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Carbon dioxide
Structural formula of carbon dioxide with bond length
Ball-and-stick model of carbon dioxide
Ball-and-stick model of carbon dioxide
Space-filling model of carbon dioxide
Space-filling model of carbon dioxide
IUPAC name
Carbon dioxide
Other names
  • Carbonic acid gas
  • Carbonic anhydride
  • Carbonic dioxide
  • Carbonic oxide
  • Carbon(IV) oxide
  • Methanedione
  • R-744 (refrigerant)
  • R744 (refrigerant alternative spelling)
  • Dry ice (solid phase)
3D model (JSmol)
ECHA InfoCard 100.004.271 Edit this at Wikidata
EC Number
  • 204-696-9
E number E290 (preservatives)
MeSH Carbon+dioxide
RTECS number
  • FF6400000
UN number 1013 (gas), 1845 (solid)
  • InChI=1S/CO2/c2-1-3 checkY
  • InChI=1/CO2/c2-1-3
  • O=C=O
  • C(=O)=O
Molar mass 44.009 g·mol−1
Appearance Colorless gas
  • Low concentrations: none
  • High concentrations: sharp; acidic[1]
  • 1562 kg/m3 (solid at 1 atm (100 kPa) and −78.5 °C (−109.3 °F))
  • 1101 kg/m3 (liquid at saturation −37 °C (−35 °F))
  • 1.977 kg/m3 (gas at 1 atm (100 kPa) and 0 °C (32 °F))
Critical point (T, P) 304.128(15) K[2] (30.978(15) °C), 7.3773(30) MPa[2] (72.808(30) atm)
194.6855(30) K (−78.4645(30) °C) at 1 atm (0.101325 MPa)
1.45 g/L at 25 °C (77 °F), 100 kPa (0.99 atm)
Vapor pressure 5.7292(30) MPa, 56.54(30) atm (20 °C (293.15 K))
Acidity (pKa) Carbonic acid:
pKa1 = 3.6
pKa1(apparent) = 6.35
pKa2 = 10.33
−20.5·10−6 cm3/mol
Thermal conductivity 0.01662 W·m−1·K−1 (300 K (27 °C; 80 °F))[3]
  • 14.90 μPa·s at 25 °C (298 K)[4]
  • 70 μPa·s at −78.5 °C (194.7 K)
0 D
37.135 J/(K·mol)
214 J·mol−1·K−1
−393.5 kJ·mol−1
V03AN02 (WHO)
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
90,000 ppm (162,000 mg/m3) (human, 5 min)[6]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 5000 ppm (9000 mg/m3)[5]
REL (Recommended)
TWA 5000 ppm (9000 mg/m3), ST 30,000 ppm (54,000 mg/m3)[5]
IDLH (Immediate danger)
40,000 ppm (72,000 mg/m3)[5]
Safety data sheet (SDS) Sigma-Aldrich
Related compounds
Other anions
Other cations
Related carbon oxides
See Oxocarbon
Related compounds
Supplementary data page
Carbon dioxide (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Carbon dioxide is a chemical compound with the chemical formula CO2. It is made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature, and as the source of available carbon in the carbon cycle, atmospheric CO2 is the primary carbon source for life on Earth. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate (HCO3), which causes ocean acidification as atmospheric CO2 levels increase.[9]

It is a trace gas in Earth's atmosphere at 421 parts per million (ppm)[a], or about 0.04% (as of May 2022) having risen from pre-industrial levels of 280 ppm or about 0.025%.[11][12] Burning fossil fuels is the primary cause of these increased CO2 concentrations and also the primary cause of climate change.[13]

Its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by organisms and geological phenomena. Plants, algae and cyanobacteria use energy from sunlight to synthesize carbohydrates from carbon dioxide and water in a process called photosynthesis, which produces oxygen as a waste product.[14] In turn, oxygen is consumed and CO2 is released as waste by all aerobic organisms when they metabolize organic compounds to produce energy by respiration.[15] CO2 is released from organic materials when they decay or combust, such as in forest fires.

Carbon dioxide is 53% more dense than dry air, but is long lived and thoroughly mixes in the atmosphere. About half of excess CO2 emissions to the atmosphere are absorbed by land and ocean carbon sinks.[16] These sinks can become saturated and are volatile, as decay and wildfires result in the CO2 being released back into the atmosphere.[17] CO2 is eventually sequestered (stored for the long term) in rocks and organic deposits like coal, petroleum and natural gas. Sequestered CO2 is released into the atmosphere through burning fossil fuels or naturally by volcanoes, hot springs, geysers, and when carbonate rocks dissolve in water or react with acids.

CO2 is a versatile industrial material, used, for example, as an inert gas in welding and fire extinguishers, as a pressurizing gas in air guns and oil recovery, and as a supercritical fluid solvent in decaffeination and supercritical drying.[18] It is a byproduct of fermentation of sugars in bread, beer and wine making, and is added to carbonated beverages like seltzer and beer for effervescence. It has a sharp and acidic odor and generates the taste of soda water in the mouth, but at normally encountered concentrations it is odorless.[1]

Chemical and physical properties

Carbon dioxide cannot be liquefied at atmospheric pressure. Low-temperature carbon dioxide is commercially used in its solid form, commonly known as "dry ice". The solid-to-gas phase transition occurs at 194.7 Kelvin and is called sublimation.

Structure, bonding and molecular vibrations

The symmetry of a carbon dioxide molecule is linear and centrosymmetric at its equilibrium geometry. The length of the carbon–oxygen bond in carbon dioxide is 116.3 pm, noticeably shorter than the roughly 140 pm length of a typical single C–O bond, and shorter than most other C–O multiply bonded functional groups such as carbonyls.[19] Since it is centrosymmetric, the molecule has no electric dipole moment.

Stretching and bending oscillations of the CO2 molecule. Upper left: symmetric stretching. Upper right: antisymmetric stretching. Lower line: degenerate pair of bending modes.

As a linear triatomic molecule, CO2 has four vibrational modes as shown in the diagram. In the symmetric and the antisymmetric stretching modes, the atoms move along the axis of the molecule. There are two bending modes, which are degenerate, meaning that they have the same frequency and same energy, because of the symmetry of the molecule. When a molecule touches a surface or touches another molecule, the two bending modes can differ in frequency because the interaction is different for the two modes. Some of the vibrational modes are observed in the infrared (IR) spectrum: the antisymmetric stretching mode at wavenumber 2349 cm−1 (wavelength 4.25 μm) and the degenerate pair of bending modes at 667 cm−1 (wavelength 15 μm). The symmetric stretching mode does not create an electric dipole so is not observed in IR spectroscopy, but it is detected in Raman spectroscopy at 1388 cm−1 (wavelength 7.2 μm).[20]

In the gas phase, carbon dioxide molecules undergo significant vibrational motions and do not keep a fixed structure. However, in a Coulomb explosion imaging experiment, an instantaneous image of the molecular structure can be deduced. Such an experiment[21] has been performed for carbon dioxide. The result of this experiment, and the conclusion of theoretical calculations[22] based on an ab initio potential energy surface of the molecule, is that none of the molecules in the gas phase are ever exactly linear. This counter-intuitive result is trivially due to the fact that the nuclear motion volume element vanishes for linear geometries.[22] This is so for all molecules except diatomic molecules.

In aqueous solution

Carbon dioxide is soluble in water, in which it reversibly forms H2CO3 (carbonic acid), which is a weak acid, because its ionization in water is incomplete.

CO2 + H2O ⇌ H2CO3

The hydration equilibrium constant of carbonic acid is, at 25 °C:

Hence, the majority of the carbon dioxide is not converted into carbonic acid, but remains as CO2 molecules, not affecting the pH.

The relative concentrations of CO2, H2CO3, and the deprotonated forms HCO3 (bicarbonate) and CO2−3(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 mg of bicarbonate per liter.

Being diprotic, carbonic acid has two acid dissociation constants, the first one for the dissociation into the bicarbonate (also called hydrogen carbonate) ion (HCO3):

H2CO3 ⇌ HCO3 + H+
Ka1 = 2.5 × 10−4 mol/L; pKa1 = 3.6 at 25 °C.[19]

This is the true first acid dissociation constant, defined as

where the denominator includes only covalently bound H2CO3 and does not include hydrated CO2(aq). The much smaller and often-quoted value near 4.16 × 10−7 (or pKa1 = 6.38) is an apparent value calculated on the (incorrect) assumption that all dissolved CO2 is present as carbonic acid, so that

Since most of the dissolved CO2 remains as CO2 molecules, Ka1(apparent) has a much larger denominator and a much smaller value than the true Ka1.[23]

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 (CO2−3):

HCO3 ⇌ CO2−3 + H+
Ka2 = 4.69 × 10−11 mol/L; pKa2 = 10.329

In organisms, carbonic acid production is catalysed by the enzyme known as carbonic anhydrase.

In addition to altering its acidity, the presence of carbon dioxide in water also affects its electrical properties.

Electrical conductivity of carbondioxide saturated desalinated water when heated from 20 to 98 °C. The shadowed regions indicate the error bars associated with the measurements. Data on github . A comparison with the temperature dependence of vented desalinated water can be found here .

When carbon dioxide dissolves in desalinated water, the electrical conductivity increases significantly from below 1 μS/cm to nearly 30 μS/cm. When heated, the water begins to gradually lose the conductivity induced by the presence of , especially noticeable as temperatures exceed 30 °C.

The temperature dependence of the electrical conductivity of fully deionized water without saturation is comparably low in relation to these data.

Chemical reactions

CO2 is a potent electrophile having an electrophilic reactivity that is comparable to benzaldehyde or strongly electrophilic α,β-unsaturated carbonyl compounds. However, unlike electrophiles of similar reactivity, the reactions of nucleophiles with CO2 are thermodynamically less favored and are often found to be highly reversible.[24] The reversible reaction of carbon dioxide with amines to make carbamates is used in CO2 scrubbers and has been suggested as a possible starting point for carbon capture and storage by amine gas treating. Only very strong nucleophiles, like the carbanions provided by Grignard reagents and organolithium compounds react with CO2 to give carboxylates:

MR + CO2 → RCO2M
where M = Li or MgBr and R = alkyl or aryl.

