Editing Carbon monoxide (section)

==Occurrence==
[[File:MOP CO M.ogv|thumb|Monthly averages of global concentrations of tropospheric carbon monoxide at an altitude of about 12,000 feet. Data were collected by the MOPITT (Measurements Of Pollution In The Troposphere) sensor on NASA's Terra satellite.<ref>[http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOP_CO_M Global Maps. Carbon Monoxide]. earthobservatory.nasa.gov</ref>]]
Carbon monoxide occurs in many environments, usually in trace levels. Photochemical degradation of plant matter, for example, generates an estimated 60 million tons/year.<ref>{{cite journal|doi= 10.1016/S1465-9972(99)00053-7|title= Atmospheric carbon monoxide|year= 1999|last1= Khalil|first1= M.A.K|last2= Pinto|first2= J.P|last3= Shearer|first3= M.J|journal= Chemosphere - Global Change Science|volume= 1|issue= 1–3|pages= ix-xi|bibcode= 1999ChGCS...1D...9K}}</ref> Typical concentrations in [[parts per million]] are as follows:

{| class="wikitable"
|+'''Composition of dry atmosphere, by volume'''<ref>Source for figures: Carbon dioxide, [http://www.esrl.noaa.gov/gmd/ccgg/trends/#mlo NOAA Earth System Research Laboratory], (updated 2010.06). Methane, [[Intergovernmental Panel on Climate Change|IPCC]] [http://www.grida.no/climate/ipcc_tar/wg1/221.htm#tab61 TAR table 6.1] {{Webarchive|url=https://web.archive.org/web/20070615161122/http://www.grida.no/climate/ipcc_tar/wg1/221.htm#tab61 |date=2007-06-15 }}, (updated to 1998). The NASA total was 17 ppmv over 100%, and {{CO2}} was increased here by 15 ppmv. To normalize, {{chem2|N2}} should be reduced by about 25 ppmv and {{chem2|O2}} by about 7 ppmv.</ref>
|-
! Concentration (ppmv{{efn|[[Parts per million]] by volume (note: [[volume fraction]] is equal to [[mole fraction]] for ideal gas only, see [[Volume (thermodynamics)#Partial volume|volume (thermodynamics)]])}})
! Source
|-
| 0.1
| Natural atmosphere level ([[MOPITT]])<ref>{{Cite book|author=Committee on Medical and Biological Effects of Environmental Pollutants|title=Carbon Monoxide|publisher=National Academy of Sciences|year=1977|isbn=978-0-309-02631-4|location=Washington, D.C.|pages=29}}</ref>
|-
| 0.5–5
| Average level in homes<ref name="EPAFAQ">{{Cite web|author=Green W|title=An Introduction to Indoor Air Quality: Carbon Monoxide (CO)|url=http://www.epa.gov/iaq/co.html|access-date=2008-12-16|publisher=United States Environmental Protection Agency}}</ref>
|-
| 5–15
| Near properly adjusted gas stoves in homes, modern vehicle exhaust emissions<ref name="Alaska_CO">{{Cite web|last=Gosink|first=Tom|date=1983-01-28|title=What Do Carbon Monoxide Levels Mean?|url=http://www.gi.alaska.edu/ScienceForum/ASF5/588.html|url-status=dead|archive-url=https://web.archive.org/web/20081225113654/http://www.gi.alaska.edu/ScienceForum/ASF5/588.html|archive-date=2008-12-25|access-date=2007-12-01|work=Alaska Science Forum|publisher=Geophysical Institute, University of Alaska Fairbanks}}</ref>{{Citation needed|date=May 2020}}
|-
| 17
| [[Atmosphere of Venus]]
|-
| 100–200
| Exhaust from automobiles in the Mexico City central area in 1975<ref>{{Cite book|last=Singer|first=Siegfried Fred|title=The Changing Global Environment|publisher=Springer|year=1975|isbn=978-9027704023|page=90}}</ref>
|-
| 700
| [[Atmosphere of Mars]]
|-
| <1,000
| Car exhaust fumes after passing through [[catalytic converter]]<ref name="Iowa_CO">{{cite web|title=Carbon Monoxide Poisoning: Vehicles (AEN-208)|url=https://www.abe.iastate.edu/extension-and-outreach/carbon-monoxide-poisoning-vehicles-aen-208/|access-date=11 February 2018|website=abe.iastate.edu}}</ref>
|-
| 5,000
| Exhaust from a home wood fire<ref name="Gosink">{{Cite web|author=Gosink T|date=January 28, 1983|title=What Do Carbon Monoxide Levels Mean?|url=http://www.gi.alaska.edu/ScienceForum/ASF5/588.html|url-status=dead|archive-url=https://web.archive.org/web/20081225113654/http://www.gi.alaska.edu/ScienceForum/ASF5/588.html|archive-date=December 25, 2008|access-date=December 16, 2008|work=Alaska Science Forum|publisher=Geophysical Institute, University of Alaska Fairbanks}}</ref>
|-
| 30,000–100,000
| Undiluted warm car exhaust without a [[catalytic converter]]<ref name="Iowa_CO" />
|-
| colspan="2" style="font-size: 85%" | {{notelist}}
|}

