Atmospheric chemistry: response to human influence

Abstract

Present understanding of global atmospheric chemistry is reviewed. Models are presented and compared with a wide range of atmospheric observations, with emphasis on the stratosphere. In general, excellent agreement is found between the calculated and observed distributions of long lived trace gases. The abundances of many shorter lived species are also satisfactorily reproduced, including NO 2 , HNO 3 , O, O 3 , OH and ClO. Discrepancies between theory and observation are examined and their significance assessed. The influence of human perturbations due to combustion, agriculture and chlorocarbon releases is discussed with emphasis on O 3 . Uncertainties associated with present models are highlighted. Combustion related releases of CO cause a decrease in the abundance of tropospheric OH with consequent increase in the concentrations of CH 4 , H 2 , CH 3 Cl and other halocarbons. CO emissions may become sufficiently large during the next century to induce substantial increases in tropospheric ozone on a global scale. Recombination of nitrogen fixed by agriculture and combustion may lead to an enhanced source of atmospheric N 2 O with a related impact on stratospheric NO x . Chlorocarbon industry provides an important source of stratospheric chlorine, and enhanced levels of stratospheric Cl x and NO x may cause a significant reduction in the abundance of atmospheric O 3 , by as much as 10% during the next century. Perturbations due to various anthropogenic activities interact in a nonlinear fashion and the influence on atmospheric chemistry is correspondingly complex.

The seasonal cycle of N2O

“…Reaction (2a) is the major source of odd nitrogen (NO x ) in the stratosphere and plays a fundamental role in regulating the ozone layer [McElroy and McConnell, 1971;Crutzen, 1971;Nicolet and Vergison, 1971;Logan et al, 1978;Wennberg et al, 1994]. Note that a consequence of the above reactions is that the mixing ratio of N 2 O in the stratosphere is depleted relative to that in the troposphere.…”

Nonlinear response of stratospheric ozone column to chlorine injections

“…Accordingly, efforts to understand the future impact of continued usage of chlorofluoromethanes (CFM), CH3CC13, and of nitrous oxide have broadened in scope to consider the coupled effects of increasing atmospheric CO2 and CFM concentrations [Luther eta [Weiss, 1981]. Further, Logan et al [1978] demonstrated the potential effects of combustion-produced gases on tropospheric 03 and OH and through these OH changes, the effects on stratospheric chlorine and ozone concentrations. The more speculative but plausible increases in tropospheric ozone due to commercial aircraft operations [Liu eta!., 1980;Derwent, 1982] would necessitate a still broader view of atmospheric ozone perturbations, especially from the point of view of trend assessment in ground-based total ozonecolumn measurements.…”

Modeling of Chemical Processes in the Troposphere and Stratosphere.

“…Stratospheric chemistry has been reviewed extensively by several authors (Nicolet, 1975;Johnston and Pokolske, 1978;Logan et al, 1978;Thrush, 1978). An excellent summary of information available up to the mid-1979 is given by NASA (1979).…”