Indication and causes of ozone trends in the planetary boundary layer over western Europe

Abstract

Air pollution problems are not of a local nature anymore. Formation of O, in the Planetary Boundary Layer (PBL) during photochemical pollution episodes has now been observed world- wide as a predominant type of regional air pollution. It may give rise to O, concentrations of more than 150 ppb over major parts of Europe. Moreover, many atmospheric trace gases are increasing in concentrations throughout the entire troposphere. These may affect atmospheric temperatures and stratospheric, tropospheric and PBL ozone. A short overview of the chemical and physical processes contributing to build-up and degradation of ozone is presented. Finally, some problems associated with trend analyses of near surface ozone are discussed.

It is now believed that O, is a critical factor in the alarming decline in Central Europe's coniferous forest (Prinz et al, 1982). High O, levels not only play a role in damaging plant species, but also lead to irritation of mucous membranes and therefore affect human health in an adverse way. Ozone is furthermore damaging to materials. Moreover, elevated 03 levels are often accompanied by a decline in visibility and O, also exhibits absorption bands in the infra-red in the atmospheric window, e.g., the 9.6 μm band. For this reason it absorbs upward directed terrestrial radiation and thus contributes to the greenhouse effect. Especially O, changes in the upper troposphere are very effective in changing the temperature of the earth. Finally, O, is a precursor molecule for OH, which plays a dominant role in oxidation processes in the atmosphere. For these reasons there is considerable interest in O, climatology and its possible changes due to human activity.