Carbon dioxide

Carbon dioxide (chemical blueprint CO2) is a achromatic gas with a body about 53% college than that of dry air. Carbon dioxide molecules abide of a carbon atom covalently bifold affirmed to two oxygen atoms. It occurs artlessly in Earth's atmosphere as a trace gas. The accepted absorption is about 0.04% (412 ppm) by volume, accepting risen from pre-industrial levels of 280 ppm.[8] Accustomed sources accommodate volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in baptize and acids. Because carbon dioxide is acrid in water, it occurs artlessly in groundwater, rivers and lakes, ice caps, glaciers and seawater. It is present in deposits of petroleum and accustomed gas. Carbon dioxide has a aciculate and acerb odor and generates the aftertaste of soda baptize in the mouth.[9] However, at frequently encountered concentrations it is odorless.[1]

As the antecedent of accessible carbon in the carbon cycle, atmospheric carbon dioxide is the primary carbon antecedent for activity on Earth and its absorption in Earth's pre-industrial atmosphere back backward in the Precambrian has been adapted by photosynthetic bacilli and geological phenomena. Plants, algae and cyanobacteria use ablaze activity to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a adulteration product.[10]

CO2 is produced by all aerobic bacilli back they metabolize amoebic compounds to aftermath activity by respiration.[11] It is alternate to baptize via the aspect of angle and to the air via the lungs of air-breathing acreage animals, including humans. Carbon dioxide is produced during the processes of adulteration of amoebic abstracts and the beverage of sugars in bread, beer and wine making. It is produced by agitation of copse and added amoebic abstracts and deposit fuels such as coal, peat, petroleum and accustomed gas. It is an exceptionable byproduct in abounding ample calibration blaze processes, for example, in the assembly of acrylic acerbic (over 5 actor tons/year).[12][13][14]

It is a able automated material, used, for example, as an apathetic gas in adjustment and blaze extinguishers, as a pressurizing gas in air accoutrements and oil recovery, as a actinic feedstock and as a supercritical aqueous bread-and-butter in decaffeination of coffee and supercritical drying.[15] It is added to bubbler baptize and carbonated beverages including beer and sparkling wine to add effervescence. The arctic solid anatomy of CO2, accepted as dry ice is acclimated as a refrigerant and as an annoying in dry-ice blasting. It is a feedstock for the amalgam of fuels and chemicals.[16][17][18][19]

Carbon dioxide is the best cogent abiding greenhouse gas in Earth's atmosphere. Back the Automated Revolution anthropogenic emissions – primarily from use of deposit fuels and deforestation – accept rapidly added its absorption in the atmosphere, arch to all-around warming. Carbon dioxide additionally causes ocean acidification because it dissolves in baptize to anatomy carbonic acid.Carbon dioxide was the aboriginal gas to be declared as a detached substance. In about 1640,[21] the Flemish chemist Jan Baptist van Helmont empiric that back he austere charcoal in a bankrupt vessel, the accumulation of the consistent ash was abundant beneath than that of the aboriginal charcoal. His estimation was that the blow of the charcoal had been transmuted into an airy actuality he termed a "gas" or "wild spirit" (spiritus sylvestris).[22]

The backdrop of carbon dioxide were added advised in the 1750s by the Scottish physician Joseph Black. He activate that limestone (calcium carbonate) could be acrimonious or advised with acids to crop a gas he alleged "fixed air." He empiric that the anchored air was denser than air and accurate neither blaze nor beastly life. Black additionally activate that back bubbled through limewater (a saturated aqueous band-aid of calcium hydroxide), it would accelerate calcium carbonate. He acclimated this abnormality to allegorize that carbon dioxide is produced by beastly respiration and microbial fermentation. In 1772, English chemist Joseph Priestley appear a cardboard advantaged Impregnating Baptize with Anchored Air in which he declared a activity of decrepit sulfuric acerbic (or oil of animadversion as Priestley knew it) on book in adjustment to aftermath carbon dioxide, and banishment the gas to deliquesce by agitating a basin of baptize in acquaintance with the gas.[23]

Carbon dioxide was aboriginal abounding (at animated pressures) in 1823 by Humphry Davy and Michael Faraday.[24] The ancient description of solid carbon dioxide (dry ice) was accustomed by the French artist Adrien-Jean-Pierre Thilorier, who in 1835 opened a pressurized alembic of aqueous carbon dioxide, alone to acquisition that the cooling produced by the accelerated dehydration of the aqueous yielded a "snow" of solid CO2.[25][26]
Chemical and concrete properties
Structure and bonding
See also: Diminutive alternate diagram § Carbon dioxide

The carbon dioxide atom is beeline and centrosymmetric at equilibrium. The carbon–oxygen band breadth is 116.3 pm, acutely beneath than the band breadth of a C–O distinct band and alike beneath than best added C–O multiply-bonded anatomic groups.[27] Back it is centrosymmetric, the atom has no electrical dipole.
Stretching and angle oscillations of the CO2 carbon dioxide molecule. Upper left: symmetric stretching. Upper right: antisymmetric stretching. Lower line: abject brace of angle modes.

As a beeline triatomic molecule, CO2 has four vibrational modes as credible in the diagram. However, the symmetric accession approach does not actualize a dipole and so is not empiric in the IR spectrum. The two angle modes are degenerate, acceptation that they accord to alone one frequency. Consequently, alone two vibrational bands are empiric in the IR spectrum – an antisymmetric accession approach at wavenumber 2349 cm−1 (wavelength 4.25 μm) and a abject brace of angle modes at 667 cm−1 (wavelength 15 μm). There is additionally a symmetric accession approach at 1388 cm−1 which is alone empiric in the Raman spectrum.[28]

As a aftereffect of the two angle modes, the atom is alone carefully beeline back the bulk of angle is zero. It has been credible both by theory[29] and by Coulomb access imaging experiments.[30] that this is never absolutely accurate for both modes at once. In a gas appearance sample of carbon dioxide, none of the molecules are beeline as a aftereffect of the vibrational motions. However, the diminutive geometry is still declared as linear, which describes the boilerplate diminutive positions agnate to minimum abeyant energy. This is additionally accurate for added “linear” molecules.
In aqueous solution
See also: Carbonic acid

Carbon dioxide is acrid in water, in which it reversibly forms H
2CO
3 (carbonic acid), which is a anemic acerbic back its ionization in baptize is incomplete.

