Carbon dioxide (
chemical formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
CO
2) is a
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
composed of two
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
atomThe atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s
covalently bondedA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
to a single
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atom. It is a
gasThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
at standard temperature and pressure and exists in
Earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
in this state. CO
2 is a
trace gasA trace gas is a gas which makes up less than 1% by volume of the Earth's atmosphere, and it includes all gases except nitrogen and oxygen . The most abundant trace gas at 0.934% is argon, which is being continually produced by radioactive decay of in the earth's rocks....
being only 0.038% of the atmosphere.
Carbon dioxide is used by plants during
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
to make sugars, which may either be consumed in
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
or used as the raw material to produce other organic compounds needed for plant growth and development. It is produced during
respirationIn animal physiology, respiration is the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
by plants, and by all animals, fungi and microorganisms that depend either directly or indirectly on plants for food. It is thus a major component of the
carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
. Carbon dioxide is generated as a by-product of the combustion of fossil fuels or the burning of vegetable matter, among other chemical processes. Small amounts of carbon dioxide are emitted from
volcano3. Conduit
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank| 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15...
es and other
geothermalGeothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
processes such as
hot springsHot Springs may refer to:* Hot Springs, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Plumas County, California* Hot Springs, Montana* Hot Springs, North Carolina...
and geysers and by the dissolution of carbonates in crustal rocks.
,
carbon dioxide in the Earth's atmosphereCarbon dioxide forms approximately 0.04% of the Earth's atmosphere. It is essential to photosynthesis in plants and other photoautotrophs, and is also a prominent greenhouse gas.-Concentration:...
is at a concentration of 387 ppm by
volumeThe volume of any solid, liquid, gas, plasma, theoretical object, or vacuum is how much three-dimensional space it occupies, often quantified numerically. One-dimensional figures and two-dimensional shapes are assigned zero volume in the three-dimensional space...
. Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the
Northern HemisphereThe Northern Hemisphere is the half of a planet that is north of the equator—the word hemisphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator...
. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay. Carbon dioxide is a
greenhouse gasGreenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
as it transmits
visible lightThe visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 380 to 750 nm...
but absorbs strongly in the
infraredInfrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves...
and near-infrared.
Carbon dioxide has no liquid state at pressures below 5.1
atmospheresThe standard atmosphere is an international reference pressure defined as 101,325 Pa and formerly used as unit of pressure . For practical purposes it has been replaced by the bar which is 100,000 Pa...
. At 1 atmosphere (near mean sea level pressure), the gas
depositsDeposition is a process in which gas transforms into solid . The reverse of deposition is sublimation.One example of deposition is the process by which, in sub-freezing air, water vapor changes directly to ice without first becoming a liquid...
directly to a solid at temperatures below −78 °C and the solid sublimes directly to a gas above −78 °C. In its solid state, carbon dioxide is commonly called
dry iceDry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide. It is commonly used as a versatile cooling agent.- Properties :...
.
CO
2 is an
acidic oxideAn acidic oxide is an oxide that either*reacts with water to form an acid; or*reacts with a base to form a salt.Examples include:...
: an aqueous solution turns
litmusLitmus is a water-soluble mixture of different dyes extracted from lichens, especially Roccella tinctoria. The mixture has CAS number 1393-92-6. It is often absorbed onto filter paper. The resulting piece of paper or solution with water becomes a pH indicator , used to test materials for acidity...
from blue to pink. It is the anhydride of
carbonic acidCarbonic acid has the formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates and carbonates. It is a weak acid...
, an acid which is unstable and is known to exist only in aqueous solution.
- + ⇌
CO
2 is toxic in higher concentrations: 1% (10,000 ppm) will make some people feel drowsy. Concentrations of 7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.
Chemical and physical properties
Carbon dioxide is colorless. At low concentrations, the gas is odorless. At higher concentrations it has a sharp, acidic odor. It will act as an asphyxiant and an irritant. When inhaled at concentrations much higher than usual atmospheric levels, it can produce a sour taste in the mouth and a stinging sensation in the nose and throat. These effects result from the gas dissolving in the mucous membranes and
salivaSaliva is the watery and usually frothy substance produced in the mouths of humans and most other animals. Saliva is produced in and secreted from the salivary glands...
, forming a weak solution of
carbonic acidCarbonic acid has the formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates and carbonates. It is a weak acid...
. This sensation can also occur during an attempt to stifle a burp after drinking a
carbonated beverageCarbonation occurs when carbon dioxide is dissolved in water or an aqueous solution. This process yields the "fizz" to carbonated water, sparkling mineral water, and soft drinks; the head to beer; and the cork pop and bubbles to champagne and sparkling wine.-Effervescence:Effervescence is the...
. Amounts above 5,000 ppm are considered very unhealthy, and those above about 50,000 ppm (equal to 5% by volume) are considered dangerous to animal life.
At
standard temperature and pressureIn physical sciences, standard conditions for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data...
, the density of carbon dioxide is around 1.98 kg/m
3, about 1.5 times that of
airThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
. The carbon dioxide molecule (O=C=O) contains two
double bondsA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
and has a linear shape. It has no electrical
dipoleIn physics, there are two kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some, usually small, distance. A permanent electric dipole is called an...
, and as it is fully
oxidizedRedox describes all chemical reactions in which atoms have their oxidation number changed....
, it is moderately
reactiveA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
and is non-flammable, but will support the combustion of metals such as
magnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole...
.
At -78.51°
CCelsius is a temperature scale that is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
or -109.3°
FFahrenheit is the temperature scale proposed in 1724 by, and named after, the physicist Daniel Gabriel Fahrenheit . Today, the scale has been replaced by the Celsius scale in most countries; it is still in use for non-scientific purposes in the United States and a few other nations, such as...
, carbon dioxide changes directly from a solid phase to a gaseous phase through sublimation, or from gaseous to solid through
depositionIn chemistry, deposition is the settling of particles or sediment from a solution, suspension and mixture or vapor onto a pre-existing surface...
. Solid carbon dioxide is normally called "
dry iceDry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide. It is commonly used as a versatile cooling agent.- Properties :...
", a generic trademark. It was first observed in 1825 by the French chemist
Charles ThilorierCharles Thilorier was a scientist who gave the earliest description of dry ice, the solid form of carbon dioxide. In 1834 he 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 ....
