Carbonic Acid Aqueous

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Carbonic Acid aqueous
Contents
Articles
Carbonic acid 1
Carbonated water 5
Carbon dioxide 10
Sodium bicarbonate 26
Carbonation 33
References
Article Sources and Contributors 35
Image Sources, Licenses and Contributors 37
Article Licenses
License 38
Carbonic acid 1
Carbonic acid
 Carbonic acid 
 [[Image:Carbonic-acid-2D.svg Structural formula]] 
 [[Image:Carbonic-acid-3D-balls.png Ball-and-stick model]] 
 Identifiers 
CAS number 463-79-6 [1]  
ChemSpider 747 [2]  
KEGG C01353 [3]  
ChEMBL CHEMBL1161632 [4]  
 Properties 
Molecular formula H2CO3
Molar mass 62.03 g/mol 
Density 1.0 g/cm3 (dilute soln.)
Melting point n/a 
Solubility in water Exists only in solution 
Acidity (pKa) 6.352 (pKa1)
 (what is this?)   (verify) [5]
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references
Not to be confused with carbolic acid, an antiquated name for phenol.
Carbonic acid is the inorganic compound with the formula H2CO3 (equivalently OC(OH)2). It is also a name
sometimes given to solutions of carbon dioxide in water, because such solutions contain small amounts of H2CO3.
Carbonic acid salts forms two kinds of salts, the carbonates and the bicarbonates. It is a weak acid.
Chemical equilibria
When dissolved in water, carbon dioxide exists in equilibrium with carbonic acid:
CO2 + H2O H2CO3
The hydration equilibrium constant at 25 °C is called Kh, which in the case of carbonic acid is [H2CO3]/[CO2] =
1.70×10−3: hence, the majority of the carbon dioxide is not converted into carbonic acid, remaining as CO2
molecules. In the absence of a catalyst, the equilibrium is reached quite slowly. The rate constants are 0.039 s−1 for
the forward reaction (CO2 + H2O → H2CO3) and 23 s
−1 for the reverse reaction (H2CO3 → CO2 + H2O). Carbonic
acid is used in the making of soft drinks, inexpensive and artificially carbonated sparkling wines, and other bubbly
drinks. The addition of two equivalents of water to CO2 would give orthocarbonic acid, C(OH)4, which is
unimportant in aqueous solution.
Addition of base to an excess of carbonic acid gives bicarbonate. With excess base, carbonic acid reacts to give
carbonate salts.
Carbonic acid 2
Role of carbonic acid in blood
Carbonic acid is an intermediate step in the transport of CO2 out of the body via respiratory gas exchange. The
hydration reaction of CO2 is generally very slow in the absence of a catalyst, but red blood cells contain carbonic
anhydrase, which both increases the reaction rate and dissociates a hydrogen ion (H+) from the resulting carbonic
acid, leaving bicarbonate (HCO3
-) dissolved in the blood plasma. This catalysed reaction is reversed in the lungs,
where it converts the bicarbonate back into CO2 and allows it to be expelled. This equilibration plays an important
role as a buffer in mammalian blood.[6]
Role of carbonic acid in ocean chemistry
The oceans of the world have absorbed almost half of the CO2 emitted by humans from the burning of fossil fuels.
[7]
  The extra dissolved carbon dioxide has caused the ocean's average surface pH to shift by about 0.1 unit from
pre-industrial levels.[8] This process is known as ocean acidification.
Acidity of carbonic acid
Carbonic acid is diprotic: it has two protons, which may dissociate from the parent molecule. Thus there are two
dissociation constants, the first one for the dissociation into the bicarbonate (also called hydrogen carbonate) ion
HCO3
−:
H2CO3 HCO3
− + H+
Ka1 = 4.45×10
−7 ; pKa1 = 6.352 at 25 °C.
With a pKa1 of 6.352, carbonic acid H2CO3 is almost 10x weaker acid than acetic acid.
The second for the dissociation of the bicarbonate ion into the carbonate ion CO3
2−:
HCO3
− CO3
2− + H+
Ka2 = 4.69×10
−11 ; pKa2 = 10.329 at 25 °C and Ionic Strength = 0.0.
Care must be taken when quoting and using the first dissociation constant of carbonic acid. In aqueous solution
carbonic acid only exists in equilibrium with carbon dioxide, and the concentration of H2CO3 is much lower than the
dissolved CO2 concentration. Since it is not possible to distinguish between H2CO3 and dissolved CO2 (referred to as
CO2(aq)) by conventional methods, H2CO3
* is used to represent the two species when writing the aqueous chemical
equilibrium equation. The equation may be rewritten as follows (cf. sulfurous acid):
H2CO3
* HCO3
− + H+
Ka = 4.6×10
−7(General Chemistry: An Integrated Approach Third Edition); pKa = 6.352 at 25 °C and Ionic
Strength = 0.0.(NIST CRITICAL Database)
Whereas this pKa is quoted as the dissociation constant of carbonic acid, it is ambiguous: it might better be referred
to as the acidity constant of dissolved carbon dioxide, as it is particularly useful for calculating the pH of
CO2-containing solutions.
pH and composition of carbonic acid solutions
At a given temperature, the composition of a pure carbonic acid solution (or of a pure CO2 solution) is completely
determined by the partial pressure of carbon dioxide above the solution. To calculate this composition, account
must be taken of the above equilibria between the three different carbonate forms (H2CO3, HCO3
− and CO3
2−) as
well as of the hydration equilibrium between dissolved CO2 and H2CO3 with constant (see above) and
of the following equilibrium between the dissolved CO2 and the gaseous CO2 above the solution:
CO2(gas) CO2(dissolved) with where kH=29.76 atm/(mol/L) at 25°C (Henry constant)
Carbonic acid 3
The corresponding equilibrium equations together with the relation and the charge neutrality
condition result in six equations for the six unknowns [CO2], [H2CO3], [H
+],
[OH−], [HCO3
−] and [CO3
2−], showing that the composition of the solution is fully determined by . The
equation obtained for [H+] is a cubic whose numerical solution yields the following values for the pH and the
different species concentrations:
(atm)
 pH [CO
2
]
(mol/L)
[H
2
CO
3
]
(mol/L)
[HCO
3
−]
(mol/L)
[CO
3
2−]
(mol/L)
10−8 7.00 3.36 × 10−10 5.71 × 10−13 1.42 × 10−9 7.90 × 10−13
10−7 6.94 3.36 × 10−9 5.71 × 10−12 5.90 × 10−9 1.90 × 10−12
10−6 6.81 3.36 × 10−8 5.71 × 10−11 9.16 × 10−8 3.30 × 10−11
10−5 6.42 3.36 × 10−7 5.71 × 10−9 3.78 × 10−7 4.53 × 10−11
10−4 5.92 3.36 × 10−6 5.71 × 10−9 1.19 × 10−6 5.57 × 10−11
3.5 × 10−4 5.65 1.18 × 10−5 2.00 × 10−8 2.23 × 10−6 5.60 × 10−11
10−3 5.42 3.36 × 10−5 5.71 × 10−8 3.78 × 10−6 5.61 × 10−11
10−2 4.92 3.36 × 10−4 5.71 × 10−7 1.19 × 10−5 5.61 × 10−11
10−1 4.42 3.36 × 10−3 5.71 × 10−6 3.78 × 10−5 5.61 × 10−11
100 3.92 3.36 × 10−2 5.71 × 10−5 1.20 × 10−4 5.61 × 10−11
2.5 × 100 3.72 8.40 × 10−2 1.43 × 10−4 1.89 × 10−4 5.61 × 10−11
101 3.42 3.36 × 10−1 5.71 × 10−4 3.78 × 10−4 5.61 × 10−11
• We see that in the total range of pressure, the pH is always largely lower than pKa2 so that the CO3
2−
concentration is always negligible with respect to HCO3
− concentration. In fact CO3
2− plays no quantitative role
in the present calculation (see remark below).
• For vanishing , the pH is close to the one of pure water (pH = 7) and the dissolved carbon is essentially in
the HCO3
− form.
• For normal atmospheric conditions ( atm), we get a slightly acid solution (pH = 5.7) and the
dissolved carbon is now essentially in the CO2 form. From this pressure on, [OH
−] becomes also negligible so
that the ionized part of the solution is now an equimolar mixture of H+ and HCO3
−.