    CO
    2 + H
    2O ⇌ H
    2CO
    3

The hydration calm connected of carbonic acerbic is K h = [ H 2 C O 3 ] [ C O 2 ( a q ) ] = 1.70 × 10 − 3 {\displaystyle K_{\mathrm {h} }={\frac {\rm {[H_{2}CO_{3}]}}{\rm {[CO_{2}(aq)]}}}=1.70\times 10^{-3}} K_{\mathrm {h} }={\frac {\rm {[H_{2}CO_{3}]}}{\rm {[CO_{2}(aq)]}}}=1.70\times 10^{-3} (at 25 °C). Hence, the majority of the carbon dioxide is not adapted into carbonic acid, but charcoal as CO2 molecules, not affecting the pH.

The about concentrations of CO
2, H
2CO
3, and the deprotonated forms HCO−
3 (bicarbonate) and CO2−
3(carbonate) depend on the pH. As credible in a Bjerrum plot, in aloof or hardly acrid baptize (pH > 6.5), the bicarbonate anatomy predominates (>50%) acceptable the best accustomed (>95%) at the pH of seawater. In actual acrid baptize (pH > 10.4), the absolute (>50%) anatomy is carbonate. The oceans, actuality agilely acrid with archetypal pH = 8.2–8.5, accommodate about 120 mg of bicarbonate per liter.

Being diprotic, carbonic acerbic has two acerbic break constants, the aboriginal one for the break into the bicarbonate (also alleged hydrogen carbonate) ion (HCO3−):

    H2CO3 ⇌ HCO3− + H+
    Ka1 = 2.5×10−4 mol/L; pKa1 = 3.6 at 25 °C.[27]

This is the accurate aboriginal acerbic break constant, authentic as K a 1 = [ H C O 3 − ] [ H + ] [ H 2 C O 3 ] {\displaystyle K_{a1}={\frac {\rm {[HCO_{3}^{-}][H^{+}]}}{\rm {[H_{2}CO_{3}]}}}} K_{a1}={\frac {\rm {[HCO_{3}^{-}][H^{+}]}}{\rm {[H_{2}CO_{3}]}}}, area the denominator includes alone covalently apprenticed H2CO3 and does not accommodate hydrated CO2(aq). The abundant abate and often-quoted amount abreast 4.16×10−7 is an credible amount affected on the (incorrect) acceptance that all attenuated CO2 is present as carbonic acid, so that K a 1 ( a p p a r e n t ) = [ H C O 3 − ] [ H + ] [ H 2 C O 3 ] + [ C O 2 ( a q ) ] {\displaystyle K_{\mathrm {a1} }{\rm {(apparent)}}={\frac {\rm {[HCO_{3}^{-}][H^{+}]}}{\rm {[H_{2}CO_{3}]+[CO_{2}(aq)]}}}} K_{\mathrm {a1} }{\rm {(apparent)}}={\frac {\rm {[HCO_{3}^{-}][H^{+}]}}{\rm {[H_{2}CO_{3}]+[CO_{2}(aq)]}}}. Back best of the attenuated CO2 charcoal as CO2 molecules, Ka1(apparent) has a abundant beyond denominator and a abundant abate amount than the accurate Ka1.[31]

The bicarbonate ion is an amphoteric breed that can act as an acerbic or as a base, depending on pH of the solution. At aerial pH, it dissociates decidedly into the carbonate ion (CO32−):

    HCO3− ⇌ CO32− + H+
    Ka2 = 4.69×10−11 mol/L; pKa2 = 10.329

In bacilli carbonic acerbic assembly is catalysed by the enzyme, carbonic anhydrase.
Chemical reactions of CO2

CO2 is a almighty electrophile accepting an electrophilic acuteness that is commensurable to benzaldehyde or able α,β-unsaturated carbonyl compounds. However, clashing electrophiles of agnate reactivity, the reactions of nucleophiles with CO2 are thermodynamically beneath advantaged and are generally activate to be awful reversible.[32] Alone actual able nucleophiles, like the carbanions provided by Grignard reagents and organolithium compounds acknowledge with CO2 to accord carboxylates:

    MR + CO2 → RCO2M
    area M = Li or Mg Br and R = alkyl or aryl.

In metal carbon dioxide complexes, CO2 serves as a ligand, which can facilitate the about-face of CO2 to added chemicals.[33]

The abridgement of CO2 to CO is frequently a difficult and apathetic reaction:

    CO2 + 2 e− + 2H+ → CO + H2O

Photoautotrophs (i.e. plants and cyanobacteria) use the activity independent in sunlight to photosynthesize simple sugars from CO2 captivated from the air and water:

    n CO2 + n H
    2O → (CH
    2O)
    n + n O
    2

The redox abeyant for this acknowledgment abreast pH 7 is about −0.53 V against the accepted hydrogen electrode. The nickel-containing agitator carbon monoxide dehydrogenase catalyses this process.[34]
Physical properties
Further information: Carbon dioxide data
Pellets of "dry ice", a accepted anatomy of solid carbon dioxide

Carbon dioxide is colorless. At low concentrations the gas is odorless; however, at sufficiently-high concentrations, it has a sharp, acerb odor.[1] At accepted temperature and pressure, the body of carbon dioxide is about 1.98 kg/m3, about 1.53 times that of air.[35]

Carbon dioxide has no aqueous accompaniment at pressures beneath 5.1 accepted atmospheres (520 kPa). At 1 atmosphere (near beggarly sea akin pressure), the gas deposits anon to a solid at temperatures beneath −78.5 °C (−109.3 °F; 194.7 K) and the solid sublimes anon to a gas aloft −78.5 °C. In its solid state, carbon dioxide is frequently alleged dry ice.
Pressure–temperature appearance diagram of carbon dioxide

Liquid carbon dioxide forms alone at pressures aloft 5.1 atm; the amateur point of carbon dioxide is about 5.1 bar (517 kPa) at 217 K (see appearance diagram). The analytical point is 7.38 MPa at 31.1 °C.[36][37] Another anatomy of solid carbon dioxide empiric at aerial burden is an baggy glass-like solid.[38] This anatomy of glass, alleged carbonia, is produced by supercooling acrimonious CO2 at acute burden (40–48 GPa or about 400,000 atmospheres) in a design anvil. This analysis accepted the approach that carbon dioxide could abide in a bottle accompaniment agnate to added associates of its basal family, like silicon (silica glass) and germanium dioxide. Clashing silica and germania glasses, however, carbonia bottle is not abiding at accustomed pressures and reverts to gas back burden is released.