In metal carbon dioxide complexes, CO2 serves as a ligand, which can facilitate the conversion of CO2 to other chemicals.[25]

The reduction of CO2 to CO is ordinarily a difficult and slow reaction:

CO2 + 2 e + 2 H+ → CO + H2O

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.[26]

Photoautotrophs (i.e. plants and cyanobacteria) use the energy contained in sunlight to photosynthesize simple sugars from CO2 absorbed from the air and water:

n CO2 + n H2O → (CH2O)n + n O2

Physical properties

Pellets of "dry ice", a common form of solid carbon dioxide

Carbon dioxide is colorless. At low concentrations, the gas is odorless; however, at sufficiently high concentrations, it has a sharp, acidic odor.[1] At standard temperature and pressure, the density of carbon dioxide is around 1.98 kg/m3, about 1.53 times that of air.[27]

Carbon dioxide has no liquid state at pressures below 0.51795(10) MPa[2] (5.11177(99) atm). At a pressure of 1 atm (0.101325 MPa), the gas deposits directly to a solid at temperatures below 194.6855(30) K[2] (−78.4645(30) °C) and the solid sublimes directly to a gas above this temperature. In its solid state, carbon dioxide is commonly called dry ice.

Pressure–temperature phase diagram of carbon dioxide. Note that it is a log-lin chart.

Liquid carbon dioxide forms only at pressures above 0.51795(10) MPa[2] (5.11177(99) atm); the triple point of carbon dioxide is 216.592(3) K[2] (−56.558(3) °C) at 0.51795(10) MPa[2] (5.11177(99) atm) (see phase diagram). The critical point is 304.128(15) K[2] (30.978(15) °C) at 7.3773(30) MPa[2] (72.808(30) atm). Another form of solid carbon dioxide observed at high pressure is an amorphous glass-like solid.[28] This form of glass, called carbonia, is produced by supercooling heated CO2 at extreme pressures (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 dioxide (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.

Table of thermal and physical properties of saturated liquid carbon dioxide:[29][30]

Temperature (°C) Density (kg/m3) Specific heat (kJ/(kg⋅K)) Kinematic viscosity (m2/s) Thermal conductivity (W/(m⋅K)) Thermal diffusivity (m2/s) Prandtl Number Bulk modulus (K^-1)[clarification needed]
−50 1156.34 1.84 1.19 × 10−7 0.0855 4.02 × 10−8 2.96
−40 1117.77 1.88 1.18 × 10−7 0.1011 4.81 × 10−8 2.46
−30 1076.76 1.97 1.17 × 10−7 0.1116 5.27 × 10−8 2.22
−20 1032.39 2.05 1.15 × 10−7 0.1151 5.45 × 10−8 2.12
−10 983.38 2.18 1.13 × 10−7 0.1099 5.13 × 10−8 2.2
0 926.99 2.47 1.08 × 10−7 0.1045 4.58 × 10−8 2.38
10 860.03 3.14 1.01 × 10−7 0.0971 3.61 × 10−8 2.8
20 772.57 5 9.10 × 10−8 0.0872 2.22 × 10−8 4.1 1.40 × 10−2[clarification needed]
30 597.81 36.4 8.00 × 10−8 0.0703 0.279 × 10−8 28.7

Table of thermal and physical properties of carbon dioxide (CO2) at atmospheric pressure:[29][30]

Temperature (K) Density (kg/m3) Specific heat (kJ/(kg⋅°C)) Dynamic viscosity (kg/(m⋅s)) Kinematic viscosity (m2/s) Thermal conductivity (W/(m⋅°C)) Thermal diffusivity (m2/s) Prandtl Number
220 2.4733 0.783 1.11 × 10−5 4.49 × 10−6 0.010805 5.92 × 10−6 0.818
250 2.1657 0.804 1.26 × 10−5 5.81 × 10−6 0.012884 7.40 × 10−6 0.793
300 1.7973 0.871 1.50 × 10−5 8.32 × 10−6 0.016572 1.06 × 10−5 0.77
350 1.5362 0.9 1.72 × 10−5 1.12 × 10−5 0.02047 1.48 × 10−5 0.755
400 1.3424 0.942 1.93 × 10−5 1.44 × 10−5 0.02461 1.95 × 10−5 0.738
450 1.1918 0.98 2.13 × 10−5 1.79 × 10−5 0.02897 2.48 × 10−5 0.721
500 1.0732 1.013 2.33 × 10−5 2.17 × 10−5 0.03352 3.08 × 10−5 0.702
550 0.9739 1.047 2.51 × 10−5 2.57 × 10−5 0.03821 3.75 × 10−5 0.685
600 0.8938 1.076 2.68 × 10−5 3.00 × 10−5 0.04311 4.48 × 10−5 0.668
650 0.8143 1.1 2.88 × 10−5 3.54 × 10−5 0.0445 4.97 × 10−5 0.712
700 0.7564 1.13 3.05 × 10−5 4.03 × 10−5 0.0481 5.63 × 10−5 0.717
750 0.7057 1.15 3.21 × 10−5 4.55 × 10−5 0.0517 6.37 × 10−5 0.714
800 0.6614 1.17 3.37 × 10−5 5.10 × 10−5 0.0551 7.12 × 10−5 0.716

Biological role

Carbon dioxide is an end product of cellular respiration in organisms that obtain energy by breaking down sugars, fats and amino acids with oxygen as part of their metabolism. This includes all plants, algae and animals and aerobic fungi and bacteria. In vertebrates, the carbon dioxide travels in the blood from the body's tissues to the skin (e.g., amphibians) or the gills (e.g., fish), from where it dissolves in the water, or to the lungs from where it is exhaled. During active photosynthesis, plants can absorb more carbon dioxide from the atmosphere than they release in respiration.

Photosynthesis and carbon fixation

Overview of the Calvin cycle and carbon fixation

Carbon fixation is a biochemical process by which atmospheric carbon dioxide is incorporated by plants, algae and cyanobacteria into energy-rich organic molecules such as glucose, thus creating their own food by photosynthesis. Photosynthesis uses carbon dioxide and water to produce sugars from which other organic compounds can be constructed, and oxygen is produced as a by-product.

Ribulose-1,5-bisphosphate carboxylase oxygenase, commonly abbreviated to RuBisCO, is the enzyme involved in the first major step of carbon fixation, the production of two molecules of 3-phosphoglycerate from CO2 and ribulose bisphosphate, as shown in the diagram at left.

RuBisCO is thought to be the single most abundant protein on Earth.[31]

Phototrophs use the products of their photosynthesis as internal food sources and as raw material for the biosynthesis of more complex organic molecules, such as polysaccharides, nucleic acids, and proteins. These are used for their own growth, and also as the basis of the food chains and webs that feed other organisms, including animals such as ourselves. Some important phototrophs, the coccolithophores synthesise hard calcium carbonate scales.[32] A globally significant species of coccolithophore is Emiliania huxleyi whose calcite scales have formed the basis of many sedimentary rocks such as limestone, where what was previously atmospheric carbon can remain fixed for geological timescales.

Overview of photosynthesis and respiration. Carbon dioxide (at right), together with water, form oxygen and organic compounds (at left) by photosynthesis (green), which can be respired (red) to water and CO2.

Plants can grow as much as 50% faster in concentrations of 1,000 ppm CO2 when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients.[33] Elevated CO2 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 CO2 in FACE experiments.[34][35]

Increased atmospheric CO2 concentrations result in fewer stomata developing on plants[36] which leads to reduced water usage and increased water-use efficiency.[37] Studies using FACE have shown that CO2 enrichment leads to decreased concentrations of micronutrients in crop plants.[38] This may have knock-on effects on other parts of ecosystems as herbivores will need to eat more food to gain the same amount of protein.[39]

The concentration of secondary metabolites such as phenylpropanoids and flavonoids can also be altered in plants exposed to high concentrations of CO2.[40][41]

Plants also emit CO2 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 CO2 each year, a mature forest will produce as much CO2 from respiration and decomposition of dead specimens (e.g., fallen branches) as is used in photosynthesis in growing plants.[42] Contrary to the long-standing view that they are carbon neutral, mature forests can continue to accumulate carbon[43] and remain valuable carbon sinks, helping to maintain the carbon balance of Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO2 in the upper ocean and thereby promotes the absorption of CO2 from the atmosphere.[44]


Symptoms of carbon dioxide toxicity, by increasing volume percent in air[45]

Carbon dioxide content in fresh air (averaged between sea-level and 10 kPa level, i.e., about 30 km (19 mi) altitude) varies between 0.036% (360 ppm) and 0.041% (412 ppm), depending on the location.[46]

CO2 is an asphyxiant gas and not classified as toxic or harmful in accordance with 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 and give the lungs a stuffy feeling.[45] Concentrations of 7% to 10% (70,000 to 100,000 ppm) 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.[47] The physiological effects of acute carbon dioxide exposure are grouped together under the term hypercapnia, a subset of asphyxiation.

Because it is heavier than air, in locations where the gas seeps from the ground (due to sub-surface volcanic or geothermal activity) in relatively high concentrations, 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. Children have been killed in the same way near the city of Goma by CO2 emissions from the nearby volcano Mount Nyiragongo.[48] The Swahili term for this phenomenon is mazuku.

Rising levels of CO2 threatened the Apollo 13 astronauts who had to adapt cartridges from the command module to supply the carbon dioxide scrubber in the Apollo Lunar Module, which they used as a lifeboat.

Adaptation to increased concentrations of CO2 occurs in humans, including modified breathing and kidney bicarbonate production, in order to balance the effects of blood acidification (acidosis). Several studies 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, as deterioration in performance or in normal physical activity does not happen at this level of exposure for five days.[49][50] Yet, other studies show a decrease in cognitive function even at much lower levels.[51][52] Also, with ongoing respiratory acidosis, adaptation or compensatory mechanisms will be unable to reverse the condition.