• For a CO2 pressure typical of the one in soda drink bottles ( ~ 2.5 atm),we get a relatively acid medium (pH
= 3.7) with a high concentration of dissolved CO2. These features contribute to the sour and sparkling taste of
these drinks.
• Between 2.5 and 10 atm, the pH crosses the pKa1 value (3.60) giving a dominant H2CO3 concentration (with
respect to HCO3
−) at high pressures.
Remark
As noted above, [CO3
2−] may be neglected for this specific problem, resulting in the following very precise
analytical expression for [H+]:
Since several months I have expressed my disagreement with the result given by the author in the paragraph
appearing in the” remark” on "Carbonic acid “ (more specifically on Line 185). I eagerly require information about
the result obtained by the author .Thanks for an answer. Bera
Carbonic acid 4
==Spectroscopic studies of carbonic acid ==
Theoretical calculations show that the presence of even a single molecule of water causes carbonic acid to revert to
carbon dioxide and water. In the absence of water, the dissociation of gaseous carbonic acid is predicted to be very
slow, with a half-life of 180,000 years.[9]
It has long been recognized that pure carbonic acid cannot be obtained at room temperatures (about 20 °C or about
70 °F). It can be generated by exposing a frozen mixture of water and carbon dioxide to high-energy radiation, and
then warming to remove the excess water. The carbonic acid that remained was characterized by infrared
spectroscopy. The fact that the carbonic acid was prepared by irradiating a solid H2O + CO2 mixture may suggest
that H2CO3 might be found in outer space, where frozen ices of H2O and CO2 are common, as are cosmic rays and
ultraviolet light, to help them react.[9] The same carbonic acid polymorph (denoted beta-carbonic acid) was prepared
by heating alternating layers of glassy aqueous solutions of bicarbonate and acid in vacuo, which causes protonation
of bicarbonate, followed by removal of the solvent. Alpha-carbonic acid was prepared by the same technique using
methanol rather than water as a solvent.
References
[1] http:/ / www. commonchemistry. org/ ChemicalDetail. aspx?ref=463-79-6
[2] http:/ / www. chemspider. com/ 747
[3] http:/ / www. kegg. jp/ entry/ C01353
[4] https:/ / www. ebi. ac. uk/ chembldb/ index. php/ compound/ inspect/ CHEMBL1161632
[5] http:/ / en. wikipedia. org/ wiki/ %3Acarbonic_acid?diff=cur& oldid=409736692
[6] "excretion." Encyclopædia Britannica. Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.
[7] Sabine, C.L.; et al. (2004). " "The Oceanic Sink for Anthropogenic CO2" (http:/ / www. sciencemag. org/ cgi/ content/ short/ 305/ 5682/ 367).
Science 305 (5682): 367–371. doi:10.1126/science.1097403. PMID 15256665. ".
[8] "Ocean Acidification Network" (http:/ / ioc3. unesco. org/ oanet/ FAQacidity. html). .
[9] Loerting, T.; Tautermann, C.; Kroemer, R.T.; Kohl, I.; Mayer, E.; Hallbrucker, A.; Liedl, K. R. (2001). "On the Surprising Kinetic Stability of
Carbonic Acid". Angew. Chem. Int. Ed. 39: 891–895. doi:10.1002/(SICI)1521-3773(20000303)39:5<891::AID-ANIE891>3.0.CO;2-E.
Further reading
• Welch, M. J.; Lipton, J. F.; Seck, J. A. (1969). "Tracer studies with radioactive oxygen-15. Exchange between
carbon dioxide and water". J. Phys. Chem. 73 (335): 3351. doi:10.1021/j100844a033.
• Jolly, W. L. (1991). Modern Inorganic Chemistry (2nd Edn.). New York: McGraw-Hill. ISBN 0-07-112651-1.
• Moore, M. H.; Khanna, R. (1991). "Infrared and Mass Spectral Studies of Proton Irradiated H2O+Co2 Ice:
Evidence for Carbonic Acid Ice: Evidence for Carbonic Acid". Spectrochimica Acta 47A: 255–262.
doi:10.1016/0584-8539(91)80097-3.
• W. Hage, K. R. Liedl; Mayer, E.; Hallbrucker, A; Mayer, E (1998). "Carbonic Acid in the Gas Phase and Its
Astrophysical Relevance". Science 279 (5355): 1332–1335. doi:10.1126/science.279.5355.1332. PMID 9478889.
• Hage, W.; Hallbrucker, A.; Mayer, E. (1993). "Carbonic Acid: Synthesis by Protonation of Bicarbonate and Ftir
Spectroscopic Characterization Via a New Cryogenic Technique". J. Am. Chem. Soc. 115: 8427–8431.
doi:10.1021/ja00071a061.
• Hage, W.; Hallbrucker, A.; Mayer, E. (1995). "A Polymorph of Carbonic Acid and Its Possible Astrophysical
Relevance". J. Chem. Soc. Farad. Trans. 91: 2823–2826. doi:10.1039/ft9959102823.
Carbonic acid 5
External links
• Ask a Scientist: Carbonic Acid Decomposition (http:/ / www. newton. dep. anl. gov/ askasci/ chem99/
chem99661. htm)
• Why was the existence of carbonic acid unfairly doubted for so long? (http:/ / www. wiley-vch. de/ vch/ journals/
2002/ press/ 200005press. html)
• Carbonic acid/bicarbonate/carbonate equilibrium in water: pH of solutions, buffer capacity, titration and species
distribution vs. pH computed with a free spreadsheet (http:/ / www2. iq. usp. br/ docente/ gutz/ Curtipot_. html)
• How to calculate concentration of Carbonic Acid in Water (http:/ / www. chem. usu. edu/ ~sbialkow/ Classes/
3600/ Overheads/ Carbonate/ CO2. html:)
Carbonated water
Carbon dioxide bubbles in Coca-Cola.
Carbonated water, also known as
seltzer, sparkling water, fizzy water,
or soda water, is plain water into
which carbon dioxide gas under
pressure has been dissolved, and thus
made effervescent. It is the major and
defining component of carbonated soft
drinks (itself a class of aerated
beverages). The process of dissolving
carbon dioxide in water is called
carbonation.
While dissolved carbon dioxide in low
concentrations (0.2%–1.0%) cannot be
tasted by humans, a small amount of
it[1] reacts with water to form carbonic
acid (H2CO3). The presence of carbonic acid in water gives the water a slightly sour taste, with a pH between 3 and
4.[2]
Etymology
In the United States, carbonated water was known as soda water until WWII due to the sodium salts it contains,
which are added as flavoring and acidity regulators to mimic the taste of natural mineral water. During the Great
Depression, it was also called two cents plain, a reference to its being the cheapest drink at soda fountains. In the
1950s terms such as sparkling water and seltzer water gained favour. "Seltzer water" is identical with carbonated
water if it contains no additives or flavourings. The term seltzer water is a genericized trademark that derives from
the German town Selters, meaning "water from Selters", which is renowned for its mineral springs. .[3] where
naturally carbonated water has been commercially bottled and shipped into all parts of the world at least since the
18th century.[4]
In many parts of the U.S., "soda" has come to mean any type of sweetened, carbonated soft drink, such as cola.
Carbonated water 6
Chemistry
Carbon dioxide and water form carbonic acid. Alkaline salts such as sodium bicarbonate are added to soda water to
reduce its acidity. The sodium, potassium, or other metallic salts in soda water can neutralise a little of the acidic
flavour of some drinks, such as cocktails made with orange juice.
The pH of soda water is between 3 and 4.[2]
Manufacture
Commercial
A modern bar soda "gun."
Commercial soda water in siphons is made by chilling filtered plain
water to 8 °C (46 °F), adding a sodium or potassium based alkaline
compound such as sodium bicarbonate to reduce acidity, and then
pressurising the water with carbon dioxide, known as carbonation. The
gas dissolves in the water, and a top-off fill of carbon dioxide is added
to finally pressurise the siphon to approximately 120 pounds per square
inch (830 kPa), some 30–40 psi (210–280 kPa) higher than is present
in fermenting champagne bottles.
In most modern restaurants and drinking establishments soda water is often manufactured on-site using devices
known as carbonators. Carbonators utilise filtered water and pressurise it to approximately 100 psi (690 kPa) using
mechanical pumps. The pressurised wateris stored in stainless steel vessels and CO2 is injected into the water
producing carbonated water.