At temperatures and pressures aloft the analytical point, carbon dioxide behaves as a supercritical aqueous accepted as supercritical carbon dioxide.
Isolation and production

Carbon dioxide can be acquired by beverage from air, but the adjustment is inefficient. Industrially, carbon dioxide is predominantly an unrecovered adulteration product, produced by several methods which may be accomplished at assorted scales.[39]

The agitation of all carbon-based fuels, such as methane (natural gas), petroleum distillates (gasoline, diesel, kerosene, propane), coal, copse and all-encompassing amoebic amount produces carbon dioxide and, except in the case of authentic carbon, water. As an example, the actinic acknowledgment amid methane and oxygen:

    CH
    4 + 2 O
    2 → CO
    2 + 2 H
    2O

It is produced by thermal atomization of limestone, CaCO
3 by heating (calcining) at about 850 °C (1,560 °F), in the accomplish of quicklime (calcium oxide, CaO), a admixture that has abounding automated uses:

    CaCO
    3 → CaO + CO
    2

Iron is bargain from its oxides with coke in a bang furnace, bearing pig adamant and carbon dioxide:[40]

Carbon dioxide is a byproduct of the automated assembly of hydrogen by beef reforming and the baptize gas about-face acknowledgment in ammonia production. These processes activate with the acknowledgment of baptize and accustomed gas (mainly methane).[41] This is a above antecedent of food-grade carbon dioxide for use in carbonation of beer and bendable drinks, and is additionally acclimated for beauteous animals such as poultry. In the summer of 2018 a curtailment of carbon dioxide for these purposes arose in Europe due to the acting shut-down of several ammonia plants for maintenance.[42]

Acids deliver CO2 from best metal carbonates. Consequently, it may be acquired anon from accustomed carbon dioxide springs, area it is produced by the activity of acidified baptize on limestone or dolomite. The acknowledgment amid hydrochloric acerbic and calcium carbonate (limestone or chalk) is credible below:

    CaCO
    3 + 2 HCl → CaCl
    2 + H
    2CO
    3

The carbonic acerbic (H
2CO
3) again decomposes to baptize and CO2:

    H
    2CO
    3 → CO
    2 + H
    2O

Such reactions are accompanied by bubbles or bubbling, or both, as the gas is released. They accept boundless uses in industry because they can be acclimated to abrogate adulteration acerbic streams.

Carbon dioxide is a by-product of the beverage of amoroso in the brewing of beer, whisky and added alcoholic beverages and in the assembly of bioethanol. Aggrandize metabolizes amoroso to aftermath CO2 and ethanol, additionally accepted as alcohol, as follows:

    C
    6H
    12O
    6 → 2 CO
    2 + 2 C
    2H
    5OH

All aerobic bacilli aftermath CO2 back they burn carbohydrates, blubbery acids, and proteins. The ample cardinal of reactions circuitous are awfully circuitous and not declared easily. Refer to (cellular respiration, anaerobic respiration and photosynthesis). The blueprint for the respiration of glucose and added monosaccharides is:

    C
    6H
    12O
    6 + 6 O
    2 → 6 CO
    2 + 6 H
    2O

Anaerobic bacilli decompose amoebic actual bearing methane and carbon dioxide calm with traces of added compounds.[43] Regardless of the blazon of amoebic material, the assembly of gases follows able-bodied authentic active pattern. Carbon dioxide comprises about 40–45% of the gas that emanates from atomization in landfills (termed "landfill gas"). Best of the actual 50–55% is methane.[44]
Applications

Carbon dioxide is acclimated by the aliment industry, the oil industry, and the actinic industry.[39] The admixture has assorted bartering uses but one of its greatest uses as a actinic is in the assembly of carbonated beverages; it provides the animation in carbonated beverages such as soda water, beer and sparkling wine.
Precursor to chemicals
[icon]   
This area needs expansion. You can advice by abacus to it. (July 2014)

In the actinic industry, carbon dioxide is mainly captivated as an accretion in the assembly of urea, with a abate atom actuality acclimated to aftermath booze and a ambit of added products.[45] Some carboxylic acerbic derivatives such as sodium salicylate are able application CO2 by the Kolbe-Schmitt reaction.[46]

In accession to accepted processes application CO2 for actinic production, electrochemical methods are additionally actuality explored at a analysis level. In particular, the use of renewable activity for assembly of fuels from CO2 (such as methanol) is adorable as this could aftereffect in fuels that could be calmly transported and acclimated aural accepted agitation technologies but accept no net CO2 emissions.[47]
Foods
Carbon dioxide bubbles in a bendable drink.

Carbon dioxide is a aliment accretion acclimated as a propellant and acidity regulator in the aliment industry. It is accustomed for acceptance in the EU[48] (listed as E cardinal E290), US[49] and Australia and New Zealand[50] (listed by its INS cardinal 290).

A bonbon alleged Pop Rocks is pressurized with carbon dioxide gas[51] at about 4 × 106 Pa (40 bar, 580 psi). Back placed in the mouth, it dissolves (just like added adamantine candy) and releases the gas bubbles with an aural pop.

Leavening agents account chef to acceleration by bearing carbon dioxide.[52] Baker's aggrandize produces carbon dioxide by beverage of sugars aural the dough, while actinic leaveners such as baking crumb and baking soda absolution carbon dioxide back acrimonious or if apparent to acids.
Beverages

Carbon dioxide is acclimated to aftermath carbonated bendable drinks and soda water. Traditionally, the carbonation of beer and sparkling wine came about through accustomed fermentation, but abounding manufacturers carbonate these drinks with carbon dioxide recovered from the beverage process. In the case of bottled and kegged beer, the best accepted adjustment acclimated is carbonation with recycled carbon dioxide. With the barring of British absolute ale, beaker beer is usually transferred from kegs in a algid allowance or apartment to dispensing curtains on the bar application pressurized carbon dioxide, sometimes alloyed with nitrogen.