Below 1%

There are few studies of the health effects of long-term continuous CO2 exposure on humans and animals at levels below 1%. Occupational CO2 exposure limits have been set in the United States at 0.5% (5000 ppm) for an eight-hour period.[53] At this CO2 concentration, International Space Station crew experienced headaches, lethargy, mental slowness, emotional irritation, and sleep disruption.[54] Studies in animals at 0.5% CO2 have demonstrated kidney calcification and bone loss after eight weeks of exposure.[55] A study of humans exposed in 2.5 hour sessions demonstrated significant negative effects on cognitive abilities at concentrations as low as 0.1% (1000 ppm) CO2 likely due to CO2 induced increases in cerebral blood flow.[51] Another study observed a decline in basic activity level and information usage at 1000 ppm, when compared to 500 ppm.[52]

However a review of the literature found that a reliable subset of studies on the phenomenon of carbon dioxide induced cognitive impairment to only show a small effect on high-level decision making (for concentrations below 5000 ppm). Most of the studies were confounded by inadequate study designs, environmental comfort, uncertainties in exposure doses and differing cognitive assessments used.[56] Similarly a study on the effects of the concentration of CO2 in motorcycle helmets has been criticized for having dubious methodology in not noting the self-reports of motorcycle riders and taking measurements using mannequins. Further when normal motorcycle conditions were achieved (such as highway or city speeds) or the visor was raised the concentration of CO2 declined to safe levels (0.2%).[57][58]

General guidelines on indoor CO2 concentration effects
Concentration Note
280 ppm Pre-industrial levels
421 ppm Current (May 2022) levels
700 ppm ASHRAE recommendation[59]
10,000 ppm Cognitive impairment, Canada's long term exposure limit[45]
10,000-20,000 ppm Drowsiness[47]
20,000-50,000 ppm Headaches, sleepiness; poor concentration, loss of attention, slight nausea also possible[53]
50,000 ppm USA 8h exposure limit[53]


A carbon dioxide sensor that measures CO2 concentration using a nondispersive infrared sensor

Poor ventilation is one of the main causes of excessive CO2 concentrations in closed spaces, leading to poor indoor air quality. Carbon dioxide differential above outdoor concentrations at steady state conditions (when the occupancy and ventilation system operation are sufficiently long that CO2 concentration has stabilized) are sometimes used to estimate ventilation rates per person.[60] Higher CO2 concentrations are associated with occupant health, comfort and performance degradation.[61][62] ASHRAE Standard 62.1–2007 ventilation rates may result in indoor concentrations up to 2,100 ppm above ambient outdoor conditions. Thus if the outdoor concentration is 400 ppm, indoor concentrations may reach 2,500 ppm with ventilation rates that meet this industry consensus standard. Concentrations in poorly ventilated spaces can be found even higher than this (range of 3,000 or 4,000 ppm).

Miners, who are particularly vulnerable to gas exposure due to insufficient ventilation, referred to mixtures of carbon dioxide and nitrogen as "blackdamp", "choke damp" or "stythe". Before more effective technologies were developed, miners would frequently monitor for dangerous levels of blackdamp and other gases in mine shafts by bringing a caged canary with them as they worked. The canary is more sensitive to asphyxiant 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 sinks, and collects near the floor) by burning less brightly, while methane, another suffocating gas and explosion risk, would make the lamp burn more brightly.

In February 2020, three people died from suffocation at a party in Moscow when dry ice (frozen CO2) was added to a swimming pool to cool it down.[63] A similar accident occurred in 2018 when a woman died from CO2 fumes emanating from the large amount of dry ice she was transporting in her car.[64]

Indoor air

Humans spend more and more time in a confined atmosphere (around 80-90% of the time in a building or vehicle). According to the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) and various actors in France, the CO2 rate in the indoor air of buildings (linked to human or animal occupancy and the presence of combustion installations), weighted by air renewal, is "usually between about 350 and 2,500 ppm".[65]

In homes, schools, nurseries and offices, there are no systematic relationships between the levels of CO2 and other pollutants, and indoor CO2 is statistically not a good predictor of pollutants linked to outdoor road (or air, etc.) traffic.[66] CO2 is the parameter that changes the fastest (with hygrometry and oxygen levels when humans or animals are gathered in a closed or poorly ventilated room). In poor countries, many open hearths are sources of CO2 and CO emitted directly into the living environment.[67]

Outdoor areas with elevated concentrations

Local concentrations of carbon dioxide can reach high values near strong sources, especially those that are isolated by surrounding terrain. At the Bossoleto hot spring near Rapolano Terme in Tuscany, Italy, situated in a bowl-shaped depression about 100 m (330 ft) in diameter, concentrations of CO2 rise to above 75% overnight, sufficient to kill insects and small animals. After sunrise the gas is dispersed by convection.[68] High concentrations of CO2 produced by disturbance of deep lake water saturated with CO2 are thought to have caused 37 fatalities at Lake Monoun, Cameroon in 1984 and 1700 casualties at Lake Nyos, Cameroon in 1986.[69]

Human physiology


Reference ranges or averages for partial pressures of carbon dioxide (abbreviated pCO2)
Blood compartment (kPa) (mm Hg)
Venous blood carbon dioxide 5.5–6.8 41–51[70]
Alveolar pulmonary
gas pressures
4.8 36
Arterial blood carbon dioxide 4.7–6.0 35–45[70]

The body produces approximately 2.3 pounds (1.0 kg) of carbon dioxide per day per person,[71] containing 0.63 pounds (290 g) of carbon. In humans, this carbon dioxide is carried through the venous system and is breathed out through the lungs, resulting in lower concentrations in the arteries. The carbon dioxide content of the blood is often given as the partial pressure, which is the pressure which carbon dioxide would have had if it alone occupied the volume.[72] In humans, the blood carbon dioxide contents are shown in the adjacent table.

Transport in the blood

CO2 is carried in blood in three different ways. Exact percentages vary between arterial and venous blood.

CO2 + H2O → H2CO3 → H+ + HCO3

Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However, the CO2 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 effects on the hemoglobin molecule, the binding of CO2 decreases the amount of oxygen that is bound for a given partial pressure of oxygen. This 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 CO2 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 concentration is high, the capillaries expand to allow a greater blood flow to that tissue.[74]

Bicarbonate ions are crucial for regulating blood pH. A person's breathing rate influences the level of CO2 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 respiratory alkalosis.[75]

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.[73]

The respiratory centers try to maintain an arterial CO2 pressure of 40 mmHg. With intentional hyperventilation, the CO2 content of arterial blood may be lowered to 10–20 mmHg (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.[76]

Concentrations and role in the environment


Atmospheric CO2 concentration measured at Mauna Loa Observatory in Hawaii from 1958 to 2023 (also called the Keeling Curve). The rise in CO2 over that time period is clearly visible. The concentration is expressed as μmole per mole, or ppm.

In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in the atmosphere of Earth. The current global average concentration of carbon dioxide (CO2) in the atmosphere is 421 ppm (0.04%) as of May 2022.[77] This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century.[78][77][79] The increase is due to human activity.[80]

As of March 2024, the monthly average concentration of CO2 reached a new record high of 425.22 parts per million (ppm), marking an increase of 4.7 ppm over March 2023. By the latest measurement, levels had further escalated to 427.48 ppm.[81] This continuous increase in CO2 concentrations is a clear indicator of ongoing global environmental stress, primarily driven by the burning of fossil fuels, which is the principal cause of this rise and also a major contributor to climate change.[82] Other significant human activities that emit CO2 include cement production, deforestation, and biomass burning.

Carbon dioxide is a greenhouse gas. It absorbs and emits infrared radiation at its two infrared-active vibrational frequencies. The two wavelengths are 4.26 μm (2,347 cm−1) (asymmetric stretching vibrational mode) and 14.99 μm (667 cm−1) (bending vibrational mode). CO2 plays a significant role in influencing Earth's surface temperature through the greenhouse effect.[83] Light emission from the Earth's surface is most intense in the infrared region between 200 and 2500 cm−1,[84] as opposed to light emission from the much hotter Sun which is most intense in the visible region. Absorption of infrared light at the vibrational frequencies of atmospheric CO2 traps energy near the surface, warming the surface of Earth and its lower atmosphere. Less energy reaches the upper atmosphere, which is therefore cooler because of this absorption.[85]

The increase in atmospheric concentrations of CO2 and other long-lived greenhouse gases such as methane increase the absorption and emission of infrared radiation by the atmosphere. This has led to a rise in average global temperature and ocean acidification. Another direct effect is the CO2 fertilization effect. The increase in atmospheric concentrations of CO2 causes a range of further effects of climate change on the environment and human living conditions.