Home
Carbonated water can be made at home, by use of a readily available 1 L (1.1 US qt) rechargeable soda-siphon, and
disposable one-shot screw-in carbon dioxide cartridges. A simple recipe is to chill filtered tap water in the fridge,
add one quarter to one half a level teaspoon of sodium bicarbonate (baking soda) to the rechargeable soda-siphon,
pour in the chilled water and add the carbon dioxide. A pH testing kit can be used to alter the amount of sodium
bicarbonate per litre of carbonised water to neutralise acidity. The siphon should be kept in the refrigerator to
preserve carbonation of the contents, and brought out for use, but many rechargeable soda-siphons are handsome
objects in their own right, and are kept out for viewing on the drinks tray in many homes. Soda water made in this
way tends not to be as 'gassy' as commercial soda water although chilling of the water before carbonation helps.
Carbonated water can be produced in the home by "charging" a refillable seltzer bottle by filling it with water and
then adding carbon dioxide. Soda water may be identical to plain carbonated water or it may contain a small amount
of table salt, sodium citrate, sodium bicarbonate, potassium bicarbonate, potassium citrate, potassium sulfate, or
disodium phosphate, depending on the bottler. These additives are included to emulate the slightly salty taste of
homemade soda water. The process can also occur naturally to produce carbonated mineral water, such as in
Mihalkovo in the Bulgarian Rhodopes, or Medzitlija in Macedonia.
Carbonated water 7
Soda siphons
An antique soda siphon circa 1922.
The gas pressure inside a siphon pressure vessel drives soda water
up through a tube inside the siphon when a valve actuation lever at
the top is depressed. Careful regulation of the valve lever is
needed by the operator of the siphon to prevent pressurised soda
water being released into the drink, which then splashes forcibly
upwards, often soaking the operator.
Use
Carbonated water is often drunk plain or mixed with fruit juice. It
is also mixed with alcoholic beverages to make cocktails, such as
Whisky and soda or Campari and soda. Flavoured carbonated
water is also commercially available. It differs from sodas in that it
contains flavors (usually sour fruit flavors such as lemon, lime,
cherry, orange, or raspberry) but no sweetener.
Carbonated water is a diluent; It works well in short drinks made
with whisky, brandy and Campari and in long drinks such as those
made with vermouth. Soda water may be used to dilute drinks
based on cordials such as orange squash. Soda water is a necessary
ingredient in many cocktails, where it is used to top-off the drink
and provide a degree of 'fizz'. Adding soda water to 'short' drinks
such as spirits dilutes them and makes them 'long'. One report
states that the presence of carbon dioxide in a cocktail may accelerate the uptake of alcohol in the blood, making
both the inebriation and recovery phases more rapid.[5]
The addition of carbonated water to dilute spirits was especially popular in hot climates and seen as a somewhat
"British" habit. Adding soda water to quality Scotch whisky has been deprecated by whisky lovers, but was a popular
lunchtime drink or early evening pre-dinner or pre-theatre drink until the late part of the 20th century. Pre-filled glass
soda-siphons were sold at many liquor stores, a deposit was charged on the siphon, to encourage the return of the
relatively expensive siphon for re-filling. In 1965 the deposit on a single soda-syphon in England was 7/6d (seven
shillings and six pence).
History
In 1767 Englishman Joseph Priestley invented carbonated water when he first discovered a method of infusing water
with carbon dioxide when he suspended a bowl of water above a beer vat at a local brewery in Leeds, England.[6]
The air blanketing the fermenting beer—called 'fixed air'—was known to kill mice suspended in it. Priestley found
water thus treated had a pleasant taste and he offered it to friends as a cool, refreshing drink. In 1772 Priestley
published a paper entitled Impregnating Water with Fixed Air in which he describes dripping oil of vitriol (sulfuric
acid) onto chalk to produce carbon dioxide gas, and encouraging the gas to dissolve into an agitated bowl of water.[7]
In 1771 Swedish chemistry professor Torbern Bergman independently invented a similar process to make carbonated
water. In poor health at the time yet frugal, he was trying to reproduce naturally-effervescent spring waters thought
at the time to be beneficial to health.
Carbonated water was introduced in the latter part of the 18th century, and reached Kolkata (formerly known as
Calcutta), India in 1822.
Carbonated water 8
In the late eighteenth century, J. J. Schweppe (1740–1821), a German-born naturalised Swiss watchmaker and
amateur scientist developed a process to manufacture carbonated mineral water, based on the process discovered by
Joseph Priestley, founding the Schweppes Company in Geneva in 1783. In 1792 he moved to London to develop the
business there.
The soda siphon, or syphon — a glass or metal pressure vessel with a release valve and spout for dispensing
pressurised soda water — was a common sight in bars and in early- to mid-20th century homes where it became a
symbol of middle-class affluence.
Ányos Jedlik (1800–95), a Hungarian, invented consumable soda-water that continues to be a popular drink today.
He also built an early carbonated water factory in Budapest, Hungary. However, the process he developed at his
factory for getting the CO2 into the water remains a mystery to this day. After this invention, a Hungarian drink
made of wine and soda water called "fröccs" (wine spritzers) was spread throughout several countries in Europe.
Since then, carbonated water is made by passing pressurized carbon dioxide through water. The pressure increases
the solubility and allows more carbon dioxide to dissolve than would be possible under standard atmospheric
pressure. When the bottle is opened, the pressure is released, allowing the gas to come out of the solution, thus
forming the characteristic bubbles.
Social popularity, decline, and renaissance
Carbonated water changed the way people drank. Instead of drinking spirits neat, soda water, and later, carbonated
soft drinks helped dilute alcohol, mitigating its harsh effects, and made having a drink more socially acceptable.
Popping into a chum's house for hospitality from a "dash and a splash" - a whisky and soda - before going out to a
social event was part of everyday activity in Britain as late as 1965. Whisky and sodas can be seen in many British
TV series and films from the 1960s and earlier and the soda siphon is ubiquitous in many movies made before 1970.
Social drinking would change with the counter-culture anti-establishment movement of the 1970s, and the decline of
soda water would begin from that point. Soda water's 'last hurrah' in Britain may have been the popular 1970s
product, 'Soda Stream' A commercially available home bottling kit, which enabled purchasers to combine fruit
syrups, and water, to create sparkling beverages. The famous advertising tag-line 'Get Bizzy With The Fizzy'
spawned a series of similar expressions, such as 'Get Buzzy With the Fuzzy'.
The popularity of soda water has declined since the late 1980s as drinking habits and fashions change and new
bottled or canned beverages arrive, but soda-siphons are still bought by the more traditional bar trade and available at
the bar in many upmarket establishments. In the UK there are now only two wholesalers of soda-water in traditional
glass siphons, and an estimated market of around 120,000 siphons per year (2009). Worldwide,preferences are for
beverages to be distributed in recyclable plastic containers which may, or may not, be recycled. The heavy glass
needed for soda siphons is seen as environmentally unsustainable despite glass soda siphons being easily repaired
and refilled by manufacturers.
Home soda siphons, and soda water are enjoying a renaissance in the 21st century as retro items become fashionable.
Contemporary soda siphons are commonly made of aluminium, although glass and stainless steel siphons are
available. The valve-heads of today are made of plastic, with metal valves, and replaceable o-ring seals. Older
siphons are in demand on on-line auction sites. Carbonated water, without the acidity regulating addition of soda, is
currently seen as fashionable although home production (see below) is mainly eschewed in favour of commercial
products.
Carbonated water 9
Health effects
Carbonated water is a negligible cause of dental erosion; also known as acid erosion. While the dissolution potential
of sparkling water is greater than still water, levels remain low: by comparison, carbonated soft drinks cause tooth
decay at a rate of several hundred times that of regular sparkling water. De-gassing of carbonated water reduces its
dissolution potential, but the total levels are still relatively low, suggesting that the addition of sugar into water, not
its carbonation, is the main cause of tooth decay.[8]
Intake of carbonated beverages has not been associated with increased bone fracture risk in observational studies,
and the net effect of carbonated beverage constituents on the amount of calcium in the body is negligible, leaving
carbonated water as harmless as regular water. The phosphoric acid present in many soft drinks is what reduces bone
density and increases bone fracture risk.
Carbonated water eases the symptoms of indigestion (dyspepsia) and constipation, according to a study in the
European Journal of Gastroenterology and Hepatology [9]
A 2004 article in the Journal of Nutrition found that fizzy waters with higher sodium levels reduced cholesterol
levels and the risk of cardiovascular problems in postmenopausal women. [10]
References
[1] "Carbon Dioxide in Water Equilibrium, Page 1" (http:/ / www. thuisexperimenteren. nl/ science/ carbonaatkinetiek/ Carbondioxide in water
equilibrium. doc). . Retrieved 2010-07-23.
