Atmospheric methane, anthropogenic sources

Concerns over atmospheric methane as a greenhouse gas and the large contribution of biomethanogenesis as a source of this gas make it important to determine the relative significance of various components of this activity. A recent paper (8) summarized estimates (28-30) of source fluxes of atmospheric methane based on several carbon isotopic studies and presented new data on natural sources and biomass burning. These data (Table III) show that of a total flux of 594 million tons (Tg) per year, 83% is produced via biomethanogenesis from a combination of natural (42%) and anthropogenic (41%) sources. 

The western Siberian region of Russia is characterized by numerous intensive natural and anthropogenic sources of methane formation. These are marshes, tundra, permafrost, oil and gas deposits. In this region, flux FlCH4 varies widely both during the year and shorter time periods. From measurements carried out by Jagovkina et al. (2000) on the Yamal coastline in June 1996, the CH4 concentration in the atmosphere... 

The first global CH4 budgets were compiled by Ehhalt (1974) and Ehhalt and Schmidt (1978), who used available published information to estimate emissions of CH4 to the atmosphere. They considered paddy fields, freshwater sources (lakes, swamps, and marshes), upland fields and forests, tundra, the ocean, and enteric fermentation by animals as biogenic sources. Anthropogenic sources included industrial natural gas losses and emission from coal mining, and were considered to be free. Observations of CH4 placed an upper limit on anthropogenic sources. Oxidation by the OH radical, as well as loss to the stratosphere by eddy diffusion and Hadley circulation, were presumed to be methane sinks. In spite of lack of data, this work correctly identified the major atmospheric sources and did... 

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. 

The total annual input of methane from all sources to the atmosphere shown in Table 6.4 is 540 Mt, while the estimated output from atmosphere to sinks is 500 Mt. The potential inaccuracies in flux data can be seen by comparing the observed carbon isotopic signature of atmospheric methane of —47%o with that calculated from the data in Table 6.4 of c— 54%o (the latter is actually equivalent to —58%o upon correcting for the kinetic isotope effect (see Box 1.3) that operates during the hydroxyl abstraction reaction). There are clearly major gaps in our understanding of the pathways of methane into and out of the atmosphere and the fluxes involved, as there are for many anthropogenic substances (see Chapter 7). 

I. 69 X 10 tons [5]. The greatest portion is due to methane from natural sources. Together with anthropogenic sources, the annual CH4 production is greater than 1.45x 10 tons. Estimates of the residence time of CH4 in the atmosphere differ from each other and range from 0.9 to 4 years [5, 8]. The second in importance to CH4 are terpenes, for which the estimates of annual emissions from natural sources are 1.45 x 10 tons [5]. The estimate of hydrocarbon emissions (except methane) in Europe in 1980 are summarized in Table 5.17 [45]. 

Chloroform is one of the chlorinated derivatives of methane, supplied into the atmosphere only from anthropogenic sources. It may be formed as a side product during the water chlorination by the following reactions [49] ... 

Methane is the most abundant hydrocarbon in the atmosphere. Table 2.9 summarizes the global sources of CH4, which are estimated at 535 Tg(CH4) yr (range 410 to 660) (IPCC, 1995). Of the estimated global annual emissions, 160 Tg(CH4) yr is attributed to natural sources, with the most prominent contribution being emissions from wetlands. Of the estimated 375 Tg(CH4) yr from anthropogenic sources, 100 Tg(CH4) yr comes from fossil fuel combustion, and the remainder from biospheric sources. Methane is removed from the atmosphere through reaction with hydroxyl radicals (OH) in the troposphere, estimated at 445 Tg(CH4) yr, and by reaction in the stratosphere, estimated at 40 Tg(CH4) yr. Microbial uptake in soils contributes an estimated 30 Tg(CH4) yr removal rate. The im-... 

Wetlands, including tropical and subtropical irrigated rice, have soil conditions suitable for both methane and nitrous oxide formation and, as a result, are major anthropogenic sources of atmospheric methane and nitrous oxide. Aerobic and anaerobic enviromnents existing in wetland soil-plant systems provide conditions for both production and consumption of methane and nitrous... 

Atmospheric methane is produced from both natural sources (e. g. wetlands) and human activities. The total sources of methane released into the atmosphere for 1990 were (the IPCC 1995 estimates are in parenthesis) in the range of 200-520 (410-660) Tg CH4 per year, of which 70-140 (110-210) Tg CH4 yr derived from natural sources and 130-380 (300-450) Tg CH4 yr" from anthropogenic sources (IPCC 2007). The anthropogenic sources are further broken down into 50-70 (70-120) Tg CH4 yr related to fossil fuels and 80-310 (200-350) Tg CH4 yr from biospheric sources (Table 2.69). All estimates are considerably smaller than those provided by IPCC (1995). 

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