Carbon dioxide: Difference between revisions

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{{Redirect|Co2|the sporadic group|Conway group Co2}}
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 477004235
| ImageFile1 = Carbon-dioxide-2D-dimensions.svg
| ImageFile1_Ref = {{Chemboximage|rect|??}}
| ImageSize1 = 170
| ImageName1 = Structural formula of carbon dioxide with bond length
| ImageFileL1 = Carbon dioxide 3D ball.png
| ImageFileL1_Ref = {{Chemboximage|correct|??}}
| ImageSizeL1 = 121
| ImageNameL1 = Ball-and-stick model of carbon dioxide
| ImageFileR1 = Carbon dioxide 3D spacefill.png
| ImageFileR1_Ref = {{Chemboximage|correct|??}}
| ImageSizeR1 = 121
| ImageNameR1 = Space-filling model of carbon dioxide
| OtherNames = Carbonic acid gas<br />Carbonic anhydride<br />Carbonic oxide<br />Carbon oxide<br />Carbon(IV) oxide<br />[[Dry ice]] (solid phase)
| Section1 = {{Chembox Identifiers
| CASNo = 124-38-9
|  CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 280
|  PubChem_Ref = {{Pubchemcite|correct|PubChem}}
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 1231871
| ChemSpiderID = 274
|  ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII = 142M471B3J
|  UNII_Ref = {{fdacite|correct|FDA}}
| EINECS = 204-696-9
| UNNumber = 1013
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = D00004
| MeSHName = Carbon+dioxide
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 16526
| RTECS = FF6400000
| ATCCode_prefix = V03
| ATCCode_suffix = AN02
| Beilstein = 1900390
| Gmelin = 989
| 3DMet = B01131
| SMILES = O=C=O
| SMILES1 = C(=O)=O
| StdInChI = 1S/CO2/c2-1-3
|  StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI = 1/CO2/c2-1-3
| StdInChIKey = CURLTUGMZLYLDI-UHFFFAOYSA-N
|  StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey = CURLTUGMZLYLDI-UHFFFAOYAO}}
| Section2 = {{Chembox Properties
| C = 1
| O = 2
| Appearance = Colorless gas
| Odor = Odorless
| Density = 1562 kg/m<sup>3</sup> <small>(solid at 1&nbsp;atm and −78.5&nbsp;°C)</small><br />770 kg/m<sup>3</sup> <small>(liquid at 56&nbsp;atm and 20&nbsp;°C)</small><br />1.977&nbsp;kg/m<sup>3</sup> <small>(gas at 1&nbsp;atm and 0&nbsp;°C)</small>
| Solubility = 1.45 g/L at 25&nbsp;°C, 100 kPa
| BoilingPtK = 216.6
| Boiling_notes = at 5.185&nbsp;bar
| MeltingPtK = 194.7
| Melting_notes = ''[[Sublimation (chemistry)|subl.]]''
| pKa = 6.35, 10.33
| RefractIndex = 1.1120
| Viscosity = 0.07 [[Poise|cP]] at −78.5&nbsp;°C
| VaporPressure = 5.73 MPa (20 °C)
| Dipole = 0 D
| pKa = 6.35, 10.33
}}
| Section3 = {{Chembox Structure
| CrystalStruct = trigonal
| MolShape = [[Linear (chemistry)|linear]]
}}
| Section4 = {{Chembox Thermochemistry
|  DeltaHf = −393.5&nbsp;kJ·mol<sup>−1</sup>
|  HeatCapacity = 37.135 J/K mol
|  Entropy = 214&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup>
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=PL&language=EN-generic&productNumber=295108&brand=ALDRICH&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F295108%3Flang%3Dpl Sigma-Aldrich]
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Carbon disulfide]]<br />[[Carbon diselenide]]
| OtherCations = [[Silicon dioxide]]<br />[[Germanium dioxide]]<br />[[Tin dioxide]]<br />[[Lead dioxide]]
| Function = [[carbon]] [[oxide]]s
| OtherFunctn = [[Carbon monoxide]]<br />[[Carbon suboxide]]<br />[[Dicarbon monoxide]]<br />[[Carbon trioxide]]
| OtherCpds = [[Carbonic acid]]<br />[[Carbonyl sulfide]]
}}
}}
'''Carbon dioxide''' ([[chemical formula]] '''CO<sub>2</sub>''') is a naturally occurring [[chemical compound]] composed of 2 [[oxygen]] [[atom]]s each [[covalent bond|covalently]] [[double bond]]ed to a single [[carbon]] atom. It is a [[gas]] at [[standard temperature and pressure]] and exists in [[Earth's atmosphere]] in this state, as a [[trace gas]] at a concentration of 0.039 per cent by volume.<ref name=NOAA/>


As part of the [[carbon cycle]], [[plant]]s, [[algae]], and [[cyanobacteria]] use [[light]] [[energy]] to [[photosynthesis|photosynthesize]] [[carbohydrate]] from carbon dioxide and [[water]], with [[oxygen]] produced as a waste product.<ref>{{cite book|author1=Donald G. Kaufman|author2=Cecilia M. Franz|title=Biosphere 2000: protecting our global environment|url=http://books.google.com/books?id=nm5FAAAAYAAJ|accessdate=11 October 2011|year=1996|publisher=Kendall/Hunt Pub. Co.|isbn=978-0-7872-0460-0}}</ref> However, photosynthesis cannot occur in darkness and at night some carbon dioxide is produced by plants during [[Cellular respiration|respiration]].<ref>[http://www.legacyproject.org/activities/foodfactories.html Food Factories]. www.legacyproject.org. Retrieved on 2011-10-10.</ref> Carbon dioxide is produced by [[combustion]] of coal or [[hydrocarbon]]s, the [[fermentation]] of sugars in [[beer]] and [[wine]]making and by respiration of all living organisms. It is exhaled in the breath of humans and other land animals. It is emitted from [[volcano]]es, [[hot spring]]s, [[geyser]]s and other places where the earth's crust is thin and is freed from [[carbonate rock]]s by [[dissolution (chemistry)|dissolution]]. CO<sub>2</sub> is also found in lakes, at depth under the sea and commingled with oil and gas deposits.<ref>{{cite web|url=http://www.globalccsinstitute.com/publications/good-plant-design-and-operation-onshore-carbon-capture-installations-and-onshore-pipe-5|title=General Properties and Uses of Carbon Dioxide, Good Plant Design and Operation for Onshore Carbon Capture Installations and Onshore Pipelines|publisher=Energy Institute|accessdate=2012-03-14}}</ref>


The environmental effects of carbon dioxide are of significant interest. Atmospheric carbon dioxide is the primary source of carbon in [[life]] on Earth and its concentration in Earth's pre-industrial atmosphere since late in the [[Precambrian]] eon was regulated by [[photosynthesis|photosynthetic]] organisms. Carbon dioxide is an important [[greenhouse gas]]; burning of carbon-based fuels since the industrial revolution has rapidly increased the concentration, leading to [[global warming]]. It is also a major source of [[ocean acidification]] since it dissolves in water to form [[carbonic acid]],<ref>National Research Council. "Summary." Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean. Washington, DC: The National Academies Press, 2010. 1. Print.</ref> which is a [[Acid strength|weak acid]] as its ionization in water is incomplete.
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: {{chem|CO|2}} + {{chem|H|2|O}} {{eqm}} {{chem|H|2|CO|3}}
 
== History ==
[[File:Carbon-dioxide-crystal-3D-vdW.png|thumb|left|upright|Crystal structure of [[dry ice]]]]
Carbon dioxide was one of the first gases to be described as a substance distinct from air. In the seventeenth century, the [[Flemish people|Flemish]] chemist [[Jan Baptist van Helmont]] observed that when he burned [[charcoal]] in a closed vessel, the mass of the resulting [[ash (analytical chemistry)|ash]] was much less than that of the original charcoal. His interpretation was that the rest of the charcoal had been transmuted into an invisible substance he termed a "gas" or "wild spirit" (''spiritus sylvestre'').<ref>Ebbe Almqvist (2003): ''History of industrial gases'', Springer, 2003, ISBN 9780306472770, p. 93</ref>
 
The properties of carbon dioxide were studied more thoroughly in the 1750s by the [[Scotland|Scottish]] physician [[Joseph Black]]. He found that [[limestone]] ([[calcium carbonate]]) could be heated or treated with [[acid]]s to yield a gas he called "fixed air." He observed that the fixed air was denser than air and supported neither flame nor animal life. Black also found that when bubbled through an aqueous solution of lime ([[calcium hydroxide]]), it would [[Precipitation (chemistry)|precipitate]] calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1772, English chemist [[Joseph Priestley]] published a paper entitled ''Impregnating Water with Fixed Air'' in which he described a process of dripping [[sulfuric acid]] (or ''oil of vitriol'' as Priestley knew it) on chalk in order to produce carbon dioxide, and forcing the gas to dissolve by agitating a bowl of water in contact with the gas.<ref name="Priestley">{{cite journal|first = Joseph|last = Priestley|authorlink = Joseph Priestley|title = Observations on Different Kinds of Air|journal = Philosophical Transactions|volume = 62|jstor=|year = 1772|pages = 147–264|url = http://web.lemoyne.edu/~GIUNTA/priestley.html|doi = 10.1098/rstl.1772.0021|last2 =Hey|first2 = Wm}}</ref>
 
Carbon dioxide was first liquefied (at elevated pressures) in 1823 by [[Humphry Davy]] and [[Michael Faraday]].<ref name="Davy">{{cite journal|first = Humphry|last = Davy|authorlink = Humphry Davy|title = On the Application of Liquids Formed by the Condensation of Gases as Mechanical Agents|url=http://archive.org/details/jstor-107649|jstor=107649|journal = Philosophical Transactions|volume = 113|issue = 0|year = 1823|pages = 199–205|doi = 10.1098/rstl.1823.0020 }}</ref> The earliest description of solid carbon dioxide was given by [[Adrien-Jean-Pierre Thilorier]], who in 1835 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO<sub>2</sub>.<ref>See:
* Thilorier (1835) [http://gallica.bnf.fr/ark:/12148/bpt6k29606/f194.image.langEN "Solidification de l’acide carbonique"] (Solidification of carbonic acid), ''Comptes rendus'' ... , '''1''' : 194-196.
*  [http://books.google.com/books?id=4GwqAAAAYAAJ&pg=PA446#v=onepage&q&f=false "Solidification of carbonic acid,"] ''The London and Edinburgh Philosophical Magazine'', '''8''' : 446-447 (1836).</ref>
 
== Chemical and physical properties ==
 
=== Structure and bonding ===
{{See also|Molecular orbital diagram#Carbon Dioxide MO Diagram}}
The carbon dioxide molecule is linear and [[centrosymmetric]]. The two C=O bonds are equivalent and are short (116.3 [[picometer|pm]]), consistent with double bonding.<ref name=Green/>  Since it is centrosymmetric, the molecule has no electrical [[dipole]]. Consistent with this fact, only two vibrational bands are observed in the [[IR spectrum]] – an antisymmetic stretching mode at 2349&nbsp;cm<sup>−1</sup> and a bending mode near 666&nbsp;cm<sup>−1</sup>. There is also a symmetric stretching mode at 1388&nbsp;cm<sup>−1</sup> which is only observed in the [[Raman spectrum]].
[[Image:co2comp.png|center|350px]]
 
=== In aqueous solution ===
Carbon dioxide is [[soluble]] in water, in which it reversibly converts to {{chem|H|2|CO|3}} ([[carbonic acid]]).
 