[2] James Monroe Jay, Martin J. Loessner, David Allen Golden (2005). Modern food microbiology (http:/ / books. google. com/
books?id=C0sO1gNFWLAC& lpg=PA210& ots=moFrD7dCTr& dq="carbonated water" ph& pg=PA210#v=onepage& q="carbonated water"
ph& f=false). シュプリンガー・ジャパン株式会社. pp. 210. ISBN 0387231803. .
[3] "Definition of seltzer - Merriam-Webster Online Dictionary" (http:/ / www. merriam-webster. com/ cgi-bin/ dictionary?book=Dictionary&
va=seltzer). . Retrieved 2007-11-07.
[4] "History of Selters" (http:/ / www. reference. com/ browse/ Nieder-Selters?jss=0). . Retrieved 2009-07-29.
[5] http:/ / www. sciencedirect. com/ science?_ob=ArticleURL& _udi=B8CY1-4NRMDG8-1& _user=10& _coverDate=10%2F31%2F2007&
_rdoc=1& _fmt=high& _orig=search& _sort=d& _docanchor=& view=c& _searchStrId=1229438662& _rerunOrigin=google&
_acct=C000050221& _version=1& _urlVersion=0& _userid=10& md5=696148487a35d107a71869c60b3405f1
[6] "Joseph Priestley - Discovery of Oxygen - Invention of Soda Water by Joseph Priestley" (http:/ / inventors. about. com/ od/ pstartinventors/ a/
JosephPriestley. htm). Inventors.about.com. 2009-09-16. . Retrieved 2009-09-23.
[7] Priestly, Joseph (1772). "Impregnating Water with Fixed Air, Page 7" (http:/ / dbhs. wvusd. k12. ca. us/ webdocs/ Chem-History/
Priestley-1772/ Priestley-1772-11. html). . Retrieved 2008-08-07.
[8] Parry J, Shaw L, Arnaud MJ, Smith AJ (2001). "Investigation of mineral waters and soft drinks in relation to dental erosion" (http:/ / www.
ncbi. nlm. nih. gov/ pubmed/ 11556958). Journal of oral rehab 28 (8): 766–72. doi:10.1046/j.1365-2842.2001.00795.x. PMID 11556958. .
[9] http:/ / bastyrcenter. org/ content/ view/ 899/
[10] http:/ / jn. nutrition. org/ content/ 134/ 5/ 1058. full
External links
• The Priestley Society (http:/ / www. priestleysociety. net)
• Priestley's paper Impregnating Water with Fixed Air 1772 (http:/ / www. truetex. com/
priestley-1772-impregnating_water_with_fixed_air. pdf)
• Interview with one of New York City's last seltzer delivery men (http:/ / www. radiodiaries. org/ transcripts/
NewYorkWorks/ seltzerman. html)
Carbon dioxide 10
Carbon dioxide
 Carbon dioxide 
 [[Image:Dry Ice Pellets Subliming.jpg Sample of solid carbon dioxide or "dry
ice", pellets]] 
[[File:Carbon-dioxide-2D-dimensions.svg
Structural formula of carbon
dioxide with a bond length]] 
 [[File:Carbon-dioxide-3D-vdW.svg Spacefill model
of carbon
dioxide]] 
 [[Image:Carbon_dioxide_structure.png Ball and stick model of carbon dioxide]]
 Identifiers 
CAS number 124-38-9 [1]  
PubChem 280 [2]
ChemSpider 274 [3]  
UNII 142M471B3J [4]  
EC number 204-696-9 [5]
UN number 1013 
KEGG D00004 [6]  
MeSH Carbon+dioxide [7]
ChEBI CHEBI:16526 [8]
RTECS number FF6400000 
ATC code V03 AN02 [9]
Beilstein Reference 1900390 
Gmelin Reference 989 
 3DMet B01131 [10]
 Properties 
Molecular formula CO2
Molar mass 44.01 g mol−1
Exact mass 43.989829244 g mol-1
 Appearance Colorless gas 
Odor Odorless 
Density 1.562 g/mL (solid at 1 atm
and −78.5 °C)
0.770 g/mL (liquid at 56 atm
and 20 °C)
1.977 g/L (gas at 1 atm and
0 °C)
Carbon dioxide 11
Melting point -78 °C, 194.7 K, -109 °F
(subl.)
Boiling point -57 °C, 216.6 K, -70 °F (at
5.185 bar) 
Solubility in water 1.45 g/L at 25 °C, 100 kPa 
Acidity (pKa) 6.35, 10.33 
Refractive index (nD) 1.1120 
Viscosity 0.07 cP at −78 °C
Dipole moment zero 
 Structure 
Molecular shape linear
 Hazards 
NFPA 704
 Related compounds 
Other anions Carbon disulfide
Carbon diselenide
Other cations Silicon dioxide
Germanium dioxide
Tin dioxide
Lead dioxide
Related carbon oxides Carbon monoxide
Carbon suboxide
Dicarbon monoxide
Carbon trioxide
 Related compounds Carbonic acid
Carbonyl sulfide
 (what is this?)   (verify) [11]
Except where noted otherwise, data are given for materials in their
standard state (at 25 °C, 100 kPa)
Infobox references
Carbon dioxide (chemical formula CO
2
) is a chemical compound composed of two oxygen atoms covalently
bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in
this state. CO2 is a trace gas comprising 0.039% of the atmosphere.
As part of the carbon cycle known as photosynthesis, plants, algae, and cyanobacteria absorb carbon dioxide,
sunlight, and water to produce carbohydrate energy for themselves and oxygen as a waste product. By contrast,
during respiration they emit carbon dioxide, as do all other living things that depend either directly or indirectly on
plants for food. Carbon dioxide is also generated as a by-product of combustion; emitted from volcanoes, hot
springs, and geysers; and freed from carbonate rocks by dissolution.
As of October 2010, carbon dioxide in the Earth's atmosphere is at a concentration of 388 ppm by volume.[12]
Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by
seasonal plant growth in the Northern Hemisphere. Concentrations of carbon dioxide fall during the northern spring
and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and
decay. Taking all this into account, the concentration of CO2 grew by about 2 ppm in 2009.
[13] Carbon dioxide is a
greenhouse gas as it transmits visible lightbut absorbs strongly in the infrared and near-infrared.
Carbon dioxide 12
Before the advent of human-caused release of carbon dioxide to the atmosphere, concentrations tended to increase
with increasing global temperatures, acting as a positive feedback for changes induced by other processes such as
orbital cycles.[14] There is a seasonal cycle in CO2 concentration associated primarily with the Northern Hemisphere
growing season.[15]
Carbon dioxide has no liquid state at pressures below 5.1 standard atmospheres (520 kPa). At 1 atmosphere (near
mean sea level pressure), the gas deposits directly to a solid at temperatures below −78 °C (−108 °F; 195.1 K) and
the solid sublimes directly to a gas above −78 °C. In its solid state, carbon dioxide is commonly called dry ice.
CO2 is an acidic oxide: an aqueous solution turns litmus from blue to pink. It is the anhydride of carbonic acid, an
acid which is unstable in aqueous solution, from which it cannot be concentrated. In organisms carbonic acid
production is catalysed by the enzyme, carbonic anhydrase.
CO2 + H2O H2CO3
CO2 is toxic in higher concentrations: 1% (10,000 ppm) will make some people feel drowsy.
[16] Concentrations of
7% to 10% cause dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to
an hour.[17]
Chemical and physical properties
Carbon dioxide pressure-temperature phase diagram
showing the triple point and critical point of carbon dioxide
Carbon dioxide is colorless. At low concentrations, the gas is
odorless. At higher concentrations it has a sharp, acidic odor.
It can cause asphyxiation and irritation. 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 saliva, forming a
weak solution of carbonic acid. This sensation can also occur
during an attempt to stifle a burp after drinking a carbonated
beverage. 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.[18]
At standard temperature and pressure, the density of carbon
dioxide is around 1.98 kg/m3, about 1.5 times that of air. The
carbon dioxide molecule (O=C=O) contains two double bonds
and has a linear shape. It has no electrical dipole, and as it is fully oxidized, it is moderately reactive and is
non-flammable, but will support the combustion of metals such as magnesium.
