Atmospheric chemistry: response to human influence

Abstract

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 NO2, HNO3, O, O3, 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 O3. 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 CH4, H2, CH3Cl 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 N2O with a related impact on stratospheric NOx. Chlorocarbon industry provides an important source of stratospheric chlorine, and enhanced levels of stratospheric Clx and NOx may cause a significant reduction in the abundance of atmospheric O3, 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.