. Dry ice is commonly used as a cooling agent, and it is relatively inexpensive. A convenient property for this purpose is that solid carbon dioxide sublimes directly into the gas phase leaving no liquid. It can often be found in grocery stores and laboratories, and it is also used in the shipping industry. The largest non-cooling use for dry ice is
blast cleaningDry ice blasting is a form of abrasive blasting, where dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it....
.
Liquid carbon dioxide forms only at
pressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
s above 5.1 atm; the
triple pointIn thermodynamics, the triple point of a substance is the temperature and pressure at which three phases of that substance coexist in thermodynamic equilibrium...
of carbon dioxide is about 518
kPaKPA may refer to:* Kenya Ports Authority* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People's Army* The Kosovo Property Agency* Also refers to the Montagnard name meaning "straight"....
at -56.6 °C (See phase diagram, above). The
critical pointIn physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions at which a phase boundary ceases to exist...
is 7.38 MPa at 31.1 °C.
An alternative form of solid carbon dioxide, an amorphous glass-like form, is possible, although not at atmospheric pressure. This form of glass, called
carboniaAmorphous carbonia, also called a-carbonia or a-CO2, is an exotic amorphous solid form of carbon dioxide that is analogous to amorphous silica glass. It was first made in the laboratory in 2006 by subjecting dry ice to high pressures...
, was produced by
supercoolingSupercooling is the process of lowering the temperature of a liquid or a gas below its freezing point, without it becoming a solid.A liquid below its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form...
heated CO
2 at extreme pressure (40–48 GPa or about 400,000 atmospheres) in a diamond anvil. This discovery confirmed the theory that carbon dioxide could exist in a glass state similar to other members of its elemental family, like
siliconSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
(silica glass) and
germaniumGermanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. Germanium has five naturally occurring isotopes ranging in atomic mass number from 70 to 76...
. Unlike silica and germania glasses, however, carbonia glass is not stable at normal pressures and reverts back to gas when pressure is released.
History of human understanding
Carbon dioxide was one of the first gases to be described as a substance distinct from air. In the seventeenth century, the
FlemishThe Flemish people , the Flemings or the Flemish are the over six million people of Flanders, the northern region of the country Belgium — and the majority of all Belgians....
chemist
Jan Baptist van HelmontJan Baptist van Helmont was an early modern period Flemish chemist, physiologist, and physician. He worked during the years just after Paracelsus and iatrochemistry, and is sometimes considered to be "the founder of pneumatic chemistry"...
observed that when he burned
charcoalCharcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen...
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" or "wild spirit" (
spiritus sylvestre).
The properties of carbon dioxide were studied more thoroughly in the 1750s by the Scottish physician
Joseph BlackJoseph Black was a Scottish physician, physicist, and chemist, known for his discoveries of latent heat, specific heat, and carbon dioxide. He was a founder of thermochemistry who developed many pre-thermodynamics concepts, such as heat capacity, and was the mentor for James Watt...
. He found that
limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
(
calcium carbonateCalcium carbonate is a chemical compound with the chemical formula CaCO
3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural...
) could be heated or treated with
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
s to yield a gas he called "fixed air." He observed that the fixed air was denser than air and did not support either flame or animal life. Black also found that when bubbled through an aqueous solution of lime (
calcium hydroxideCalcium hydroxide, traditionally called slaked lime, hydrated lime, slack lime, or pickling lime, is a chemical compound with the chemical formula Ca2. It is a colourless crystal or white powder, and is obtained when calcium oxide is mixed, or "slaked" with water...
), it would
precipitatePrecipitation is the formation of a solid in a solution during a chemical reaction. When the reaction occurs, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate...
calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1772, English chemist
Joseph PriestleyJoseph Priestley was an 18th-century English theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works...
published a paper entitled
Impregnating Water with Fixed Air in which he described a process of dripping
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
(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.
Carbon dioxide was first liquefied (at elevated pressures) in 1823 by
Humphry DavySir Humphry Davy, 1st Baronet FRS MRIA was a British chemist and inventor. He is probably best remembered today for his discoveries of several alkali and alkaline earth metals, as well as contributions to the discoveries of the elemental nature of chlorine and iodine. He invented the Davy lamp,...
and
Michael FaradayMichael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
. The earliest description of solid carbon dioxide was given by
Charles ThilorierCharles Thilorier was a scientist who gave the earliest description of dry ice, the solid form of carbon dioxide. In 1834 he 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 ....
, who in 1834 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO
2.
Isolation and production
Carbon dioxide may be obtained from air
distillationDistillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
. However, this yields only very small quantities of CO
2. A large variety of chemical reactions yield carbon dioxide, such as the reaction between most acids and most metal carbonates. For example, the reaction between
hydrochloric acidHydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong mineral acid and has major industrial uses. It is found naturally in gastric acid....
and calcium carbonate (limestone or chalk) is depicted below:
-
The then decomposes to water and CO
2. Such reactions are accompanied by foaming or bubbling, or both. In industry such reactions are widespread because they can be used to neutralize waste acid streams.
The production of quicklime (CaO) a chemical that has widespread use, from limestone by heating at about 850 °C also produces CO
2:
-
The
combustionCombustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering.Direct combustion by atmospheric oxygen is a reaction...
of all carbon containing fuels, such as
methaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean...
(
natural gasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills...
), petroleum distillates (
gasolineGasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines...
, diesel,
keroseneKerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
,
propanePropane is a three-carbon alkane, normally a gas, but compressible to a transportable liquid. It is derived from other petroleum products during oil or natural gas processing...
), but also of coal and wood, will yield carbon dioxide and, in most cases, water. As an example the chemical reaction between methane and oxygen is given below.
-
IronIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
is reduced from its oxides with
cokeCoke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous.-Production:Coke is usually produced from coal; the process is called coking....
in a
blast furnaceA blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions take place...
, producing
pig ironPig iron is the intermediate product of smelting iron ore with coke, usually with limestone as a flux. Pig iron has a very high carbon content, typically 3.5–4.5%, which makes it very brittle and not useful directly as a material except for limited applications.The traditional shape of the molds...
and carbon dioxide:
-
YeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
metabolizes
sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
to produce carbon dioxide and
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
, also known as alcohol, in the production of wines, beers and other spirits, but also in the production of bioethanol:
- →
All
aerobicCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
organisms produce when they oxidize
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s,
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail , which is either saturated or unsaturated...
s, and proteins in the mitochondria of cells. The large number of reactions involved are exceedingly complex and not described easily. Refer to (
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
,
anaerobic respirationIn biology, anaerobic respiration is a way for an organism to produce usable energy carriers without the involvement of oxygen; it is respiration without oxygen. Respiration is a redox reaction that processes energy in a form usable by an organism, chiefly the process of producing ATP, the...
and
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
). Photoautotrophs (i.e. plants,
cyanobacteriaCyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria = blue)...
