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<p><b>New page</b></p><div>{{short description|Partial pressure of carbon dioxide, often used in reference to blood}}<br />
{{DISPLAYTITLE:pCO<sub>2</sub>}}<br />
[[File:Carbon-dioxide-3D-vdW.svg|thumb|[[Carbon dioxide]] molecule.]]<br />
'''''p''CO<sub>2</sub>, pCO<sub>2</sub>''', or <math chem="">P_\ce{CO2}</math> is the [[partial pressure]] of [[carbon dioxide]] (CO<sub>2</sub>), often used in reference to [[blood]] but also used in [[meteorology]], [[Climatology|climate science]], [[oceanography]], and [[limnology]] to describe the fractional pressure of CO<sub>2</sub> as a function of its concentration in gas or dissolved phases. The units of ''p''CO<sub>2</sub> are [[Millimetre of mercury|mmHg]], [[Standard atmosphere (unit)|atm]], [[torr]], [[Pascal (unit)|Pa]], or any other standard unit of [[atmospheric pressure]]. The ''p''CO<sub>2</sub> of [[Earth|Earth's]] atmosphere has risen from approximately 280 ppm ([[Parts-per notation|parts-per-million]]) to a mean 2019 value of 409.8 ppm as a result of [[Climate change|anthropogenic]] release of carbon dioxide from [[fossil fuel]] burning.<ref>{{Cite web|last=Lindsey|first=Rebecca|date=2020|title=Climate Change: Atmospheric Carbon Dioxide|url=https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide|archive-url=https://web.archive.org/web/20130624204311/http://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide|url-status=dead|archive-date=June 24, 2013|access-date=2021-02-25|website=www.climate.gov|language=en}}</ref> This is the highest atmospheric concentration to have existed on Earth for at least the last 800,000 years.<ref>{{Cite web|last=Lindsey|first=Rebecca|date=2020|title=Climate Change: Atmospheric Carbon Dioxide|url=https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide|archive-url=https://web.archive.org/web/20130624204311/http://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide|url-status=dead|archive-date=June 24, 2013|access-date=2021-02-25|website=www.climate.gov|language=en}}</ref><br />
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== Medicine ==<br />
{{Main|Hypercapnia|Hypocapnia}}<br />
In medicine, the partial pressure of carbon dioxide in [[arterial blood]] is called '''<math chem="">P_{a_\ce{CO2}}</math>''' or '''PaCO<sub>2</sub>'''. Measurement of <math chem="">P_{a_\ce{CO2}}</math> in the [[systemic circulation]] indicates the effectiveness of [[ventilation (physiology)|ventilation]] at the lungs' [[pulmonary alveolus|alveoli]], given the [[diffusing capacity]] of the gas. It is a good indicator of respiratory function and the closely related factor of [[acid–base homeostasis]], reflecting the amount of acid in the blood (without lactic acid). Normal values for humans are in the range of 35–45 [[Millimetre of mercury|mmHg]]. Values less than this may indicate [[hyperventilation]] and (if blood [[pH]] is greater than 7.45) [[respiratory alkalosis]]. Values greater than 45 mmHg may indicate [[hypoventilation]], and (if blood pH is less than 7.35) respiratory [[acidosis]].<ref>[https://www.nlm.nih.gov/medlineplus/spanish/ency/article/003855.htm Dugdale DC, Zieve D. Gasometría arterial. Medline Plus. 09/01/2012.]</ref><ref>[http://www.redentor.inf.br/arquivos/pos/publicacoes/21082012Microsoft%20Word%20-%20trabalho%20conclusao%20de%20curso.pdf Leticia Godoy Dias Sanderson. Gasometria arterial - Artigo de revisão. Fevereiro 2012.] {{webarchive|url=https://web.archive.org/web/20141017103958/http://www.redentor.inf.br/arquivos/pos/publicacoes/21082012Microsoft%20Word%20-%20trabalho%20conclusao%20de%20curso.pdf|date=2014-10-17}}</ref><br />
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== Aquatic sciences ==<br />
{{see also|Ocean acidification|Freshwater acidification}}<br />
Oceanographers and limnologists use ''p''CO<sub>2</sub> to measure the amount of carbon dioxide dissolved in water, as well as to parameterize its [[flux]] into (influx) and out of (efflux) the atmosphere. Carbon dioxide reacts with water to form [[bicarbonate]] and [[carbonate]] ions, such that the relative solubility of carbon dioxide in water is greater than that of other unreactive gasses (e.g. [[Helium]]). As more carbon dioxide dissolves in water, its ''p''CO<sub>2</sub> rises until it equals the ''p''CO<sub>2</sub> of the overlying atmosphere. Conversely, a body of water with a ''p''CO<sub>2</sub> greater than that of the atmosphere effluxes carbon dioxide.<ref name=":0">{{Cite book|last=Millero|first=Frank J.|url=https://www.worldcat.org/oclc/958798815|title=Chemical oceanography|date=2013|publisher=Taylor & Francis|isbn=978-1-4665-1255-9|edition=4|location=Boca Raton|oclc=958798815}}</ref><ref name=":1">{{Cite book|last=Zeebe|first=Richard E.|url=https://www.worldcat.org/oclc/246683387|title=CO2 in seawater : equilibrium, kinetics, isotopes|date=2001|others=Dieter A. Wolf-Gladrow|isbn=978-0-08-052922-6|location=Amsterdam|oclc=246683387}}</ref><br />
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''p''CO<sub>2</sub> is additionally affected by water [[temperature]] and [[salinity]]. Carbon dioxide is less soluble in warmer water than cooler water, so hot water will exhibit a larger ''p''CO<sub>2</sub> than cold water with the same concentration of carbon dioxide. ''p''CO<sub>2</sub> can be used to describe the inorganic carbon system of a body of water, together with other parameters such as pH, [[dissolved inorganic carbon]], and [[alkalinity]]. Together, these parameters describe the concentration and speciation of inorganic carbon species (CO<sub>2 (aq)</sub>, HCO<sub>3</sub><sup>−</sup>, CO<sub>3</sub><sup>2-</sup>) in water.<ref name=":1" /><br />
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Biological processes such as [[Cellular respiration|respiration]] and [[photosynthesis]] affect and can be affected by aquatic ''p''CO<sub>2</sub>. Respiration degrades [[organic matter]], releasing CO<sub>2</sub> into the water column and increasing ''p''CO<sub>2</sub>. Photosynthesis assimilates inorganic carbon, thereby decreasing aquatic ''p''CO<sub>2</sub>.<ref name=":0" /><br />
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== See also ==<br />
* [[Acidosis]]<br />
* [[Alkalosis]]<br />
* [[Arterial blood gas]]<br />
* [[Blood gas tension]]<br />
* [[Chemical equilibrium]]<br />
* [[Hypercapnia]]<br />
* [[pH]]<br />
*[[Carbon cycle|Carbon Cycle]]<br />
* [[xCO2|xCO<sub>2</sub>]]<br />
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== References ==<br />
{{reflist}}<br />
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[[Category:Acid–base chemistry]]<br />
[[Category:Analytical chemistry]]<br />
[[Category:Equilibrium chemistry]]<br />
[[Category:Units of measurement]]<br />
[[Category:Chemical oceanography]]<br />
[[Category:Limnology]]<br />
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