Above –78.51° C or –109.3° F, carbon dioxide changes directly from a solid phase to a gaseous phase through
sublimation, or from gaseous to solid through deposition. Solid carbon dioxide is commonly called "dry ice", a
generic trademark. It was first observed in 1825 by the French chemist Charles Thilorier. 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 is also used in the shipping industry. The largest non-cooling use for dry ice is blast cleaning.
Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon dioxide is about 518 kPa at
–56.6 °C (see phase diagram, above). The critical point is 7.38 MPa at 31.1 °C.[19]
Solid carbon dioxide, an amorphous glass-like solid, is known, although not at atmospheric pressure.[20] This form of 
glass, called carbonia, was produced by supercooling heated CO2 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
Carbon dioxide 13
similar to other members of its elemental family, like silicon (silica glass) and germanium. Unlike silica and
germania glasses, however, carbonia glass is not stable at normal pressures and reverts back to gas when pressure is
released.
History
Crystal structure of dry ice
Carbon dioxide was one of the first gases to be described as a
substance distinct from air. In the seventeenth century, the
Flemish 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" or
"wild spirit" (spiritus sylvestre).
The properties of carbon dioxide were studied more
thoroughly 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 an aqueous solution of lime (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.[21] This was the invention of Soda water.
Carbon dioxide was first liquefied (at elevated pressures) in 1823 by Humphry Davy and Michael Faraday.[22] The
earliest description of solid carbon dioxide was given by Charles Thilorier, 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 CO2.
[23]
Isolation and production
Carbon dioxide can be obtained from air distillation, however, this method is inefficient. A variety of chemical
routes to carbon dioxide are known, such as the reaction between most acids and most metal carbonates. For
example, the reaction between hydrochloric acid and calcium carbonate (limestone or chalk) is depicted below:
2 HCl + CaCO3 → CaCl2 + H2CO3
The carbonic acid (H2CO3) then decomposes to water and CO2. 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 CO2:
CaCO3 → CaO + CO2
The combustion of all carbon containing fuels, such as methane (natural gas), petroleum distillates (gasoline, diesel,
kerosene, propane), but also of coal and wood, will yield carbon dioxide and, in most cases, water. As an example
the chemical reaction between methane and oxygen is given below.
Carbon dioxide 14
CH4 + 2 O2 → CO2 + 2 H2O
Iron is reduced from its oxides with coke in a blast furnace, producing pig iron and carbon dioxide:[24]
Fe2O3 + 3 CO → 2 Fe + 3 CO2
Yeast metabolizes sugar to produce carbon dioxide and ethanol, also known as alcohol, in the production of wines,
beers and other spirits, but also in the production of bioethanol:
C6H12O6 → 2 CO2 + 2 C2H5OH
All aerobic organisms produce CO2 when they oxidize carbohydrates, fatty acids, and proteins in the mitochondria of
cells. The large number of reactions involved are exceedingly complex and not described easily. Refer to (cellular
respiration, anaerobic respiration and photosynthesis). Photoautotrophs(i.e. plants, cyanobacteria) use another
modus operandi: Plants absorb CO2 from the air, and, together with water, react it to form carbohydrates:
nCO2 + nH2O → (CH2O)n + nO2
Carbon dioxide is soluble in water, in which it spontaneously interconverts between CO2 and H2CO3 (carbonic acid).
The relative concentrations of CO2, H2CO3, and the deprotonated forms HCO3− (bicarbonate) and
CO32−(carbonate) depend on the pH. 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
Industrial carbon dioxide is produced mainly from six processes:[25]
• Directly from natural carbon dioxide springs, where it is produced by the action of acidified water on limestone or
dolomite.
• As a by-product of hydrogen production plants, where methane is converted to CO2;
• From combustion of fossil fuels and wood;
• As a by-product of fermentation of sugar in the brewing of beer, whisky and other alcoholic beverages;
• From thermal decomposition of limestone, CaCO3, in the manufacture of lime, CaO;
Uses
Carbon dioxide bubbles in a soft drink.
Carbon dioxide is used by the food industry, the oil
industry, and the chemical industry.[25] It is used in
many consumer products that require pressurized gas
because it is inexpensive and nonflammable, and
because it undergoes a phase transition from gas to
liquid at room temperature at an attainable pressure of
approximately 60 bar (870 psi, 59 atm), allowing far
more carbon dioxide to fit in a given container than
otherwise would. Life jackets often contain canisters of
pressured carbon dioxide for quick inflation.
Aluminum capsules of CO2 are also sold as supplies of
compressed gas for airguns, paintball markers, inflating
bicycle tires, and for making carbonated water. Rapid
vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can
also be used to kill pests.
Carbon dioxide 15
Foods
A candy called Pop Rocks 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 agents produce carbon dioxide to cause dough to rise. 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.
Beverages
Carbon dioxide is used to produce carbonated soft drinks and soda water. 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 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.
Wine making
Carbon dioxide in the form of dry ice is often used in the wine making process to cool down bunches of grapes
quickly after picking to help prevent spontaneous fermentation by wild yeasts. The main advantage of using dry ice
over regular water ice is that it cools the grapes without adding any additional water that may decrease the sugar
concentration in the grape must, and therefore also decrease the alcohol concentration in the finished wine.
Dry ice is also used during the cold soak phase of the wine making process to keep grapes cool. The carbon dioxide
gas that results from the sublimation of the dry ice tends to settle to the bottom of tanks because it is heavier than
regular air. The settled carbon dioxide gas creates a hypoxic environment which helps to prevent bacteria from
growing on the grapes until it is time to start the fermentation with the desired strain of yeast.
Carbon dioxide is also used to create a hypoxic environment for carbonic maceration, the process used to produce
Beaujolais wine.
Carbon dioxide is sometimes used to top up wine bottles or other storage 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 nitrogen or argon are preferred for this process by professional wine makers.
Pneumatic systems
Carbon dioxide is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in
portable pressure tools and combat robots.
Fire extinguisher
Carbon dioxide extinguishes flames, and 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, as it is so dry. 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, (National Fire Protection Association Code 12). International Maritime Organization standards also
recognize carbon dioxide systems for fire protection of ship holds and engine rooms. Carbon dioxide based fire
protection systems have been linked to several deaths, because it does not support life in the concentrations used to
extinguish fire (40% or so), however, it is not considered to be toxic to humans. A review of CO2 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.
Carbon dioxide 16
Welding
Carbon dioxide also finds use 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, and that such weld joints deteriorate over time because of
the formation of carbonic acid. It is used as a welding gas primarily because it is much less expensive than more
inert gases such as argon or helium.
When used for MIG welding, 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.
Pharmaceutical and other chemical processing
Liquid carbon dioxide is a good solvent for many lipophilic organic compounds and is used to remove caffeine from
coffee. Carbon dioxide has attracted attention in the pharmaceutical and other chemical processing industries as a
less toxic alternative to more traditional solvents such as organochlorides. It is used by some dry cleaners for this
reason. (See green chemistry.)
Carbon dioxide is used as an ingredient in the production of urea, carbonates and bicarbonates, and sodium
salicylate.[26] Carbon dioxide is known to react with Grignard reagents to form carboxylic acids. In a metal carbon
dioxide complexes, CO2 serves as a ligand, which can facilitate the conversion of CO2 to other chemicals.
Agricultural and biologicalapplications
Plants require carbon dioxide to conduct photosynthesis. Greenhouses may (if of large size, must) enrich their
atmospheres with additional CO2 to sustain and increase plant growth.
[27] [28] [29] A photosynthesis-related drop (by
a factor less than two) in carbon dioxide concentration in a greenhouse compartment would kill green plants, or, at
least, completely stop their growth. At very high concentrations (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 whiteflies and spider mites in a greenhouse.[30] Carbon dioxide is used
in greenhouses as the main carbon source for Spirulina algae.
In medicine, up to 5% carbon dioxide (130 times the atmospheric concentration) is added to oxygen for stimulation
of breathing after apnea and to stabilize the O2/CO2 balance in blood.
It has been proposed that carbon dioxide from power generation be bubbled into ponds to grow algae that could then
be converted into biodiesel fuel.[31]
Carbon dioxide 17
Lasers
A carbon dioxide laser.
A common type of industrial gas laser is the
carbon dioxide laser.
Oil recovery
Carbon dioxide is used in enhanced oil
recovery where it is injected into or adjacent
to producing oil wells, usually under
supercritical 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.[32] In mature oil fields, extensive pipe networks are used to carry the carbon dioxide to the injection
points.