) use another
modus operandi: Plants absorb from the air, and, together with water, react it to form carbohydrates:
- nCO2 + nO → n + n
Carbon dioxide is soluble in water, in which it spontaneously interconverts between CO
2 and (
carbonic acidCarbonic acid has the formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates and carbonates. It is a weak acid...
). The relative concentrations of , and the deprotonated forms (
bicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
) and (
carbonateIn chemistry, a carbonate is a salt or ester of carbonic acid, characterized by the presence of the carbonate ion, or a carbonate functional group O=C2....
) depend on the
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
. In neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater, while in very alkaline water (pH > 10.4) the predominant (>50%) form is carbonate. The bicarbonate and carbonate forms are very soluble, such that air-equilibrated ocean water (mildly alkaline with typical pH = 8.2 – 8.5) contains about 120 mg of bicarbonate per liter.
Industrial production
Carbon dioxide is produced mainly from six processes:
- From combustion of fossil fuel
Fossil fuels or mineral fuels are fuels formed by natural resources such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s and woodWood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of trees . In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves...
;
- As a by-product of hydrogen production plants, where methane is converted to CO2;
- As a by-product of fermentation
Fermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. This is in contrast to cellular respiration, where electrons are donated to an exogenous electron acceptor,...
of sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
in the brewingBrewing is the production of alcoholic beverages and alcohol fuel through fermentation. The term is used for the production of beer, although the word "brewing" is also used to describe the fermentation process used to create wine and mead. It can also refer to the process of producing sake and soy...
of beerBeer is the world's oldest and most widely consumed alcoholic beverage and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from cereal grains—most commonly malted barley, although wheat, maize , and rice are widely...
, whiskyWhisky or whiskey is a type of alcoholic beverage distilled from fermented grain mash. Different grains are used for different varieties, including barley, malted barley, rye, malted rye, wheat, and maize...
and other alcoholIn chemistry, an alcohol is any organic compound in which a hydroxyl group is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is C
nH
2n+1OH...
ic beverages;
- From thermal decomposition of limestone, , in the manufacture of lime
Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...
, ;
- As a by-product of sodium phosphate manufacture;
- Directly from natural carbon dioxide springs
A spring is any natural occurrence where water flows on to the surface of the earth from below the surface, and is thus where the aquifer surface meets the ground surface.- Formation :...
, where it is produced by the action of acidified water on limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
or dolomiteDolomite is the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate CaMg
2 found in crystals....
.
Uses
Carbon dioxide is used by the food industry, the oil industry, and the chemical industry. It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60
barThe bar is a unit of pressure equal to 100 kilopascals, and rougly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the decibar , centibar , and millibar...
(870 psi, 59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Aluminum capsules are also sold as supplies of compressed gas for
airgunsAn air gun is a rifle, pistol, or shotgun which fires projectiles by means of compressed air or other gas, in contrast to a firearm which burns a propellant. Most air guns use metallic projectiles as ammunition...
,
paintballPaintball is a sport, in which players compete, in teams or individually, to eliminate opponents by hitting them with pellets containing paint from a special gun called a paintball marker. Depending on the venue, games are played on either indoor or outdoor fields of varying size...
markers, for inflating bicycle tires, and for making
seltzerCarbonated water, also known as sparkling water, fizzy water, seltzer, and water with gas, , is plain water into which carbon dioxide gas has been dissolved, and is the major and defining component of most soft drinks. The process of dissolving carbon dioxide gas is called carbonation...
. Rapid vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can also be used to kill pests, such as the Common Clothes Moth.
Drinks
Carbon dioxide is used to produce
carbonatedCarbonation occurs when carbon dioxide is dissolved in water or an aqueous solution. This process yields the "fizz" to carbonated water, sparkling mineral water, and soft drinks; the head to beer; and the cork pop and bubbles to champagne and sparkling wine.-Effervescence:Effervescence is the...
soft drinkA soft drink is a drink that does not contain alcohol . Soft drinks are often carbonated and commonly consumed while cold. The most common soft drinks are colas, flavored water, sparkling water, iced tea, sweet tea, lemonade, squash and fruit punch....
s and
soda waterSoda water, also known as seltzer in the US and Canada, is water which is carbonated and thus made effervescent by the addition of carbon dioxide gas under pressure. Soda water is sometimes used to dilute strong alcoholic drinks, e.g. cocktails such as a whisky and soda, or Campari and soda. It can...
. Traditionally, the carbonation in beer and sparkling wine came about through natural fermentation, but many manufacturers carbonate these drinks artificially. In the case of bottled and kegged beer, artificial carbonation is now the most common method used. With the exception of British Real Ale, draught (draft) beer is usually transferred from kegs in a cold room or cellar to dispensing taps on the bar using pressurised carbon dioxide, often mixed with nitrogen.
Foods
A candy called
Pop RocksPop Rocks is a carbonated candy with ingredients including sugar, lactose , corn syrup, and flavoring.-Background and history:The idea of the product was patented by...
is pressurized with carbon dioxide gas at about 40 bar (600 psi). When placed in the mouth, it dissolves (just like other hard candy) and releases the gas bubbles with an audible pop.
Leavening agentA leavening agent is any one of a number of substances used in doughs and batters that cause a foaming action which lightens and softens the finished product...
s produce carbon dioxide to cause dough to rise.
Baker's yeastBaker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and related products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol. The use of potatoes, water from potato boiling, eggs, or sugar in a bread...
produces carbon dioxide by fermentation of sugars within the dough, while chemical leaveners such as
baking powderBaking powder is a dry chemical leavening agent used to increase the volume and lighten the texture of baked goods such as muffins, cakes, scones and North American biscuits. Baking powder works by releasing carbon dioxide gas into a batter or dough through an acid-base reaction, causing bubbles in...
and baking soda release carbon dioxide when heated or if exposed to
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
s.
Pneumatic systems
Carbon dioxide is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in portable pressure tools and
combat robotsRobot Combat is a hobby/sport in which two custom-built machines use varied methods of destroying or disabling the other. As of today, in most cases these machines are remote-controlled vehicles rather than autonomous robots, although there are exceptions, particularly in the field of...
