Global warming tropospheric

Recent estimates indicate that the level of carbon dioxide in the atmosphere has increased by a third since the beginning of the industrial age, and that it contributes significantly to global warming. Other major contributors include methane, tropospheric ozone, and nitrous oxide. Methane is the principal component of natural gas, but it is also produced by other sources such as rice paddies and farm animals. Tropospheric ozone is generated naturally and by the sunlight-... 

Nitrous oxide (N2O) is an important greenhonse gas with a radiative forcing effect 310 times that of CO2 and a lifetime in the troposphere of approximately 120 years. Part of the N2O is converted to NO in the stratosphere, and so contributes to depletion of ozone. Nitric oxide (NO) is very reactive in the atmosphere and has a lifetime of only 1-10 days. It contribntes to acidification and to reactions leading to the formation of ozone in the troposphere, and so also to global warming. 

In the discussion of ecotoxicity the perhalogenated chlorofluorocarbons (CFCs), hydrogen-containing hydrochlorofluorocarbons (HCFCs) and the chlorine-free hydrofluorocarbons (HCFs) have been for several years in the headlines (the depletion of the ozone layer in the stratosphere, the greenhouse or global warming effects in the troposphere).75... 

Conversely, generating hydrogen from sustainable sources would reduce emissions of carbon monoxide and NOx, with a consequent fall in tropospheric ozone levels. This would improve air quality in many regions of the world. Furthermore, C02 emissions would be reduced, thereby slowing the global warming trend. 

Globally, the oxides of nitrogen, NO (nitric oxide), NO2 (nitrogen oxide), and N2O (nitrous oxide), are key species involved in the chemistry of the troposphere and stratosphere. NO and N2O are produced mostly by microbial soil activity, whereas biomass burning is also an important source of NO. Nitric oxide is a species involved in the photochemical production of ozone in the troposphere, is involved in the chemical produaion of nitric acid, and is an important component of acid precipitation. Nitrous oxide plays a key role in stratospheric ozone depletion and is an important greenhouse gas, with a global warming potential more than 200 times that of CO2. 

Table 6.5 Direct global warming potential (GWP) of tropospheric gases (molecule for molecule) relative to C02 (after Highwood Shine 2000 Jain et al.2000 Houghton et al. 2001)...

As instanced further in Chapters 3 and 5, ozone is formed in the troposphere as a result of urban air pollution and forest and grass fires. As a result of these anthropogenic activities, the levels of ozone in the troposphere have probably increased since pre-industrial times. The best guess is that approximately 10% of the increased global warming potential of the atmosphere results from increases in tropospheric ozone, although this value is very uncertain. 

The ability of these compounds to absorb infrared radiation varies widely from compound to compound, as does their life in the atmosphere before they undergo photochemical reactions or are absorbed in the oceans or on land. Methane has a concentration of only l.Vppmv in the troposphere, which is much less than that of carbon dioxide. On the other hand, each molecule of methane has a global warming potential (GWP) value that is 21 times that of carbon dioxide over the course of 100 years. (Note the GWP value has been developed to compare the ability of each greenhouse gas to trap infrared radiation over 100 years relative to another gas by convention, carbon dioxide has a GWP of 1.) Although methane has a relatively short lifetime (a few years)... 

Johnson, C., Henshaw, J., and Mclnnes, G. (1992) The impact of aircraft NO, emissions on tropospheric ozone and global warming. Nature, 355,69-71. 

Global warming (greenhouse effect) Hypothesis that buildup of carbon dioxide in the troposphere from combustion of fossil fuels and other gases with similar properties will allow solar radiation to reach the earth but impede radiation of infrared energy from the earth to the troposphere, thus increasing the temperature of the earth and its immediate atmosphere in this century. 

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