Editing Ozone (section)

====Ground-level ozone in urban areas====
Certain examples of cities with elevated ozone readings are [[Denver|Denver, Colorado]]; [[Houston, Texas]]; and [[Mexico City]], [[Mexico]]. Houston has a reading of around 41&nbsp;nmol/mol, while Mexico City is far more hazardous, with a reading of about 125&nbsp;nmol/mol.<ref name="arb.ca.gov"/>

Ground-level ozone, or tropospheric ozone, is the most concerning type of ozone pollution in urban areas and is increasing in general.<ref>{{cite book |title=Rethinking the Ozone Problem in Urban and Regional Air Pollution |date=1991-01-01 |isbn=978-0-309-04631-2 |doi=10.17226/1889 |url=https://archive.org/details/rethinkingozonep0000unse |url-access=registration}}</ref> Ozone pollution in urban areas affects denser populations, and is worsened by high populations of vehicles, which emit pollutants NO<sub>2</sub> and [[volatile organic compound|VOCs]], the main contributors to problematic ozone levels.<ref name="Sharma-2016">{{cite journal |last1=Sharma |first1=Sumit |last2=Sharma |first2=Prateek |last3=Khare |first3=Mukesh |last4=Kwatra |first4=Swati |title=Statistical behavior of ozone in urban environment |date=May 2016 |journal=Sustainable Environment Research |volume=26 |issue=3 |pages=142–148 |bibcode= 2016SusER..26..142S|doi=10.1016/j.serj.2016.04.006 |doi-access=free}}</ref> Ozone pollution in urban areas is especially concerning with increasing temperatures, raising heat-related mortality during [[heat wave]]s.<ref>{{cite journal |last1=Diem |first1=Jeremy E. |last2=Stauber |first2=Christine E. |last3=Rothenberg |first3=Richard |date=2017-05-16 |editor-last=Añel |editor-first=Juan A. |title=Heat in the southeastern United States: Characteristics, trends, and potential health impact |journal=PLOS ONE |volume=12 |issue=5 |pages=e0177937 |issn=1932-6203 |bibcode=2017PLoSO..1277937D |pmid=28520817 |doi=10.1371/journal.pone.0177937 |doi-access=free |pmc=5433771}}</ref> During heat waves in urban areas, [[ground level ozone]] pollution can be 20% higher than usual.<ref>{{cite journal |last1=Hou |first1=Pei |last2=Wu |first2=Shiliang |title=Long-term Changes in Extreme Air Pollution Meteorology and the Implications for Air Quality |date=July 2016 |journal=Scientific Reports |volume=6 |issue=1 |page=23792 |issn=2045-2322 |bibcode=2016NatSR...623792H |pmid=27029386 |doi=10.1038/srep23792 |pmc=4815017}}</ref> Ozone pollution in urban areas reaches higher levels of exceedance in the summer and autumn, which may be explained by weather patterns and traffic patterns.<ref name="Sharma-2016"/> People experiencing poverty are more affected by pollution in general, even though these populations are less likely to be contributing to pollution levels.<ref>{{cite journal |last1=Tessum |first1=Christopher W. |last2=Apte |first2=Joshua S. |last3=Good kind |first3=Andrew L. |last4=Muller |first4=Nicholas Z. |last5=Mullins |first5=Kimberley A. |last6=Paolella |first6=David A. |last7=Polasky |first7=Stephen |last8=Springer |first8=Nathaniel P. |last9=Thakrar |first9=Sumil K. |title=Inequity in consumption of goods and services adds to racial–ethnic disparities in air pollution exposure |date=2019-03-11 |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=13 |pages=6001–6006 |bibcode=2019PNAS..116.6001T |issn=0027-8424 |pmid=30858319 |doi=10.1073/pnas.1818859116 |doi-access=free |pmc=6442600}}</ref>

