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Methane (CH4)

Methane (CH4)


Methane is an invisible, odorless, and combustible gas present in trace concentrations in the atmosphere. It is the major component of natural gas, a fossil fuel commonly used for heating and cooking. The molecule consists of one carbon atom bonded to four hydrogen atoms (CH4), making it the simplest member of a chemical family known as hydrocarbons. Other hydrocarbons include ethane (C2H6), propane (C3H8), and butane (C4H10).

As a greenhouse gas , methane ranks second to carbon dioxide. Methane levels, based on ice core samples, have more than doubled since 1750 (from 0.7 to 1.7 parts per million), largely due to human activity. On a molecule-for-molecule basis, methane is twenty-three times more potent as a greenhouse gas than carbon dioxide. Both gases are targeted for emissions reduction in the Kyoto Protocol.

Methane enters the atmosphere from both natural (30 percent) and anthropogenic (70 percent) sources. Methanogens (methane-producing bacteria in swamps and wetlands) are the largest natural source.

Anthropogenic sources of methane include leaks during fossil fuel mining, rice agriculture, raising livestock (cattle and sheep), and municipal landfills. Methanogens thrive in the oxygen-free (anaerobic) environment of landfills, releasing the gas in significant quantities. The gas is purposefully ignited to prevent explosion or captured for its commercial value as a fuel.

Livestock such as sheep, goats, camel, cattle, and buffalo currently account for 15 percent of the annual anthropogenic methane emissions. These grass-eating animals have a unique, four-chambered stomach. In the chamber called the rumen, bacteria break down food and generate methane as a by-product. Better grazing management and dietary supplementation have been identified as the most effective ways to reduce livestock methane emissions because they improve animal nutrition and reproductive efficiency. This general approach has been demonstrated by the U.S. dairy industry over the past several decades as milk production increased and methane emissions decreased.

see also Fossil Fuels; Global Warming; Greenhouse Gases; Landfill; Petroleum.

Bibliography

DeLong, Eward F. (2000). "Resolving a Methane Mystery." Nature 407:577579.

Simpson, Sarah. (2000). "Methane Fever." Scientific American 282(2):2427.

Turco, Richard P. (1997). Earth under Siege: From Air Pollution to Global Change. New York: Oxford University Press.


internet resource

Intergovernmental Panel on Climate Change, Working Group I. "Atmospheric Chemistry and Greenhouse Gases." Climate Change 2001: The Scientific Basis. Available from http://www.ipcc.ch.

Marin Sands Robinson

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methane

methane (mĕth´ān), CH4, colorless, odorless, gaseous saturated hydrocarbon; the simplest alkane. It is less dense than air, melts at -184°C, and boils at -161.4°C. It is combustible and can form explosive mixtures with air. Methane occurs naturally as the principal component of natural gas; it is formed by the decomposition of plant and animal matter. When this decomposition occurs underwater in swamps and marshes, marsh gas is released. The firedamp of coal mines is chiefly methane. In the atmosphere methane is a greenhouse gas, helping to trap infrared radiation and warm the earth (see also global warming). Methane, in the form of icelike methane hydrate (composed of methane and frozen water), also is stored in seabed sediments at ocean depths where sufficiently low temperatures and high pressures prevail.

Methane can be prepared in the laboratory by heating sodium acetate with sodium hydroxide, by the reaction of aluminum carbide with water, by the direct combination of carbon and hydrogen, or by the destructive distillation of coal or wood. As natural gas, methane is widely used for fuel. It is also used for carbonizing steel. It is unaffected by many common chemical reagents but reacts violently with chlorine or fluorine in the presence of light and is therefore important as a starting material for the synthesis of solvents, e.g., methylene chloride, chloroform, and carbon tetrachloride, and of some of the Freon refrigerants.

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methane

methane (CH4) Colourless, odourless hydrocarbon, the simplest alkane (paraffin). It is the chief constituent of natural gas, from which it is obtained. It is produced by decomposing organic matter, such as in marshes, which led to its original name of ‘marsh gas’. In the air, it contributes to the greenhouse effect and an increase in global temperature. Methane is used in the form of natural gas as a fuel. Properties: m.p. −182.5°C (−296.5°F); b.p. −164°C (−263.2°F).

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methane

methane(CH4) The simplest hydrocarbon compound, which is released as a gaseous by-product of the metabolic activity of certain bacteria. The principal sources of atmospheric methane are swamps, marshes, and natural wetlands (which may also be nature reserves), paddy-rice fields, and cellulose-digesting bacteria in the guts of termites and ruminant cattle. Methane is an important greenhouse gas, absorbing long-wave radiation at wavelengths of about 10 μm.

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methane

meth·ane / ˈme[unvoicedth]ˌān/ • n. Chem. a colorless, odorless flammable gas, CH4, that is the main constituent of natural gas. It is the simplest member of the alkane series of hydrocarbons.

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methane

methane XIX. f. METH(YL) + -ANE.

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methane

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