Refrigerant
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 oC 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 discovery of
R-12 and may enjoy a renaissance due to fears that r134a contributes to climate change. Its physical properties are
highly favorable for cooling, refrigeration, and heating purposes, having a high volumetric cooling capacity. Due to
its operation at pressures of up to 130 bar (1880 psi), CO2 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 (GWP of 1, non-ozone depleting, non-toxic, non-flammable) could make it the future
working fluid to replace current HFCs in cars, supermarkets, hot water heat pumps, among others. Coca-Cola has
fielded CO2-based beverage coolers and the U.S. Army is interested in CO2 refrigeration and heating technology.
[33]
[34]
By the end of 2007, the global automobile industry is expected to decide on the next-generation refrigerant in car air
conditioning. CO2 is one discussed option.(see The Cool War)
Coal bed methane recovery
In enhanced coal bed methane recovery, carbon dioxide is pumped into the coal seam to displace methane.[35]
pH control
Carbon dioxide can be used as a mean of controlling the pH of swimming pools, by continuously adding gas to the
water, thus keeping the pH level from rising. Among the advantages of this is the avoidance of handling (more
hazardous) acids.
CO2 is also used in the keeping of 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.
Carbon dioxide 18
In the Earth's atmosphere
The Keeling Curve of atmospheric CO2 concentrations measured at Mauna
Loa Observatory.
Carbon dioxide in earth's atmosphere is
considered a trace gas currently occurring at an
average concentration of about 390 parts per
million by volume or 591 parts per million by
mass.[36] The total mass of atmospheric carbon
dioxide is 3.16×1015 kg (about 3,000
gigatonnes). Its concentration varies seasonally
(see graph at right) and also considerably on a
regional basis, especially near the ground. In
urban areas concentrations are generally higher
and indoors they can reach 10 times background
levels. Carbon dioxide is a greenhouse gas.
Yearly increase of atmospheric CO2: In the
1960s, the average annual increase was 37% of
the 2000-2007 average.[37]
Five hundred million years ago carbon dioxide was 20 times more
prevalent than today, decreasing to 4-5 times during the Jurassic period
and then slowly declining with a particularly swift reduction occurring
49 million years ago.[38] [39] Human activities such as the combustion
of fossil fuels and deforestation have caused the atmospheric
concentration of carbon dioxide to increase by about 35% since the
beginning of the age of industrialization.[40]
Up to 40% of the gas emitted by some volcanoes during subaerial
eruptions is carbon dioxide.[41] It is estimated that volcanoes release
about 130-230 million tonnes (145-255 million tons) of CO2 into the
atmosphere each year. Carbon dioxide is also produced by hot springs
such as those at the Bossoleto site near Rapolano Terme in Tuscany,
Italy. Here, in a bowl-shaped depression of about 100 m diameter,
local concentrations of CO2 rise to above 75% overnight, sufficient to kill insects and small animals, but it warms
rapidly when sunlit and the gas is dispersed by convection during the day.[42] Locally 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.[43] Emissions of CO2 by human
activities are currently more than 130 times greater than the quantity emitted by volcanoes, amounting to about 27
billion tonnes per year.[44]
In the oceans
There is about fifty times as much carbon dissolved in the sea water of the oceans in the form of CO2 and carbonic
acid, bicarbonate and carbonate ions 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.
[45] Gas solubility decreases as the temperature of
water increases (except when both pressure exceeds 300 bar and temperature exceeds 393 K, only found near deep
geothermal vents)[46] and therefore the rate of uptake from the atmosphere decreases as ocean temperatures rise.
Most of the CO2 taken up by the ocean, which is about 30% of the total released into the atmosphere,
[47] 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 CO2 in the atmosphere has
Carbon dioxide 19
led to decreasing alkalinity of seawater and there is concern that this may adversely affect organisms living in the
water. In particular, with decreasing alkalinity, the availability of carbonates for forming shells decreases,[48]
although there's evidence of increased shell production by certain species under increased CO2 content.
[49]
NOAA states in their May 2008 "State of the science fact sheet for ocean acidification" that:
"The oceans have absorbed about50% of the carbon dioxide (CO2) released from the burning of fossil fuels,
resulting in chemical reactions that lower ocean pH. This has caused an increase in hydrogen ion (acidity) of about
30% since the start of the industrial age through a process known as “ocean acidification.” A growing number of
studies have demonstrated adverse impacts on marine organisms, including:
• The rate at which reef-building corals produce their skeletons decreases, while production of numerous varieties
of jellyfish increases.
• The ability of marine algae and free-swimming zooplankton to maintain protective shells is reduced.
• The survival of larval marine species, including commercial fish and shellfish, is reduced."
Also, the Intergovernmental Panel on Climate Change (IPCC) writes in their Climate Change 2007: Synthesis Report
[50] :
"The uptake of anthropogenic carbon since 1750 has led to the ocean becoming more acidic with an average
decrease in pH of 0.1 units. Increasing atmospheric CO2 concentrations lead to further acidification.... While the
effects of observed ocean acidification on the marine biosphere are as yet undocumented, the progressive
acidification of oceans is expected to have negative impacts on marine shell-forming organisms (e.g. corals) and
their dependent species."
Some marine calcifying organisms (including coral reefs) have been singled out by major research agencies,
including NOAA, OSPAR commission, NANOOS and the IPCC, because their most current research shows that
ocean acidification should be expected to impact them negatively.[51]
The Champagne hydrothermal vent, found at the Northwest Eifuku volcano at Marianas Trench Marine National
Monument, produces almost pure liquid carbon dioxide, one of only two known sites in the world.[52]
Carbon dioxide 20
Biological role
Carbon dioxide is an end product in organisms that obtain energy from breaking down sugars, fats and amino acids
with oxygen as part of their metabolism, in a process known as cellular respiration. This includes all plants, animals,
many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood from the body's tissues to
the lungs where it is exhaled. In plants using photosynthesis, carbon dioxide is absorbed from the atmosphere.
Photosynthesis and carbon fixation
Overview of photosynthesis and respiration. Carbon
dioxide (at right), together with water, form oxygen
and organic compounds (at left) by photosynthesis,
which can be respired to water and (CO2).
Carbon fixation is the removal of carbon dioxide from the air and
its incorporation into solid compounds. Plants, algae, and many
species of bacteria (cyanobacteria) fix carbon and create their own
food by photosynthesis. Photosynthesis uses carbon dioxide and
water to produce sugars and occasionally other organic
compounds, releasing oxygen as a waste product. These
phototrophs use the products of their photosynthesis as internal
food sources and as raw material for the construction of more
complex organic molecules, such as polysaccharides, nucleic acids
and proteins. These are used for their own growth, and also as the
basis for the food chains and webs whereby other organisms,
including animals such as ourselves, are fed. Some important
phototrophs, the coccolithophores synthesise hard calcium
carbonate scales. 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.
Plants can grow up to 50 percent 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.[53] Some people (for
example David Bellamy) believe that as the concentration of CO2 rises in the atmosphere that it will lead to faster
plant growth and therefore increase food production.[54] Recent research supports this position: 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.[55] [56]
Studies have shown that increased CO2 leads to fewer stomata developing on plants
[57] which leads to reduced water
usage.[58] Studies using FACE have shown that increases in CO2 lead to decreased concentration of micronutrients in
crop plants.[59] 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.[60]
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, the World Bank
writes that a mature forest will produce as much CO2 from respiration and decomposition of dead specimens (e.g.,
fallen branches) as is used in biosynthesis in growing plants.[61] 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." [62] 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 CO2 in the upper ocean and thereby promotes the
absorption of CO2 from the atmosphere.
