Methane global concentration

After water vapor and C02, methane (CH4) is the third most important greenhouse gas. Each additional molecule of CH4 added to the atmosphere absorbs about 20 times as much long-wave infrared radiation as does a molecule of carbon dioxide. This occurs in part because some of the absorption spectrum of methane lies in windows in the carbon dioxide absorption spectrum (see Fig. 4-42) therefore, methane absorbs wavelengths that are not already being highly attenuated by carbon dioxide. Currently, the global concentration of methane in the atmosphere is approximately 1.7 ppm and is increasing at an annual rate of approximately 0.01 ppm per year (Table 4-14). The seasonal fluctuations shown in Fig. 4-44 may correspond to seasonal... 

The Anthropocene could be said to have started in the late eighteenth century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane. 

Byrd GT, Fisher FM, Sass RL. Relationships between methane production and emission to lacunal methane concentrations in rice. Global Biogeochem. Cycl. 2000 14 73-... 

The first thing that stands out in Table 6.2 is that the OH-CH4 rate constant, 6.2 X 10 15 cm3 molecule 1 s-1, is much smaller than those for the higher alkanes, a factor of 40 below that for ethane. This relatively slow reaction between OH and CH4 is the reason that the focus is on non-methane hydrocarbons (NMHC) in terms of ozone control in urban areas. Thus, even at a typical peak OH concentration of 5 X 106 molecules cm 3, the calculated lifetime of CH4 at 298 K is 373 days, far too long to play a significant role on urban and even regional scales. Clearly, however, this reaction is important in the global troposphere (see Chapter 14.B.2b). 

There were relatively few measurements of atmospheric methane concentrations prior to about 1980, except for a set from 1963 to 1970 by Stephens and co-workers (Stephens and Burleson, 1969 Stephens, 1985), which were in the 1.37-1.57 ppm range. The current global mean concentration of methane is 1.72 ppm, with higher concentrations in the Northern than... 

GLOBAL IMPACT OF AIRCRAFT EMISSION ON OZONE CONCENTRATIONS AND METHANE LIFETIME RESULTS FROM THE 1999IPCC AIRCRAFT ASSESSMENT... 

Table 3. Base background scenarios and subsonic aircraft NOx scenarios used in the global model studies. These scenarios are used to study ozone increases, non linearity in ozone productions from aircraft emissions and the impact on methane lifetime and methane concentrations for future aircraft emissions.

Since TO is a greenhouse gas, emissions of it can indirectly affect the formation of atmospheric greenhouse effect by influencing the TO concentration field. Moreover, MGC/TO precursors change the hydroxyl concentration field and, hence, the oxidation power of the troposphere. In its turn, the distribution of hydroxyl concentration in the troposphere controls the lifetime and, thus, the level of concentration of methane at the global scale. 

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