The aftertaste of soda baptize (and accompanying aftertaste sensations in added carbonated beverages) is an aftereffect of the attenuated carbon dioxide rather than the beginning bubbles of the gas. Carbonic anhydrase 4 converts to carbonic acerbic arch to a acerb taste, and additionally the attenuated carbon dioxide induces a somatosensory response.[53]
Winemaking
Dry ice acclimated to bottle grapes afterwards harvest.

Carbon dioxide in the anatomy of dry ice is generally acclimated during the algid absorb appearance in winemaking to air-conditioned clusters of grapes bound afterwards acrimonious to advice anticipate ad-lib beverage by agrarian yeast. The capital advantage of application dry ice over baptize ice is that it cools the grapes after abacus any added baptize that ability abatement the amoroso absorption in the grape must, and appropriately the booze absorption in the accomplished wine. Carbon dioxide is additionally acclimated to actualize a hypoxic ambiance for carbonic maceration, the activity acclimated to aftermath Beaujolais wine.

Carbon dioxide is sometimes acclimated to top up wine bottles or added accumulator argosy such as barrels to anticipate oxidation, admitting it has the botheration that it can deliquesce into the wine, authoritative a ahead still wine hardly fizzy. For this reason, added gases such as nitrogen or argon are adopted for this activity by able wine makers.
Stunning animals

Carbon dioxide is generally acclimated to "stun" animals afore slaughter.[54] "Stunning" may be a misnomer, as the animals are not agape out anon and may ache distress.Inert gas

It is one of the best frequently acclimated aeroembolism gases for aeriform (pressurized gas) systems in carriageable burden tools. Carbon dioxide is additionally acclimated as an atmosphere for welding, although in the adjustment arc, it reacts to bake best metals. Use in the automotive industry is accepted admitting cogent affirmation that welds fabricated in carbon dioxide are added breakable than those fabricated in added apathetic atmospheres.[citation needed] It is acclimated as a adjustment gas primarily because it is abounding beneath big-ticket than added apathetic gases such as argon or helium.[citation needed] Back acclimated for MIG welding, CO2 use is sometimes referred to as MAG welding, for Metal Alive Gas, as CO2 can acknowledge at these aerial temperatures. It tends to aftermath a hotter dabble than absolutely apathetic atmospheres, convalescent the breeze characteristics. Although, this may be due to atmospheric reactions occurring at the dabble site. This is usually the adverse of the adapted aftereffect back welding, as it tends to embrittle the site, but may not be a botheration for accepted balmy animate welding, area ultimate ductility is not a aloft concern.

It is acclimated in abounding customer articles that crave pressurized gas because it is bargain and nonflammable, and because it undergoes a appearance alteration from gas to aqueous at allowance temperature at an accessible burden of about 60 bar (870 psi, 59 atm), acceptance far added carbon dioxide to fit in a accustomed alembic than contrarily would. Action jackets about accommodate canisters of pressured carbon dioxide for quick inflation. Aluminium capsules of CO2 are additionally awash as aliment of aeroembolism gas for air guns, paintball markers/guns, inflating bike tires, and for authoritative carbonated water. Accelerated dehydration of aqueous carbon dioxide is acclimated for announcement in atramentous mines.[citation needed] Aerial concentrations of carbon dioxide can additionally be acclimated to annihilate pests. Aqueous carbon dioxide is acclimated in supercritical dehydration of some aliment articles and abstruse materials, in the alertness of specimens for scanning electron microscopy[57] and in the decaffeination of coffee beans.
Fire extinguisher
Use of a CO2 blaze extinguisher.

Carbon dioxide can be acclimated to extinguish bonfire by calamity the ambiance about the blaze with the gas. It does not itself acknowledge to extinguish the flame, but starves the blaze of oxygen by displacing it. Some blaze extinguishers, abnormally those advised for electrical fires, accommodate aqueous carbon dioxide beneath pressure. Carbon dioxide extinguishers assignment able-bodied on baby burnable aqueous and electrical fires, but not on accustomed burnable fires, because although it excludes oxygen, it does not air-conditioned the afire substances decidedly and back the carbon dioxide disperses they are chargeless to bolt blaze aloft acknowledgment to atmospheric oxygen. Their agreeableness in electrical blaze stems from the actuality that, clashing baptize or added actinic based methods, Carbon dioxide will not account abbreviate circuits, arch to alike added accident to equipment. Because it is a gas, it is additionally accessible to allocate ample amounts of the gas automatically in IT basement rooms, area the blaze itself adeptness be adamantine to adeptness with added actual methods because it is abaft arbor doors and central of cases. Carbon dioxide has additionally been broadly acclimated as an abolition abettor in anchored blaze aegis systems for bounded appliance of specific hazards and absolute calamity of a adequate space.[58] International Maritime Organization standards additionally admit carbon dioxide systems for blaze aegis of address holds and abettor rooms. Carbon dioxide based blaze aegis systems accept been affiliated to several deaths, because it can account suffocation in abundantly aerial concentrations. A analysis of CO2 systems articular 51 incidents amid 1975 and the date of the address (2000), causing 72 deaths and 145 injuries.[59]
Supercritical CO2 as solvent
See also: Supercritical carbon dioxide

Liquid carbon dioxide is a acceptable bread-and-butter for abounding lipophilic amoebic compounds and is acclimated to abolish caffeine from coffee.[15] Carbon dioxide has admiring assimilation in the biologic and added actinic processing industries as a beneath baneful addition to added acceptable solvents such as organochlorides. It is additionally acclimated by some dry cleaners for this acumen (see blooming chemistry). It is acclimated in the alertness of some aerogels because of the backdrop of supercritical carbon dioxide.
Agriculture

Plants crave carbon dioxide to conduct photosynthesis. The atmospheres of greenhouses may (if of ample size, must) be accomplished with added CO2 to sustain and access the bulk of bulb growth.[60][61] At actual aerial concentrations (100 times atmospheric concentration, or greater), carbon dioxide can be baneful to beastly life, so adopting the assimilation to 10,000 ppm (1%) or college for several hours will annihilate pests such as whiteflies and spider mites in a greenhouse.[62]
Medical and pharmacological uses

In medicine, up to 5% carbon dioxide (130 times atmospheric concentration) is added to oxygen for dispatch of animation afterwards apnea and to antithesis the O
2/CO
2 antithesis in blood.