[63]
Carbon dioxide 21
Toxicity
Main symptoms of carbon dioxide toxicity, by increasing volume percent
in air.[16] [64]
Carbon dioxide content in fresh air (averaged
between sea-level and 10 kPa level, i.e., about
30 km altitude) varies between 0.036% (360 ppm)
and 0.039% (390 ppm), depending on the
location.[65]
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.[64]
Toxicity and its effects increase with the
concentration of CO2, here given in volume
percent of CO2 in the air:
• 1% can cause drowsiness with prolonged
exposure.[16]
• At 2% it is mildly narcotic and causes increased
blood pressure and pulse rate, and causes reduced hearing.[64]
• At about 5% it causes stimulation of the respiratory center, dizziness, confusion and difficulty in breathing
accompanied by headache and shortness of breath.[64] Panic attacks may also occur at this concentration.[66] [67]
• At about 8% it causes headache, sweating, dim vision, tremor and loss of consciousness after exposure for
between five and ten minutes.[64]
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[68] although physiological experiments show that such levels can be tolerated for some time.[69]
Adaptation to increased levels of CO2 occurs in humans. Continuous inhalation of CO2 can be tolerated at three
percent inspired concentrations for at least one month and four percent inspired concentrations for over a week. It
was suggestedthat 2.0 percent inspired concentrations could be used for closed air spaces (e.g. a submarine) since
the adaptation is physiological and reversible. Decrement in performance or in normal physical activity does not
happen at this level.[69] [70] However, it should be noted that submarines have carbon dioxide scrubbers which reduce
a significant amount of the CO2 present.
[71]
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 CO2 concentration. The
discomfort will be caused by various gases coming from human respiration and perspiration, and not by CO2 itself.
At 2,000 ppm the majority of occupants will feel a significant degree of discomfort, and many will develop nausea
and headaches. The CO2 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: blackdamp (also called choke 
damp or stythe). Blackdamp is primarily nitrogen and carbon dioxide and kills via suffocation (having displaced 
oxygen). Miners would try to alert themselves to dangerous levels of blackdamp and other gasses in a mine shaft by
Carbon dioxide 22
bringing a caged canary with them as they worked. The canary is more sensitive to environmental gasses than
humans and as it became unconscious would stop singing and fall off its perch. The Davey lamp could also detect
high levels of blackdamp (which collect near the floor) by burning less brightly, while methane, another suffocating
gas and explosion risk would make the lamp burn more brightly).
Carbon dioxide differential above outdoor levels at steady state conditions (when the occupancy and ventilation
system operation are sufficiently long that CO2 concentration has stabilized) are sometimes used to estimate
ventilation rates per person. CO2 is considered to be a surrogate for human bio-effluents and may correlate with other
indoor pollutants. Higher CO2 concentrations are associated with occupant health, comfort and performance
degradation. ASHRAE Standard 62.1-2007 ventilation rates may result in indoor levels up to 2,100 ppm above
ambient outdoor conditions. Thus if the outdoor ambient is 400 ppm, indoor levels may reach 2,500 ppm with
ventilation rates that meet this industry consensus standard. Levels in poorly ventilated spaces can be found even
higher than this (range of 3,000 or 4,000). [Mendell and Shendell references]
Human physiology
CO2 is carried in blood in three different ways. (The exact percentages vary depending whether it is arterial or
venous blood).
• Most of it (about 70% to 80%) is converted to bicarbonate ions HCO3− by the enzyme carbonic anhydrase in the
red blood cells,[72] by the reaction CO2 + H2O → H2CO3 → H
+ + HCO3−.
• 5% – 10% is dissolved in the plasma[72]
• 5% – 10% is bound to hemoglobin as carbamino compounds[72]
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. The decreased
binding to carbon dioxide in the blood due to increased oxygen levels is known as the Haldane Effect, and is
important in the transport of carbon dioxide from the tissues to the lungs. Conversely, a rise in the partial pressure of
CO2 or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the Bohr Effect.
Carbon dioxide is one of the mediators of local autoregulation of blood supply. If its levels are high, the capillaries
expand to allow a greater blood flow to that tissue.
Bicarbonate ions are crucial for regulating blood pH. A person's breathing rate influences the level of 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.
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 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.[72]
The respiratory centers try to maintain an arterial CO2 pressure of 40 mm Hg. With intentional hyperventilation, the
CO2 content of arterial blood may be lowered to 10–20 mm Hg (the oxygen content of the blood is little affected),
and the respiratory drive is diminished. This is why one can hold one's breath longer after hyperventilating than
without hyperventilating. This carries the risk that unconsciousness may result before the need to breathe becomes
overwhelming, which is why hyperventilation is particularly dangerous before free diving.
Breathing produces approximately 2.3 pounds (1 kg) of carbon dioxide per day per person.[73]
Carbon dioxide 23
References
[1] http:/ / www. commonchemistry. org/ ChemicalDetail. aspx?ref=124-38-9
[2] http:/ / pubchem. ncbi. nlm. nih. gov/ summary/ summary. cgi?cid=280
[3] http:/ / www. chemspider. com/ 274
[4] http:/ / fdasis. nlm. nih. gov/ srs/ srsdirect. jsp?regno=142M471B3J
[5] http:/ / ecb. jrc. ec. europa. eu/ esis/ index. php?GENRE=ECNO& ENTREE=204-696-9
[6] http:/ / www. kegg. jp/ entry/ D00004
[7] http:/ / www. nlm. nih. gov/ cgi/ mesh/ 2007/ MB_cgi?mode=& term=Carbon+ dioxide
[8] https:/ / www. ebi. ac. uk/ chebi/ searchId. do?chebiId=16526
[9] http:/ / www. whocc. no/ atc_ddd_index/ ?code=V03AN02
[10] http:/ / www. 3dmet. dna. affrc. go. jp/ html/ B01131. html
[11] http:/ / en. wikipedia. org/ wiki/ %3Acarbon_dioxide?diff=cur& oldid=407813374
[12] Mauna Loa CO2 annual mean data (ftp:/ / ftp. cmdl. noaa. gov/ ccg/ co2/ trends/ co2_mm_mlo. txt) from NOAA. "Trend" data was used. See
also: Trends in Carbon Dioxide (http:/ / www. esrl. noaa. gov/ gmd/ ccgg/ trends/ ) from NOAA.
[13] "Annual Mean Growth Rate for Mauna Loa, Hawaii" (http:/ / www. esrl. noaa. gov/ gmd/ ccgg/ trends/ #mlo_growth). Trends in
Atmospheric Carbon Dioxide. NOAA Earth System Research Laboratory. . Retrieved 28 April 2010.
[14]
This citation will be automatically completed in the next few minutes. You can jump the queue or expand by hand (http:/ / en. wikipedia. org/
wiki/ Template:cite_doi/ _10. 1038. 2f329414a0_?preload=Template:Cite_doi/ preload& editintro=Template:Cite_doi/ editintro& action=edit)
[15] Enting, I.G., 1987: Interannual variation in the seasonal cycle of carbon dioxide concentration at Mauna Loa. Journal of Geophysical
Research 92:D5, 5497-5504.
[16] Toxicity of Carbon Dioxide Gas Exposure, CO2 Poisoning Symptoms, Carbon Dioxide Exposure Limits, and Links to Toxic Gas Testing
Procedures (http:/ / www. inspect-ny. com/ hazmat/ CO2gashaz. htm) By Daniel Friedman - InspectAPedia
[17] "Carbon Dioxide as a Fire Suppressant: Examining the Risks" (http:/ / www. epa. gov/ ozone/ snap/ fire/ co2/ co2report. html). U.S.
Environmental Protection Agency:. .
[18] Staff (16 August 2006). "Carbon dioxide: IDLH Documentation" (http:/ / www. cdc. gov/ niosh/ idlh/ 124389. html). National Institute for
Occupational Safety and Health. . Retrieved 2007-07-05.[19] "Phase change data for Carbon dioxide" (http:/ / webbook. nist. gov/ cgi/ cbook. cgi?ID=C124389& Units=SI& Mask=4#Thermo-Phase).
National Institute of Standards and Technology. . Retrieved 2008-01-21.
[20] Santoro, M.; Gorelli, FA; Bini, R; Ruocco, G; Scandolo, S; Crichton, WA (2006). "Amorphous silica-like carbon dioxide". Nature 441
(7095): 857–860. doi:10.1038/nature04879. PMID 16778885.
[21] Priestley, Joseph; Hey, Wm (1772). "Observations on Different Kinds of Air" (http:/ / web. lemoyne. edu/ ~GIUNTA/ priestley. html).
Philosophical Transactions 62: 147–264. doi:10.1098/rstl.1772.0021. .
[22] Davy, Humphry (1823). "On the Application of Liquids Formed by the Condensation of Gases as Mechanical Agents" (PDF). Philosophical
Transactions 113: 199–205. doi:10.1098/rstl.1823.0020.
[23] Duane, H.D. Roller; Thilorier, M. (1952). "Thilorier and the First Solidification of a "Permanent" Gas (1835)". Isis 43 (2): 109–113.
doi:10.1086/349402.