.
Fire extinguisher
Carbon dioxide extinguishes flames, and some fire extinguishers, especially those designed for electrical fires, contain liquid carbon dioxide under pressure. Carbon dioxide has also been widely used as an extinguishing agent in fixed fire protection systems for total flooding of a protected space, (National Fire Protection Association Code 12). International Maritime Organisation standards also recognise carbon dioxide systems for fire protection of ship holds and engine rooms. Carbon dioxide based fire protection systems have been linked to several deaths. A review of CO
2 systems (Carbon Dioxide as a Fire Suppressant: Examining the Risks, US EPA) identified 51 incidents between 1975 and the date of the report, causing 72 deaths and 145 injuries.
Welding
Carbon dioxide also finds use as an atmosphere for
weldingWelding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
, 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
brittleA material is brittle if it is liable to fracture when subjected to stress. That is, it has little tendency to deform before fracture...
than those made in more inert atmospheres, and that such weld joints deteriorate over time because of the formation of carbonic acid. It is used as a welding gas primarily because it is much less expensive than more inert gases such as
argonArgon is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is present in the Earth's atmosphere at 0.94%. Terrestrially, it is the most abundant and most frequently used of the noble gases...
or
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
.
Caffeine removal
Liquid carbon dioxide is a good
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water. Most other commonly-used solvents are organic chemicals. These are called organic solvents...
for many
lipophilicLipophilicity, , refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic — the axiom that like dissolves like generally holds true...
organic compoundsOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
, and is used to remove
caffeineCaffeine is a bitter, white crystalline xanthine alkaloid that is a psychoactive stimulant drug. Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819. He coined the term kaffein, a chemical compound in coffee, which in English became caffeine...
from
coffeeCoffee is a brewed beverage prepared from roasted seeds, commonly called coffee beans, of the coffee plant. They are seeds of "coffee cherries" that grow on trees in over 70 countries. It has been said that green coffee is the second most traded commodity in the world behind crude oil. Due to its...
. First, the green coffee beans are soaked in water. The beans are placed in the top of a column seventy feet (21 m) high. Then
supercriticalA supercritical fluid is any substance at a temperature and pressure above its critical point. It can diffuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density,...
carbon dioxide in fluid form at about 93 °C enters at the bottom of the column. The caffeine
diffusesMolecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material...
out of the beans and into the carbon dioxide.
Pharmaceutical and other chemical processing
Carbon dioxide has begun to attract attention in the pharmaceutical and other chemical processing industries as a less toxic alternative to more traditional solvents such as
organochlorideAn organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...
s. It's used by some
dry cleanersDry cleaning is any cleaning process for clothing and textiles using an organic solvent rather than water. The solvent used is typically tetrachloroethylene , abbreviated "perc" in the industry and "dry-cleaning fluid" by the public. Dry cleaning is necessary for cleaning items that would...
for this reason. (See
green chemistryGreen chemistry, also called sustainable chemistry, is a chemical philosophy encouraging the design of products and processes that reduce or eliminate the use and generation of hazardous substances. Whereas environmental chemistry is the chemistry of the natural environment, and of pollutant...
.)
In the chemical industry, carbon dioxide is used for the production of
ureaUrea or carbamide is an organic compound with the chemical formula
2CO. The molecule has two amine residues joined by a carbonyl functional group....
,
carbonateIn chemistry, a carbonate is a salt or ester of carbonic acid, characterized by the presence of the carbonate ion, or a carbonate functional group O=C2....
s and
bicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
s, and
sodium salicylateSodium salicylate is a sodium salt of salicylic acid. It can be prepared from sodium phenolate and carbon dioxide under higher temperature and pressure...
.
Agricultural and biological applications
Plants require carbon dioxide to conduct
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
. Greenhouses may (and of large size - must) enrich their atmospheres with additional CO
2 to sustain plant life and growth. A
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
-related drop (by a factor less than two) in carbon dioxide concentration in a greenhouse compartment would kill green plants, or, at least, completely stop their growth. At very high concentrations (a factor of 100 or more higher than its atmospheric concentration), 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
whitefliesThe whiteflies, comprising only the family Aleyrodidae, are small hemipterans. More than 1550 species have been described. Whiteflies typically feed on the underside of plant leaves.-Agricultural threat:...
and
spider miteSpider mites are members of the Acari family Tetranychidae, which includes about 1600 species. They generally live on the under sides of leaves of plants, where they may spin protective silk webs, and they can cause damage by puncturing the plant cells to feed...
s in a greenhouse.
It has been proposed that carbon dioxide from power generation be bubbled into ponds to grow algae that could then be converted into
biodieselBiodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl esters. Biodiesel is typically made by chemically reacting lipids with an alcohol....
fuel. Carbon dioxide is already increasingly used in greenhouses as the main carbon source for
SpirulinaSpirulina may refer to:* Spirulina , a health-food supplement* Spirulina , a cyanobacterium group* Spirulina , a group of cephalopods including Spirula spirula...
algae.
In medicine, up to 5% carbon dioxide (130 times the atmospheric concentration) is added to pure
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
for stimulation of breathing after
apneaApnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...
and to stabilize the balance in blood.
Polymers and plastics
Carbon dioxide can also be combined with
limoneneLimonene is a hydrocarbon, classified as a cyclic terpene. It is a colourless liquid at room temperatures with an extremely strong smell of oranges. It takes its name from the lemon, as the rind of the lemon, like other citrus fruits, contains considerable amounts of this chemical compound, which...
oxide from orange peels or other epoxides to create polymers and plastics.
Oil recovery
Carbon dioxide is used in
enhanced oil recoveryEnhanced Oil Recovery is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field...
where it is injected into or adjacent to producing oil wells, usually under
supercriticalA supercritical fluid is any substance at a temperature and pressure above its critical point. It can diffuse through solids like a gas, and dissolve materials like a liquid. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density,...
conditions. It acts as both a pressurizing agent and, when dissolved into the underground crude oil, significantly reduces its viscosity, enabling the oil to flow more rapidly through the earth to the removal well. In mature oil fields, extensive pipe networks are used to carry the carbon dioxide to the injection points.
As refrigerants
Liquid and solid carbon dioxide are important
refrigerantA refrigerant is a compound used in a heat cycle that reversibly undergoes a phase change from a gas to a liquid. Traditionally, fluorocarbons, especially chlorofluorocarbons are the traditional refrigerants, but they are being phased out because of their ozone depletion effects...
s, especially in the food industry, where they are employed during the transportation and storage of ice cream and other frozen foods. Solid carbon dioxide is called "dry ice" and is used for small shipments where refrigeration equipment is not practical.
