a few decades, either through direct effects by ozone itself or indirectly through its effect on other radiatively active trace species. Further­ more, ozone may have adverse effects on vegetation over large continental areas due to enhanced levels which have been measured to take place. As it is well known that ozone plays a key role in the oxidation of a large number of chemical species in the troposphere, natural as well as man-made, the atmospheric distribution of important trace species like sulfur dioxide, nitrogen oxides and hydrocarbons could be markedly changed as a result of ozone changes. The rapidly increasing interest in tropospheric ozone, and the key role ozone plays in several atmospheric areas as well the obvious increase in the tropospheric concentration of ozone made ozone a natural choice as a topic for the workshop.