[24] Strassburger, Julius (1969). Blast Furnace Theory and Practice. New York: American Institute of Mining, Metallurgical, and Petroleum
Engineers. ISBN 0677104200.
[25] Pierantozzi, Ronald (2001). "Carbon Dioxide". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.
doi:10.1002/0471238961.0301180216090518.a01.pub2.
[26] M. Aresta (Ed.) "Carbon Dioxide as a Chemical Feedstock" 2010, Wiley-VCH: Weinheim. ISBN 978-3-527-32475-0
[27] Plant Growth Factors: Photosynthesis, Respiration, and Transpiration (http:/ / www. ext. colostate. edu/ mg/ gardennotes/ 141. html)
[28] http:/ / www. imok. ufl. edu/ veghort/ docs/ physio_121202b. pdf
[29] Carbon dioxide (http:/ / www-formal. stanford. edu/ jmc/ nature/ node21. html)
[30] Stafford, Ned (2007). "Future crops: The other greenhouse effect". Nature 448 (7153): 7153. doi:10.1038/448526a. PMID 17671477.
[31] Clayton, Mark (2006-01-11). "Algae - like a breath mint for smokestacks" (http:/ / www. csmonitor. com/ 2006/ 0111/ p01s03-sten. html).
Christian Science Monitor. . Retrieved 2007-10-11.
[32] Austell, J Michael (2005). "CO2 for Enhanced Oil Recovery Needs - Enhanced Fiscal Incentives" (http:/ / www. touchoilandgas. com/
enhanced-recovery-needs-enhanced-a423-1. html). Exploration & Production: the Oil & Gas Review. . Retrieved 2007-09-28.
[33] "The Coca-Cola Company Announces Adoption of HFC-Free Insulation in Refrigeration Units to Combat Global Warming" (http:/ / www.
thecoca-colacompany. com/ presscenter/ nr_20060605_corporate_hfc-free. html). The Coca-Cola Company. 2006-06-05. . Retrieved
2007-10-11.
[34] "Modine reinforces its CO2 research efforts" (http:/ / www. r744. com/ news/ news_ida145. php). R744.com. 2007-06-28. .
[35] "Enhanced coal bed methane recovery" (http:/ / www. ipe. ethz. ch/ laboratories/ spl/ research/ adsorption/ project03). ETH Zurich.
2006-08-31. .
[36] NOAA ESRL, Trends in Carbon Dioxide (http:/ / www. esrl. noaa. gov/ gmd/ ccgg/ trends/ #mlo), accessed 2010.06
Carbon dioxide 24
[37] Dr. Pieter Tans (3 May 2008) "Annual CO2 mole fraction increase (ppm)" for 1959-2007 (ftp:/ / ftp. cmdl. noaa. gov/ ccg/ co2/ trends/
co2_gr_mlo. txt) National Oceanic and Atmospheric Administration Earth System Research Laboratory, Global Monitoring Division (
additional details (http:/ / www. esrl. noaa. gov/ gmd/ ccgg/ trends/ ).)
[38] "Climate and CO2 in the Atmosphere" (http:/ / earthguide. ucsd. edu/ virtualmuseum/ climatechange2/ 07_1. shtml). . Retrieved 2007-10-10.
[39] Berner, Robert A.; Kothavala, Zavareth (2001). "GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time" (http:/ /
www. geocraft. com/ WVFossils/ Reference_Docs/ Geocarb_III-Berner. pdf) (PDF). American Journal of Science 301: 182–204.
doi:10.2475/ajs.301.2.182. . Retrieved 2008-02-15.
[40] "After two large annual gains, rate of atmospheric CO2 increase returns to average" (http:/ / www. noaanews. noaa. gov/ stories2005/ s2412.
htm). NOAA News Online, Story 2412. 2005-03-31. .
[41] Sigurdsson, Haraldur; Houghton, B. F. (2000). Encyclopedia of volcanoes. San Diego: Academic Press. ISBN 012643140X.
[42] van Gardingen, P.R.; Grace, J.; Jeffree, C.E.; Byari, S.H.; 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, P.R.
(Eds.). Plant responses to elevated CO2: Evidence from natural springs. Cambridge: Cambridge University Press. pp. 69–86.
ISBN 0521582032.
[43] Martini, M. (1997). "CO2 emissions in volcanic areas: case histories and hazaards". In Raschi, A.; Miglietta, F.; Tognetti, R.; van Gardingen,
P.R. (Eds.). Plant responses to elevated CO2: Evidence from natural springs. Cambridge: Cambridge University Press. pp. 69–86.
ISBN 0521582032.
[44] "Volcanic Gases and Their Effects" (http:/ / volcanoes. usgs. gov/ Hazards/ What/ VolGas/ volgas. html). . Retrieved 2007-09-07.
[45] Doney, Scott C.; Naomi M. Levine (2006-11-29). "How Long Can the Ocean Slow Global Warming?" (http:/ / www. whoi. edu/ oceanus/
viewArticle. do?id=17726). Oceanus. . Retrieved 2007-11-21.
[46] Duana, Zhenhao; Rui Sun (2003). "An improved model calculating CO2 solubility in pure water and aqueous NaCl solutions from 273 to
533 K and from 0 to 2000 bar". Chemical Geology 193: 260–271.
[47] Cai, W. -J.; Chen, L.; Chen, B.; Gao, Z.; Lee, S. H.; Chen, J.; Pierrot, D.; Sullivan, K. et al. (2010). "Decrease in the CO2 Uptake Capacity
in an Ice-Free Arctic Ocean Basin". Science 329 (5991): 556–559. doi:10.1126/science.1189338. PMID 20651119.
[48] Garrison, Tom (2004). Oceanography: An Invitation to Marine Science. Thomson Brooks. pp. 125. ISBN 0534408877.
[49] Ries, Justin B.; Anne L. Cohen, Daniel C. McCorkle (2009-12-01). "Marine calcifiers exhibit mixed responses to CO2-induced ocean
acidification" (http:/ / geology. gsapubs. org/ content/ 37/ 12/ 1131. abstract). Geology. .
[50] Climate Change 2007: Synthesis Report (http:/ / www. ipcc. ch/ publications_and_data/
publications_ipcc_fourth_assessment_report_synthesis_report. htm), IPCC
[51] PMEL Ocean Acidification Home Page (http:/ / www. pmel. noaa. gov/ co2/ OA/ )
[52] Lupton, J.; Lilley, M.; Butterfield, D.; Evans, L.; Embley, R.; Olson, E.; Proskurowski, G.; Resing, J.; Roe, K.; Greene, R.; Lebon, G.
(2004). "Liquid Carbon Dioxide Venting at the Champagne Hydrothermal Site, NW Eifuku Volcano, Mariana Arc" (http:/ / adsabs. harvard.
edu/ abs/ 2004AGUFM. V43F. . 08L). American Geophysical Union Fall Meeting (abstract #V43F-08). . Retrieved 21 June 2010.
[53] Blom, T.J.; W.A. Straver; F.J. Ingratta; Shalin Khosla; Wayne Brown (2002-12). "Carbon Dioxide In Greenhouses" (http:/ / www. omafra.
gov. on. ca/ english/ crops/ facts/ 00-077. htm). . Retrieved 2007-06-12.
[54] Global Warming? What a load of poppycock! by Professor David Bellamy Daily Mail, July 9, 2004
[55] Ainsworth, Elizabeth A. (2008). "Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and
elevated ozone concentration" (http:/ / www. plant-biotech. dk/ Meetings/ PBD_Symposium_Plant Stress_litterature/ LisaAinsworth_pdf2.
pdf). Global Change Biology 14: 1642. doi:10.1111/j.1365-2486.2008.01594.x. .
[56] Long, SP; Ainsworth, EA; Leakey, AD; N�sberger, J; Ort, DR (2006). "Food for thought: lower-than-expected crop yield stimulation with
rising CO2 concentrations.". Science 312 (5782): 1918–21. doi:10.1126/science.1114722. PMID 16809532.
[57] F. Woodward and C. Kelly (1995). "The influence of CO2 concentration on stomatal density". New Phytologist 131: 311–327.
doi:10.1111/j.1469-8137.1995.tb03067.x.
[58] Bert G. Drake; Gonzalez-Meler, Miquel A.; Long, Steve P. (1997). "More efficient plants: A Consequence of Rising Atmospheric CO2?".
Annual Review of Plant Physiology and Plant Molecular Biology 48: 609. doi:10.1146/annurev.arplant.48.1.609.