie |first=Ragnhild Bieltvedt |last2=Myhre |first2=Gunnar |last3=Hodnebrog |first3=Øivind |last4=Cameron-Smith |first4=Philip J. |last5=Deushi |first5=Makoto |last6=Hegglin |first6=Michaela I. |last7=Horowitz |first7=Larry W. |last8=Kramer |first8=Ryan J. |last9=Michou |first9=Martine |last10=Mills |first10=Michael J. |last11=Olivié |first11=Dirk J. L. |last12=O'Connor |first12=Fiona M. |last13=Paynter |first13=David |last14=Samset |first14=Bjørn H. |last15=Sellar |first15=Alistair |title=Historical total ozone radiative forcing derived from CMIP6 simulations |date=2020-08-17 |journal=npj Climate and Atmospheric Science |language=en |volume=3 |issue=1 |pages=1–10 |issn=2397-3722 |doi=10.1038/s41612-020-00131-0 |doi-access=free |hdl=11250/2771140 |hdl-access=free |url=https://www.nature.com/articles/s41612-020-00131-0}}</ref><ref>{{cite journal |last=Checa-Garcia |first=Ramiro |last2=Hegglin |first2=Michaela I. |last3=Kinnison |first3=Douglas |last4=Plummer |first4=David A. |last5=Shine |first5=Keith P. |title=Historical Tropospheric and Stratospheric Ozone Radiative Forcing Using the CMIP6 Database |date=2018-04-16 |journal=Geophysical Research Letters |language=en |volume=45 |issue=7 |pages=3264–3273 |issn=0094-8276 |doi=10.1002/2017GL076770 |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017GL076770}}</ref>

[[Photochemistry|Photochemical]] and chemical reactions involving ozone drive many of the chemical processes that occur in the troposphere by day and by night. At abnormally high concentrations (the largest source being emissions from [[combustion]] of [[fossil fuels]]), it is a [[pollutant]], and a constituent of [[smog]].<ref name=":12">{{cite web |title=Tropospheric ozone |publisher=Climate & Clean Air Coalition|website=ccacoalition.org |url=https://www.ccacoalition.org/en/slcps/tropospheric-ozone|access-date=2018-11-12}}</ref><ref name=":42"/> Its levels have increased significantly since the industrial revolution, as NOx gasses and VOCs are some of the byproducts of combustion.<ref name="US EPA">{{cite web |title=Ground-level Ozone Basics |last=US EPA |first=OAR |date=2015-05-29 |website=US EPA |url=https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics |access-date=2019-10-26}}</ref> With more heat and sunlight in the summer months, more ozone is formed which is why regions often experience higher levels of pollution in the summer months.<ref>{{cite journal |last1=Bloomer |first1=Bryan J. |last2=Stehr |first2=Jeffrey W. |last3=Piety |first3=Charles A. |last4=Salawitch |first4=Ross J. |last5=Dickerson |first5=Russell R. |title=Observed relationships of ozone air pollution with temperature and emissions |journal=Geophysical Research Letters |volume=36 |issue=9 |year=2009 |issn=1944-8007 |doi=10.1029/2009GL037308 |url=https://onlinelibrary.wiley.com/doi/abs/10.1029/2009GL037308 |access-date=2024-01-03}}</ref> Although the same molecule, ground-level ozone can be harmful to human health, unlike stratospheric ozone that protects the earth from excess UV radiation.<ref name="US EPA"/>

[[Photolysis]] of ozone occurs at wavelengths below approximately 310–320 [[nanometre]]s.<ref>{{cite journal |last1=Taniguchi |first1=Nori |last2=Takahashi |first2=Kenshi |last3=Matsumi |first3=Yutaka |title=Photodissociation of O3around 309 nm |journal=The Journal of Physical Chemistry A |volume=104 |issue=39 |pages=8936–8944 |issn=1089-5639 |year=2000 |bibcode=2000JPCA..104.8936T |doi=10.1021/jp001706i}}</ref><ref name=":22">{{cite journal |last1=Reeves |first1=Claire E. |last2=Penkett |first2=Stuart A. |last3=Bauguitte |first3=Stephane |last4=Law |first4=Kathy S. |last5=Evans |first5=Mathew J. |last6=Bandy |first6=Brian J. |last7=Monks |first7=Paul S. |last8=Edwards |first8=Gavin D. |last9=Phillips |first9=Gavin |title=Potential for photochemical ozone formation in the troposphere over the North Atlantic as derived from aircraft observations during ACSOE |date=2002-12-11 |journal=Journal of Geophysical Research: Atmospheres |volume=107 |issue=D23 |pages=ACH 14–1–ACH 14–14 |issn=0148-0227 |bibcode=2002JGRD..107.4707R |doi=10.1029/2002jd002415 |doi-access=free |url=https://juser.fz-juelich.de/record/34366|url-access=subscription }}</ref> This reaction initiates a chain of chemical reactions that remove [[carbon monoxide]], [[methane]], and other [[hydrocarbon]]s from the atmosphere via [[redox|oxidation]]. Therefore, the concentration of tropospheric ozone affects how long these compounds remain in the air. If the oxidation of carbon monoxide or methane occur in the presence of [[nitric oxide|nitrogen monoxide]] (NO), this chain of reactions has a net product of ozone added to the system.<ref name=":32"/><ref name=":42"/>