The [[Henry's law|hydration equilibrium constant]] of carbonic acid is <math>K_{\mathrm h}=\frac{\rm{[H_2CO_3]}}{\rm{[CO_2(aq)]}}=1.70\times 10^{-3}</math> (at 25 °C). Hence, the majority of the carbon dioxide is not converted into carbonic acid, but remains as CO<sub>2</sub> molecules not affecting the pH.
 
The relative concentrations of {{chem|CO|2|, H|2|CO|3}}, and the [[deprotonation|deprotonated]] forms {{chem|HCO|3|−}} ([[bicarbonate]]) and {{chem|CO|3|2−}}([[carbonate]]) depend on the [[pH]]. As shown in a [[Bjerrum plot]], in neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater. In very alkaline water (pH > 10.4), the predominant (>50%) form is carbonate. The oceans, being mildly alkaline with typical pH = 8.2–8.5, contain about 120&nbsp;mg of bicarbonate per liter.
 
Being [[diprotic acid|diprotic]], carbonic acid has two [[acid dissociation constant]]s, the first one for the dissociation into the [[bicarbonate]] (also called hydrogen carbonate) ion (HCO<sub>3</sub><sup>−</sup>):
 
:H<sub>2</sub>CO<sub>3</sub> {{eqm}} HCO<sub>3</sub><sup>−</sup> + H<sup>+</sup>
:''K''<sub>a1</sub> = {{val|2.5|e=-4|u=mol/litre}}; p''K''<sub>a1</sub> = 3.6 at 25 °C.<ref name=Green>{{Greenwood&Earnshaw2nd}}</ref>
This is the ''true'' first acid dissociation constant, defined as <math>K_{a1}=\frac{\rm{[HCO_3^-] [H^+]}}{\rm{[H_2CO_3]}}</math>, where the denominator includes only covalently bound H<sub>2</sub>CO<sub>3</sub> and excludes hydrated CO<sub>2</sub>(aq). The much smaller and often-quoted value near {{val|4.16|e=-7}} is an ''apparent'' value calculated on the (incorrect) assumption that all dissolved CO<sub>2</sub> is present as carbonic acid, so that <math>K_{\mathrm{a1}}{\rm{(apparent)}}=\frac{\rm{[HCO_3^-] [H^+]}}{\rm{[H_2CO_3] + [CO_2(aq)]}}</math>. Since most of the dissolved CO<sub>2</sub> remains as CO<sub>2</sub> molecules, ''K''<sub>a1</sub>(apparent) has a much larger denominator and a much smaller value than the true ''K''<sub>a1</sub>.<ref>Jolly, William L., ''Modern Inorganic Chemistry'' (McGraw-Hill 1984), p. 196</ref>
 
The [[bicarbonate]] ion is an [[amphoteric]] species that can act as an acid or as a base, depending on pH of the solution. At high [[pH]], it dissociates significantly into the [[carbonate]] ion (CO<sub>3</sub><sup>2−</sup>):
:HCO<sub>3</sub><sup>−</sup> {{eqm}} CO<sub>3</sub><sup>2−</sup> + H<sup>+</sup>
:''K''<sub>a2</sub> = {{val|4.69|e=-11|u=mol/litre}}; p''K''<sub>a2</sub> = 10.329
 
In organisms carbonic acid production is catalysed by the [[enzyme]], [[carbonic anhydrase]].
 
=== Chemical reactions of CO<sub>2</sub> ===
CO<sub>2</sub> is a weak [[electrophile]]. Its reaction with basic water illustrates this property, in which case [[hydroxide]] is the [[nucleophile]]. Other nucleophiles react as well. For example, [[carbanion]]s as provided by  [[Grignard reagent]]s and [[organolithium compound]]s react with CO<sub>2</sub> to give carboxylates:
:MR  +  CO<sub>2</sub>  →  RCO<sub>2</sub>M  (where M = Li or MgBr and R = [[alkyl]] or [[aryl]]).
 
In [[metal carbon dioxide complex]]es, CO<sub>2</sub> serves as a ligand, which can facilitate the conversion of CO<sub>2</sub> to other chemicals.<ref>M. Aresta (Ed.) "Carbon Dioxide as a Chemical Feedstock" 2010, Wiley-VCH: Weinheim. ISBN 978-3-527-32475-0</ref>
 
The reduction of CO<sub>2</sub> to CO is ordinarily a difficult and slow reaction:
:CO<sub>2</sub> +  2 e<sup>−</sup>  +  2H<sup>+</sup>  →  CO  +  H<sub>2</sub>O
The redox potential for this reaction near pH 7 is about −0.53 V ''versus'' the [[standard hydrogen electrode]]. The nickel-containing enzyme [[carbon monoxide dehydrogenase]] catalyses this process.<ref>Colin Finn, Sorcha Schnittger, Lesley J. Yellowlees, Jason B. Love "Molecular approaches to the electrochemical reduction of carbon dioxide" Chemical Communications 2011, 0000.  {{DOI|10.1039/c1cc15393e}}</ref>
 
=== Physical properties ===
{{details|Carbon dioxide data}}
[[File:Carbon dioxide pressure-temperature phase diagram.svg|left|thumb|220px|Carbon dioxide pressure-temperature phase diagram showing the [[triple point]] and [[Critical point (thermodynamics)|critical point]] of carbon dioxide]]
[[File:Dry Ice Pellets Subliming.jpg|thumb|Sample of solid carbon dioxide or "dry ice" pellets]]
Carbon dioxide is colorless. At low concentrations, the gas is odorless. At higher concentrations it has a sharp, acidic odor. At [[Standard conditions for temperature and pressure|standard temperature and pressure]], the density of carbon dioxide is around 1.98&nbsp;kg/m<sup>3</sup>, about 1.67 times that of [[Earth's atmosphere|air]].
 
Carbon dioxide has no liquid state at pressures below {{convert|5.1|atm|lk=in}}. At 1 atmosphere (near mean sea level pressure), the gas [[deposition (physics)|deposits]] directly to a solid at temperatures below {{convert|-78.5|C|F K}} and the solid [[sublimation (chemistry)|sublimes]] directly to a gas above −78.5&nbsp;°C. In its solid state, carbon dioxide is commonly called [[dry ice]].
 
Liquid carbon dioxide forms only at [[pressure]]s above 5.1 atm; the [[triple point]] of carbon dioxide is about 518 [[kPa]] at −56.6&nbsp;°C (see phase diagram, above). The [[Critical point (thermodynamics)|critical point]] is 7.38 MPa at 31.1&nbsp;°C.<ref>{{cite web|url=http://webbook.nist.gov/cgi/cbook.cgi?ID=C124389&Units=SI&Mask=4#Thermo-Phase|title=Phase change data for Carbon dioxide|publisher=National Institute of Standards and Technology|accessdate=2008-01-21}}</ref> Another form of solid carbon dioxide observed at high pressure is an [[amorphous]] glass-like solid.<ref>{{cite journal|last=Santoro|first=M.|year=2006|title=Amorphous silica-like carbon dioxide|journal=Nature|volume=441|pages=857–860|doi=10.1038/nature04879|pmid=16778885| last2=Gorelli|first2=FA|last3=Bini|first3=R|last4= Ruocco|first4=G|last5=Scandolo|first5=S|last6=Crichton|first6=WA|issue=7095|bibcode = 2006Natur.441..857S }}</ref> This form of glass, called ''[[amorphous carbonia|carbonia]]'', is produced by [[supercooling]] heated CO<sub>2</sub> at extreme pressure (40–48 [[GPa]] or about 400,000 atmospheres) in a [[diamond anvil]]. This discovery confirmed the theory that carbon dioxide could exist in a glass state similar to other members of its elemental family, like [[silicon]] ([[silica|silica glass]]) and [[germanium dioxide]]. Unlike silica and germania glasses, however, carbonia glass is not stable at normal pressures and reverts to gas when pressure is released.
 
At temperatures and pressures above the critical point, carbon dioxide behaves as a [[supercritical fluid]] known as [[supercritical carbon dioxide]].
 
== Isolation and production ==
Carbon dioxide is mainly produced as an unrecovered side product of four technologies: combustion of fossil fuels, production of hydrogen by steam reforming, ammonia synthesis, and fermentation. It can be obtained by or from air [[distillation]], however, this method is inefficient.
 
The [[combustion]] of all carbon-containing fuels, such as [[methane]] ([[natural gas]]), petroleum distillates ([[gasoline]], [[Diesel fuel|diesel]], [[kerosene]], [[propane]]), but also of coal and wood, will yield carbon dioxide and, in most cases, water. As an example the chemical reaction between methane and oxygen is given below.
 
: {{chem|CH|4| + 2 O|2| → CO|2| + 2 H|2|O}}
 
The production of [[quicklime]] (CaO), a compound that enjoys widespread use, involves the heating ([[calcining]]) of limestone at about 850&nbsp;°C:
: {{chem|CaCO|3| → CaO + CO|2}}
 
[[Iron]] is reduced from its oxides with [[coke (fuel)|coke]] in a [[blast furnace]], producing [[pig iron]] and carbon dioxide:<ref>
{{Cite book
| last = Strassburger
| first = Julius
| title = Blast Furnace Theory and Practice
| publisher = American Institute of Mining, Metallurgical, and Petroleum Engineers
| place = New York
| year = 1969
| isbn = 0-677-10420-0
}}
</ref>
: {{chem|Fe|2|O|3| + 3 CO → 2 Fe + 3 CO|2}}
 
[[Yeast]] metabolizes [[sugar]] to produce carbon dioxide and [[ethanol]], also known as alcohol, in the production of wines, beers and other spirits, but also in the production of [[bioethanol]]:
 
: {{chem|C|6|H|12|O|6}} → {{chem|2 CO|2| + 2 C|2|H|5|OH}}
 
All [[cellular respiration|aerobic]] organisms produce {{chem|CO|2}} when they oxidize [[carbohydrate]]s, [[fatty acid]]s, and proteins in the mitochondria of cells. The large number of reactions involved are exceedingly complex and not described easily. Refer to ([[cellular respiration]], [[anaerobic respiration]] and [[photosynthesis]]). The equation for the respiration of glucose and other [[Monosaccharide|monosachharides]] is:
 
: {{chem|C|6|H|12|O|6}} + {{chem|6 O|2}} → {{chem|6 CO|2}} + {{chem|6 H|2|O}}
 
[[Photoautotrophs]] (i.e. plants, [[cyanobacteria]]) use another ''modus operandi'': Plants absorb {{chem|CO|2}} from the air, and, together with water, react it to form carbohydrates:
 
: ''n''CO<sub>2</sub> + ''n''{{chem|H|2}}O → ({{chem|CH|2|O}})<sub>n</sub> + ''n''{{chem|O|2}}
 
=== Laboratory methods ===
A variety of chemical routes to carbon dioxide are known, such as the reaction between most acids and most metal carbonates. For example, the reaction between [[hydrochloric acid]] and calcium carbonate (limestone or chalk) is depicted below:
 
: {{chem|2 HCl|| + CaCO|3| → CaCl|2| + H|2|CO|3}}
 
The [[carbonic acid]] (H<sub>2</sub>CO<sub>3</sub>) then decomposes to water and CO<sub>2</sub>. Such reactions are accompanied by foaming or bubbling, or both. In industry such reactions are widespread because they can be used to neutralize waste acid streams.
 