The present atmospheric concentration of CO2 is the highest for 14 million years.[86] Concentrations of CO2 in the atmosphere were as high as 4,000 ppm during the Cambrian period about 500 million years ago, and as low as 180 ppm during the Quaternary glaciation of the last two million years.[78] Reconstructed temperature records for the last 420 million years indicate that atmospheric CO2 concentrations peaked at approximately 2,000 ppm. This peak happened during the Devonian period (400 million years ago). Another peak occurred in the Triassic period (220–200 million years ago).[87]
Annual CO2 flows from anthropogenic sources (left) into Earth's atmosphere, land, and ocean sinks (right) since the 1960s. Units in equivalent gigatonnes carbon per year.[88]


Ocean acidification

Carbon dioxide dissolves in the ocean to form carbonic acid (H2CO3), bicarbonate (HCO3), and carbonate (CO2−3). There is about fifty times as much carbon dioxide dissolved in the oceans as exists in the atmosphere. The oceans act as an enormous carbon sink, and have taken up about a third of CO2 emitted by human activity.[89]

Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Or ocean acidification is a process that occurs when carbon dioxide (CO2) from the atmosphere is absorbed by seawater, leading to a decrease in pH levels. This results in an increase in acidity and a reduction in carbonate ions, which are crucial for marine organisms like corals, shellfish, and plankton to build their shells and skeletons. Over the past 200 years, the rapid increase in anthropogenic CO2 (carbon dioxide) production has led to an increase in the acidity of the Earth's oceans. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05.[90] Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide (CO2) levels exceeding 410 ppm (in 2020). CO2 from the atmosphere is absorbed by the oceans. This chemical reaction produces carbonic acid (H2CO3) which dissociates into a bicarbonate ion (HCO3) and a hydrogen ion (H+). The presence of free hydrogen ions (H+) lowers the pH of the ocean, increasing acidity (this does not mean that seawater is acidic yet; it is still alkaline, with a pH higher than 8). Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.[91]

A change in pH by 0.1 represents a 26% increase in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH units is equivalent to a tenfold change in hydrogen ion concentration). Sea-surface pH and carbonate saturation states vary depending on ocean depth and location. Colder and higher latitude waters are capable of absorbing more CO2. This can cause acidity to rise, lowering the pH and carbonate saturation levels in these areas. There are several other factors that influence the atmosphere-ocean CO2 exchange, and thus local ocean acidification. These include ocean currents and upwelling zones, proximity to large continental rivers, sea ice coverage, and atmospheric exchange with nitrogen and sulfur from fossil fuel burning and agriculture.[92][93][94]
Pterapod shell dissolved in seawater adjusted to an ocean chemistry projected for the year 2100

Changes in ocean chemistry can have extensive direct and indirect effects on organisms and their habitats. One of the most important repercussions of increasing ocean acidity relates to the production of shells out of calcium carbonate (CaCO3).[91] This process is called calcification and is important to the biology and survival of a wide range of marine organisms. Calcification involves the precipitation of dissolved ions into solid CaCO3 structures, structures for many marine organisms, such as coccolithophores, foraminifera, crustaceans, mollusks, etc. After they are formed, these CaCO3 structures are vulnerable to dissolution unless the surrounding seawater contains saturating concentrations of carbonate ions (CO2−3).

Very little of the extra carbon dioxide that is added into the ocean remains as dissolved carbon dioxide. The majority dissociates into additional bicarbonate and free hydrogen ions. The increase in hydrogen is larger than the increase in bicarbonate,[95] creating an imbalance in the reaction:

HCO3 ⇌ CO2−3 + H+

To maintain chemical equilibrium, some of the carbonate ions already in the ocean combine with some of the hydrogen ions to make further bicarbonate. Thus the ocean's concentration of carbonate ions is reduced, removing an essential building block for marine organisms to build shells, or calcify:

Ca2+ + CO2−3 ⇌ CaCO3

Hydrothermal vents

Carbon dioxide is also introduced into the oceans through hydrothermal vents. The Champagne hydrothermal vent, found at the Northwest Eifuku volcano in the Mariana Trench, produces almost pure liquid carbon dioxide, one of only two known sites in the world as of 2004, the other being in the Okinawa Trough.[96] The finding of a submarine lake of liquid carbon dioxide in the Okinawa Trough was reported in 2006.[97]


Biological processes

Carbon dioxide is a by-product of the fermentation of sugar in the brewing of beer, whisky and other alcoholic beverages and in the production of bioethanol. Yeast metabolizes sugar to produce CO2 and ethanol, also known as alcohol, as follows:

C6H12O6 → 2 CO2 + 2 CH3CH2OH

All aerobic organisms produce CO2 when they oxidize carbohydrates, fatty acids, and proteins. 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 monosaccharides is:

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

Anaerobic organisms decompose organic material producing methane and carbon dioxide together with traces of other compounds.[98] Regardless of the type of organic material, the production of gases follows well defined kinetic pattern. Carbon dioxide comprises about 40–45% of the gas that emanates from decomposition in landfills (termed "landfill gas"). Most of the remaining 50–55% is methane.[99]

Industrial processes

Carbon dioxide can be obtained by distillation from air, but the method is inefficient. Industrially, carbon dioxide is predominantly an unrecovered waste product, produced by several methods which may be practiced at various scales.[100]


The combustion of all carbon-based fuels, such as methane (natural gas), petroleum distillates (gasoline, diesel, kerosene, propane), coal, wood and generic organic matter produces carbon dioxide and, except in the case of pure carbon, water. As an example, the chemical reaction between methane and oxygen:

CH4 + 2 O2 → CO2 + 2 H2O

Iron is reduced from its oxides with coke in a blast furnace, producing pig iron and carbon dioxide:[101]

Fe2O3 + 3 CO → 3 CO2 + 2 Fe

By-product from hydrogen production

Carbon dioxide is a byproduct of the industrial production of hydrogen by steam reforming and the water gas shift reaction in ammonia production. These processes begin with the reaction of water and natural gas (mainly methane).[102] This is a major source of food-grade carbon dioxide for use in carbonation of beer and soft drinks, and is also used for stunning animals such as poultry. In the summer of 2018 a shortage of carbon dioxide for these purposes arose in Europe due to the temporary shut-down of several ammonia plants for maintenance.[103]

Thermal decomposition of limestone

It is produced by thermal decomposition of limestone, CaCO3 by heating (calcining) at about 850 °C (1,560 °F), in the manufacture of quicklime (calcium oxide, CaO), a compound that has many industrial uses:

CaCO3 → CaO + CO2

Acids liberate CO2 from most metal carbonates. Consequently, it may be obtained directly from natural carbon dioxide springs, where it is produced by the action of acidified water on limestone or dolomite. The reaction between hydrochloric acid and calcium carbonate (limestone or chalk) is shown below:

CaCO3 + 2 HCl → CaCl2 + H2CO3

The carbonic acid (H2CO3) then decomposes to water and CO2:

H2CO3 → CO2 + H2O

Such reactions are accompanied by foaming or bubbling, or both, as the gas is released. They have widespread uses in industry because they can be used to neutralize waste acid streams.

Commercial uses

Carbon dioxide is used by the food industry, the oil industry, and the chemical industry.[100] The compound has varied commercial uses but one of its greatest uses as a chemical is in the production of carbonated beverages; it provides the sparkle in carbonated beverages such as soda water, beer and sparkling wine.

Precursor to chemicals

In the chemical industry, carbon dioxide is mainly consumed as an ingredient in the production of urea, with a smaller fraction being used to produce methanol and a range of other products.[104] Some carboxylic acid derivatives such as sodium salicylate are prepared using CO2 by the Kolbe–Schmitt reaction.[105]

In addition to conventional processes using CO2 for chemical production, electrochemical methods are also being explored at a research level. In particular, the use of renewable energy for production of fuels from CO2 (such as methanol) is attractive as this could result in fuels that could be easily transported and used within conventional combustion technologies but have no net CO2 emissions.[106]


Plants require carbon dioxide to conduct photosynthesis. The atmospheres of greenhouses may (if of large size, must) be enriched with additional CO2 to sustain and increase the rate of plant growth.[107][108] 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 whiteflies and spider mites in a greenhouse.[109] Some plants respond more favorably to rising carbon dioxide concentrations than others, which can lead to vegetation regime shifts like woody plant encroachment.[110]


Carbon dioxide bubbles in a soft drink

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[111] (listed as E number E290), US,[112] Australia and New Zealand[113] (listed by its INS number 290).

A candy called Pop Rocks is pressurized with carbon dioxide gas[114] at about 4,000 kPa (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 agents cause dough to rise by producing carbon dioxide.[115] 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 acids.


Carbon dioxide is used to produce carbonated soft drinks and soda water. Traditionally, the carbonation of 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, the most common method used is carbonation with recycled carbon dioxide. 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.

The taste of soda water (and related taste sensations in other carbonated beverages) is an effect of the dissolved carbon dioxide rather than the bursting bubbles of the gas. Carbonic anhydrase 4 converts carbon dioxide to carbonic acid leading to a sour taste, and also the dissolved carbon dioxide induces a somatosensory response.[116]


Dry ice used to preserve grapes after harvest

Carbon dioxide in the form of dry ice is often used during the cold soak phase in winemaking to cool clusters of grapes quickly after picking to help prevent spontaneous fermentation by wild yeast. The main advantage of using dry ice over water ice is that it cools the grapes without adding any additional water that might decrease the sugar concentration in the grape must, and thus the alcohol concentration in the finished wine. 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 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.

Stunning animals

Carbon dioxide is often used to "stun" animals before slaughter.[117] "Stunning" may be a misnomer, as the animals are not knocked out immediately and may suffer distress.[118][119]

Inert gas

Carbon dioxide is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in portable pressure tools. Carbon dioxide is also used as an atmosphere for welding, although in the welding arc, it reacts to 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.[120] When used for MIG welding, CO2 use is sometimes referred to as MAG welding, for Metal Active Gas, as CO2 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.

Carbon dioxide 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 (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. Aluminium capsules of CO2 are also sold as supplies of compressed gas for air guns, paintball markers/guns, inflating bicycle tires, and for making carbonated water. 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[121] and in the decaffeination of coffee beans.

Fire extinguisher

Use of a CO2 fire extinguisher

Carbon dioxide can be used to extinguish flames by flooding the environment around the flame with the gas. It does not itself react to extinguish the flame, but starves the flame of oxygen by displacing it. Some 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 they do not cool the burning substances significantly, and when the carbon dioxide disperses, they can catch fire upon exposure to atmospheric oxygen. They are mainly used in server rooms.[122]

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.[123] International Maritime Organization standards 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 CO2 systems identified 51 incidents between 1975 and the date of the report (2000), causing 72 deaths and 145 injuries.[124]

Supercritical CO2 as solvent

Liquid carbon dioxide is a good solvent for many lipophilic organic compounds and is used to decaffeinate coffee.[18] Carbon dioxide has attracted attention in the pharmaceutical and other chemical processing industries as a less toxic alternative to more traditional solvents such as organochlorides. It is also used by some dry cleaners for this reason. It is used in the preparation of some aerogels because of the properties of supercritical carbon dioxide.

Medical and pharmacological uses

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 O2/CO2 balance in blood.