As mentioned above, Denver, Colorado, is one of the many cities in the U.S. that have high amounts of ozone. According to the [[American Lung Association]], the [[Denver–Aurora combined statistical area|Denver–Aurora area]] is the 14th most ozone-polluted area in the U.S.<ref>American Lung Association. (n.d.). How healthy is the air you breathe? Retrieved March 20, 2019, from [https://www.lung.org/our-initiatives/healthy-air/sota/city-rankings/most-polluted-cities.html lung.org]</ref> The problem of high ozone levels is not new to this area. In 2004, the EPA allotted the [[Denver metropolitan area|Denver Metro]]/North Front Range{{efn|This includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson, and parts of Larimer and Weld counties.}} as [[non-attainment area]]s per 1997's 8-hour ozone standard,<ref>{{cite web |title=History of ozone in Colorado |website=Colorado Department of Public Health & Environment |url=https://cdphe.colorado.gov/history-of-ozone-in-colorado |access-date=2023-04-18}}</ref> but later deferred this status until 2007. The non-attainment standard indicates that an area does not meet the EPA's air quality standards. The Colorado Ozone Action Plan was created in response, and numerous changes were implemented from this plan. The first major change was that car emission testing was expanded across the state to more counties that did not previously mandate emissions testing, like areas of Larimer and Weld County. There have also been changes made to decrease Nitrogen Oxides (NOx) and [[Volatile Organic Compound]] (VOC) emissions, which should help lower ozone levels.

One large contributor to high ozone levels in the area is the oil and [[natural gas]] industry situated in the Denver-Julesburg Basin (DJB) which overlaps with a majority of Colorado's metropolitan areas. Ozone is produced naturally in the Earth's stratosphere, but is also produced in the troposphere from human efforts. Briefly mentioned above, NOx and VOCs react with sunlight to create ozone through a process called photochemistry. One hour elevated ozone events (<75&nbsp;ppb) "occur during June–August indicating that elevated ozone levels are driven by regional photochemistry".<ref name="Evans-2017">{{cite journal |last1=Evans |first1=Jason M. |last2=Helmig |first2=Detlev |title=Investigation of the influence of transport from oil and natural gas regions on elevated ozone levels in the northern Colorado front range |date=February 2017 |journal=Journal of the Air & Waste Management Association |volume=67 |issue=2 |pages=196–211 |bibcode=2017JAWMA..67..196E |issn=1096-2247 |pmid=27629587 |doi=10.1080/10962247.2016.1226989 |doi-access=free}}</ref> According to an article from the University of Colorado-Boulder, "Oil and natural gas VOC emission have a major role in ozone production and bear the potential to contribute to elevated O<sub>3</sub> levels in the Northern Colorado Front Range (NCFR)".<ref name="Evans-2017"/> Using complex analyses to research wind patterns and emissions from large oil and natural gas operations, the authors concluded that "elevated O<sub>3</sub> levels in the NCFR are predominantly correlated with air transport from N– ESE, which are the upwind sectors where the O&NG operations in the Wattenberg Field area of the DJB are located".<ref name="Evans-2017"/>

Contained in the Colorado Ozone Action Plan, created in 2008, plans exist to evaluate "emission controls for large industrial sources of NOx" and "statewide control requirements for new oil and gas condensate tanks and pneumatic valves".<ref>{{cite web |title=Colorado Ozone Action Plan |author=((Colorado Department of Public Health and Environment, Regional Air Quality Council, & North Front Range Metropolitan Planning Organization)) |url=https://massless.info/images/AP_PO_Denver-Ozone-Action-Plan-2008.pdf |access-date=2019-03-21}}</ref> In 2011, the Regional Haze Plan was released that included a more specific plan to help decrease NOx emissions. These efforts are increasingly difficult to implement and take many years to come to pass. Of course there are also other reasons that ozone levels remain high. These include: a growing population meaning more car emissions, and the mountains along the NCFR that can trap emissions. If interested, daily air quality readings can be found at the Colorado Department of Public Health and Environment's website.<ref>Colorado Department of Public Health and Environment. (n.d.). Colorado Air Quality. Retrieved March 20, 2019, from https://www.colorado.gov/airquality/air_quality.aspx</ref> As noted earlier, Denver continues to experience high levels of ozone to this day. It will take many years and a systems-thinking approach to combat this issue of high ozone levels in the Front Range of Colorado.