=== Industrial production ===
Industrial carbon dioxide can be produced by several methods, many of which are practiced at various scales.<ref name="kirk">{{cite encyclopedia|title = Kirk-Othmer Encyclopedia of Chemical Technology|first = Ronald|last = Pierantozzi|encyclopedia = Kirk-Othmer Encyclopedia of Chemical Technology|publisher = Wiley|year = 2001|doi = 10.1002/0471238961.0301180216090518.a01.pub2|chapter = Carbon Dioxide|isbn = 0-471-23896-1}}</ref>  In its dominant route, carbon dioxide is produced as a side product of the industrial production of [[ammonia]] and [[hydrogen]]. These processes begin with the reaction of water and natural gas (mainly methane).<ref>Susan Topham  "Carbon Dioxide" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim.  {{DOI|10.1002/14356007.a05_165}}</ref>
 
Although carbon dioxide is not often recovered, carbon dioxide results from combustion of [[fossil fuel]]s and [[wood]] as well  [[Fermentation (biochemistry)|fermentation]] of [[sugar]] in the [[brewing]] of [[beer]], [[whisky]] and other [[alcoholic beverage]]s. It also results from thermal decomposition of limestone, {{chem|CaCO|3}}, in the manufacture of lime ([[calcium oxide]], {{chem|CaO}}). It may be obtained directly from natural carbon dioxide [[spring (hydrosphere)|springs]], where it is produced by the action of acidified water on [[limestone]] or [[dolomite]].
 
== Uses ==
[[File:Soda bubbles macro.jpg|thumb|250px|Carbon dioxide bubbles in a soft drink.]]
Carbon dioxide is used by the food industry, the oil industry, and the chemical industry.<ref name="kirk" />
 
=== Precursor to chemicals ===
In the chemical industry, carbon dioxide is mainly consumed as an ingredient in the production of [[urea]] and [[methanol]]. Metal [[carbonate]]s and [[bicarbonate]]s, as well as some carboxylic acids derivatives (e.g., [[sodium salicylate]]) are prepared from CO<sub>2</sub>.
 
=== Foods ===
Carbon dioxide is a [[food additive]] used as a propellant and acidity regulator in the food industry. It is approved for usage in the EU<ref>UK Food Standards Agency: {{cite web |url=http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist |title=Current EU approved additives and their E Numbers |accessdate=2011-10-27}}</ref> (listed as [[E number]] E290), USA<ref>US Food and Drug Administration: {{cite web |url=http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/FoodAdditiveListings/ucm091048.htm |title=Listing of Food Additives Status Part I |accessdate=2011-10-27}}</ref> and Australia and New Zealand<ref>Australia New Zealand Food Standards Code{{cite web |url=http://www.comlaw.gov.au/Details/F2011C00827 |title=Standard 1.2.4 – Labelling of ingredients |accessdate=2011-10-27}}</ref> (listed by its INS number 290).
 
A candy called [[Pop Rocks]] is pressurized with carbon dioxide gas at about 4 x 10<sup>6</sup> Pa (40 bar, 580 psi). When placed in the mouth, it dissolves (just like other hard candy) and releases the gas bubbles with an audible pop.
 
[[Leavening agent]]s cause dough to rise by producing carbon dioxide. [[Baker's yeast]] produces carbon dioxide by fermentation of sugars within the dough, while chemical leaveners such as [[baking powder]] and [[baking soda]] release carbon dioxide when heated or if exposed to [[acid]]s.
 
==== Beverages ====
Carbon dioxide is used to produce [[carbonation|carbonated]] [[soft drink]]s and [[soda water]]. Traditionally, the carbonation in beer and sparkling wine came about through natural fermentation, but many manufacturers carbonate these drinks with carbon dioxide recovered from the fermentation process. In the case of bottled and kegged beer, recycled carbon dioxide carbonation is the most common method used. With the exception of British [[Real Ale]], draught beer is usually transferred from kegs in a cold room or cellar to dispensing taps on the bar using pressurized carbon dioxide, sometimes mixed with nitrogen.
 
==== Wine making ====
Carbon dioxide in the form of [[dry ice]] is often used in the [[wine making]] process to cool down bunches of [[grape]]s quickly after picking to help prevent spontaneous [[Fermentation (wine)|fermentation]] by wild [[yeast (wine)|yeast]]. The main advantage of using dry ice over regular water ice is that it cools the grapes without adding any additional water that may decrease the [[sugar]] concentration in the [[grape must]], and therefore also decrease the [[alcohol]] concentration in the finished wine.
 
Dry ice is also used during the [[cold soak]] phase of the wine making process to keep grapes cool. The carbon dioxide gas that results from the sublimation of the dry ice tends to settle to the bottom of tanks because it is denser than air. The settled carbon dioxide gas creates a hypoxic environment which helps to prevent bacteria from growing on the grapes until it is time to start the fermentation with the desired strain of yeast.
 
Carbon dioxide is also used to create a hypoxic environment for [[carbonic maceration]], the process used to produce [[Beaujolais]] wine.
 
Carbon dioxide is sometimes used to top up wine bottles or other [[storage (wine)|storage]] vessels such as barrels to prevent oxidation, though it has the problem that it can dissolve into the wine, making a previously still wine slightly fizzy. For this reason, other gases such as [[nitrogen]] or [[argon]] are preferred for this process by professional wine makers.
 
=== Inert gas ===
It is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in portable pressure tools. Carbon dioxide also finds use as an atmosphere for [[welding]], although in the welding arc, it reacts to [[oxidation|oxidize]] most metals. Use in the automotive industry is common despite significant evidence that welds made in carbon dioxide are more [[brittle]] than those made in more inert atmospheres, and that such weld joints deteriorate over time because of the formation of carbonic acid. It is used as a welding gas primarily because it is much less expensive than more inert gases such as [[argon]] or [[helium]]. When used for [[MIG welding]], CO<sub>2</sub> use is sometimes referred to as MAG welding, for Metal Active Gas, as CO<sub>2</sub> can react at these high temperatures. It tends to produce a hotter puddle than truly inert atmospheres, improving the flow characteristics. Although, this may be due to atmospheric reactions occurring at the puddle site. This is usually the opposite of the desired effect when welding, as it tends to embrittle the site, but may not be a problem for general mild steel welding, where ultimate ductility is not a major concern.
 
It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60 [[Bar (unit)|bar]] (870 psi, 59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Aluminum capsules of CO<sub>2</sub> are also sold as supplies of compressed gas for [[Air gun|airguns]], [[paintball]] markers, inflating bicycle tires, and for making [[carbonated water]]. Rapid vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can also be used to kill pests. Liquid carbon dioxide is used in [[supercritical drying]] of some food products and technological materials, in the preparation of specimens for [[scanning electron microscopy]] and in the [[decaffeination]] of [[coffee]] beans.
 
=== Fire extinguisher ===
Carbon dioxide extinguishes flames, and some [[Fire extinguisher#Clean agents and carbon dioxide|fire extinguishers]], especially those designed for electrical fires, contain liquid carbon dioxide under pressure. Carbon dioxide extinguishers work well on small flammable liquid and electrical fires, but not on ordinary combustible fires, because although it excludes oxygen, it does not cool the burning substances significantly and when the carbon dioxide disperses they are free to catch fire upon exposure to atmospheric oxygen. Carbon dioxide has also been widely used as an extinguishing agent in fixed fire protection systems for local application of specific hazards and total flooding of a protected space.<ref>National Fire Protection Association Code 12</ref> International Maritime Organization standards also recognize carbon dioxide systems for fire protection of ship holds and engine rooms. Carbon dioxide based fire protection systems have been linked to several deaths, because it can cause suffocation in sufficiently high concentrations. A review of CO<sub>2</sub> systems identified 51 incidents between 1975 and the date of the report, causing 72 deaths and 145 injuries.<ref>Carbon Dioxide as a Fire Suppressant: Examining the Risks, US EPA</ref>
 
=== Supercritical CO<sub>2</sub> as solvent ===
{{See also|Supercritical carbon dioxide}}
 
Liquid carbon dioxide is a good [[solvent]] for many [[lipophilic]] [[organic compound]]s and is used to remove [[caffeine]] from [[coffee]]. Carbon dioxide has attracted attention in the [[pharmaceutical]] and other chemical processing industries as a less toxic alternative to more traditional solvents such as [[organochloride]]s. It is used by some [[dry cleaning|dry cleaners]] for this reason (see [[green chemistry]]).
 
=== Agricultural and biological applications ===
Plants require carbon dioxide to conduct [[photosynthesis]]. Greenhouses may (if of large size, must) enrich their atmospheres with additional CO<sub>2</sub> to sustain and increase plant growth.<ref>[http://www.ext.colostate.edu/mg/gardennotes/141.html Plant Growth Factors: Photosynthesis, Respiration, and Transpiration]. Ext.colostate.edu. Retrieved on 2011-10-10.</ref><ref>[http://www-formal.stanford.edu/jmc/nature/node21.html Carbon dioxide]. Formal.stanford.edu. Retrieved on 2011-10-10.</ref> A photosynthesis-related drop (by a factor less than two) in carbon dioxide concentration in a greenhouse compartment would kill green plants, or, at least, completely stop their growth. At very high concentrations (100 times atmospheric concentration, or greater), carbon dioxide can be toxic to animal life, so raising the concentration to 10,000 ppm (1%) or higher for several hours will eliminate pests such as [[whitefly|whiteflies]] and [[spider mite]]s in a greenhouse.<ref>{{cite journal|author=Stafford, Ned|title=Future crops: The other greenhouse effect|journal=Nature|volume=448|date=7 February 2007|doi=10.1038/448526a|pmid=17671477|issue=7153|bibcode = 2007Natur.448..526S|pages=526–8 }}</ref> Carbon dioxide is used in greenhouses as the main carbon source for ''[[Spirulina (genus)|Spirulina]]'' algae.
 