===Atmospheric presence===
[[File:Carbon Monoxide.ogv|thumb|The streak of red, orange, and yellow across [[South America]], [[Africa]], and the [[Atlantic Ocean]] in this animation points to high levels of carbon monoxide on September 30, 2005.]]
[[File:Carbon Monoxide concentrations in spring..jpg|thumb|Carbon monoxide concentrations in Northern Hemisphere spring as measured with the MOPITT instrument]]

Carbon monoxide (CO) is present in small amounts (about 80 [[Parts per billion|ppb]]) in the [[Atmosphere of Earth|Earth's atmosphere]]. Most of the rest comes from chemical reactions with [[organic compound]]s emitted by human activities and natural origins due to [[photochemistry|photochemical]] reactions in the [[troposphere]] that generate about 5 × 10<sup>12</sup> kilograms per year.<ref name="Weinstock-1972">{{Cite journal|last1=Weinstock|first1=B.|last2=Niki|first2=H.|year=1972|title=Carbon Monoxide Balance in Nature|journal=Science|volume=176|issue=4032|pages=290–2|bibcode=1972Sci...176..290W|doi=10.1126/science.176.4032.290|pmid=5019781|s2cid=25223868}}</ref> Other natural sources of CO include volcanoes, [[forest fires|forest]] and [[bushfire]]s, and other miscellaneous forms of combustion such as [[fossil fuel]]s.<ref name="Seinfeld2006">{{cite book|last1=Seinfeld|first1=John|title=Atmospheric Chemistry and Physics: From Air Pollution to Climate Change|last2=Pandis|first2=Spyros|date=2006|publisher=John Wiley & Sons|isbn=978-0-471-72018-8}}</ref> Small amounts are also emitted from the ocean, and from geological activity because carbon monoxide occurs dissolved in molten volcanic rock at high pressures in the Earth's [[mantle (geology)|mantle]].<ref>{{Cite book|author1=Sigel, Astrid|url=https://books.google.com/books?id=kcllhZcy53cC&pg=PA243|title=Metal-Carbon Bonds in Enzymes and Cofactors|author2=Sigel, Roland K. O.|publisher=Royal Society of Chemistry|year=2009|isbn=978-1-84755-915-9|page=243}}</ref> Because natural sources of carbon monoxide vary from year to year, it is difficult to accurately measure natural emissions of the gas.

