The Natural and Perturbed Troposphere

It is now generally accepted that the troposphere is a region of great chemical complexity and that many human activities may alter the chemical structure of the region. A prerequisite to any realistic assessment of human impacts on pollution and climate is an understanding of the natural budgets of atmospheric gases. This requires a detailed knowledge of physical, chemical, and biological processes within the various reservoirs which are involved in the cycles of these gases. This paper first reviews the processes important in establishing the concentrations of a number of tropospheric species and discusses gaps in our current understanding of these processes. We identify the points at which man may intervene in the major cycles of atmospheric gases and describe the possible consequences of such interventions. Pollutants released into the troposphere may adversely affect the environment by virtue of their chemical interactions with other atmospheric species, their radiative properties, or both. Problems discussed in this review include the growth of atmospheric CO2 resulting from the burning of fossil fuels and its possible climatic effects, the consequences of increased levels of CO emission on the self-cleansing ability of the troposphere and on the radiation budget, and possible changes in the stratospheric odd nitrogen and ozone amounts due to increased use of fertilizers in agriculture. The magnitude of the perturbations predicted by various model studies are reviewed with particular attention to uncertainties which may affect the results.