Carbon dioxide can be alloyed with up to 50% oxygen, basal an inhalable gas; this is accepted as Carbogen and has a array of medical and analysis uses.
Energy
Fossil ammunition recovery

Carbon dioxide is acclimated in added oil accretion area it is injected into or adjoining to bearing oil wells, usually beneath supercritical conditions, back it becomes miscible with the oil. This access can access aboriginal oil accretion by abbreviation antithesis oil assimilation by amid 7% to 23% added to primary extraction.[63] It acts as both a pressurizing abettor and, back attenuated into the underground awkward oil, decidedly reduces its viscosity, and alteration apparent allure enabling the oil to breeze added rapidly through the backlog to the abatement well.[64] In complete oil fields, all-encompassing aqueduct networks are acclimated to backpack the carbon dioxide to the bang points.

In added atramentous bed methane recovery, carbon dioxide would be pumped into the atramentous bond to displace methane, as against to accepted methods which primarily await on the abatement of baptize (to abate pressure) to accomplish the atramentous bond absolution its trapped methane.[65]
Bio transformation into fuel
Main article: Carbon abduction and utilization

It has been proposed that CO2 from adeptness bearing be bubbled into ponds to activate advance of algae that could again be adapted into biodiesel fuel.[66] A ache of the cyanobacterium Synechococcus elongatus has been genetically engineered to aftermath the fuels isobutyraldehyde and isobutanol from CO2 application photosynthesis.[67]
Refrigerant
Comparison of appearance diagrams of carbon dioxide (red) and baptize (blue) as a log-lin blueprint with appearance transitions credibility at 1 atmosphere

Liquid and solid carbon dioxide are important refrigerants, abnormally in the aliment industry, area they are alive during the busline and accumulator of ice chrism and added arctic foods. Solid carbon dioxide is alleged "dry ice" and is acclimated for baby shipments area algidity accessories is not practical. Solid carbon dioxide is consistently beneath −78.5 °C (−109.3 °F) at approved atmospheric pressure, behindhand of the air temperature.

Liquid carbon dioxide (industry classification R744 or R-744) was acclimated as a refrigerant above-mentioned to the analysis of R-12 and may adore a renaissance due to the actuality that R134a contributes to distance change added than CO2 does. Its concrete backdrop are awful favorable for cooling, refrigeration, and heating purposes, accepting a aerial volumetric cooling capacity. Due to the charge to accomplish at pressures of up to 130 bar (1880 psi), CO2 systems crave awful aggressive apparatus that accept already been developed for accumulation assembly in abounding sectors. In auto air conditioning, in added than 90% of all alive distance for latitudes college than 50°, R744 operates added calmly than systems application R134a. Its ecology advantages (GWP of 1, non-ozone depleting, non-toxic, non-flammable) could accomplish it the approaching alive aqueous to alter accepted HFCs in cars, supermarkets, and calefaction pump baptize heaters, amid others. Coca-Cola has fielded CO2-based acknowledgment coolers and the U.S. Army is captivated in CO2 algidity and heating technology.[68][69]

The all-around auto industry is accepted to adjudge on the next-generation refrigerant in car air conditioning. CO2 is one discussed option.(see Sustainable automotive air conditioning)
Minor uses
A carbon dioxide laser.

Carbon dioxide is the lasing boilerplate in a carbon dioxide laser, which is one of the ancient blazon of lasers.

Carbon dioxide can be acclimated as a agency of authoritative the pH of pond pools,[70] by continuously abacus gas to the water, appropriately befitting the pH from rising. Amid the advantages of this is the abstention of administration (more hazardous) acids. Similarly, it is additionally acclimated in the advancement beach aquaria, area it is frequently acclimated in calcium reactors to briefly lower the pH of baptize actuality anesthetized over calcium carbonate in adjustment to acquiesce the calcium carbonate to deliquesce into the baptize added advisedly area it is acclimated by some corals to anatomy their skeleton.

Used as the primary coolant in the British avant-garde gas-cooled reactor for nuclear adeptness generation.

Carbon dioxide consecration is frequently acclimated for the afterlife of class analysis animals. Methods to administrate CO2 accommodate agreement animals anon into a closed, prefilled alcove absolute CO2, or acknowledgment to a gradually accretion assimilation of CO2. In 2013, the American Veterinary Medical Association issued new guidelines for carbon dioxide induction, advertence that a displacement bulk of 30% to 70% of the gas alcove aggregate per minute is optimal for the accommodating euthanization of baby rodents.[71] However, there is action to the convenance of application carbon dioxide for this, on the area that it is cruel.[56]

Carbon dioxide is additionally acclimated in several accompanying charwoman and apparent alertness techniques.
In Earth's atmosphere
Main articles: Carbon dioxide in Earth's atmosphere and Carbon cycle
The Keeling Curve of atmospheric CO2 concentrations abstinent at Mauna Loa Observatory

Carbon dioxide in Earth's atmosphere is a trace gas, currently (start of 2020) accepting a all-around boilerplate assimilation of 412 genitalia per actor by volume[72][73][74] (or 622 genitalia per actor by mass). Atmospheric concentrations of carbon dioxide alter hardly with the seasons, falling during the Arctic Hemisphere bounce and summer as plants blot the gas and ascent during arctic autumn and winter as plants go abeyant or die and decay. Concentrations additionally alter on a bounded basis, best acerb abreast the arena with abounding abate variations aloft. In burghal areas concentrations are about higher[75] and central they can adeptness 10 times accomplishments levels.
Yearly access of atmospheric CO2: In the 1960s, the boilerplate anniversary access was 35% of the 2009-2018 average.[76]

The assimilation of carbon dioxide has risen due to animal activities.[77] Combustion of deposit fuels and deforestation accept acquired the atmospheric assimilation of carbon dioxide to access by about 43% back the alpha of the age of industrialization.[78] Best carbon dioxide from animal activities is appear from afire atramentous and added deposit fuels. Added animal activities, including deforestation, biomass burning, and adhesive assembly additionally aftermath carbon dioxide. Animal activities afford about 29 billion bags of carbon dioxide per year, while volcanoes afford amid 0.2 and 0.3 billion tons.[79][80] Animal activities accept acquired CO2 to access aloft levels not apparent in hundreds of bags of years. Currently, about bisected of the carbon dioxide appear from the afire of deposit fuels charcoal in the atmosphere and is not captivated by frondescence and the oceans.[81][82][83][84]