In medicine, up to 5% carbon dioxide (130 times atmospheric concentration) is added to [[oxygen]] for stimulation of breathing after [[apnea]] and to stabilize the {{chem|O|2|/CO|2}} balance in blood.
 
It has been proposed that carbon dioxide from power generation be bubbled into ponds to grow algae that could then be converted into [[biodiesel]] fuel.<ref name='csmon'>{{cite news|first=Mark|last=Clayton|title=Algae – like a breath mint for smokestacks|date=2006-01-11| url =http://www.csmonitor.com/2006/0111/p01s03-sten.html|work =[[Christian Science Monitor]]| accessdate = 2007-10-11}}</ref>
 
=== Oil recovery ===
Carbon dioxide is used in [[enhanced oil recovery]] where it is injected into or adjacent to producing oil wells, usually under [[Supercritical fluid|supercritical]] conditions, when it becomes miscible with the oil. This approach can increase original oil recovery by reducing residual oil saturation by between 7 per cent to 23 per cent additional to [[Extraction of petroleum#Primary recovery|primary extraction]].<ref>{{cite web|url=http://www.globalccsinstitute.com/publications/accelerating-uptake-ccs-industrial-use-captured-carbon-dioxide/online/28496|title=CO<sub>2</sub> for use in enhanced oil recovery (EOR)|publisher=Global CCS Institute|accessdate=2012-02-25}}</ref> It acts as both a pressurizing agent and, when dissolved into the underground [[crude oil]], significantly reduces its viscosity, and changing surface chemistry enabling the oil to flow more rapidly through the reservoir to the removal well.<ref>{{cite journal |last=Austell |first=J Michael |year=2005 |title=CO<sub>2</sub> for Enhanced Oil Recovery Needs – Enhanced Fiscal Incentives |journal=Exploration & Production: the Oil & Gas Review |url=http://www.touchoilandgas.com/enhanced-recovery-needs-enhanced-a423-1.html |accessdate= 2007-09-28}}{{dead link|date=January 2014}}</ref> In mature oil fields, extensive pipe networks are used to carry the carbon dioxide to the injection points.
 
=== Bio transformation into fuel ===
 
Researchers have genetically modified a strain of the [[cyanobacterium]] ''[[Synechococcus|Synechococcus elongatus]]'' to produce the fuels [[isobutyraldehyde]] and [[isobutanol]] from {{CO2}} using photosynthesis.<ref>{{cite journal|url=http://www.nature.com/nbt/journal/v27/n12/abs/nbt.1586.html|journal=Nature Biotechnology|volume=27|pages=1177–1180|date=November 2009|author1=Shota Atsum|author2=Wendy Higashide|author3=James C Liauo|doi=10.1038/nbt.1586|pmid=19915552|title=Direct photosynthetic recycling of carbon dioxide to isobutyraldehyde|issue=12}}</ref>
 
=== Refrigerant ===
[[File:Comparison carbon dioxide water phase diagrams.svg|thumb|400px|Comparison of phase diagrams of carbon dioxide (red) and water (blue) as a log-lin chart with phase transitions points at 1 atmosphere]]
Liquid and solid carbon dioxide are important [[refrigerant]]s, especially in the food industry, where they are employed during the transportation and storage of ice cream and other frozen foods. Solid carbon dioxide is called "dry ice" and is used for small shipments where refrigeration equipment is not practical. Solid carbon dioxide is always below −78.5&nbsp;°C at regular atmospheric pressure, regardless of the air temperature.
 
<span id="R744" /> Liquid carbon dioxide (industry nomenclature R744 or R-744) was used as a refrigerant prior to the discovery of [[Dichlorodifluoromethane|R-12]] and may enjoy a renaissance due to the fact that [[R134a]] contributes to [[climate change]]. Its physical properties are highly favorable for cooling, refrigeration, and heating purposes, having a high volumetric cooling capacity. Due to its operation at pressures of up to 130 [[Bar (unit)|bar]] (1880 [[Pounds per square inch|psi]]), CO<sub>2</sub> systems require highly resistant components that have already been developed for mass production in many sectors. In automobile air conditioning, in more than 90% of all driving conditions for latitudes higher than 50°, R744 operates more efficiently than systems using R134a. Its environmental advantages ([[Global warming potential|GWP]] of 1, non-ozone depleting, non-toxic, non-flammable) could make it the future working fluid to replace current HFCs in cars, supermarkets, hot water heat pumps, among others. [[Coca-Cola]] has fielded CO<sub>2</sub>-based beverage coolers and the [[United States Army|U.S. Army]] is interested in CO<sub>2</sub> refrigeration and heating technology.<ref name='ccref1'>{{cite web|url=http://www.coca-colacompany.com/cooling-equipment-pushing-forward-with-hfc-free |title=The Coca-Cola Company Announces Adoption of HFC-Free Insulation in Refrigeration Units to Combat Global Warming |accessdate=2007-10-11 |date=2006-06-05 |publisher=The Coca-Cola Company}}</ref><ref name='usforces'>{{cite news|title = Modine reinforces its CO<sub>2</sub> research efforts|url = http://www.r744.com/news/news_ida145.php|date = 2007-06-28|publisher = R744.com}}</ref>
 
The global automobile industry is expected to decide on the next-generation refrigerant in car air conditioning. CO<sub>2</sub> is one discussed option.(see [[Sustainable automotive air conditioning]])
 
=== Coal bed methane recovery ===
In [[enhanced coal bed methane recovery]], carbon dioxide would be pumped into the coal seam to displace methane, as opposed to current methods which primarily use water to make the coal seam release its trapped methane.<ref>{{cite web|url=http://www.ipe.ethz.ch/laboratories/spl/research/adsorption/project03|title=Enhanced coal bed methane recovery|publisher=ETH Zurich|date=2006-08-31}}</ref>
 
=== Niche uses ===
[[File:Carbon Dioxide Laser At The Laser Effects Test Facility.jpg|thumb|right|300px|A [[carbon dioxide laser]].]]
Carbon dioxide is so inexpensive and so innocuous, that it finds many small uses that represent what might be called niche uses. For example it is used in the [[carbon dioxide laser]], which is one of the earliest type of lasers.
 
Carbon dioxide can be used as a means of controlling the [[pH]] of swimming pools, by continuously adding gas to the water, thus keeping the pH level from rising. Among the advantages of this is the avoidance of handling (more hazardous) acids. Similarly, it is also used in the maintaining [[Reef aquarium|reef aquaria]], where it is commonly used in [[calcium reactor]]s to temporarily lower the pH of water being passed over [[calcium carbonate]] in order to allow the calcium carbonate to dissolve into the water more freely where it is used by some [[coral]]s to build their skeleton. It is also used as the primary coolant in [[advanced gas-cooled reactor]]s in the nuclear power generation industry.
 
Carbon dioxide induction is commonly used for the euthanasia of laboratory research animals. Methods to administer CO<sub>2</sub> include placing animals directly into a closed, prefilled chamber containing CO<sub>2</sub>, or exposure to a gradually increasing concentration of CO<sub>2</sub>. In 2013, the [[American Veterinary Medical Association]] issued new guidelines for carbon dioxide induction, stating that a flow rate of 10% to 30% volume/min is optimal for the humane euthanization of small rodents.<ref name="2013 AVMA Guidelines for the Euthanasia of Animals: 2013 Edition">{{cite web|url=https://www.avma.org/kb/policies/documents/euthanasia.pdf |title=2013 AVMA Guidelines for the Euthanasia of Animals |format=PDF |date= |accessdate=2014-01-14}}</ref>
 
== In the Earth's atmosphere ==
{{Main|Carbon dioxide in Earth's atmosphere|Carbon cycle}}
[[File:Mauna Loa Carbon Dioxide Apr2013.svg|thumb|280px|The [[Keeling Curve]] of atmospheric CO<sub>2</sub> concentrations measured at [[Mauna Loa Observatory]].]]
 
Carbon dioxide in [[Earth's atmosphere]] is considered a [[trace gas]] currently occurring at an average concentration of about 400 parts per million by volume<ref name=NOAA>[http://www.esrl.noaa.gov/gmd/ccgg/trends/#mlo National Oceanic & Atmospheric Administration (NOAA) – Earth System Research Laboratory (ESRL), Trends in Carbon Dioxide] Values given are dry air [[mole fraction]]s expressed in parts per million ([[Parts per million|ppm]]). For an [[ideal gas]] mixture this is equivalent to parts per million by volume (ppmv).</ref> (or 591 parts per million by mass). The total mass of atmospheric carbon dioxide is 3.16×10<sup>15</sup> kg (about 3,000 gigatonnes).{{citation needed|date=October 2012}} Its concentration varies seasonally (see graph at right) and also considerably on a regional basis, especially [[planetary boundary layer|near the ground]]. In urban areas concentrations are generally higher and indoors they can reach 10 times background levels. Carbon dioxide is a [[greenhouse gas]].
 