Carbon dioxide can be mixed with up to 50% oxygen, forming an inhalable gas; this is known as Carbogen and has a variety of medical and research uses.

Another medical use are the mofette, dry spas that use carbon dioxide from post-volcanic discharge for therapeutic purposes.


Supercritical CO2 is used as the working fluid in the Allam power cycle engine.

Fossil fuel recovery

Carbon dioxide is used in enhanced oil recovery where it is injected into or adjacent to producing oil wells, usually under supercritical conditions, when it becomes miscible with the oil. This approach can increase original oil recovery by reducing residual oil saturation by 7–23% additional to primary extraction.[125] 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.[126] In mature oil fields, extensive pipe networks are used to carry the carbon dioxide to the injection points.

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 rely on the removal of water (to reduce pressure) to make the coal seam release its trapped methane.[127]

Bio transformation into fuel

It has been proposed that CO2 from power generation be bubbled into ponds to stimulate growth of algae that could then be converted into biodiesel fuel.[128] A strain of the cyanobacterium Synechococcus elongatus has been genetically engineered to produce the fuels isobutyraldehyde and isobutanol from CO2 using photosynthesis.[129]

Researchers have developed an electrocatalytic technique using enzymes isolated from bacteria to power the chemical reactions which convert CO2 into fuels.[130][131][132]

Comparison of the pressure–temperature 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 refrigerants, 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 °C (−109.3 °F) at regular atmospheric pressure, regardless of the air temperature.

Liquid carbon dioxide (industry nomenclature R744 or R-744) was used as a refrigerant prior to the use of dichlorodifluoromethane (R12, a chlorofluorocarbon (CFC) compound).[133] CO2 might enjoy a renaissance because one of the main substitutes to CFCs, 1,1,1,2-tetrafluoroethane (R134a, a hydrofluorocarbon (HFC) compound) contributes to climate change more than CO2 does. CO2 physical properties are highly favorable for cooling, refrigeration, and heating purposes, having a high volumetric cooling capacity. Due to the need to operate at pressures of up to 130 bars (1,900 psi; 13,000 kPa), CO2 systems require highly mechanically resistant reservoirs and 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°, CO2 (R744) operates more efficiently than systems using HFCs (e.g., R134a). Its environmental advantages (GWP of 1, non-ozone depleting, non-toxic, non-flammable) could make it the future working fluid to replace current HFCs in cars, supermarkets, and heat pump water heaters, among others. Coca-Cola has fielded CO2-based beverage coolers and the U.S. Army is interested in CO2 refrigeration and heating technology.[134][135]

Minor uses

A carbon-dioxide laser

Carbon dioxide is the lasing medium in a 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,[136] by continuously adding gas to the water, thus keeping the pH from rising. Among the advantages of this is the avoidance of handling (more hazardous) acids. Similarly, it is also used in the maintaining reef aquaria, where it is commonly used in calcium reactors 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 corals to build their skeleton.

Used as the primary coolant in the British advanced gas-cooled reactor for nuclear power generation.

Carbon dioxide induction is commonly used for the euthanasia of laboratory research animals. Methods to administer CO2 include placing animals directly into a closed, prefilled chamber containing CO2, or exposure to a gradually increasing concentration of CO2. The American Veterinary Medical Association's 2020 guidelines for carbon dioxide induction state that a displacement rate of 30–70% of the chamber or cage volume per minute is optimal for the humane euthanasia of small rodents.[137]: 5, 31  Percentages of CO2 vary for different species, based on identified optimal percentages to minimize distress.[137]: 22 

Carbon dioxide is also used in several related cleaning and surface-preparation techniques.

History of discovery

Crystal structure of dry ice

Carbon dioxide was the first gas to be described as a discrete substance. In about 1640,[138] the Flemish chemist Jan Baptist van Helmont observed that when he burned charcoal in a closed vessel, the mass of the resulting 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" (from Greek "chaos") or "wild spirit" (spiritus sylvestris).[139]

The properties of carbon dioxide were further studied in the 1750s by the Scottish physician Joseph Black. He found that limestone (calcium carbonate) could be heated or treated with acids 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 limewater (a saturated aqueous solution of calcium hydroxide), it would 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.[140]

Carbon dioxide was first liquefied (at elevated pressures) in 1823 by Humphry Davy and Michael Faraday.[141] The earliest description of solid carbon dioxide (dry ice) was given by the French inventor 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 CO2.[142][143]

Carbon dioxide in combination with nitrogen was known from earlier times as Blackdamp, stythe or choke damp.[b] Along with the other types of damp it was encountered in mining operations and well sinking. Slow oxidation of coal and biological processes replaced the oxygen to create a suffocating mixture of nitrogen and carbon dioxide.[144]

See also


  1. ^ where "part" here means per molecule[10]
  2. ^ Sometimes spelt "choak-damp" in 19th Century texts.