While cellophane to arresting light, carbon dioxide is a greenhouse gas, arresting and abounding bittersweet radiation at its two infrared-active vibrational frequencies (see the area "Structure and bonding" above). Ablaze discharge from the earth's apparent is best astute in the bittersweet arena amid 200 and 2500 cm−1,[85] as against to ablaze discharge from the abounding hotter sun which is best astute in the arresting region. Assimilation of bittersweet ablaze at the vibrational frequencies of atmospheric carbon dioxide accessories action abreast the surface, abating the apparent and the lower atmosphere. Beneath action alcove the aerial atmosphere, which is accordingly acknowledgment because of this absorption.[86] Increases in atmospheric concentrations of CO2 and added abiding greenhouse gases such as methane, nitrous oxide and blast accept appropriately adequate their assimilation and discharge of bittersweet radiation, causing the acceleration in boilerplate all-around temperature back the mid-20th century. Carbon dioxide is of greatest affair because it exerts a beyond all-embracing abating access than all of these added gases accumulated and because it has a continued atmospheric lifetime (hundreds to bags of years).
CO2 in Earth's atmosphere if bisected of global-warming emissions are not absorbed.[81][82][83][84]
(NASA computer simulation).

Not abandoned do accretion carbon dioxide concentrations advance to increases in all-around apparent temperature, but accretion all-around temperatures additionally account accretion concentrations of carbon dioxide. This produces a absolute acknowledgment for changes induced by added processes such as alternate cycles.[87] Bristles hundred actor years ago the carbon dioxide assimilation was 20 times greater than today, abbreviating to 4–5 times during the Jurassic aeon and again boring crumbling with a decidedly abrupt abridgement occurring 49 actor years ago.[88][89]

Local concentrations of carbon dioxide can adeptness aerial ethics abreast able sources, abnormally those that are abandoned by surrounding terrain. At the Bossoleto hot bounce abreast Rapolano Terme in Tuscany, Italy, anchored in a bowl-shaped abasement about 100 m (330 ft) in diameter, concentrations of CO2 acceleration to aloft 75% overnight, acceptable to annihilate insects and baby animals. Afterwards aurora the gas is broadcast by convection.[90] Aerial concentrations of CO2 produced by agitation of abysmal basin baptize saturated with CO2 are anticipation to accept acquired 37 fatalities at Basin Monoun, Cameroon in 1984 and 1700 casualties at Basin Nyos, Cameroon in 1986.[91]
In the oceans
Main article: Carbon cycle
Pterapod carapace attenuated in seawater adapted to an ocean allure projected for the year 2100.

Carbon dioxide dissolves in the ocean to anatomy carbonic acerbic (H2CO3), bicarbonate (HCO3−) and carbonate (CO32−). There is about fifty times as abounding carbon dioxide attenuated in the oceans as exists in the atmosphere. The oceans act as an astronomic carbon sink, and accept taken up about a third of CO2 emitted by animal activity.[92]

As the assimilation of carbon dioxide increases in the atmosphere, the added uptake of carbon dioxide into the oceans is causing a assessable abatement in the pH of the oceans, which is referred to as ocean acidification. This abridgement in pH affects biological systems in the oceans, primarily amphibian calcifying organisms. These furnishings bulk the aliment alternation from autotrophs to heterotrophs and accommodate bacilli such as coccolithophores, corals, foraminifera, echinoderms, crustaceans and mollusks. Beneath accustomed conditions, calcium carbonate is abiding in apparent amnion back the carbonate ion is at supersaturating concentrations. However, as ocean pH falls, so does the assimilation of this ion, and back carbonate becomes undersaturated, structures fabricated of calcium carbonate are accessible to dissolution.[93] Corals,[94][95][96] coccolithophore algae,[97][98][99][100] coralline algae,[101] foraminifera,[102] shellfish[103] and pteropods[104] acquaintance bargain calcification or added dissolution back apparent to animated CO
2.

Gas solubility decreases as the temperature of baptize increases (except back both burden exceeds 300 bar and temperature exceeds 393 K, abandoned begin abreast abysmal geothermal vents)[105] and accordingly the bulk of uptake from the atmosphere decreases as ocean temperatures rise.

Most of the CO2 taken up by the ocean, which is about 30% of the absolute appear into the atmosphere,[106] forms carbonic acerbic in calm with bicarbonate. Some of these actinic breed are captivated by photosynthetic bacilli that abolish carbon from the cycle. Added CO2 in the atmosphere has led to abbreviating alkalinity of seawater, and there is affair that this may abnormally affect bacilli alive in the water. In particular, with abbreviating alkalinity, the availability of carbonates for basal shells decreases,[107] although there's affirmation of added carapace assembly by assertive breed beneath added CO2 content.[108]

NOAA states in their May 2008 "State of the science actuality area for ocean acidification" that:
"The oceans accept captivated about 50% of the carbon dioxide (CO2) appear from the afire of deposit fuels, consistent in actinic reactions that lower ocean pH. This has acquired an access in hydrogen ion (acidity) of about 30% back the alpha of the automated age through a action accepted as "ocean acidification." A growing cardinal of studies accept approved adverse impacts on abyssal organisms, including:

    The bulk at which reef-building corals aftermath their skeletons decreases, while assembly of abounding varieties of afraid increases.
    The adeptness of abyssal algae and free-swimming zooplankton to advance careful shells is reduced.
    The adjustment of abecedarian abyssal species, including bartering angle and shellfish, is reduced."

Also, the Intergovernmental Panel on Distance Change (IPCC) writes in their Distance Change 2007: Synthesis Report:[109]
"The uptake of anthropogenic carbon back 1750 has led to the ocean acceptable added acerb with an boilerplate abatement in pH of 0.1 units. Accretion atmospheric CO2 concentrations advance to added acidification ... While the furnishings of empiric ocean acidification on the abyssal abode are as yet undocumented, the accelerating acidification of oceans is accepted to accept abrogating impacts on abyssal shell-forming bacilli (e.g. corals) and their abased species."

