The tropospheric ozone problem.

Derived from measurements it has been concluded that in the last hundred years the ground-based ozone concentration has risen by about a factor of two. Models also show a doubling of the tropospheric ozone content due to human activities. It is very likely that mean ozone concentration will further increase. In contrast, episodes with excess ozone levels ("summer smog") have become rare in Central Europe during the last five years. This controversial finding is explained by the reduction of NOx (being the "catalyst" in ozone formation) as well as of reactive ozone precursors like non-methane volatile organic compounds (NMVOC) due to catalytic converters in motor cars. On the other hand, a further increase of methane emissions and probably carbon monoxide is responsible for regional and even global background increase of ozone. The principal formation mechanisms are well understood, despite some open questions concerning the contribution of specified organic substances, especially from biogenic sources. Less known, however, are chemical sinks, especially heterogeneous processes. A better knowledge of these processes may influence the global ozone budget by up to 30% and the regional/local even more. The key question considering ozone abatement is that for determining precursors in time and space. Air quality control has also to consider the question of ozone impact on vegetation, animals and man. Moreover, ozone also contributes to the greenhouse effect. Air pollution control, based on ecological and economic principles, needs a complex understanding of the atmosphere and its interaction with the biosphere. Measures should not be focused on single pollutants, but on impacts, which always have complex causes. Only quantified impacts with consequences unaccepted by society may be a problem.