Liquid carbon dioxide (industry nomenclature R744 or R-744) was used as a refrigerant prior to the discovery of
R-12Dichlorodifluoromethane , usually sold under the brand name Freon-12, is a chlorofluorocarbon halomethane , used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in the United States along with many other countries in 1994 due to...
and is likely to enjoy a renaissance due to environmental concerns. Its physical properties are highly favorable for cooling, refrigeration, and heating purposes, having a high volumetric cooling capacity. Due to its operation at pressures of up to 130 bars, CO
2 systems require highly resistant components that have already been developed for mass production in many sectors. In automobile air conditioning, in more than 90% of all driving conditions for latitudes higher than 50°, R744 operates more efficiently than systems using R-134a. Its environmental advantages (
GWPGlobal warming potential is a measure of how much a given mass of greenhouse gas is estimated to contribute to global warming. It is a relative scale which compares the gas in question to that of the same mass of carbon dioxide...
of 1, non-ozone depleting, non-toxic, non-flammable) could make it the future working fluid to replace current HFCs in cars, supermarkets, hot water heat pumps, among others. Some applications: Coca-Cola has fielded CO
2-based beverage coolers and the
U.S. ArmyThe United States Army is the branch of the United States Military responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military and is one of seven uniformed services...
is interested in CO
2 refrigeration and heating technology.
By the end of 2007, the global automobile industry is expected to decide on the next-generation refrigerant in car air conditioning. CO
2 is one discussed option.(see
The Cool WarThe Cool War refers to the debate about the next-generation refrigerant in car air conditioning worldwide, with an ongoing dispute between the Alliance for CO2 Solutions supporting the uptake of sustainable CO2 Technology in passenger cars, and chemical giants developing new...
)
Coal bed methane recovery
In
enhanced coal bed methane recoveryEnhanced coal bed methane recovery is a method of producing additional coalbed methane from a source rock, similar to enhanced oil recovery applied to oil fields...
, carbon dioxide is pumped into the coal seam to displace methane.
Wine making
Carbon dioxide in the form of
dry iceDry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide. It is commonly used as a versatile cooling agent.- Properties :...
is often used in the wine making process to cool down bunches of
grapeA grape is the non-climacteric fruit, botanically a true berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, and grape seed oil...
s quickly after picking to help prevent spontaneous
fermentationThe process of fermentation in wine is the catalyst function that turns grape juice into an alcoholic beverage. During fermentation yeast interact with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide...
by wild
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
s. The main advantage of using dry ice over regular water ice is that it cools the grapes without adding any additional water that may decrease the
sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
concentration in the grape must, and therefore also decrease the
alcoholIn chemistry, an alcohol is any organic compound in which a hydroxyl group is bound to a carbon atom of an alkyl or substituted alkyl group. An important group of acohols is formed by the simple acyclic alcohols, the general formula for which is C
nH
2n+1OH...
concentration in the finished wine.
Dry ice is also used during the cold soak phase of the wine making process to keep grapes cool. The carbon dioxide gas that results from the sublimation of the dry ice tends to settle to the bottom of tanks because it is heavier than regular air. The settled carbon dioxide gas creates an hypoxic environment which helps to prevent bacteria from growing on the grapes until it is time to start the fermentation with the desired strain of yeast.
Carbon dioxide is also used to create a hypoxic environment for
carbonic macerationCarbonic maceration is a winemaking technique, often associated with the French wine region of Beaujolais, in which whole grapes are fermented in a carbon dioxide rich environment prior to crushing. Conventional alcoholic fermentation involves crushing the grapes to free the juice and pulp from the...
, the process used to produce
BeaujolaisBeaujolais is a French Appellation d'Origine Contrôlée wine generally made of the Gamay grape which has a thin skin and few tannins. Like most AOC wines they are not labeled varietally. Whites from the region, which make up only 1% of its production, are made mostly with Chardonnay grapes though...
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 gasses such as
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
or
argonArgon is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is present in the Earth's atmosphere at 0.94%. Terrestrially, it is the most abundant and most frequently used of the noble gases...
are preferred for this process by professional wine makers.
pH control
Carbon dioxide can be used as a mean of controlling the
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
of swimming pools, by continuously adding gas to the water, thus keeping the pH level from rising. Among the advantages of this is the avoidance of handling (more hazardous) acids.
In the Earth's atmosphere
Carbon dioxide in
earth's atmosphereThe Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
is considered a
trace gasA trace gas is a gas which makes up less than 1% by volume of the Earth's atmosphere, and it includes all gases except nitrogen and oxygen . The most abundant trace gas at 0.934% is argon, which is being continually produced by radioactive decay of in the earth's rocks....
currently occurring at an average concentration of about 383 parts per million by volume or 582 parts per million by mass. The total mass of atmospheric carbon dioxide is 3.0×10
15 kg (3,000 gigatonnes). Its concentration varies seasonally (see graph at right) and also considerably on a regional basis, especially
near the groundThe planetary boundary layer , also known as the atmospheric boundary layer , is the lowest part of the atmosphere and its behavior is directly influenced by its contact with a planetary surface. On Earth it usually responds to changes in surface forcing in an hour or less...
. In urban areas concentrations are generally higher and indoors they can reach 10 times background levels. Carbon dioxide is a
greenhouse gasGreenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
.
Five hundred million years ago carbon dioxide was 20 times more prevalent than today, decreasing to 4-5 times during the
JurassicThe Jurassic is a geologic period and system that extends from about Ma to Ma, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Reptiles". The start of the period is marked by...
period and then slowly declining with
a particularly swift reductionThe Azolla event occurred in the middle Eocene period, around , when blooms of the freshwater fern Azolla occurred in the Arctic Ocean. As they sank to the stagnant sea floor, they were incorporated into the sediment; the resulting draw down of carbon dioxide has been speculated to have helped...
occurring 49 million years ago. Human activities such as the combustion of fossil fuels and
deforestationDeforestation is the clearance of naturally occurring forests by the processes of logging and/or burning of trees in a forested area. There are several reasons deforestation occurs: trees or derived charcoal can be sold as a commodity and used by humans, while cleared land is used as pasture,...
have caused the atmospheric concentration of carbon dioxide to increase by about 35% since the beginning of the
age of industrializationThe Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, and transport had a profound effect on the socioeconomic and cultural conditions in the United Kingdom. The changes subsequently spread throughout Europe, North...