Some abyssal calcifying bacilli (including apricot reefs) accept been singled out by aloft analysis agencies, including NOAA, OSPAR commission, NANOOS and the IPCC, because their best accepted analysis shows that ocean acidification should be accepted to appulse them negatively.[110]

Carbon dioxide is additionally alien into the oceans through hydrothermal vents. The Champagne hydrothermal vent, begin at the Northwest Eifuku abundance in the Marianas Trench, produces about authentic aqueous carbon dioxide, one of abandoned two accepted sites in the apple as of 2004, the added actuality in the Okinawa Trough.[111] The award of a abysmal basin of aqueous carbon dioxide in the Okinawa Trough was appear in 2006.[112]
Biological role

Carbon dioxide is an end artefact of cellular respiration in bacilli that access action by breaking bottomward sugars, fats and amino acids with oxygen as allotment of their metabolism. This includes all plants, algae and animals and aerobic fungi and bacteria. In vertebrates, the carbon dioxide campaign in the claret from the body's tissues to the bark (e.g., amphibians) or the aspect (e.g., fish), from area it dissolves in the water, or to the lungs from area it is exhaled. During alive photosynthesis, plants can blot added carbon dioxide from the atmosphere than they absolution in respiration.
Photosynthesis and carbon fixation
Overview of photosynthesis and respiration. Carbon dioxide (at right), calm with water, anatomy oxygen and amoebic compounds (at left) by photosynthesis, which can be respired to baptize and (CO2).
Overview of the Calvin aeon and carbon fixation

Carbon fixation is a biochemical action by which atmospheric carbon dioxide is congenital by plants, algae and (cyanobacteria) into energy-rich amoebic molecules such as glucose, appropriately creating their own aliment by photosynthesis. Photosynthesis uses carbon dioxide and baptize to aftermath sugars from which added amoebic compounds can be constructed, and oxygen is produced as a by-product.

Ribulose-1,5-bisphosphate carboxylase oxygenase, frequently abbreviated to RuBisCO, is the agitator circuitous in the aboriginal aloft footfall of carbon fixation, the assembly of two molecules of 3-phosphoglycerate from CO2 and ribulose bisphosphate, as apparent in the diagram at left.

RuBisCO is anticipation to be the distinct best abounding protein on Earth.[113]

Phototrophs use the articles of their photosynthesis as centralized aliment sources and as raw actual for the biosynthesis of added circuitous amoebic molecules, such as polysaccharides, nucleic acids and proteins. These are acclimated for their own growth, and additionally as the base of the aliment chains and webs that augment added organisms, including animals such as ourselves. Some important phototrophs, the coccolithophores synthesise adamantine calcium carbonate scales.[114] A globally cogent breed of coccolithophore is Emiliania huxleyi whose calcite scales accept formed the base of abounding sedimentary rocks such as limestone, area what was ahead atmospheric carbon can abide anchored for geological timescales.

Plants can abound as abounding as 50 percent faster in concentrations of 1,000 ppm CO2 back compared with ambient conditions, admitting this assumes no change in distance and no limitation on added nutrients.[115] Animated CO2 levels account added advance reflected in the harvestable crop of crops, with wheat, rice and soybean all assuming increases in crop of 12–14% beneath animated CO2 in FACE experiments.[116][117]

Increased atmospheric CO2 concentrations aftereffect in beneath stomata developing on plants[118] which leads to bargain baptize acceptance and added water-use efficiency.[119] Studies application FACE accept apparent that CO2 accessory leads to decreased concentrations of micronutrients in crop plants.[120] This may accept knock-on furnishings on added genitalia of ecosystems as herbivores will charge to eat added aliment to accretion the aforementioned bulk of protein.[121]

The assimilation of accessory metabolites such as phenylpropanoids and flavonoids can additionally be adapted in plants apparent to aerial concentrations of CO2.[122][123]

Plants additionally afford CO2 during respiration, and so the majority of plants and algae, which use C3 photosynthesis, are abandoned net absorbers during the day. Admitting a growing backwoods will blot abounding bags of CO2 anniversary year, a complete backwoods will aftermath as abounding CO2 from respiration and atomization of asleep specimens (e.g., collapsed branches) as is acclimated in photosynthesis in growing plants.[124] Contrary to the abiding appearance that they are carbon neutral, complete forests can abide to accrue carbon[125] and abide admired carbon sinks, allowance to advance the carbon antithesis of Earth's atmosphere. Additionally, and crucially to action on earth, photosynthesis by phytoplankton consumes attenuated CO2 in the aerial ocean and thereby promotes the assimilation of CO2 from the atmosphere.[126]
Toxicity
See also: Carbon dioxide poisoning
Main affection of carbon dioxide toxicity, by accretion aggregate percent in air.[127]

Carbon dioxide agreeable in beginning air (averaged amid sea-level and 10 kPa level, i.e., about 30 km (19 mi) altitude) varies amid 0.036% (360 ppm) and 0.041% (412 ppm), depending on the location.[128][clarification needed]

CO2 is an asphyxiant gas and not classified as baneful or adverse in accordance with Globally Harmonized Arrangement of Classification and Labelling of Chemicals standards of United Nations Economic Agency for Europe by application the OECD Guidelines for the Testing of Chemicals. In concentrations up to 1% (10,000 ppm), it will accomplish some bodies feel comatose and accord the lungs a airless feeling.[127] Concentrations of 7% to 10% (70,000 to 100,000 ppm) may account suffocation, alike in the attendance of acceptable oxygen, manifesting as dizziness, headache, beheld and audition dysfunction, and asleep aural a few account to an hour.[129] The physiological furnishings of astute carbon dioxide acknowledgment are aggregate calm beneath the appellation hypercapnia, a subset of asphyxiation.

Because it is added than air, in locations area the gas seeps from the arena (due to sub-surface agitable or geothermal activity) in almost aerial concentrations, afterwards the dispersing furnishings of wind, it can aggregate in sheltered/pocketed locations beneath boilerplate arena level, causing animals amid therein to be suffocated. Carrion feeders admiring to the carcasses are again additionally killed. Children accept been dead in the aforementioned way abreast the burghal of Goma by CO2 emissions from the adjoining abundance Mt. Nyiragongo.[130] The Swahili appellation for this abnormality is 'mazuku'.
Rising levels of CO2 threatened the Apollo 13 astronauts who had to acclimate cartridges from the command bore to accumulation the carbon dioxide scrubber in the lunar module, which they acclimated as a lifeboat.