[[File:CO2 increase rate.png|thumb|left|Yearly increase of atmospheric CO<sub>2</sub>: In the 1960s, the average annual increase was 37% of the 2000–2007 average.<ref>Dr. Pieter Tans (3 May 2008) [ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_gr_mlo.txt "Annual CO<sub>2</sub> mole fraction increase (ppm)" for 1959–2007] [[National Oceanic and Atmospheric Administration]] Earth System Research Laboratory, Global Monitoring Division ([http://www.esrl.noaa.gov/gmd/ccgg/trends/ additional details].)</ref>]]
 
{{As of|2011|11}}, [[carbon dioxide in the Earth's atmosphere]] is at a concentration of approximately 390 [[parts per million|ppm]] by [[volume]].<ref>[ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt Mauna Loa CO<sub>2</sub> annual mean data] from NOAA. "Trend" data was used. Values given are dry air [[mole fraction]]s expressed in parts per million ([[Parts per million|ppm]]). For an [[ideal gas]] mixture this is equivalent to parts per million by volume (ppmv). See also: [http://www.esrl.noaa.gov/gmd/ccgg/trends/ Trends in Carbon Dioxide] from NOAA.</ref> Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the [[Northern Hemisphere]]. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay. Taking all this into account, the concentration of CO<sub>2</sub> grew by about 2 ppm in 2009.<ref>{{cite web|url=http://www.esrl.noaa.gov/gmd/ccgg/trends/#mlo_growth|title=Annual Mean Growth Rate for Mauna Loa, Hawaii|work=Trends in Atmospheric Carbon Dioxide|publisher=NOAA Earth System Research Laboratory|accessdate=28 April 2010}}</ref>  "The main cause of the current global warming trend is human expansion of the "greenhouse effect"warming that results when the atmosphere traps heat radiating from Earth toward space."<ref>{{cite web|last=Jenkins|first=Amber|title=Global Climate Change|url=http://climate.nasa.gov/causes|publisher=Randal Jackson|accessdate=10-5-13}}</ref> Carbon dioxide is a greenhouse gas as it is transparent to [[visible spectrum|visible light]] but absorbs strongly in the [[infrared]] and [[near-infrared]], before slowly re-emitting the infrared at the same wavelength as what was absorbed.<ref>[http://www.epa.gov/climatechange/science/recentac.html Climate Change Indicators in the United States]. EPA.gov</ref>
 
Before the advent of human-caused release of carbon dioxide to the atmosphere, concentrations tended to increase with increasing global temperatures, acting as a [[positive feedback]] for changes induced by other processes such as [[Milankovitch cycles|orbital cycles]].<ref>{{cite doi | 10.1038/329414a0 }}</ref> There is a seasonal cycle in CO<sub>2</sub> concentration associated primarily with the Northern Hemisphere growing season.<ref>{{cite doi|10.1029/JD092iD05p05497}}</ref>
 
Five hundred million years ago carbon dioxide was 20 times more prevalent than today, decreasing to 4–5 times during the [[Jurassic]] period and then slowly declining with [[Azolla Event|a particularly swift reduction]] occurring 49 million years ago.<ref>{{cite web|title = Climate and CO<sub>2</sub> in the Atmosphere|url=http://earthguide.ucsd.edu/virtualmuseum/climatechange2/07_1.shtml| accessdate=2007-10-10}}</ref><ref>
{{Cite journal|first1=Robert A.|last1=Berner| first2=Zavareth|last2=Kothavala |title = GEOCARB III: A revised model of atmospheric CO<sub>2</sub> over Phanerozoic Time|url=http://www.geocraft.com/WVFossils/Reference_Docs/Geocarb_III-Berner.pdf|journal=[[American Journal of Science]]|volume=301|year=2001|issue=2|pages=182–204|doi=10.2475/ajs.301.2.182|accessdate=2008-02-15 |format=PDF}}</ref> Human activities such as the combustion of [[fossil fuels]] and [[deforestation]] have caused the atmospheric concentration of carbon dioxide to increase by about 35% since the beginning of the [[Industrial Revolution|age of industrialization]].<ref name="nonanews">{{cite news |title=After two large annual gains, rate of atmospheric CO<sub>2</sub> increase returns to average| url=http://www.noaanews.noaa.gov/stories2005/s2412.htm |date=2005-03-31 |publisher =NOAA News Online, Story 2412}}</ref>
 
Up to 40% of the gas emitted by some [[volcano]]es during [[subaerial eruption]]s is carbon dioxide.<ref>{{Cite book|last=Sigurdsson |first=Haraldur |coauthors=Houghton, B. F. |title=Encyclopedia of volcanoes |year=2000 |publisher=Academic Press |location=San Diego |isbn=0-12-643140-X}}</ref> It is estimated that volcanoes release about 130–230 million tonnes (145–255 million [[short tons]]) of CO<sub>2</sub> into the atmosphere each year. Carbon dioxide is also produced by hot springs such as those at the Bossoleto site near [[Rapolano Terme]] in [[Tuscany]], [[Italy]]. Here, in a bowl-shaped depression of about 100 m diameter, local concentrations of CO<sub>2</sub> rise to above 75% overnight, sufficient to kill insects and small animals, but it warms rapidly when sunlit and the gas is dispersed by convection during the day.<ref>{{Cite book |last=van Gardingen |first=P.R. |coauthors=Grace, J.; Jeffree, C.E.; Byari, S.H.; Miglietta, F.; Raschi, A.; Bettarini, I. |chapter=Long-term effects of enhanced CO<sub>2</sub> concentrations on leaf gas exchange: research opportunities using CO<sub>2</sub> springs |title=Plant responses to elevated CO<sub>2</sub>: Evidence from natural springs |editor=Raschi, A.; Miglietta, F.; Tognetti, R.; van Gardingen, P.R. (Eds.) |year=1997 |publisher=Cambridge University Press |location=Cambridge |isbn=0-521-58203-2|pages=69–86}}</ref> Locally high concentrations of CO<sub>2</sub>, produced by disturbance of deep lake water saturated with CO<sub>2</sub> are thought to have caused 37 fatalities at [[Lake Monoun]], [[Cameroon]] in 1984 and 1700 casualties at [[Lake Nyos]], Cameroon in 1986.<ref>{{Cite book |last=Martini |first=M. |chapter=CO<sub>2</sub> emissions in volcanic areas: case histories and hazaards |title=Plant responses to elevated CO<sub>2</sub>: Evidence from natural springs |editor=Raschi, A.; Miglietta, F.; Tognetti, R.; van Gardingen, P.R. (Eds.) |year=1997 |publisher=Cambridge University Press |location=Cambridge |isbn=0-521-58203-2|pages=69–86}}</ref> Emissions of CO<sub>2</sub> by human activities are estimated to be 135 times greater than the quantity emitted by volcanoes.<ref>{{cite web|title = Volcanic Gases and Climate Change Overview | url=http://volcanoes.usgs.gov/hazards/gas/climate.php | publisher = US Geological Survey | accessdate=2013-02-26}}</ref>
 
The [[cement]] industry is one of the three primary producers of carbon dioxide along with the energy production and transportation industries. As of 2011 concrete contributes 7% to global anthropogenic CO<sub>2</sub> emissions.<ref>{{cite web|url=http://www.intechopen.com/download/get/type/pdfs/id/28663|author1=Navdeep Kaur Dhami|author2=Sudhakara M. Reddy|author3=Abhijit Mukherjee|title=Biofilm and Microbial Applications in Biomineralized Concrete|page=142}}</ref>
{{-}}
 
== In the oceans ==
{{Main|Carbon cycle}}
Carbon dioxide dissolves in the ocean to form [[carbonic acid]] (H<sub>2</sub>CO<sub>3</sub>), [[bicarbonate]] (HCO<sub>3</sub><sup>−</sup>) and [[carbonate]] (CO<sub>3</sub><sup>2−</sup>), and there is about fifty times as much carbon dissolved in the [[sea water]] of the oceans as exists in the atmosphere. The oceans act as an enormous [[carbon sink]], and have taken up about a third of CO<sub>2</sub> emitted by human activity.<ref>{{cite web|last = Doney|first = Scott C.|coauthors = Naomi M. Levine|title = How Long Can the Ocean Slow Global Warming?|publisher = Oceanus|date = 2006-11-29|url = http://www.whoi.edu/oceanus/viewArticle.do?id=17726|accessdate = 2007-11-21}}</ref>
 
As the concentration of carbon dioxide increases in the atmosphere, the increased uptake of carbon dioxide into the oceans is causing a measurable decrease in the pH of the oceans which is referred to as [[ocean acidification]]. Although the [[solubility pump|natural absorption of {{chem|CO|2}}]] by the world's oceans helps mitigate the [[climate change|climatic]] effects of anthropogenic emissions of {{chem|CO|2}}, it also results in a decrease in the pH of the oceans. This reduction in pH impacts the biological systems in the oceans, primarily oceanic [[calcification|calcifying]] organisms. These impacts span the [[food chain]] from [[autotroph]]s to [[heterotroph]]s and include organisms such as [[coccolithophore]]s, [[coral]]s, [[foraminifera]], [[echinoderm]]s, [[crustacea]]ns and [[mollusca|molluscs]]. Under normal conditions, calcite and aragonite are stable in surface waters since the carbonate ion is at [[supersaturation|supersaturating]] concentrations. However, as ocean pH falls, so does the concentration of this ion, and when carbonate becomes undersaturated, structures made of calcium carbonate are vulnerable to dissolution. Even if there is no change in the rate of calcification, therefore, the rate of dissolution of calcareous material increases.<ref>{{Cite journal |last1 = Nienhuis |first1 = S. |last2 = Palmer |first2 = A. |last3 = Harley |first3 = C. |year = 2010 |title = Elevated CO<sub>2</sub> affects shell dissolution rate but not calcification rate in a marine snail |journal = [[Proceedings of the Royal Society B: Biological Sciences]] |volume = 277 |issue = 1693 |pages = 2553–2558 |pmc = 2894921 |doi = 10.1098/rspb.2010.0206 |pmid = 20392726}}</ref>
 
