Environmental Engineering Reference
In-Depth Information
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Figure 10.8 Trend of CO 2 concentrations in the atmosphere 1000-2000 A . D . (Data from Carbon Dioxide
Information Analysis Center, 2000. Trends Online: A Compendium of Data on Global Change. Oak Ridge:
Oak Ridge National Laboratory.)
10.3.2
Methane
Methane is emitted by natural processes, such as (a) the anaerobic decomposition of organic matter
in swamps and marshes and (b) enteric fermentation of fodder in guts of animals. Anthropogenic
emissions of CH 4 come from leakage of oil and gas wells, gas pipe lines, and storage and trans-
portation vessels. Accumulated CH 4 in coal seams is mostly vented into the atmosphere when
mine shafts are dug into the seams. Worldwide concentrations are presently about 1.7 ppmv and
are growing by about 0.6% per year. Considering that CH 4 is a stronger absorber of IR radiation
per molecule than CO 2 (see Section 10.2.3), its contribution to the greenhouse effect is significant
even though its present concentration in the atmosphere is only about 5E(
3) times that of CO 2 .
Assuming continued growth of CH 4 and CO 2 in the atmosphere, by 2100 CH 4 may contribute as
much as 15% to global warming. 9
10.3.3
Nitrous Oxide
Nitrous oxide (N 2 O) is to be distinguished from the air pollutants NO and NO 2 , emitted during
fossil fuel combustion. 10 Nitrous oxide is emitted naturally during bacterial nitrogen fixation in soils
9 Houghton, J. T., G. J. Jenkins, and J. J. Ephraums, Eds., 1995. Climate Change, the IPCC Scientific Assessment .
Cambridge: Cambridge University Press.
10 N 2 O, called laughing gas, is used as an anesthetic in dental surgery.
 
 
 
 
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