.
Up to 40% of the gas emitted by some
volcano3. Conduit
4. Base
5. Sill
6. Dike
7. Layers of ash emitted by the volcano
8. Flank| 9. Layers of lava emitted by the volcano
10. Throat
11. Parasitic cone
12. Lava flow
13. Vent
14. Crater
15...
es during
subaerial eruptionA subaerial eruption is a volcanic eruption that has occurred on the surface. They generally produce pyroclastic flows, lava fountains and lava flows, which are commonly classified in different subearial eruption types, including Plinian, Peléan and Hawaiian eruptions. Subaerial eruptions contrast...
s is carbon dioxide. It is estimated that volcanoes release about 130-230 million tonnes (145-255 million tons) of CO
2 into the atmosphere each year. This is about a factor of 1000 smaller than the sum of the other natural sources and about factor of about 100 smaller than the sources from human activity. Carbon dioxide is also produced by hot springs such as those at the Bossoleto site near
Rapolano TermeRapolano Terme is a comune in the Province of Siena in the Italian region Tuscany, located about 60 km southeast of Florence and about 20 km east of Siena in the area known as the Crete Senesi....
in
TuscanyTuscany is a region in North-Central Italy. It has an area of and a population of about 3.6 million inhabitants. The regional capital is Florence.Tuscany is known for its landscapes and its artistic legacy...
,
ItalyItaly , officially the Italian Republic , is a country located on the Italian Peninsula in Southern Europe and on the two largest islands in the Mediterranean Sea, Sicily and Sardinia. Italy shares its northern, Alpine boundary with France, Switzerland, Austria and Slovenia...
. Here, in a bowl-shaped depression of about 100 m diameter, local concentrations of CO
2 rise to above 75% overnight, sufficient to kill insects and small animals, but warm rapidly when sunlit and disperse by convection during the day. Locally high concentrations of CO
2, produced by disturbance of deep lake water saturated with CO
2 are thought to have caused 37 fatalities at
Lake MonounLake Monoun is a lake in West Province, Cameroon, that lies in the Oku Volcanic Field . On August 15, 1984, the lake exploded in a limnic eruption, which resulted in the release of a large amount of carbon dioxide that killed 37 people. At first, the cause of the deaths was a mystery, and...
,
CameroonThe Republic of Cameroon is a unitary republic of central and western Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the Bight of...
in 1984 and 1700 casualties at
Lake NyosLake Nyos is a crater lake in the Northwest Province of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...
, Cameroon in 1986. Emissions of CO
2 by human activities are currently more than 130 times greater than the quantity emitted by volcanoes, amounting to about 27 billion tonnes per year.
In the oceans
There is about 50 times as much carbon dissolved in the oceans in the form of CO
2 and carbonic acid,
bicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
and
carbonateIn chemistry, a carbonate is a salt or ester of carbonic acid, characterized by the presence of the carbonate ion, or a carbonate functional group O=C2....
ions as exists in the atmosphere. The oceans act as an enormous carbon sink, and have taken up about a third of CO
2 emitted by human activity. Gas solubility decreases as the temperature of water increases and therefore the rate of uptake from the atmosphere decreases as ocean temperatures rise.
Most of the CO
2 taken up by the ocean forms carbonic acid in equilibrium with bicarbonate and carbonate ions. Some is consumed in photosynthesis by organisms in the water, and a small proportion of that sinks and leaves the carbon cycle. Increased CO
2 in the atmosphere has led to decreasing
alkalinityAlkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity of a solution and ANC is often incorrectly used to refer to alkalinity.The alkalinity is...
of seawater and there is some concern that this may adversely affect organisms living in the water. In particular, with decreasing alkalinity, the availability of carbonates for forming shells decreases.
Biological role
Carbon dioxide is an end product in organisms that obtain energy from breaking down sugars, fats and
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
s with
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
as part of their
metabolismMetabolism is the set of chemical reactions that occur in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter,...
, in a process known as
cellular respirationCellular respiration is one of the key ways a cell gains useful energy. It is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products...
. This includes all plants, animals, many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood from the body's tissues to the lungs where it is exhaled. In plants using photosynthesis, carbon dioxide is absorbed from the atmosphere.
Role in photosynthesis
Plants remove carbon dioxide from the atmosphere by
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
, also called
carbon assimilationCarbon fixation refers to any process through which gaseous carbon dioxide is converted into a solid compound. It mostly refers to the processes found in autotrophs , usually driven by photosynthesis, whereby carbon dioxide is changed into sugars...
, which uses light energy to produce organic compounds (
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
,
lipidLipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others...
s, and various
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s) by combining carbon dioxide and water. Free oxygen is released as gas from the decomposition of water molecules, while the hydrogen is split into its protons and electrons and used to generate chemical energy via
photophosphorylationThe production of ATP using the energy of sunlight is called photophosphorylation. Only two sources of energy are available to living organisms: sunlight and oxidation-reduction reactions...
. This energy is required for the fixation of carbon dioxide in the
Calvin cycleThe Calvin cycle or Calvin-Benson-Bassham cycle is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms. It was discovered by Melvin Calvin, James Bassham and Andrew Benson at the University of California, Berkeley by using the radioactive...
to make 3-phosphoglycerate that is used in metabolism, to construct sugars that can be used as an energy source within the plant through respiration and as the raw material for the construction of more complex organic molecules, such as polysaccharides,
nucleic acidA nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid and ribonucleic acid . Nucleic acids are universal in living things, as...
s and proteins during growth.
Plants can grow up to 50 percent faster in concentrations of 1,000 ppm CO
2 when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients. Some people (for example
David BellamyDavid J. Bellamy OBE is a British botanist, author, broadcaster, and environmental campaigner.-Background:Bellamy was born in London, England. He was brought up as a strict Baptist...
) believe that as the concentration of CO
2 rises in the atmosphere that it will lead to faster plant growth and therefore increase food production. Such views are too simplistic; studies have shown that increased CO
2 leads to fewer stomata developing on plants which leads to reduced water usage. Studies using
FACEFree-Air Carbon dioxide Enrichment is a method used by ecologists and plant biologists that raises the concentration of in a specified area and allows the response of plant growth to be measured...
have shown that increases in CO
2 lead to decreased concentration of micronutrients in crop plants. This may have knock-on effects on other parts of
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
s as herbivores will need to eat more food to gain the same amount of protein.
