| 词条 | Tropospheric ozone |
| 释义 |
Photo-chemical 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.[5][4] Photolysis of ozone occurs at wavelengths below approximately 310-320 nano-meters.[6][7] This reaction initiates the chain of chemical reactions that remove carbon monoxide, methane, and other hydrocarbons from the atmosphere via 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 nitrogen monoxide (NO), this chain of reactions has a net product of ozone added to the system.[2][4]MeasurementOzone in the atmosphere can be measured by remote sensing technology, or by in-situ monitoring technology. Because ozone absorbs light in the UV spectrum, the most common way to measure ozone is to measure how much of this light spectrum is absorbed in the atmosphere.[8][9] Because the stratosphere has higher ozone concentration than the troposphere, it is important for remote sensing instruments to be able to determine altitude along with the concentration measurements. The [https://eospso.nasa.gov/missions/total-ozone-mapping-spectrometer-earth-probe TOMS-EP] instrument aboard a satellite from NASA is an example of an ozone layer measuring satellite,[10] and [https://tes.jpl.nasa.gov/ TES] is an example of an ozone measuring satellite that is specifically for the troposphere.[11] Lidar is a common ground based remote sensing technique to measure ozone. [https://www-air.larc.nasa.gov/missions/TOLNet/ TOLnet] is the network of ozone observing lidars across the United States.[12]Ozonesondes are a form of in situ, or local measurements. An ozonesonde is an ozone measuring instrument attached to a meteorological balloon, so that the instrument can directly measure ozone concentration at the varying altitudes along the balloon's upward path. The information collected from the instrument attached to the balloon is transmitted back using radiosonde technology.[8] NOAA has worked to create a global network of tropospheric ozone measurements using ozonesondes.[13] Ozone is also measured in air quality environmental monitoring networks. In these networks, in-situ ozone monitors based on ozone's UV-absorption properties are used to measure ppb-levels in ambient air. FormationThe majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs), react in the atmosphere in the presence of sunlight, specifically the UV spectrum. NOx, CO, and VOCs are considered ozone precursors.[5][4] Motor vehicle exhaust, industrial emissions, and chemical solvents are the major anthropogenic sources of these ozone precursors.[4] Although the ozone precursors often originate in urban areas, winds can carry NOx hundreds of kilometers, causing ozone formation to occur in less populated regions as well. The chemical reactions that produce tropospheric ozone are a series of interrelated cycles (known as the HOx and NOx cycles); They start with the oxidation of carbon monoxide (CO) or VOCs (such as butane). To begin the process, CO and VOCs are oxidized by the hydroxyl radical (•OH) to form carbon dioxide (CO2), and water (H2O) in the CO oxidation case. These oxidizing reactions then produce the peroxy radical (HO2•) that will react with NO to produce NO2. NO2 is subsequently photolyzed during by daytime, thus resulting in NO and a single oxygen atom. This single oxygen atom reacts with molecular oxygen O2 to produce ozone.[1][7] An outline of the chain reaction that occurs in oxidation of CO, producing O3:[2][7] The reaction begins with the oxidation of CO by the hydroxyl radical (•OH). The radical adduct (•HOCO) is unstable and reacts rapidly with oxygen to give a peroxy radical, HO2•: •OH + CO → •HOCO •HOCO + O2 → HO2• + CO2 Peroxy-radicals then go on to react with NO to produce NO2, which is photolysed by UV-A radiation to give a ground-state atomic oxygen, which then reacts with molecular oxygen to form ozone.[1] HO2• + NO → •OH + NO2 NO2 + hν → NO + O(3P) , λ<400 nm O(3P) + O2 → O3 note that these three reactions are what forms the ozone molecule, and will occur the same way in the oxidation of CO or VOCs case. The amount of ozone produced through these reactions in ambient air can be estimated using a modified Leighton relationship. The limit on these interrelated cycles producing ozone is the reaction of •OH with NO2 to form nitric acid at high NOx levels. If nitrogen monoxide (NO) is instead present at very low levels in the atmosphere (less than 10 approximately ppt), the of peroxy radicals (HO2• ) formed from the oxidation will instead react with themselves to form peroxides, and not produce ozone. [1] Health effects{{See also|Ozone#Health_effects}}Health effects depend on ozone precursors, which is a group of pollutants, primarily generated during the combustion of fossil fuels. Reaction with daylight ultraviolet (UV) rays and these precursors create ground-level ozone pollution (Tropospheric Ozone). Ozone is known to have the following health effects at concentrations common in urban air:
A statistical study of 95 large urban communities in the United States found significant association between ozone levels and premature death. The study estimated that a one-third reduction in urban ozone concentrations would save roughly 4000 lives per year (Bell et al., 2004). Tropospheric Ozone causes approximately 22,000 premature deaths per year in 25 countries in the European Union. (WHO, 2008) Problem areasThe United States Environmental Protection Agency has developed an Air Quality index to help explain air pollution levels to the general public. 8-hour average ozone mole fractions of 76 to 95 nmol/mol are described as "Unhealthy for Sensitive Groups", 96 nmol/mol to 115 nmol/mol as "unhealthy" and 116 nmol/mol to 404 nmol/mol as "very unhealthy" . The EPA has designated over 300 counties of the United States, clustered around the most heavily populated areas (especially in California and the Northeast), as failing to comply with the National Ambient Air Quality Standards. Climate changeMelting of sea ice releases molecular chlorine, which reacts with UV radiation to produce chlorine radicals. Because chlorine radicals are highly reactive, they can expedite the degradation of methane and tropospheric ozone and the oxidation of mercury to more toxic forms.[14] Ozone production rises during heat waves, because plants absorb less ozone. It is estimated that curtailed ozone absorption by plants is responsible for the loss of 460 lives in the UK in the hot summer of 2006.[15] 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.[16] See also
References1. ^1 2 3 {{Cite book|title=Chemistry of The Natural Atmosphere|last=Warneck|first=Peter|publisher=Academic Press|year=1999|isbn=9780080529066|location=|pages=}} {{refbegin}}2. ^1 2 {{Cite web|url=http://elte.prompt.hu/sites/default/files/tananyagok/AtmosphericChemistry/ch08s02.html|title=8.2 Tropospheric ozone|website=elte.prompt.hu|access-date=2018-11-12}} 3. ^1 {{Cite web|url=https://ozonewatch.gsfc.nasa.gov/facts/SH.html|title=Nasa Ozone Watch: Ozone facts|website=ozonewatch.gsfc.nasa.gov|language=en-us|access-date=2018-11-12}} 4. ^1 2 3 4 5 {{Cite web|url=https://scied.ucar.edu/ozone-troposphere|title=Ozone in the Troposphere {{!}} UCAR Center for Science Education|website=scied.ucar.edu|language=en|access-date=2018-11-12}} 5. ^1 {{Cite web|url=http://ccacoalition.org/en/slcps/tropospheric-ozone|title=Tropospheric ozone {{!}} Climate & Clean Air Coalition|website=ccacoalition.org|language=en|access-date=2018-11-12}} 6. ^{{Cite journal|last=Taniguchi|first=Nori|last2=Takahashi|first2=Kenshi|last3=Matsumi|first3=Yutaka|title=Photodissociation of O3around 309 nm|journal=The Journal of Physical Chemistry A|language=en|volume=104|issue=39|pages=8936–8944|doi=10.1021/jp001706i|issn=1089-5639|year=2000}} 7. ^1 2 {{Cite journal|last=Reeves|first=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|date=2002-12-11|title=Potential for photochemical ozone formation in the troposphere over the North Atlantic as derived from aircraft observations during ACSOE|journal=Journal of Geophysical Research: Atmospheres|language=en|volume=107|issue=D23|pages=ACH 14–1–ACH 14–14|doi=10.1029/2002jd002415|issn=0148-0227}} 8. ^1 {{Cite web|url=https://www.esrl.noaa.gov/csd/assessments/ozone/2010/twentyquestions/Q5.pdf|title=How is ozone measured in the atmosphere?|last=ERSL NOAA|date=|website=/www.esrl.noaa.gov/|archive-url=|archive-date=|dead-url=|access-date=}} 9. ^{{Cite news|url=https://phys.org/news/2016-09-ozone-space.html|title=Measuring ozone from space|access-date=2018-11-12}} 10. ^{{Cite web|url=https://eospso.nasa.gov/missions/total-ozone-mapping-spectrometer-earth-probe|title=total-ozone-mapping-spectrometer-earth-probe|last=NASA|date=|website=|archive-url=|archive-date=|dead-url=|access-date=}} 11. ^{{Cite web|url=https://tes.jpl.nasa.gov/|title=TES|last=NASA|date=|website=tes.jpl.nasa.gov|archive-url=|archive-date=|dead-url=|access-date=2018-11-12}} 12. ^{{Cite web|url=https://www-air.larc.nasa.gov/missions/TOLNet/|title=NASA Tropospheric Chemistry Integrated Data Center|last=LaRC|first=Ali Aknan |date=2005-06-22|website=www-air.larc.nasa.gov|language=en|access-date=2018-11-12}} 13. ^{{Cite web|url=https://www.esrl.noaa.gov/gmd/ozwv/ozsondes/|title=ESRL Global Monitoring Division - Ozone and Water Vapor Group|last=Laboratory|first=US Department of Commerce, NOAA, Earth System Research|website=www.esrl.noaa.gov|language=EN-US|access-date=2018-11-12}} 14. ^{{cite journal | author = Jin Liao | display-authors = etal | date=January 2014 | title = High levels of molecular chlorine in the Arctic atmosphere | journal = Nature Geoscience | doi = 10.1038/ngeo2046 | url = http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2046.html | volume=7 | issue = 2 | pages=91–94 | bibcode=2014NatGe...7...91L }} 15. ^{{cite news| title = It's not just the heat – it's the ozone: Study highlights hidden dangers| publisher = University of York| accessdate = January 14, 2014 | url = http://www.york.ac.uk/news-and-events/news/2013/research/heat-ozone/}} 16. ^{{cite journal | author = Kosatsky T. |date=July 2005 | title = The 2003 European heat waves | journal = Eurosurveillance | volume = 10 | issue = 7 | url = http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=552 | accessdate = January 14, 2014 }}
Further reading{{refbegin}}
External links
5 : Atmosphere|Atmosphere of Earth|Airborne pollutants|Smog|Ozone |
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