  1. ^ a b c "Carbon Dioxide" (PDF). Air Products. Archived from the original (PDF) on 29 July 2020. Retrieved 28 April 2017.
  2. ^ a b c d e f g h i Span R, Wagner W (1 November 1996). "A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple-Point Temperature to 1100 K at Pressures up to 800 MPa". Journal of Physical and Chemical Reference Data. 25 (6): 1519. Bibcode:1996JPCRD..25.1509S. doi:10.1063/1.555991.
  3. ^ Touloukian YS, Liley PE, Saxena SC (1970). "Thermophysical properties of matter - the TPRC data series". Thermal Conductivity - Nonmetallic Liquids and Gases. 3. Data book.
  4. ^ Schäfer M, Richter M, Span R (2015). "Measurements of the viscosity of carbon dioxide at temperatures from (253.15 to 473.15) K with pressures up to 1.2 MPa". The Journal of Chemical Thermodynamics. 89: 7–15. doi:10.1016/j.jct.2015.04.015.
  5. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0103". National Institute for Occupational Safety and Health (NIOSH).
  6. ^ "Carbon dioxide". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  7. ^ "Safety Data Sheet – Carbon Dioxide Gas – version 0.03 11/11" (PDF). AirGas.com. 12 February 2018. Archived (PDF) from the original on 4 August 2018. Retrieved 4 August 2018.
  8. ^ "Carbon dioxide, refrigerated liquid" (PDF). Praxair. p. 9. Archived from the original (PDF) on 29 July 2018. Retrieved 26 July 2018.
  9. ^ Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean. Washington, DC: National Academies Press. 22 April 2010. pp. 23–24. doi:10.17226/12904. ISBN 978-0-309-15359-1. Archived from the original on 5 February 2016. Retrieved 29 February 2016.
  10. ^ "CO2 Gas Concentration Defined". CO2 Meter. 18 November 2022. Retrieved 5 September 2023.
  11. ^ Eggleton T (2013). A Short Introduction to Climate Change. Cambridge University Press. p. 52. ISBN 9781107618763. Retrieved 9 November 2020.
  12. ^ "Carbon dioxide now more than 50% higher than pre-industrial levels | National Oceanic and Atmospheric Administration". www.noaa.gov. 3 June 2022. Retrieved 14 June 2022.
  13. ^ IPCC (2022) Summary for policy makers in Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, US
  14. ^ Kaufman DG, Franz CM (1996). Biosphere 2000: protecting our global environment. Kendall/Hunt Pub. Co. ISBN 978-0-7872-0460-0.
  15. ^ "Food Factories". www.legacyproject.org. Archived from the original on 12 August 2017. Retrieved 10 October 2011.
  16. ^ IPCC (2021). "Summary for Policymakers" (PDF). Climate Change 2021: The Physical Science Basis. p. 20. Archived (PDF) from the original on 10 October 2022.
  17. ^ Myles, Allen (September 2020). "The Oxford Principles for Net Zero Aligned Carbon Offsetting" (PDF). Archived (PDF) from the original on 2 October 2020. Retrieved 10 December 2021.
  18. ^ a b Tsotsas E, Mujumdar AS (2011). Modern drying technology. Vol. 3: Product quality and formulation. John Wiley & Sons. ISBN 978-3-527-31558-1. Archived from the original on 21 March 2020. Retrieved 3 December 2019.
  19. ^ a b Greenwood NN, Earnshaw A (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 305–314. ISBN 978-0-08-037941-8.
  20. ^ Atkins P, de Paula J (2006). Physical Chemistry (8th ed.). W.H. Freeman. pp. 461, 464. ISBN 978-0-7167-8759-4.
  21. ^ Siegmann B, Werner U, Lutz HO, Mann R (2002). "Complete Coulomb fragmentation of CO2 in collisions with 5.9 MeV u−1 Xe18+ and Xe43+". J Phys B Atom Mol Opt Phys. 35 (17): 3755. Bibcode:2002JPhB...35.3755S. doi:10.1088/0953-4075/35/17/311. S2CID 250782825.
  22. ^ a b Jensen P, Spanner M, Bunker PR (2020). "The CO2 molecule is never linear−". J Mol Struct. 1212: 128087. Bibcode:2020JMoSt121228087J. doi:10.1016/j.molstruc.2020.128087. hdl:2142/107329.
  23. ^ Jolly WL (1984). Modern Inorganic Chemistry. McGraw-Hill. p. 196. ISBN 978-0-07-032760-3.
  24. ^ Li Z, Mayer RJ, Ofial AR, Mayr H (May 2020). "From Carbodiimides to Carbon Dioxide: Quantification of the Electrophilic Reactivities of Heteroallenes". Journal of the American Chemical Society. 142 (18): 8383–8402. doi:10.1021/jacs.0c01960. PMID 32338511. S2CID 216557447.
  25. ^ Aresta M, ed. (2010). Carbon Dioxide as a Chemical Feedstock. Weinheim: Wiley-VCH. ISBN 978-3-527-32475-0.
  26. ^ Finn C, Schnittger S, Yellowlees LJ, Love JB (February 2012). "Molecular approaches to the electrochemical reduction of carbon dioxide" (PDF). Chemical Communications. 48 (10): 1392–1399. doi:10.1039/c1cc15393e. hdl:20.500.11820/b530915d-451c-493c-8251-da2ea2f50912. PMID 22116300. S2CID 14356014. Archived (PDF) from the original on 19 April 2021. Retrieved 6 December 2019.
  27. ^ "Gases – Densities". Engineering Toolbox. Archived from the original on 2 March 2006. Retrieved 21 November 2020.
  28. ^ Santoro M, Gorelli FA, Bini R, Ruocco G, Scandolo S, Crichton WA (June 2006). "Amorphous silica-like carbon dioxide". Nature. 441 (7095): 857–860. Bibcode:2006Natur.441..857S. doi:10.1038/nature04879. PMID 16778885. S2CID 4363092.
  29. ^ a b Holman, Jack P. (2002). Heat Transfer (9th ed.). New York, NY: McGraw-Hill Companies, Inc. pp. 600–606. ISBN 9780072406559.
  30. ^ a b Incropera, Frank P.; Dewitt, David P.; Bergman, Theodore L.; Lavigne, Adrienne S. (2007). Fundamentals of Heat and Mass Transfer (6th ed.). Hoboken, NJ: John Wiley and Sons, Inc. pp. 941–950. ISBN 9780471457282.
  31. ^ Dhingra A, Portis AR, Daniell H (April 2004). "Enhanced translation of a chloroplast-expressed RbcS gene restores small subunit levels and photosynthesis in nuclear RbcS antisense plants". Proceedings of the National Academy of Sciences of the United States of America. 101 (16): 6315–6320. Bibcode:2004PNAS..101.6315D. doi:10.1073/pnas.0400981101. PMC 395966. PMID 15067115. (Rubisco) is the most prevalent enzyme on this planet, accounting for 30–50% of total soluble protein in the chloroplast
  32. ^ Falkowski P, Knoll AH (1 January 2007). Evolution of primary producers in the sea. Elsevier, Academic Press. ISBN 978-0-12-370518-1. OCLC 845654016.
  33. ^ Blom TJ, Straver WA, Ingratta FJ, Khosla S, Brown W (December 2002). "Carbon Dioxide In Greenhouses". Archived from the original on 29 April 2019. Retrieved 12 June 2007.
  34. ^ Ainsworth EA (2008). "Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and elevated ozone concentration" (PDF). Global Change Biology. 14 (7): 1642–1650. Bibcode:2008GCBio..14.1642A. doi:10.1111/j.1365-2486.2008.01594.x. S2CID 19200429. Archived from the original (PDF) on 19 July 2011.
  35. ^ Long SP, Ainsworth EA, Leakey AD, Nösberger J, Ort DR (June 2006). "Food for thought: lower-than-expected crop yield stimulation with rising CO2 concentrations" (PDF). Science. 312 (5782): 1918–1921. Bibcode:2006Sci...312.1918L. CiteSeerX doi:10.1126/science.1114722. PMID 16809532. S2CID 2232629. Archived (PDF) from the original on 20 October 2016. Retrieved 27 October 2017.
  36. ^ Woodward F, Kelly C (1995). "The influence of CO2 concentration on stomatal density". New Phytologist. 131 (3): 311–327. doi:10.1111/j.1469-8137.1995.tb03067.x.
  37. ^ Drake BG, Gonzalez-Meler MA, Long SP (June 1997). "More Efficient Plants: A Consequence of Rising Atmospheric CO2?". Annual Review of Plant Physiology and Plant Molecular Biology. 48 (1): 609–639. doi:10.1146/annurev.arplant.48.1.609. PMID 15012276. S2CID 33415877.
  38. ^ Loladze I (2002). "Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry?". Trends in Ecology & Evolution. 17 (10): 457–461. doi:10.1016/S0169-5347(02)02587-9. S2CID 16074723.
  39. ^ Coviella CE, Trumble JT (1999). "Effects of Elevated Atmospheric Carbon Dioxide on Insect-Plant Interactions". Conservation Biology. 13 (4): 700–712. Bibcode:1999ConBi..13..700C. doi:10.1046/j.1523-1739.1999.98267.x. JSTOR 2641685. S2CID 52262618.
  40. ^ Davey MP, Harmens H, Ashenden TW, Edwards R, Baxter R (2007). "Species-specific effects of elevated CO2 on resource allocation in Plantago maritima and Armeria maritima". Biochemical Systematics and Ecology. 35 (3): 121–129. doi:10.1016/j.bse.2006.09.004.
  41. ^ Davey MP, Bryant DN, Cummins I, Ashenden TW, Gates P, Baxter R, Edwards R (August 2004). "Effects of elevated CO2 on the vasculature and phenolic secondary metabolism of Plantago maritima". Phytochemistry. 65 (15): 2197–2204. Bibcode:2004PChem..65.2197D. doi:10.1016/j.phytochem.2004.06.016. PMID 15587703.
  42. ^ "Global Environment Division Greenhouse Gas Assessment Handbook – A Practical Guidance Document for the Assessment of Project-level Greenhouse Gas Emissions". World Bank. Archived from the original on 3 June 2016. Retrieved 10 November 2007.
  43. ^ Luyssaert S, Schulze ED, Börner A, Knohl A, Hessenmöller D, Law BE, et al. (September 2008). "Old-growth forests as global carbon sinks" (PDF). Nature. 455 (7210): 213–215. Bibcode:2008Natur.455..213L. doi:10.1038/nature07276. PMID 18784722. S2CID 4424430.
  44. ^ Falkowski P, Scholes RJ, Boyle E, Canadell J, Canfield D, Elser J, et al. (October 2000). "The global carbon cycle: a test of our knowledge of earth as a system". Science. 290 (5490): 291–296. Bibcode:2000Sci...290..291F. doi:10.1126/science.290.5490.291. PMID 11030643. S2CID 1779934.
  45. ^ a b c Friedman D. "Toxicity of Carbon Dioxide Gas Exposure, CO2 Poisoning Symptoms, Carbon Dioxide Exposure Limits, and Links to Toxic Gas Testing Procedures". InspectAPedia. Archived from the original on 28 September 2009.
  46. ^ "CarbonTracker CT2011_oi (Graphical map of CO2)". esrl.noaa.gov. Archived from the original on 13 February 2021. Retrieved 20 April 2007.
  47. ^ a b "Carbon Dioxide as a Fire Suppressant: Examining the Risks". U.S. Environmental Protection Agency. Archived from the original on 2 October 2015.
  48. ^ "Volcano Under the City". A NOVA Production by Bonne Pioche and Greenspace for WGBH/Boston. Public Broadcasting System. 1 November 2005. Archived from the original on 5 April 2011..
  49. ^ Glatte Jr HA, Motsay GJ, Welch BE (1967). Carbon Dioxide Tolerance Studies (Report). Brooks AFB, TX School of Aerospace Medicine Technical Report. SAM-TR-67-77. Archived from the original on 9 May 2008. Retrieved 2 May 2008.{{cite report}}: CS1 maint: unfit URL (link)