Research has already found that corals,<ref name=gatt98>
{{Cite journal
|last=Gattuso|first=J.-P.|coauthors=Frankignoulle, M.; Bourge, I.; Romaine, S. and Buddemeier, R. W.
|year=1998
|title=Effect of calcium carbonate saturation of seawater on coral calcification
|url=http://www.obs-vlfr.fr/~gattuso/jpg_papers_list.php
|journal=[[Global and Planetary Change]]
|volume=18|issue=1–2|pages=37–46|doi=10.1016/S0921-8181(98)00035-6
|bibcode = 1998GPC....18...37G }}</ref><ref name=gatt99>
{{Cite journal
|last=Gattuso|first=J.-P.|coauthors=Allemand, D.; Frankignoulle, M
|year=1999
|title=Photosynthesis and calcification at cellular, organismal and community levels in coral reefs: a review on interactions and control by carbonate chemistry
|url=http://www.obs-vlfr.fr/~gattuso/jpg_papers_list.php
|journal=[[American Zoologist]]
|volume=39|pages=160–183
}}</ref><ref name=lan05>
{{Cite journal
|last=Langdon|first=C|coauthors=Atkinson, M. J.
|year=2005
|title=Effect of elevated p{{CO2}} on photosynthesis and calcification of corals and interactions with seasonal change in temperature/irradiance and nutrient enrichment
|journal=[[Journal of Geophysical Research]]
|volume=110|issue=C09S07|doi=10.1029/2004JC002576
|pages=C09S07 |bibcode=2005JGRC..11009S07L
}}</ref> coccolithophore algae,<ref name=rieb00>
{{Cite journal
|last=Riebesell|first=Ulf|coauthors=Zondervan, Ingrid; Rost, Björn; Tortell, Philippe D.; Zeebe, Richard E. and François M. M. Morel
|year=2000
|title=Reduced calcification of marine plankton in response to increased atmospheric {{chem|CO|2}}
|journal=[[Nature (journal)|Nature]]
|volume=407|issue=6802|pages=364–367|doi=10.1038/35030078
|pmid=11014189
}}</ref><ref name=zond01>
{{Cite journal | last=Zondervan | first=I. | coauthors=Zeebe, R.E., Rost, B. and Rieblesell, U. | year=2001 | title=Decreasing marine biogenic calcification: a negative feedback on rising atmospheric CO<sub>2</sub> | journal=[[Global Biogeochemical Cycles]] | volume=15 | pages=507–516 | doi=10.1029/2000GB001321 | bibcode=2001GBioC..15..507Z | issue=2}}</ref><ref name=zond02>{{Cite journal | last=Zondervan | first=I. | coauthors=Rost, B. and Rieblesell, U. | year=2002 | title=Effect of CO<sub>2</sub> concentration on the PIC/POC ratio in the coccolithophore ''Emiliania huxleyi'' grown under light limiting conditions and different day lengths | journal=[[Journal of Experimental Marine Biology and Ecology]] | volume=272 |issue=1 |pages=55–70 | doi=10.1016/S0022-0981(02)00037-0}}</ref><ref name=delille05>{{Cite journal | last=Delille | first=B. | coauthors=Harlay, J., Zondervan, I., Jacquet, S., Chou, L., Wollast, R., Bellerby, R.G.J., Frankignoulle, M., Borges, A.V., Riebesell, U. and Gattuso, J.-P. | year=2005 | title=Response of primary production and calcification to changes of pCO<sub>2</sub> during experimental blooms of the coccolithophorid ''Emiliania huxleyi'' | url=http://www.obs-vlfr.fr/~gattuso/jpg_papers_list.php | journal=[[Global Biogeochemical Cycles]] | volume=19 |doi=10.1029/2004GB002318 | pages=GB2023 | bibcode=2005GBioC..19.2023D | issue=2}}</ref> coralline algae,<ref name=kuffner>{{Cite journal | last=Kuffner | first=I.B. | coauthors=Andersson, A.J., Jokiel, P.L., Rodgers, K.S. and Mackenzie, F.T. | year=2007 | title=Decreased abundance of crustose coralline algae due to ocean acidification | journal=[[Nature Geoscience]] | volume=1 |issue=2 |pages=114–117 |doi=10.1038/ngeo100 |bibcode=2008NatGe...1..114K}}</ref> foraminifera,<ref name='catalyst-2007-09-13-OAtbgws'>
{{Cite news
|last=Phillips|first=Graham|coauthors=Chris Branagan
|title=Ocean Acidification – The BIG global warming story
|date=2007-09-13
|publisher=Australian Broadcasting Corporation
|url=http://www.abc.net.au/catalyst/stories/s2029333.htm
|work =ABC TV Science: Catalyst
|accessdate=2007-09-18
}}</ref> [[shellfish]]<ref name=gaz07>
{{Cite journal
|last=Gazeau|first=F.|coauthors=Quiblier, C.; Jansen, J. M.; Gattuso, J.-P.; Middelburg, J. J. and Heip, C. H. R.
|year=2007
|title=Impact of elevated {{chem|CO|2}} on shellfish calcification
|url=http://www.obs-vlfr.fr/~gattuso/jpg_papers_list.php
|journal=[[Geophysical Research Letters]]
|volume=34|issue=7|pages=L07603|doi=10.1029/2006GL028554 |bibcode=2007GeoRL..3407603G
}}</ref> and [[pteropod]]s<ref name=comeau09>
{{Cite journal| last=Comeau | first=C. | coauthors=Gorsky, G., Jeffree, R., Teyssié, J.-L. and Gattuso, J.-P. | journal=[[Biogeosciences]] | year=2009 | volume=6 | pages=1877–1882 | title=Impact of ocean acidification on a key Arctic pelagic mollusc ("Limacina helicina") | url=http://www.biogeosciences.net/6/1877/2009/ | doi=10.5194/bg-6-1877-2009| issue=9}}</ref> experience reduced calcification or enhanced dissolution when exposed to elevated {{chem|CO|2}}.
 
Gas solubility decreases as the temperature of water increases (except when both pressure exceeds 300 bar and temperature exceeds 393 K, only found near deep geothermal vents)<ref>{{cite journal|last=Duana|first=Zhenhao|coauthors=Rui Sun|year=2003|title=An improved model calculating CO<sub>2</sub> solubility in pure water and aqueous NaCl solutions from 273 to 533 K and from 0 to 2000 bar|journal=Chemical Geology|volume=193|pages=260–271}}</ref> and therefore the rate of uptake from the atmosphere decreases as ocean temperatures rise.
 
Most of the CO<sub>2</sub> taken up by the ocean, which is about 30% of the total released into the atmosphere,<ref>{{cite doi|10.1126/science.1189338}}</ref> forms carbonic acid in equilibrium with bicarbonate. Some of these chemical species are consumed by photosynthestic organisms, that remove carbon from the cycle. Increased CO<sub>2</sub> in the atmosphere has led to decreasing [[alkalinity]] of seawater, and there is concern that this may adversely affect organisms living in the water. In particular, with decreasing alkalinity, the availability of carbonates for forming shells decreases,<ref>{{cite book |title= Oceanography: An Invitation to Marine Science |last= Garrison |first= Tom |year= 2004 |publisher= [[The Thomson Corporation|Thomson Brooks]] |isbn= 0-534-40887-7 |page= 125}}</ref> although there's evidence of increased shell production by certain species under increased CO<sub>2</sub> content.<ref>{{cite web|url = http://geology.gsapubs.org/content/37/12/1131.abstract|title = Marine calcifiers exhibit mixed responses to CO<sub>2</sub>-induced ocean acidification|publisher = Geology|date=2009-12-01|last = Ries|first = Justin B.|coauthors = Anne L. Cohen, Daniel C. McCorkle}}</ref>
 
NOAA states in their May 2008 "State of the science fact sheet for [[ocean acidification]]" that:<br />
"The oceans have absorbed about 50% of the carbon dioxide (CO<sub>2</sub>) released from the burning of fossil fuels, resulting in chemical reactions that lower ocean pH. This has caused an increase in hydrogen ion (acidity) of about 30% since the start of the industrial age through a process known as "ocean acidification." A growing number of studies have demonstrated adverse impacts on marine organisms, including:
* The rate at which reef-building corals produce their skeletons decreases, while production of numerous varieties of jellyfish increases.
* The ability of marine algae and free-swimming zooplankton to maintain protective shells is reduced.
* The survival of larval marine species, including commercial fish and shellfish, is reduced."
 
Also, the Intergovernmental Panel on Climate Change (IPCC) writes in their Climate Change 2007: Synthesis Report:<ref>[http://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_synthesis_report.htm Climate Change 2007: Synthesis Report], IPCC</ref> <br />
"The uptake of anthropogenic carbon since 1750 has led to the ocean becoming more acidic with an average decrease in pH of 0.1 units. Increasing atmospheric CO<sub>2</sub> concentrations lead to further acidification&nbsp;... While the effects of observed ocean acidification on the marine biosphere are as yet undocumented, the progressive acidification of oceans is expected to have negative impacts on marine shell-forming organisms (e.g. corals) and their dependent species."
 
Some marine calcifying organisms (including coral reefs) have been singled out by major research agencies, including NOAA, OSPAR commission, NANOOS and the IPCC, because their most current research shows that ocean acidification should be expected to impact them negatively.<ref>{{cite web|url=http://www.pmel.noaa.gov/co2/story/Ocean+Acidification |title=PMEL Ocean Acidification Home Page |publisher=Pmel.noaa.gov |date= |accessdate=2014-01-14}}</ref>
 
Carbon dioxide is also introduced into the oceans through hydrothermal vents. The ''Champagne'' hydrothermal vent, found at the Northwest Eifuku volcano at [[Marianas Trench Marine National Monument]], produces almost pure liquid carbon dioxide, one of only two known sites in the world.<ref>{{cite journal
|author=Lupton, J.; Lilley, M.; Butterfield, D.; Evans, L.; Embley, R.; Olson, E.; Proskurowski, G.; Resing, J.; Roe, K.; Greene, R.; Lebon, G.
|title=Liquid Carbon Dioxide Venting at the Champagne Hydrothermal Site, NW Eifuku Volcano, Mariana Arc
|series=Fall
|journal=American Geophysical Union
|volume=Meeting
|issue=abstract #V43F–08
|year=2004
|bibcode=2004AGUFM.V43F..08L
|page=08}}</ref>
 
[[Sea urchin]]s have been discovered to be able to convert carbon dioxide into raw material for their shells.<ref>{{cite web|url=http://www.gizmag.com/carbon-capture-calcium-carbonate/26101/|title=Sea urchins reveal promising carbon capture alternative|publisher=Gizmag|date=4 February 2013|accessdate=5 February 2013}}</ref>
 
== Biological role ==
Carbon dioxide is an end product in organisms that obtain energy from breaking down sugars, fats and [[amino acid]]s with [[oxygen]] as part of their [[metabolism]], in a process known as [[cellular respiration]]. This includes all plants, animals, many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood from the body's tissues to the lungs where it is exhaled. In plants using photosynthesis, carbon dioxide is absorbed from the atmosphere.
 
=== Photosynthesis and carbon fixation ===
[[File:Auto-and heterotrophs.png|thumb|200px|Overview of photosynthesis and respiration. Carbon dioxide (at right), together with water, form oxygen and organic compounds (at left) by [[photosynthesis|<span style="color:green;">photosynthesis</span>]], which can be [[cellular respiration|<span style="color:red;">respired</span>]] to water and (CO<sub>2</sub>).]]
 
[[Image:Calvin-cycle4.svg|thumb|left|300px|'''Figure 2'''. Overview of the [[Calvin cycle]] and carbon fixation]]
[[Carbon fixation]] is the removal of carbon dioxide from the air and its incorporation into solid compounds. [[Plant]]s, [[algae]], and many species of [[bacteria]] ([[cyanobacteria]]) fix carbon and create their own food by [[photosynthesis]]. Photosynthesis uses carbon dioxide and [[water]] to produce [[sugar]]s and occasionally other [[organic compound]]s, releasing [[oxygen]] as a waste product.
 
[[RuBisCO|Ribulose-1,5-bisphosphate carboxylase oxygenase]], commonly known by the shorter name RuBisCO, is an [[enzyme]] involved in the first major step of [[carbon fixation]], a process by which atmospheric carbon dioxide is converted by plants to [[fuel|energy-rich]] [[molecule]]s such as [[glucose]]. It is also thought to be the single most abundant protein on Earth.<ref>{{cite journal | author = Dhingra A, Portis AR, Daniell H | title = Enhanced translation of a chloroplast-expressed RbcS gene restores small subunit levels and photosynthesis in nuclear RbcS antisense plants | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 101 | issue = 16 | pages = 6315–20 |date=April 2004 | pmid = 15067115 | pmc = 395966 | doi = 10.1073/pnas.0400981101 | url = | quote = (Rubisco) is the most prevalent enzyme on this planet, accounting for 30–50% of total soluble protein in the chloroplast;  |bibcode = 2004PNAS..101.6315D }}</ref>
 
These [[phototroph]]s use the products of their photosynthesis as internal food sources and as raw material for the construction of more complex organic molecules, such as [[polysaccharides]], [[nucleic acid]]s and [[protein]]s. These are used for their own growth, and also as the basis for the [[food chain]]s and webs whereby other organisms, including animals such as ourselves, are fed. Some important phototrophs, the [[coccolithophore]]s synthesise hard [[calcium carbonate]] scales. A globally significant species of coccolithophore is ''[[Emiliania huxleyi]]'' whose [[calcite]] scales have formed the basis of many [[sedimentary rock]]s such as [[limestone]], where what was previously atmospheric carbon can remain fixed for geological timescales.
 