Plants also emit CO
2 during respiration, and so the majority of plants and algae, which use C3 photosynthesis, are only net absorbers during the day. Though a growing forest will absorb many tons of CO
2 each year, the World Bank writes that a mature forest will produce as much CO
2 from respiration and decomposition of dead specimens (e.g. fallen branches) as is used in
biosynthesisBiosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
in growing plants. However six experts in biochemistry, biogeology, forestry and related areas writing in the science journal Nature that "Our results demonstrate that old-growth forests can continue to accumulate carbon, contrary to the long-standing view that they are carbon neutral." Mature forests are valuable carbon sinks, helping maintain balance in the Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO
2 in the upper ocean and thereby promotes the absorption of CO
2 from the atmosphere.
Toxicity
Carbon dioxide content in fresh air (averaged between sea-level and 10 hPa level, i.e. about 30 km altitude) varies between 0.036% (360 ppm) and 0.039% (390 ppm), depending on the location.
Prolonged exposure to moderate concentrations can cause acidosis and adverse effects on calcium phosphorus metabolism resulting in increased calcium deposits in soft tissue. Carbon dioxide is toxic to the heart and causes diminished contractile force.
Toxicity and its effects increase with the concentration of CO
2, here given in
volume percentVolume percent is a common expression of a solution's concentration. It is defined as:Volume percent is usually used when the solution is made by mixing two fluids, such as liquids or gases. However, percentages are only additive for ideal gases....
of CO
2 in the air:
- 1%, as can occur in a crowded auditorium with poor ventilation, can cause drowsiness with prolonged exposure.
- At 2% it is mildly narcotic and causes increased blood pressure and pulse rate, and causes reduced hearing.
- At about 5% it causes stimulation of the respiratory centre, dizziness, confusion and difficulty in breathing accompanied by headache and shortness of breath.
- At about 8% it causes headache, sweating, dim vision, tremor and loss of consciousness after exposure for between five and ten minutes.
A natural disaster linked to CO
2 intoxication occurred during the
limnic eruptionA limnic eruption, also referred to as a lake overturn, is a rare type of natural disaster in which carbon dioxide suddenly erupts from deep lake water, suffocating wildlife, livestock and humans. Such an eruption may also cause tsunamis in the lake as the rising CO2 displaces water...
s in the CO
2-rich lakes of
MonounLake Monoun is a lake in West Province, Cameroon, that lies in the Oku Volcanic Field . On August 15, 1984, the lake exploded in a limnic eruption, which resulted in the release of a large amount of carbon dioxide that killed 37 people. At first, the cause of the deaths was a mystery, and...
and
NyosLake Nyos is a crater lake in the Northwest Province of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...
in the Okun range of North-West
CameroonThe Republic of Cameroon is a unitary republic of central and western Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the Bight of...
: the gas was brutally expelled from the mountain lakes and leaked into the surrounding valleys, killing most animal forms. During the Lake Nyos tragedy of 1988, 1700 villagers and 3500 livestock died.
Due to the health risks associated with carbon dioxide exposure, the U.S. Occupational Safety and Health Administration says that average exposure for healthy adults during an eight-hour work day should not exceed 5,000 ppm (0.5%). The maximum safe level for infants, children, the elderly and individuals with cardio-pulmonary health issues is significantly less. For short-term (under ten minutes) exposure, the U.S. National Institute for Occupational Safety and Health (NIOSH) and American Conference of Government Industrial Hygienists (ACGIH) limit is 30,000 ppm (3%). NIOSH also states that carbon dioxide concentrations exceeding 4% are immediately dangerous to life and health.
Adaptation to increased levels of CO
2 occurs in humans. Continuous inhalation of CO
2 can be tolerated at three percent inspired concentrations for at least one month and four percent inspired concentrations for over a week. It was suggested that 2.0 percent inspired concentrations could be used for closed air spaces (e.g. a
submarineA submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has only limited underwater capability...
) since the adaptation is physiological and reversible. Decrement in performance or in normal physical activity does not happen at this level.
These figures are valid for pure carbon dioxide. In indoor spaces occupied by people the carbon dioxide concentration will reach higher levels than in pure outdoor air. Concentrations higher than 1,000 ppm will cause discomfort in more than 20% of occupants, and the discomfort will increase with increasing CO
2 concentration. The discomfort will be caused by various gases coming from human respiration and perspiration, and not by CO
2 itself. At 2,000 ppm the majority of occupants will feel a significant degree of discomfort, and many will develop nausea and headaches. The CO
2 concentration between 300 and 2,500 ppm is used as an indicator of indoor air quality.
Acute carbon dioxide toxicity is sometimes known by the names given to it by miners:
blackdampBlackdamp is a mixture of unbreathable gases formed when oxygen is removed from an enclosed atmosphere and largely replaced by nitrogen, argon, carbon dioxide and water vapour...
(also called
choke damp or
stythe). Miners would try to alert themselves to dangerous levels of carbon dioxide in a mine shaft by bringing a caged canary with them as they worked. The canary would inevitably die before CO
2 reached levels toxic to people.
Carbon dioxide ppm levels (CDPL) are a surrogate for measuring indoor pollutants that may cause occupants to grow drowsy, get headaches, or function at lower activity levels. To eliminate most
indoor air qualityIndoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants....
complaints, total indoor CDPL must be reduced to below 600. NIOSH considers that indoor air concentrations that exceed 1,000 are a marker suggesting inadequate ventilation. ASHRAE recommends they not exceed 1,000 inside a space.
Human physiology
CO
2 is carried in blood in three different ways. (The exact percentages vary depending whether it is arterial or venous blood).
- Most of it (about 70% – 80%) is converted to bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
ions by the enzyme carbonic anhydraseThe carbonic anhydrases form a family of enzymes that catalyze the rapid conversion of carbon dioxide to bicarbonate and protons, a reaction that occurs rather slowly in the absence of a catalyst...
in the red blood cells, by the reaction CO2 + H2O → H2CO3 → H+ + .
- 5% – 10% is dissolved in the plasma
Blood plasma is the yellow liquid component of blood, in which the blood cells in whole blood would normally be suspended. It makes up about 55% of the total blood volume. It is mostly water and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide...
- 5% – 10% is bound to hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
as carbaminoCarbamino refers to a compound composed by the addition of carbon dioxide with a free amino group in an amino acid or a protein, such as hemoglobin forming carbaminohemoglobin....
compounds
HemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of vertebrates, and the tissues of some invertebrates....