  50. ^ Lambertsen CJ (1971). Carbon Dioxide Tolerance and Toxicity (Report). IFEM Report. Environmental Biomedical Stress Data Center, Institute for Environmental Medicine, University of Pennsylvania Medical Center. No. 2-71. Archived from the original on 24 July 2011. Retrieved 2 May 2008.{{cite report}}: CS1 maint: unfit URL (link)
  51. ^ a b Satish U, Mendell MJ, Shekhar K, Hotchi T, Sullivan D, Streufert S, Fisk WJ (December 2012). "Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance" (PDF). Environmental Health Perspectives. 120 (12): 1671–1677. doi:10.1289/ehp.1104789. PMC 3548274. PMID 23008272. Archived from the original (PDF) on 5 March 2016. Retrieved 11 December 2014.
  52. ^ a b Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD (June 2016). "Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments". Environmental Health Perspectives. 124 (6): 805–812. doi:10.1289/ehp.1510037. PMC 4892924. PMID 26502459.
  53. ^ a b c "Exposure Limits for Carbon Dioxide Gas – CO2 Limits". InspectAPedia.com. Archived from the original on 16 September 2018. Retrieved 19 October 2014.
  54. ^ Law J, Watkins S, Alexander D (2010). In-Flight Carbon Dioxide Exposures and Related Symptoms: Associations, Susceptibility and Operational Implications (PDF) (Report). NASA Technical Report. TP–2010–216126. Archived from the original (PDF) on 27 June 2011. Retrieved 26 August 2014.
  55. ^ Schaefer KE, Douglas WH, Messier AA, Shea ML, Gohman PA (1979). "Effect of prolonged exposure to 0.5% CO2 on kidney calcification and ultrastructure of lungs". Undersea Biomedical Research. 6 (Suppl): S155–S161. PMID 505623. Archived from the original on 19 October 2014. Retrieved 19 October 2014.
  56. ^ Du B, Tandoc MC, Mack ML, Siegel JA (November 2020). "Indoor CO2 concentrations and cognitive function: A critical review". Indoor Air. 30 (6): 1067–1082. Bibcode:2020InAir..30.1067D. doi:10.1111/ina.12706. PMID 32557862. S2CID 219915861.
  57. ^ Kaplan L (4 June 2019). "Ask the doc: Does my helmet make me stupid? - RevZilla". www.revzilla.com. Archived from the original on 22 May 2021. Retrieved 22 May 2021.
  58. ^ Brühwiler PA, Stämpfli R, Huber R, Camenzind M (September 2005). "CO2 and O2 concentrations in integral motorcycle helmets". Applied Ergonomics. 36 (5): 625–633. doi:10.1016/j.apergo.2005.01.018. PMID 15893291.
  59. ^ "Ventilation for Acceptable Indoor Air Quality" (PDF). 2018. ISSN 1041-2336. Archived (PDF) from the original on 26 October 2022. Retrieved 10 August 2023.
  60. ^ "Standard Guide for Using Indoor Carbon Dioxide Concentrations to Evaluate Indoor Air Quality and Ventilation". www.astm.org. Retrieved 12 June 2024.
  61. ^ Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD (June 2016). "Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments". Environmental Health Perspectives. 124 (6): 805–812. doi:10.1289/ehp.1510037. PMC 4892924. PMID 26502459.
  62. ^ Romm J (26 October 2015). "Exclusive: Elevated CO2 Levels Directly Affect Human Cognition, New Harvard Study Shows". ThinkProgress. Archived from the original on 9 October 2019. Retrieved 14 October 2019.
  63. ^ "Three die in dry-ice incident at Moscow pool party". BBC News. 29 February 2020. Archived from the original on 29 February 2020. The victims were connected to Instagram influencer Yekaterina Didenko.
  64. ^ Rettner R (2 August 2018). "A Woman Died from Dry Ice Fumes. Here's How It Can Happen". Live Science. Archived from the original on 22 May 2021. Retrieved 22 May 2021.
  65. ^ Concentrations de CO2 dans l'air intérieur et effets sur la santé (PDF) (Report) (in French). ANSES. July 2013. p. 294.
  66. ^ Chatzidiakou, Lia; Mumovic, Dejan; Summerfield, Alex (March 2015). "Is CO 2 a good proxy for indoor air quality in classrooms? Part 1: The interrelationships between thermal conditions, CO 2 levels, ventilation rates and selected indoor pollutants". Building Services Engineering Research and Technology. 36 (2): 129–161. doi:10.1177/0143624414566244. ISSN 0143-6244. S2CID 111182451.
  67. ^ Cetin, Mehmet; Sevik, Hakan (2016). "INDOOR QUALITY ANALYSIS OF CO2 FOR KASTAMONU UNIVERSITY" (PDF). Conference of the International Journal of Arts & Sciences. 9 (3): 71.
  68. ^ van Gardingen PR, Grace J, Jeffree CE, Byari SH, Miglietta F, Raschi A, Bettarini I (1997). "Long-term effects of enhanced CO2 concentrations on leaf gas exchange: research opportunities using CO2 springs". In Raschi A, Miglietta F, Tognetti R, van Gardingen PR (eds.). Plant responses to elevated CO2: Evidence from natural springs. Cambridge: Cambridge University Press. pp. 69–86. ISBN 978-0-521-58203-2.
  69. ^ Martini M (1997). "CO2 emissions in volcanic areas: case histories and hazards". In Raschi A, Miglietta F, Tognetti R, van Gardingen PR (eds.). Plant responses to elevated CO2: Evidence from natural springs. Cambridge: Cambridge University Press. pp. 69–86. ISBN 978-0-521-58203-2.
  70. ^ a b "ABG (Arterial Blood Gas)". Brookside Associates. Archived from the original on 12 August 2017. Retrieved 2 January 2017.
  71. ^ "How much carbon dioxide do humans contribute through breathing?". EPA.gov. Archived from the original on 2 February 2011. Retrieved 30 April 2009.
  72. ^ Henrickson C (2005). Chemistry. Cliffs Notes. ISBN 978-0-7645-7419-1.
  73. ^ a b c d "Carbon dioxide". solarnavigator.net. Archived from the original on 14 September 2008. Retrieved 12 October 2007.
  74. ^ Battisti-Charbonney, A.; Fisher, J.; Duffin, J. (15 June 2011). "The cerebrovascular response to carbon dioxide in humans". J. Physiol. 589 (12): 3039–3048. doi:10.1113/jphysiol.2011.206052. PMC 3139085. PMID 21521758.
  75. ^ Patel, S.; Miao, J.H.; Yetiskul, E.; Anokhin, A.; Majmunder, S.H. (2022). "Physiology, Carbon Dioxide Retention". National Library of Medicine. National Center for Biotechnology Information, NIH. PMID 29494063. Retrieved 20 August 2022.
  76. ^ Wilmshurst, Peter (1998). "ABC of oxygen". BMJ. 317 (7164): 996–999. doi:10.1136/bmj.317.7164.996. PMC 1114047. PMID 9765173.
  77. ^ a b "Carbon dioxide now more than 50% higher than pre-industrial levels | National Oceanic and Atmospheric Administration". www.noaa.gov. 3 June 2022. Archived from the original on 5 June 2022. Retrieved 14 June 2022.
  78. ^ a b Eggleton, Tony (2013). A Short Introduction to Climate Change. Cambridge University Press. p. 52. ISBN 9781107618763. Archived from the original on 14 March 2023. Retrieved 14 March 2023.
  79. ^ "The NOAA Annual Greenhouse Gas Index (AGGI) – An Introduction". NOAA Global Monitoring Laboratory/Earth System Research Laboratories. Archived from the original on 27 November 2020. Retrieved 18 December 2020.
  80. ^ Etheridge, D.M.; L.P. Steele; R.L. Langenfelds; R.J. Francey; J.-M. Barnola; V.I. Morgan (1996). "Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn". Journal of Geophysical Research. 101 (D2): 4115–28. Bibcode:1996JGR...101.4115E. doi:10.1029/95JD03410. ISSN 0148-0227. S2CID 19674607.
  81. ^ Pierre-Louis, Kendra (10 May 2024). "Carbon Dioxide Just Took an Ominous, Record-Breaking Jump". www.bloomberg.com. Retrieved 13 May 2024.
  82. ^ IPCC (2022) Summary for policy makers Archived 12 March 2023 at the Wayback Machine in Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Archived 2 August 2022 at the Wayback Machine, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
  83. ^ Petty, G.W. (2004). "A First Course in Atmospheric Radiation". Eos Transactions. 85 (36): 229–51. Bibcode:2004EOSTr..85..341P. doi:10.1029/2004EO360007.
  84. ^ Atkins P, de Paula J (2006). Atkins' Physical Chemistry (8th ed.). W. H. Freeman. p. 462. ISBN 978-0-7167-8759-4.
  85. ^ "Carbon Dioxide Absorbs and Re-emits Infrared Radiation". UCAR Center for Science Education. 2012. Archived from the original on 21 September 2017. Retrieved 9 September 2017.
  86. ^ AHMED, Issam. "Current carbon dioxide levels last seen 14 million years ago". phys.org. Retrieved 8 February 2024.
  87. ^ "Climate and CO2 in the Atmosphere". Archived from the original on 6 October 2018. Retrieved 10 October 2007.
  88. ^ Friedlingstein P, Jones MW, O'sullivan M, Andrew RM, Hauck J, Peters GP, et al. (2019). "Global Carbon Budget 2019". Earth System Science Data. 11 (4): 1783–1838. Bibcode:2019ESSD...11.1783F. doi:10.5194/essd-11-1783-2019. hdl:20.500.11850/385668..
  89. ^ Doney SC, Levine NM (29 November 2006). "How Long Can the Ocean Slow Global Warming?". Oceanus. Archived from the original on 4 January 2008. Retrieved 21 November 2007.
  90. ^ Terhaar, Jens; Frölicher, Thomas L.; Joos, Fortunat (2023). "Ocean acidification in emission-driven temperature stabilization scenarios: the role of TCRE and non-CO2 greenhouse gases". Environmental Research Letters. 18 (2): 024033. Bibcode:2023ERL....18b4033T. doi:10.1088/1748-9326/acaf91. ISSN 1748-9326. S2CID 255431338. Figure 1f
  91. ^ a b Ocean acidification due to increasing atmospheric carbon dioxide (PDF). Royal Society. 2005. ISBN 0-85403-617-2.
  92. ^ Jiang, Li-Qing; Carter, Brendan R.; Feely, Richard A.; Lauvset, Siv K.; Olsen, Are (2019). "Surface ocean pH and buffer capacity: past, present and future". Scientific Reports. 9 (1): 18624. Bibcode:2019NatSR...918624J. doi:10.1038/s41598-019-55039-4. PMC 6901524. PMID 31819102. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License Archived 16 October 2017 at the Wayback Machine
  93. ^ Zhang, Y.; Yamamoto-Kawai, M.; Williams, W.J. (16 February 2020). "Two Decades of Ocean Acidification in the Surface Waters of the Beaufort Gyre, Arctic Ocean: Effects of Sea Ice Melt and Retreat From 1997–2016". Geophysical Research Letters. 47 (3). doi:10.1029/2019GL086421. S2CID 214271838.
  94. ^ Beaupré-Laperrière, Alexis; Mucci, Alfonso; Thomas, Helmuth (31 July 2020). "The recent state and variability of the carbonate system of the Canadian Arctic Archipelago and adjacent basins in the context of ocean acidification". Biogeosciences. 17 (14): 3923–3942. Bibcode:2020BGeo...17.3923B. doi:10.5194/bg-17-3923-2020. S2CID 221369828.