Plants can grow up to 50 percent faster in concentrations of 1,000 ppm CO<sub>2</sub> when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients.<ref>{{cite web|title=Carbon Dioxide In Greenhouses|last=Blom|first=T.J.|coauthors=W.A. Straver; F.J. Ingratta; Shalin Khosla; Wayne Brown|url=http://www.omafra.gov.on.ca/english/crops/facts/00-077.htm|date=December 2002|accessdate=2007-06-12}}</ref> Research has shown that elevated CO<sub>2</sub> levels cause increased growth reflected in the harvestable yield of crops, with wheat, rice and soybean all showing increases in yield of 12–14% under elevated CO<sub>2</sub> in FACE experiments.<ref>{{cite journal|last1=Ainsworth|first1=Elizabeth A.|doi=10.1111/j.1365-2486.2008.01594.x|title=Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and elevated ozone concentration|year=2008|page=1642|issue=7|volume=14|journal=Global Change Biology|url=http://www.plant-biotech.dk/Meetings/PBD_Symposium_Plant%20Stress_litterature/LisaAinsworth_pdf2.pdf}}{{dead link|date=January 2014}}</ref><ref>{{cite journal|last1=Long|first1=SP|last2=Ainsworth|first2=EA|last3=Leakey|first3=AD|last4=Nösberger|first4=J|last5=Ort|first5=DR|title=Food for thought: lower-than-expected crop yield stimulation with rising CO<sub>2</sub> concentrations |journal=Science|volume=312|issue=5782|pages=1918–21|year=2006|pmid=16809532|doi=10.1126/science.1114722|bibcode = 2006Sci...312.1918L }}</ref>
 
Studies have shown that increased CO<sub>2</sub> leads to fewer stomata developing on plants<ref>{{cite journal|author=F. Woodward and C. Kelly |journal=New Phytologist|year=1995 |volume= 131|issue=3|pages=311–327 |title=The influence of CO<sub>2</sub> concentration on stomatal density|doi=10.1111/j.1469-8137.1995.tb03067.x}}</ref> which leads to reduced water usage.<ref>{{cite journal|doi=10.1146/annurev.arplant.48.1.609|journal=Annual Review of Plant Physiology and Plant Molecular Biology|volume=48|issue=1|year=1997|title=More efficient plants: A consequence of rising atmospheric CO<sub>2</sub>?|author=Bert G. Drake|last2=Gonzalez-Meler|first2=Miquel A.|last3=Long|first3=Steve P.|pmid=15012276|pages=609–639}}</ref> Studies using [[Free-Air Concentration Enrichment|FACE]] have shown that increases in CO<sub>2</sub> lead to decreased concentration of micronutrients in crop plants.<ref>{{cite journal|doi=10.1016/S0169-5347(02)02587-9|title=Rising atmospheric CO<sub>2</sub> and human nutrition: toward globally imbalanced plant stoichiometry?|year=2002|author=Loladze, I|journal=Trends in Ecology & Evolution|volume=17|issue=10|page=457}}</ref> This may have knock-on effects on other parts of [[ecosystem]]s as herbivores will need to eat more food to gain the same amount of protein.<ref>{{cite journal|jstor=2641685|author=Carlos E. Coviella and John T. Trumble |journal=Conservation Biology|volume= 13|issue= 4|year=1999|page=700|title=Effects of Elevated Atmospheric Carbon Dioxide on Insect-Plant Interactions|doi=10.1046/j.1523-1739.1999.98267.x}}</ref>
 
The concentration of secondary [[metabolites]] such as phenylpropanoids and flavonoids
can also be altered in plants exposed to high concentrations of CO<sub>2</sub>.<ref>{{cite doi|10.1016/j.bse.2006.09.004}}</ref><ref>{{cite pmid|15587703}}</ref>
 
Plants also emit CO<sub>2</sub> during respiration, and so the majority of plants and algae, which use [[C3 photosynthesis]], are only net absorbers during the day. Though a growing forest will absorb many tons of CO<sub>2</sub> each year, the World Bank writes that a mature forest will produce as much CO<sub>2</sub> from respiration and decomposition of dead specimens (e.g., fallen branches) as is used in [[biosynthesis]] in growing plants.<ref>{{cite web|url=http://www-wds.worldbank.org/external/default/WDSContentServer/WDSP/IB/2002/09/07/000094946_02081604154234/Rendered/INDEX/multi0page.txt|title=Global Environment Division Greenhouse Gas Assessment Handbook – A Practical Guidance Document for the Assessment of Project-level Greenhouse Gas Emissions|accessdate=2007-11-10|work=[[World Bank]]}}</ref> However six experts in biochemistry, biogeology, forestry and related areas writing in the science journal Nature that "Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral."<ref>{{cite journal|doi=10.1038/nature07276|title=Old-growth forests as global carbon sinks|year=2008|last1=Luyssaert|first1=Sebastiaan|last2=Schulze|first2=E. -Detlef|last3=Börner|first3=Annett|last4=Knohl|first4=Alexander|last5=Hessenmöller|first5=Dominik|last6=Law|first6=Beverly E.|last7=Ciais|first7=Philippe|last8=Grace|first8=John|journal=Nature|volume=455|pmid=18784722|issue=7210|bibcode = 2008Natur.455..213L|pages=213–5 }}</ref> Mature forests are valuable [[carbon sink]]s, helping maintain balance in the Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO<sub>2</sub> in the upper ocean and thereby promotes the absorption of CO<sub>2</sub> from the atmosphere.<ref>{{cite journal|author=Falkowski P, Scholes RJ, Boyle E, Canadell J, Canfield D, Elser J, Gruber N, Hibbard K, Högberg P, Linder S, Mackenzie FT, Moore B 3rd, Pedersen T, Rosenthal Y, Seitzinger S, Smetacek V, Steffen W.| year=2000|title=The global carbon cycle: a test of our knowledge of earth as a system|journal=Science|volume=290|issue=5490|pages=291–296|doi=10.1126/science.290.5490.291|pmid=11030643|bibcode = 2000Sci...290..291F }}</ref>
 
=== Toxicity ===
{{See also|Carbon dioxide poisoning}}
[[File:Main symptoms of carbon dioxide toxicity.svg|thumb|right|270px|Main symptoms of carbon dioxide toxicity, by increasing [[volume percent]] in air.<ref name=friedman>[http://www.inspect-ny.com/hazmat/CO2gashaz.htm Toxicity of Carbon Dioxide Gas Exposure, CO2 Poisoning Symptoms, Carbon Dioxide Exposure Limits, and Links to Toxic Gas Testing Procedures] By Daniel Friedman – InspectAPedia</ref>]]
 
Carbon dioxide content in fresh air (averaged between sea-level and 10 kPa level, i.e., about 30&nbsp;km altitude) varies between 0.036% (360 ppm) and 0.039% (390 ppm), depending on the location.<ref>{{cite web|url=http://www.esrl.noaa.gov/gmd/ccgg/carbontracker/|title=CarbonTracker CT2011_oi (Graphical map of CO<sub>2</sub>)|work=esrl.noaa.gov}}</ref>
 
CO<sub>2</sub> is an [[asphyxiant gas]] and not classified as toxic or harmful in accordance with [[Globally Harmonized System of Classification and Labelling of Chemicals|Globally Harmonized System of Classification and Labelling of Chemicals standards]] of [[United Nations Economic Commission for Europe]] by using the [[OECD Guidelines for the Testing of Chemicals]]. In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy.<ref name=friedman/> Concentrations of 7% to 10% may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.<ref>{{cite news|publisher=U.S. Environmental Protection Agency: |url=http://www.epa.gov/ozone/snap/fire/co2/co2report.html |title=Carbon Dioxide as a Fire Suppressant: Examining the Risks}}</ref>
 
Because it's heavier than air, in locations where the gas seeps from the ground (due to sub-surface volcanic or geothermal activity) in relatively high levels, without the dispersing effects of wind, it can collect in sheltered/pocketed locations below average ground level, causing animals located therein to be suffocated. Carrion feeders attracted to the carcasses are then also killed. For example, children have been killed in the same way near the city of [[Goma]] due to nearby volcanic [[Mt. Nyiragongo]].<ref>[http://www.pbs.org/wgbh/nova/transcripts/3215_volcanoc.html Volcano Under the City]. PBS.org (1 November 2005).</ref>
The [[Swahili language|Swahili]] term for this phenomena is '[[mazuku]]'.
 
Adaptation to increased levels of CO<sub>2</sub> occurs in humans. Continuous inhalation of CO<sub>2</sub> can be tolerated at three percent inspired concentrations for at least one month and four percent inspired concentrations for over a week. It was suggested that 2.0 percent inspired concentrations could be used for closed air spaces (e.g. a [[submarine]]) since the adaptation is physiological and reversible. Decrement in performance or in normal physical activity does not happen at this level.<ref name="Glatte Jr H. A., Motsay G. J., Welch B. E. 1967">{{cite journal |title=Carbon Dioxide Tolerance Studies |author=Glatte Jr H. A., Motsay G. J., Welch B. E. |year=1967 |volume=SAM-TR-67-77 |journal=Brooks AFB, TX School of Aerospace Medicine Technical Report|url=http://archive.rubicon-foundation.org/6045 |accessdate=2008-05-02}}</ref><ref>{{cite journal |title=Carbon Dioxide Tolerance and Toxicity |author=Lambertsen, C. J. |year=1971 |journal=Environmental Biomedical Stress Data Center, Institute for Environmental Medicine, University of Pennsylvania Medical Center |volume=Report No. 2-71 |location=Philadelphia, PA |series=IFEM |url=http://archive.rubicon-foundation.org/3861 |accessdate=2008-05-02}}</ref> However, it should be noted that submarines have [[carbon dioxide scrubber]]s which reduce a significant amount of the CO<sub>2</sub> present.<ref>[http://www.howstuffworks.com/question83.htm How are people able to breathe inside a submarine?]. Howstuffworks.com (2000-04-01). Retrieved on 2011-10-10.</ref>
 
Acute carbon dioxide physiological effect is [[hypercapnia]] or [[Asphyxiant gas|asphyxiation]] sometimes known by the names given to it by miners: [[blackdamp]] (also called ''choke damp'' or ''stythe''). Blackdamp is primarily nitrogen and carbon dioxide and kills via suffocation (having displaced oxygen). [[Miners]] would try to alert themselves to dangerous levels of blackdamp and other gases in a mine shaft by bringing a caged [[Domestic Canary|canary]] with them as they worked. The canary is more sensitive to environmental gases than humans and as it became unconscious would stop singing and fall off its perch. The [[Davy lamp]] could also detect high levels of blackdamp (which collect near the floor) by burning less brightly, while [[methane]], another suffocating gas and explosion risk would make the lamp burn more brightly.
 
