Methane atmospheric concentration

Rasmussen, R. A. and Khalil, M. A. K. (1984). Atmospheric methane in recent and ancient atmospheres Concentrations, trends, and interhemispheric gradient. /. Geophys. Res. 89,11599-11604. 

Problems may arise when the atmospheric concentration of greenhouse gases increases. Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. These increases have enhanced the heat-trapping capability of the earth s atmosphere. 

Atmospheric concentrations of (a) carbon methane, and (c) nitrous oxide over the past... 

Attention also must be given to the explosion and fire hazards presented by combustible organic vapors and combustible gases such as hydrogen and methane. These vapors are readily ignited by static electricity, electrical sparks from most laboratory appliances, open flames, and other highly exothermic reactions. Thus appreciable atmospheric concentrations of combustible vapors should be avoided. 

Methane is removed continually from the atmosphere by reaction with OH radicals (Section 8.3). In contrast, chlorofluorocarbons and related volatile compounds are inert under the conditions of the lower atmosphere (troposphere), so atmospheric concentrations of these refrigerants and solvents will tend to increase as long as releases continue. The chief concern over chlorofluorocarbons is that they are a major factor in destruction of the stratospheric ozone layer (Section 8.3). They have been banned under the Montreal Protocol of 1988, but it is important that whatever substitutes (inevitably greenhouse active) are introduced to replace them degrade relatively quickly in the troposphere to minimize any contribution they may be capable of making to greenhouse warming. 

Mayer E.W., Blake D.R., Tyler S.C., Makide Y., Montague D.C. and Rowland F.S., Methane-, interhemispheric concentration gradient and atmospheric residence time. Proc. Natl. Acad. Sci. USA , 79, 1366-1370 (1982). 

It is estimated that about 500 million tons of methane are being added to the air each year (Craig and Chou, 1982), largely by anaerobic production in rice paddies and wetlands as well as from the metabolism of ruminant domestic animals and, possibly, African termites (Rasmussen and Khalil, 1981 Zimmerman et d., 1982). This gas is slowly oxidized by reactions with Hydroxyl free radical. Its atmospheric content is around 5 gigatons, indicating that the residence time in the atmosphere is about 10 years. As Figure 12 shows, since 1965 the atmospheric concentration of methane has increased by about 3096. If this rate continues, the methane concentration will have doubled early in the 21st century. 

Future changes in atmospheric concentration of other greenhouse gases (methane N2O, chlorofluorocarbons, tropospheric ozone). 

There also are major sources of organic compounds from nature. Methane is a major emission from the natural environment and in non-urban atmospheres concentrations generally range between 1-1.5 ppm (6). The major source of atmospheric methane is the decomposition of organic material in swamps, marshes, and other bodies of water. Natural gas seepage possibly significantly contributes methane to the atmosphere in certain petroleum areas. It is estimated that natural sources of methane are about 1600 X 10 tons annually (7). 

Methane is highly flammable and is therefore an explosion and fire hazard the lower explosive limit is 5-15% by volume. Extreme care must be taken to keep areas of high concentration free from ignition sources, such as sparks from static electricity. Explosion-proof equipment should be used in these areas. Many people believe that methane is an important greenhouse gas, and that the apparent threefold increase in atmospheric concentrations over the last 200 years affects the stratospheric ozone layer and the oxidizing capacity of the atmosphere. 

In this work atmospheric concentrations of a large number of non-methane volatile organic compounds (NMVOCs) emitted by different anthropogenic sources, in particular from traffic exhaust and solvent use, have been investigated. The results from the studies should provide more information about the relative importance of road traffic and solvent use to the total NMVOC emission in Europe. 

If anything, the atmospheric concentration of methane follows the air-temperature trend in Fig. 6.25 more closely than does the C02 record.The more direct coupling of methane to air temperature suggests that terrestrial sources of the gas were probably responsible for the fluctuations in concentration. Increased humidity in the tropics and active plant growth in high-latitude wetlands can be expected to increase methane production during interstadials (Brook etal. 1996). 

During the next half-century, the atmospheric concentration of these is likely to rise to 400 ppm and even 600 ppm if we continue to bum fossil fuels. Such concentrations will lead to methane from the tundra and the temperature rise from that may well make the surface of this earth uninhabitable. 

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