  95. ^ Mitchell, Mark J.; Jensen, Oliver E.; Cliffe, K. Andrew; Maroto-Valer, M. Mercedes (8 May 2010). "A model of carbon dioxide dissolution and mineral carbonation kinetics". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. 466 (2117): 1265–1290. Bibcode:2010RSPSA.466.1265M. doi:10.1098/rspa.2009.0349.
  96. ^ Lupton J, Lilley M, Butterfield D, Evans L, Embley R, Olson E, et al. (2004). "Liquid Carbon Dioxide Venting at the Champagne Hydrothermal Site, NW Eifuku Volcano, Mariana Arc". American Geophysical Union. 2004 (Fall Meeting). V43F–08. Bibcode:2004AGUFM.V43F..08L.
  97. ^ Inagaki F, Kuypers MM, Tsunogai U, Ishibashi J, Nakamura K, Treude T, et al. (September 2006). "Microbial community in a sediment-hosted CO2 lake of the southern Okinawa Trough hydrothermal system". Proceedings of the National Academy of Sciences of the United States of America. 103 (38): 14164–14169. Bibcode:2006PNAS..10314164I. doi:10.1073/pnas.0606083103. PMC 1599929. PMID 16959888. Videos can be downloaded at "Supporting Information". Archived from the original on 19 October 2018.
  98. ^ "Collecting and using biogas from landfills". U.S. Energy Information Administration. 11 January 2017. Archived from the original on 11 July 2018. Retrieved 22 November 2015.
  99. ^ "Facts About Landfill Gas" (PDF). U.S. Environmental Protection Agency. January 2000. Archived (PDF) from the original on 23 September 2015. Retrieved 4 September 2015.
  100. ^ a b Pierantozzi R (2001). "Carbon Dioxide". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley. doi:10.1002/0471238961.0301180216090518.a01.pub2. ISBN 978-0-471-23896-6.
  101. ^ Strassburger J (1969). Blast Furnace Theory and Practice. New York: American Institute of Mining, Metallurgical, and Petroleum Engineers. ISBN 978-0-677-10420-1.
  102. ^ Topham S (2000). "Carbon Dioxide". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a05_165. ISBN 3527306730.
  103. ^ "CO2 shortage: Food industry calls for government action". BBC. 21 June 2018. Archived from the original on 23 May 2021. Retrieved 24 June 2018.
  104. ^ "IPCC Special Report on Carbon dioxide Capture and Storage" (PDF). The Intergovernmental Panel on Climate Change. Archived from the original (PDF) on 24 September 2015. Retrieved 4 September 2015.
  105. ^ Morrison RT, Boyd RN (1983). Organic Chemistry (4th ed.). Allyn and Bacon. pp. 976–977. ISBN 978-0-205-05838-9.
  106. ^ Badwal SP, Giddey SS, Munnings C, Bhatt AI, Hollenkamp AF (24 September 2014). "Emerging electrochemical energy conversion and storage technologies". Frontiers in Chemistry. 2: 79. Bibcode:2014FrCh....2...79B. doi:10.3389/fchem.2014.00079. PMC 4174133. PMID 25309898.
  107. ^ Whiting D, Roll M, Vickerman L (August 2010). "Plant Growth Factors: Photosynthesis, Respiration, and Transpiration". CMG GardenNotes. Colorado Master Gardener Program. Archived from the original on 2 September 2014. Retrieved 10 October 2011.
  108. ^ Waggoner PE (February 1994). "Carbon dioxide". How Much Land Can Ten Billion People Spare for Nature?. Archived from the original on 12 October 2011. Retrieved 10 October 2011.
  109. ^ Stafford N (August 2007). "Future crops: the other greenhouse effect". Nature. 448 (7153): 526–528. Bibcode:2007Natur.448..526S. doi:10.1038/448526a. PMID 17671477. S2CID 9845813.
  110. ^ Archer, Steven R.; Andersen, Erik M.; Predick, Katharine I.; Schwinning, Susanne; Steidl, Robert J.; Woods, Steven R. (2017), Briske, David D. (ed.), "Woody Plant Encroachment: Causes and Consequences", Rangeland Systems, Cham: Springer International Publishing, pp. 25–84, doi:10.1007/978-3-319-46709-2_2, ISBN 978-3-319-46707-8
  111. ^ UK Food Standards Agency: "Current EU approved additives and their E Numbers". Archived from the original on 7 October 2010. Retrieved 27 October 2011.
  112. ^ US Food and Drug Administration: "Food Additive Status List". Food and Drug Administration. Archived from the original on 4 November 2017. Retrieved 13 June 2015.
  113. ^ Australia New Zealand Food Standards Code"Standard 1.2.4 – Labelling of ingredients". 8 September 2011. Archived from the original on 19 January 2012. Retrieved 27 October 2011.
  114. ^ Futurific Leading Indicators Magazine. Vol. 1. CRAES LLC. ISBN 978-0-9847670-1-4. Archived from the original on 15 August 2021. Retrieved 9 November 2020.
  115. ^ Vijay GP (25 September 2015). Indian Breads: A Comprehensive Guide to Traditional and Innovative Indian Breads. Westland. ISBN 978-93-85724-46-6.[permanent dead link]
  116. ^ "Scientists Discover Protein Receptor For Carbonation Taste". ScienceDaily. 16 October 2009. Archived from the original on 29 March 2020. Retrieved 29 March 2020.
  117. ^ Coghlan A (3 February 2018). "A more humane way of slaughtering chickens might get EU approval". New Scientist. Archived from the original on 24 June 2018. Retrieved 24 June 2018.
  118. ^ "What is CO2 stunning?". RSPCA. Archived from the original on 9 April 2014.
  119. ^ Campbell A (10 March 2018). "Humane execution and the fear of the tumbril". New Scientist. Archived from the original on 24 June 2018. Retrieved 24 June 2018.
  120. ^ International, Petrogav. Production Course for Hiring on Offshore Oil and Gas Rigs. Petrogav International. p. 214.
  121. ^ Nordestgaard BG, Rostgaard J (February 1985). "Critical-point drying versus freeze drying for scanning electron microscopy: a quantitative and qualitative study on isolated hepatocytes". Journal of Microscopy. 137 (Pt 2): 189–207. doi:10.1111/j.1365-2818.1985.tb02577.x. PMID 3989858. S2CID 32065173.
  122. ^ "Types of Fire Extinguishers". The Fire Safety Advice Centre. Archived from the original on 28 June 2021. Retrieved 28 June 2021.
  123. ^ National Fire Protection Association Code 12.
  124. ^ Carbon Dioxide as a Fire Suppressant: Examining the Risks, US EPA. 2000.
  125. ^ "Appendix A: CO2 for use in enhanced oil recovery (EOR)". Accelerating the uptake of CCS: industrial use of captured carbon dioxide. 20 December 2011. Archived from the original on 28 April 2017. Retrieved 2 January 2017. {{cite book}}: |website= ignored (help)
  126. ^ Austell JM (2005). "CO2 for Enhanced Oil Recovery Needs – Enhanced Fiscal Incentives". Exploration & Production: The Oil & Gas Review. Archived from the original on 7 February 2012. Retrieved 28 September 2007.
  127. ^ "Enhanced coal bed methane recovery". ETH Zurich. 31 August 2006. Archived from the original on 6 July 2011.
  128. ^ Clayton M (11 January 2006). "Algae – like a breath mint for smokestacks". The Christian Science Monitor. Archived from the original on 14 September 2008. Retrieved 11 October 2007.
  129. ^ Atsumi S, Higashide W, Liao JC (December 2009). "Direct photosynthetic recycling of carbon dioxide to isobutyraldehyde". Nature Biotechnology. 27 (12): 1177–1180. doi:10.1038/nbt.1586. PMID 19915552. S2CID 1492698.
  130. ^ Cobb S, Badiani V, Dharani A, Wagner A, Zacarias S, Oliveira AR, et al. (28 February 2022). "Fast CO2 hydration kinetics impair heterogeneous but improve enzymatic CO2 reduction catalysis". Nature Chemistry. 14 (4): 417–424. Bibcode:2022NatCh..14..417C. doi:10.1038/s41557-021-00880-2. ISSN 1755-4349. PMC 7612589. PMID 35228690. S2CID 247160910.
  131. ^ Edwardes Moore E, Cobb SJ, Coito AM, Oliveira AR, Pereira IA, Reisner E (January 2022). "Understanding the local chemical environment of bioelectrocatalysis". Proceedings of the National Academy of Sciences of the United States of America. 119 (4): e2114097119. Bibcode:2022PNAS..11914097E. doi:10.1073/pnas.2114097119. PMC 8795565. PMID 35058361.
  132. ^ "Clean Way To Turn CO2 Into Fuel Inspired by Nature". Applied Sciences from Technology Networks. 1 March 2022. Retrieved 2 March 2022.
  133. ^ Pearson, S. Forbes. "Refrigerants Past, Present and Future" (PDF). R744. Archived from the original (PDF) on 13 July 2018. Retrieved 30 March 2021.
  134. ^ "The Coca-Cola Company Announces Adoption of HFC-Free Insulation in Refrigeration Units to Combat Global Warming". The Coca-Cola Company. 5 June 2006. Archived from the original on 1 November 2013. Retrieved 11 October 2007.
  135. ^ "Modine reinforces its CO2 research efforts". R744.com. 28 June 2007. Archived from the original on 10 February 2008.
  136. ^ TCE, the Chemical Engineer. Institution of Chemical Engineers. 1990. Archived from the original on 17 August 2021. Retrieved 2 June 2020.
  137. ^ a b "AVMA guidelines for the euthanasia of animals: 2020 Edition" (PDF). American Veterinary Medical Association. 2020. Archived (PDF) from the original on 1 February 2014. Retrieved 13 August 2021.
  138. ^ Harris D (September 1910). "The Pioneer in the Hygiene of Ventilation". The Lancet. 176 (4542): 906–908. doi:10.1016/S0140-6736(00)52420-9. Archived from the original on 17 March 2020. Retrieved 6 December 2019.
  139. ^ Almqvist E (2003). History of industrial gases. Springer. p. 93. ISBN 978-0-306-47277-0.
  140. ^ Priestley J, Hey W (1772). "Observations on Different Kinds of Air". Philosophical Transactions. 62: 147–264. doi:10.1098/rstl.1772.0021. S2CID 186210131. Archived from the original on 7 June 2010. Retrieved 11 October 2007.
  141. ^ Davy H (1823). "On the Application of Liquids Formed by the Condensation of Gases as Mechanical Agents". Philosophical Transactions. 113: 199–205. doi:10.1098/rstl.1823.0020. JSTOR 107649.
  142. ^ Thilorier AJ (1835). "Solidification de l'Acide carbonique". Comptes Rendus. 1: 194–196. Archived from the original on 2 September 2017. Retrieved 1 September 2017.
  143. ^ Thilorier AJ (1836). "Solidification of carbonic acid". The London and Edinburgh Philosophical Magazine. 8 (48): 446–447. doi:10.1080/14786443608648911. Archived from the original on 2 May 2016. Retrieved 15 November 2015.
  144. ^ Haldane, John (1894). "Notes of an Enquiry into the Nature and Physiological Action of Black-Damp, as Met with in Podmore Colliery, Staffordshire, and Lilleshall Colliery, Shropshire". Proceedings of the Royal Society of London. 57: 249–257. Bibcode:1894RSPS...57..249H. JSTOR 115391.