, the main oxygen-carrying molecule in
red blood cellRed blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen to the body tissues via the blood. They take up oxygen in the lungs or gills and release it while squeezing through the body's capillaries. The cells are filled with hemoglobin, a...
s, carries both oxygen and carbon dioxide. However, the CO
2 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
allostericIn biochemistry, allosteric regulation is the regulation of an enzyme or other protein by binding an effector molecule at the protein's allosteric site . Effectors that enhance the protein's activity are referred to as allosteric activators, whereas those that decrease the protein's activity are...
effects on the hemoglobin molecule, the binding of CO
2 decreases the amount of oxygen that is bound for a given partial pressure of oxygen. The decreased binding to carbon dioxide in the blood due to increased oxygen levels is known as the
Haldane EffectThe Haldane effect is a property of hemoglobin first described by the Scottish physician John Scott Haldane. Deoxygenation of the blood increases its ability to carry carbon dioxide; this property is the Haldane effect. Conversely, oxygenated blood has a reduced capacity for carbon...
, and is important in the transport of carbon dioxide from the tissues to the lungs. Conversely, a rise in the partial pressure of CO
2 or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the
Bohr EffectBohr effect is a property of hemoglobin first described in 1904 by the Danish physiologist Christian Bohr , which states that at lower pH , hemoglobin will bind to oxygen with less affinity...
.
Carbon dioxide is one of the mediators of local
autoregulationAutoregulation is a process within many biological systems, resulting from some internal adaptive mechanism that works to adjust the systems response to stimuli. While most systems of the body show some degree of autoregulation, it is most clearly observed in the kidney, the heart, and the brain...
of blood supply. If its levels are high, the capillaries expand to allow a greater blood flow to that tissue.
Bicarbonate ions are crucial for regulating blood pH. A person's breathing rate influences the level of CO
2 in their blood. Breathing that is too slow or shallow causes
respiratory acidosisRespiratory acidosis is a medical condition in which decreased respiration causes increased blood carbon dioxide and decreased pH ....
, while breathing that is too rapid leads to
hyperventilationIn medicine, hyperventilation is the state of breathing faster and/or deeper than necessary, bringing about lightheadedness and other undesirable symptoms often associated with panic attacks...
, which can cause
respiratory alkalosisAlkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally alkalosis is said to occur when pH of the blood exceeds 7.45...
.
Although the body requires oxygen for metabolism, low oxygen levels 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 hungerAir hunger is the sensation of the urge to breathe. It is usually caused by the detection of high levels of carbon dioxide in the blood by sensors in the carotid sinus and is one of the body's homeostatic mechanisms to ensure proper oxygenation. Natural chemicals in the blood such as epinephrine ...
. 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 going unconscious.
Typically the gas we
exhaleBreathing is the process that takes oxygen in and carbon dioxide out of the body. Aerobic organisms require oxygen to release energy via respiration, in the form of the metabolism of energy-rich molecules such as glucose...
is about 4% to 5% carbon dioxide and 4% to 5% less oxygen than was inhaled.
Breathing produces approximately 2.3 pounds (1 kg) of carbon dioxide per day per person.
See also
- Bosch reaction
The Bosch reaction is a chemical reaction between carbon dioxide and hydrogen that produces elemental carbon , water and a 10% return of invested heat. This reaction requires the introduction of iron as a catalyst and requires a temperature level of 530-730 degrees C...
- Carbogen
Carbogen, also called Meduna's Mixture after its inventor Ladislas Meduna, is a mixture of carbon dioxide and oxygen gas. Meduna's original formula was 30% CO2 and 70% oxygen, but the term carbogen can refer to any mixture of these two gases, from 1.5% to 50% CO2.- Mechanism...
- Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
- Carbon dioxide (data page)
- Material Safety Data Sheet : The handling of this chemical may incur notable safety precautions. It is highly recommended that you seek the Material Safety Datasheet for this chemical from a reliable source such as , and follow its directions...
- Carbon dioxide sensor
- Carbon dioxide sink
A carbon sink is a natural or manmade reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period.The main natural sinks are:*Absorption of carbon dioxide by the oceans*Photosynthesis by plants and algae...
- Carbon monoxide
Carbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
- Center for the Study of Carbon Dioxide and Global Change
The Center for the Study of Carbon Dioxide and Global Change is a non-profit organization based in Arizona. Its stated purpose is to "disseminate factual reports and sound commentary on new developments in the world-wide scientific quest to determine the climatic and biological consequences of the...
- CO2 sequestration
- CO2 degassing in Lake Nyos
Lake Nyos is a crater lake in the Northwest Province of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity...
- Dry ice
Dry ice, sometimes referred to as "Cardice" or as "card ice" is the solid form of carbon dioxide. It is commonly used as a versatile cooling agent.- Properties :...
- EcoCute
The EcoCute is an energy efficient electric heat pump that uses heat extracted from the air to heat water for domestic use. Instead of the more conventional ammonia or haloalkane gases, EcoCute uses carbon dioxide as a refrigerant...
- As refrigerants
- Emission standard
Emissions standards are requirements that set specific limits to the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other powered vehicles but they can also regulate emissions from industry, power...
s
- Global warming
Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century...
- Greenhouse gas
Greenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
- Kaya identity
The Kaya identity is an equation relating factors that determine the level of human impact on climate, in the form of emissions of the greenhouse gas carbon dioxide. It states that total emission level can be expressed as the product of four inputs: population, GDP per capita, energy use per unit...
- Sabatier process
The Sabatier reaction or Sabatier process involves the reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst to produce methane and water. Optionally ruthenium on alumina makes a more efficient catalyst...
Further reading
- Tyler Volk
Tyler Volk is an Associate Professor in the Department of Biology at New York University. Volk is an active proponent of the Gaia hypothesis. A 1989 study, co-authored by Volk, published in the journal Nature asserts that without the cooling effects of living things, Earth would be 80 degrees...
(2008), CO2 Rising: The World's Greatest Environmental Challenge, The MIT Press, 223 pages, ISBN 978-0262220835. A short, balanced primer on CO2's role as a greenhouse gasGreenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
. Review at Environmental Health PerspectivesEnvironmental Health Perspectives is a peer-reviewed journal of the United States' National Institute of Environmental Health Sciences, published monthly. Its stated role is to disseminate environmental health information and research findings. As of 2008, EHP is considered a top ranking journal...
External links