Carbon monoxide has an indirect effect on [[radiative forcing]] by elevating concentrations of direct [[greenhouse gas]]es, including [[methane]] and [[troposphere|tropospheric]] [[ozone]]. CO can react chemically with other atmospheric constituents (primarily the [[hydroxyl]] [[Radical (chemistry)|radical]], <sup>•</sup>OH) that would otherwise destroy methane.<ref>{{Cite book|author=White, James Carrick|url=https://books.google.com/books?id=gnaNHeU4rgQC&pg=PA106|title=Global climate change linkages: acid rain, air quality, and stratospheric ozone|publisher=Springer|year=1989|isbn=978-0-444-01515-0|page=106|display-authors=etal}}</ref> Through natural processes in the atmosphere, it is oxidized to [[carbon dioxide]] and ozone. Carbon monoxide is short-lived in the atmosphere (with an average lifetime of about one to two months), and spatially variable in concentration.<ref>{{cite web|last=Drummond|first=James|date=February 2, 2018|title=MOPITT, Atmospheric Pollution, and Me: A Personal Story|url=http://bulletin.cmos.ca/mopitt-atmospheric-pollution/|access-date=August 1, 2018|publisher=Canadian Meteorological and Oceanographic Society}}</ref>

Due to its long lifetime in the mid-troposphere, carbon monoxide is also used as a tracer for pollutant plumes.<ref>{{cite journal|last1=Pommier|first1=M.|last2=Law|first2=K. S.|last3=Clerbaux|first3=C.|last4=Turquety|first4=S.|last5=Hurtmans|first5=D.|last6=Hadji-Lazaro|first6=J.|last7=Coheur|first7=P.-F.|last8=Schlager|first8=H.|last9=Ancellet|first9=G.|last10=Paris|first10=J.-D.|last11=Nédélec|first11=P.|year=2010|title=IASI carbon monoxide validation over the Arctic during POLARCAT spring and summer campaigns|url=https://hal.archives-ouvertes.fr/hal-00491181|journal=Atmospheric Chemistry and Physics|volume=10|issue=21|pages=10655–10678|bibcode=2010ACP....1010655P|doi=10.5194/acp-10-10655-2010|doi-access=free|last15=Bernath|first15=P.|first14=J. S.|last14=Holloway|first13=J. R.|last13=Podolske|first12=G. S.|last12=Diskin}}</ref>

=== Astronomy ===
Beyond Earth, carbon monoxide is the second-most common diatomic molecule in the [[interstellar medium]], after [[molecular hydrogen]].  Because of its asymmetry, this [[polar molecule]] produces far brighter [[spectral line]]s than the hydrogen molecule, making CO much easier to detect.  Interstellar CO was first detected with [[radio telescope]]s in 1970. It is now the most commonly used tracer of molecular gas in general in the interstellar medium of galaxies, as molecular hydrogen can only be detected using ultraviolet light, which requires [[space telescopes]]. Carbon monoxide observations provide much of the information about the [[molecular cloud]]s in which most [[star formation|stars form]].<ref>{{cite journal |author=Combes, Françoise |year=1991 |title=Distribution of CO in the Milky Way |journal=Annual Review of Astronomy & Astrophysics |volume=29 |pages=195–237 |bibcode=1991ARA&A..29..195C |doi=10.1146/annurev.aa.29.090191.001211}}</ref><ref>{{cite journal |author=Hamed, M. |year=2021 |title=Multiwavelength dissection of a massive heavily dust-obscured galaxy and its blue companion at z~2 |journal=Astronomy & Astrophysics |volume=646 |pages=A127 |arxiv=2101.07724 |bibcode=2021A&A...646A.127H |doi=10.1051/0004-6361/202039577 |s2cid=231639096}}</ref>