Carbon dioxide differential above outdoor levels at steady state conditions (when the occupancy and ventilation system operation are sufficiently long that CO<sub>2</sub> concentration has stabilized) are sometimes used to estimate ventilation rates per person. CO<sub>2</sub> is considered to be a surrogate for human bio-effluents and may correlate with other indoor pollutants. Higher CO<sub>2</sub> concentrations are associated with occupant health, comfort and performance degradation. [[ASHRAE]] Standard 62.1–2007 ventilation rates may result in indoor levels up to 2,100 ppm above ambient outdoor conditions. Thus if the outdoor ambient is 400 ppm, indoor levels may reach 2,500 ppm with ventilation rates that meet this industry consensus standard. Levels in poorly ventilated spaces can be found even higher than this (range of 3,000 or 4,000).
 
=== Human physiology ===
 
==== Content ====
The body produces approximately {{convert|2.3|lb|kg}} of carbon dioxide per day per person,<ref>{{cite web|url=http://www.epa.gov/climatechange/fq/emissions.html#q7|title=How much carbon dioxide do humans contribute through breathing?|accessdate=2009-04-30}}{{dead link|date=January 2014}}</ref> containing {{convert|0.63|lb|g}} of carbon.
 
{{anchor|partial pressure}}In humans, this carbon dioxide is carried through the venous system and is breathed out through the lungs. Therefore, the carbon dioxide content in the body is high in the [[venous system]], and decreases in the [[respiratory system]], resulting in lower levels along any [[arterial system]]. Carbon dioxide content in this sense is often given as the [[partial pressure]], which is the pressure which carbon dioxide would have had if it alone occupied the volume.<ref>{{cite book|author=Charles Henrickson|title=Chemistry|edition=|publisher=Cliffs Notes|year=2005|isbn=0-7645-7419-1}}</ref>
 
In humans, the carbon dioxide contents are as follows:
{|class="wikitable"
|+[[Reference range]]s or averages for [[partial pressure]]s of carbon dioxide (abbreviated PCO<sub>2</sub>)
|-
! Unit !! [[vein|Venous]] blood gas  || Alveolar [[pulmonary gas pressures|pulmonary<br /> gas pressures]] !! [[Arterial blood gas#carbon dioxide|Arterial blood carbon dioxide]]
|-
|| [[kilopascal|kPa]] || 5.5<ref name=mmHg/>-6.8<ref name=mmHg/> || 4.8 || 4.7<ref name=mmHg>Derived from mmHg values using 0.133322 kPa/mmHg</ref>-6.0<ref name=mmHg/>
|-
| [[mmHg]] || 41<ref name=brookside>[http://www.brooksidepress.org/Products/OperationalMedicine/DATA/operationalmed/Lab/ABG_ArterialBloodGas.htm The Medical Education Division of the Brookside Associates--> ABG (Arterial Blood Gas)]{{dead link|date=January 2014}} Retrieved on December 6, 2009</ref>-51<ref name=brookside/> || 36 || 35<ref name=southwest>[http://pathcuric1.swmed.edu/PathDemo/nrrt.htm Normal Reference Range Table]{{dead link|date=January 2014}} from The University of Texas Southwestern Medical Center at Dallas. Used in Interactive Case Study Companion to Pathologic basis of disease.</ref>-45<ref name=southwest/>
|}
 
==== Transport in the blood ====
CO<sub>2</sub> is carried in blood in three different ways. (The exact percentages vary depending whether it is arterial or venous blood).
* Most of it (about 70% to 80%) is converted to [[bicarbonate]] ions {{chem|HCO|3|−}} by the enzyme [[carbonic anhydrase]] in the red blood cells,<ref name='solarnav'>{{cite web|url=http://www.solarnavigator.net/solar_cola/carbon_dioxide.htm |title=Carbon dioxide |accessdate=2007-10-12 |work=solarnavigator.net}}</ref> by the reaction CO<sub>2</sub> + H<sub>2</sub>O → H<sub>2</sub>CO<sub>3</sub> → H<sup>+</sup> + {{chem|HCO|3|−}}.
* 5% – 10% is dissolved in the [[Blood plasma|plasma]]<ref name='solarnav' />
* 5% – 10% is bound to [[hemoglobin]] as [[carbamino]] compounds<ref name='solarnav' />
 
[[Hemoglobin]], the main oxygen-carrying molecule in [[red blood cell]]s, carries both oxygen and carbon dioxide. However, the CO<sub>2</sub> bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because of [[allosteric regulation|allosteric]] effects on the hemoglobin molecule, the binding of CO<sub>2</sub> decreases the amount of oxygen that is bound for a given partial pressure of oxygen. The decreased binding to carbon dioxide in the blood due to increased oxygen levels is known as the [[Haldane Effect]], and is important in the transport of carbon dioxide from the tissues to the lungs. Conversely, a rise in the partial pressure of CO<sub>2</sub> or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the [[Bohr Effect]].
 
==== Regulation of respiration ====
Carbon dioxide is one of the mediators of local [[autoregulation]] of blood supply. If its levels are high, the [[capillaries]] expand to allow a greater blood flow to that tissue.
 
Bicarbonate ions are crucial for regulating blood pH. A person's breathing rate influences the level of CO<sub>2</sub> in their blood. Breathing that is too slow or shallow causes [[respiratory acidosis]], while breathing that is too rapid leads to [[hyperventilation]], which can cause [[alkalosis|respiratory alkalosis]].
 
Although the body requires oxygen for metabolism, low oxygen levels normally do not stimulate breathing. Rather, breathing is stimulated by higher carbon dioxide levels. As a result, breathing low-pressure air or a gas mixture with no oxygen at all (such as pure nitrogen) can lead to loss of consciousness without ever experiencing [[air hunger]]. This is especially perilous for high-altitude fighter pilots. It is also why flight attendants instruct passengers, in case of loss of cabin pressure, to apply the [[oxygen mask]] to themselves first before helping others; otherwise, one risks losing consciousness.<ref name='solarnav' />
 
The respiratory centers try to maintain an arterial CO<sub>2</sub> pressure of 40&nbsp;mm Hg. With intentional hyperventilation, the CO<sub>2</sub> content of arterial blood may be lowered to 10–20&nbsp;mm Hg (the oxygen content of the blood is little affected), and the respiratory drive is diminished. This is why one can hold one's breath longer after hyperventilating than without hyperventilating. This carries the risk that unconsciousness may result before the need to breathe becomes overwhelming, which is why hyperventilation is particularly dangerous before free diving.
 
== See also ==
{{colbegin|3}}
* [[Bosch reaction]]
* [[Bottled gas]]
* [[Carbogen]]
* [[Carbon dioxide sensor]]
* [[Carbon sequestration|CO<sub>2</sub> sequestration]]
* [[EcoCute]] – As refrigerants
* [[Emission standard]]s
* [[Industrial gas]]
* [[Kaya identity]]
* [[Lake Kivu]]
* [[List of least carbon efficient power stations]]
* [[List of countries by carbon dioxide emissions]]
* [[Meromictic lake]]
{{colend}}
 
== References ==
{{reflist|30em}}
 
== Further reading ==
* [[Tyler Volk]] (2008), ''CO<sub>2</sub> Rising: The World's Greatest Environmental Challenge'', The MIT Press, 223 pages, ISBN 978-0-262-22083-5. A short, balanced primer on CO<sub>2</sub>'s role as a greenhouse gas. [http://www.ehponline.org/docs/2009/117-2/newbooks.html Review]{{dead link|date=January 2014}} at ''[[Environmental Health Perspectives]]''
* Shendell, Prill, Fisk, Apte1, Blake & Faulkner, Associations between classroom CO<sub>2</sub> concentrations and student attendance in Washington and Idaho, Indoor Air 2004.
* Seppanen, Fisk and Mendell, Association of Ventilation Rates and CO<sub>2</sub> Concentrations with Health and Other Responses in Commercial and Institutional Buildings, Indoor Air 1999.
 
== External links ==
* {{ICSC|0021}}<!-- in general: {{ICSC|AllDigits|TwoDigits}} -->
* {{PubChemLink|280}}
* [http://www.cdc.gov/niosh/npg/npgd0103.html CDC – NIOSH Pocket Guide to Chemical Hazards – Carbon Dioxide]
* [http://www.uigi.com/carbondioxide.html CO<sub>2</sub> Carbon Dioxide Properties, Uses, Applications]
* [http://www.dryiceinfo.com/science.htm Dry Ice information]
* [http://www.cmdl.noaa.gov/ccgg/trends/ Trends in Atmospheric Carbon Dioxide] ''(NOAA)''
* [http://books.google.com/books?id=RicDAAAAMBAJ&pg=PA53 "A War Gas That Saves Lives."] ''Popular Science'', June 1942, pp.&nbsp;53–57.
* [http://oco.jpl.nasa.gov/ NASA's Orbiting Carbon Observatory]
* [http://googas.ov.ingv.it/ The on-line catalogue of CO<sub>2</sub> natural emissions in Italy]
* [http://www.chemistry-reference.com/q_compounds.asp?CAS=124-38-9 Reactions, Thermochemistry, Uses, and Function of Carbon Dioxide]
* [http://www.periodicvideos.com/videos/mv_carbon_dioxide_one.htm Carbon Dioxide – Part One] and [http://www.periodicvideos.com/videos/mv_carbon_dioxide_two.htm Carbon Dioxide – Part Two] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
 
{{Oxides of carbon}}
{{Global Warming}}
 
{{DEFAULTSORT:Carbon Dioxide}}
[[Category:Carbon dioxide| ]]
[[Category:Oxocarbons]]
[[Category:Acid anhydrides]]
[[Category:Acidic oxides]]
[[Category:Greenhouse gases]]
[[Category:Propellants]]
[[Category:Household chemicals]]
[[Category:Inorganic solvents]]
[[Category:Refrigerants]]
[[Category:Fire suppression agents]]
[[Category:Coolants]]
[[Category:Nuclear reactor coolants]]
[[Category:Laser gain media]]
 
{{Link GA|de}}
{{Link FA|scn}}

Latest revision as of 20:15, 12 January 2015


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