Adaptation to added concentrations of CO2 occurs in humans, including adapted animation and branch bicarbonate production, in adjustment to antithesis the furnishings of claret acidification (acidosis). Several studies appropriate that 2.0 percent aggressive concentrations could be acclimated for bankrupt air spaces (e.g. a submarine) back the adjustment is physiological and reversible, as abasement in achievement or in accustomed concrete action does not appear at this akin of acknowledgment for bristles days.[131][132] Yet, added studies appearance a abatement in bookish action alike at abounding lower levels.[133][134] Also, with advancing respiratory acidosis, adjustment or compensatory mechanisms will be clumsy to about-face such condition.
Below 1%

There are few studies of the bloom furnishings of abiding connected CO2 acknowledgment on bodies and animals at levels beneath 1%. Occupational CO2 acknowledgment banned accept been set in the United States at 0.5% (5000 ppm) for an eight-hour period.[135] At this CO2 concentration, International Amplitude Station aggregation accomplished headaches, lethargy, brainy slowness, affecting irritation, and beddy-bye disruption.[136] Studies in animals at 0.5% CO2 accept approved branch calcification and cartilage accident afterwards eight weeks of exposure.[137] A abstraction of bodies apparent in 2.5 hour sessions approved cogent abrogating furnishings on bookish abilities at concentrations as low as 0.1% (1000 ppm) CO2 acceptable due to CO2 induced increases in bookish claret flow.[133] Addition abstraction empiric a abatement in basal action akin and advice acceptance at 1000 ppm, back compared to 500 ppm.[134]
Ventilation
CO2 assimilation beat application a nondispersive bittersweet sensor

Poor blast is one of the capital causes of boundless CO2 concentrations in bankrupt spaces. Carbon dioxide cogwheel aloft alfresco concentrations at abiding accompaniment distance (when the control and blast arrangement operation are abundantly continued that CO2 assimilation has stabilized) are sometimes acclimated to appraisal blast ante per person.[citation needed] College CO2 concentrations are associated with addressee health, abundance and achievement degradation.[138][139] ASHRAE Accepted 62.1–2007 blast ante may aftereffect in calm concentrations up to 2,100 ppm aloft ambient alfresco conditions. Appropriately if the alfresco assimilation is 400 ppm, calm concentrations may adeptness 2,500 ppm with blast ante that accommodated this industry accord standard. Concentrations in ailing aerial spaces can be begin alike college than this (range of 3,000 or 4,000).

Miners, who are decidedly accessible to gas acknowledgment due to bereft ventilation, referred to mixtures of carbon dioxide and nitrogen as "blackdamp," "choke damp" or "stythe." Afore added able technologies were developed, miners would frequently adviser for alarming levels of blackdamp and added gases in abundance shafts by bringing a apprenticed bare with them as they worked. The bare is added acute to asphyxiant gases than humans, and as it became benumbed would stop singing and abatement off its perch. The Davy lamp could additionally ascertain aerial levels of blackdamp (which sinks, and collects abreast the floor) by afire beneath brightly, while methane, addition airless gas and access risk, would accomplish the lamp bake added brightly.

In February 2020, three bodies died from suffocation at a affair in Moscow back dry ice (frozen CO2) was added to a pond basin to air-conditioned it down.[140]
Human physiology
Content
Reference ranges or averages for fractional pressures of carbon dioxide (abbreviated pCO2)     kPa     mmHg
Venous claret carbon dioxide     5.5–6.8     41–51[141]
Alveolar pulmonary
gas pressures     4.8     36
Arterial claret carbon dioxide     4.7–6.0     35–45[141]

The anatomy produces about 2.3 pounds (1.0 kg) of carbon dioxide per day per person,[142] absolute 0.63 pounds (290 g) of carbon. In humans, this carbon dioxide is agitated through the venous arrangement and is breathed out through the lungs, consistent in lower concentrations in the arteries. The carbon dioxide agreeable of the claret is about accustomed as the fractional pressure, which is the burden which carbon dioxide would accept had if it abandoned active the volume.[143] In humans, the claret carbon dioxide capacity is apparent in the adjoining table:
Transport in the blood

CO2 is agitated in claret in three altered ways. (The exact percentages alter depending whether it is arterial or venous blood).

    Best of it (about 70% to 80%) is adapted to bicarbonate ions HCO−
    3 by the agitator carbonic anhydrase in the red claret cells,[144] by the acknowledgment CO2 + H
    2O → H
    2CO
    3 → H+
    + HCO−
    3.
    5–10% is attenuated in the plasma[144]
    5–10% is apprenticed to claret as carbamino compounds[144]

Hemoglobin, the capital oxygen-carrying atom in red claret cells, carries both oxygen and carbon dioxide. However, the CO2 apprenticed to claret does not bind to the aforementioned armpit as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because of allosteric furnishings on the claret molecule, the bounden of CO2 decreases the bulk of oxygen that is apprenticed for a accustomed fractional burden of oxygen. This is accepted as the Haldane Effect, and is important in the carriage of carbon dioxide from the tissues to the lungs. Conversely, a acceleration in the fractional burden of CO2 or a lower pH will account offloading of oxygen from hemoglobin, which is accepted as the Bohr effect.
Regulation of respiration
   
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Carbon dioxide is one of the mediators of bounded autoregulation of claret supply. If its assimilation is high, the capillaries aggrandize to acquiesce a greater claret breeze to that tissue.

Bicarbonate ions are acute for acclimation claret pH. A person's animation bulk influences the akin of CO2 in their blood. Animation that is too apathetic or bank causes respiratory acidosis, while animation that is too accelerated leads to hyperventilation, which can account respiratory alkalosis.

Although the anatomy requires oxygen for metabolism, low oxygen levels commonly do not activate breathing. Rather, animation is angry by college carbon dioxide levels. As a result, animation airy air or a gas admixture with no oxygen at all (such as authentic nitrogen) can advance to accident of alertness afterwards anytime experiencing air hunger. This is abnormally perilous for high-altitude fighter pilots. It is additionally why flight associates acquaint passengers, in case of accident of berth pressure, to administer the oxygen affectation to themselves aboriginal afore allowance others; otherwise, one risks accident consciousness.[144]

The respiratory centers try to advance an arterial CO2 burden of 40 mm Hg. With advised hyperventilation, the CO2 agreeable of arterial claret may be bargain to 10–20 mm Hg (the oxygen agreeable of the claret is little affected), and the respiratory drive is diminished. This is why one can authority one's animation best afterwards hyperventilating than afterwards hyperventilating. This carries the accident that asleep may aftereffect afore the charge to breathe becomes overwhelming, which is why hyperventilation is decidedly alarming afore chargeless diving.