[[Beta Pictoris]], the second brightest star in the constellation [[Pictor]], shows an [[infrared excess|excess of infrared emission]] compared to normal stars of its type, which is caused by large quantities of dust and gas (including carbon monoxide)<ref name="LAT-20140308">{{cite news |last=Khan |first=Amina |title=Did two planets around nearby star collide? Toxic gas holds hints |url=http://www.latimes.com/science/sciencenow/la-sci-sn-beta-pictoris-star-planet-gas-collision-comets-carbon-monoxide-20140307,0,1884709.story |access-date=March 9, 2014 |work=[[Los Angeles Times]]}}</ref><ref name="SCI-20140306">{{cite journal |vauthors=Dent, WR, Wyatt, MC, Roberge, A, Augereau, JC, Casassus, S, Corder, S, Greaves, JS, ((de Gregorio-Monsalvo, I)), Hales, A, Jackson, AP, Hughes, AM, Meredith A, Lagrange, AM, Matthews, B, Wilner, D |date=March 6, 2014 |title=Molecular Gas Clumps from the Destruction of Icy Bodies in the β Pictoris Debris Disk |url=https://www.science.org/doi/abs/10.1126/science.1248726 |journal=[[Science (journal)|Science]] |volume=343 |issue=6178 |pages=1490–1492 |arxiv=1404.1380 |bibcode=2014Sci...343.1490D |doi=10.1126/science.1248726 |pmid=24603151 |s2cid=206553853 |access-date=March 9, 2014}}</ref> near the star.

In the [[atmosphere of Venus]] carbon monoxide occurs as a result of the photodissociation of carbon dioxide by electromagnetic radiation of wavelengths shorter than 169 [[nanometre|nm]]. It has also been identified spectroscopically on the surface of Neptune's moon [[Triton (moon)|Triton]].<ref name="Lellouchde Bergh2010">{{cite journal |last1=Lellouch |first1=E. |last2=de Bergh |first2=C. |last3=Sicardy |first3=B. |last4=Ferron |first4=S. |last5=Käufl |first5=H.-U. |year=2010 |title=Detection of CO in Triton's atmosphere and the nature of surface-atmosphere interactions |journal=Astronomy and Astrophysics |volume=512 |pages=L8 |arxiv=1003.2866 |bibcode=2010A&A...512L...8L |doi=10.1051/0004-6361/201014339 |issn=0004-6361 |s2cid=58889896}}</ref>

Solid carbon monoxide is a component of [[comet]]s.<ref>{{cite journal |last1=Greenberg |first1=J. Mayo |date=1998 |title=Making a comet nucleus |journal=Astronomy and Astrophysics |volume=330 |pages=375 |bibcode=1998A&A...330..375G}}</ref> The [[Volatile (astrogeology)|volatile or "ice"]] component of [[Halley's Comet]] is about 15% CO.<ref name="Yeomans">{{cite web |last=Yeomans |first=Donald K. |date=2005 |title=Comets (World Book Online Reference Center 125580) |url=http://www.nasa.gov/worldbook/comet_worldbook.html |url-status=dead |archive-url=https://web.archive.org/web/20050429084558/http://www.nasa.gov/worldbook/comet_worldbook.html |archive-date=29 April 2005 |access-date=18 August 2022 |publisher=NASA |quote=About 80 percent of the ice is water ice, and frozen carbon monoxide makes up another 15 percent. |df=dmy-all}}</ref> At room temperature and at atmospheric pressure, carbon monoxide is actually only metastable (see [[Boudouard reaction]]) and the same is true at low temperatures where CO and {{chem2|CO2}} are solid, but nevertheless it can exist for billions of years in comets. There is very little CO in the atmosphere of [[Pluto]], which seems to have been formed from comets. This may be because there is (or was) liquid water inside Pluto.

Carbon monoxide can react with water to form carbon dioxide and hydrogen:
:{{chem2|CO + H2O -> H2 + CO2}}

This is called the [[water-gas shift reaction]] when occurring in the gas phase, but it can also take place (very slowly) in an aqueous solution.
If the hydrogen partial pressure is high enough (for instance in an underground sea), [[formic acid]] will be formed:
:{{chem2|CO + H2O -> HCOOH}}

These reactions can take place in a few million years even at temperatures such as found on Pluto.<ref>{{cite journal |last1=Christopher Glein and Hunter Waite |date=May 11, 2018 |title=Primordial N2 provides a cosmo chemical explanation for the existence of Sputnik Planitia, Pluto |journal=Icarus |volume=313 |pages=79–92 |arxiv=1805.09285 |bibcode=2018Icar..313...79G |doi=10.1016/j.icarus.2018.05.007 |s2cid=102343522}}</ref>