Tropospheric Ozone: An Overview

Abstract

Although only about 10% of all atmospheric ozone is located in the troposphere, it is the main driver of the photochemical processes which lead to the recycling of most of the gases that are emitted into the atmosphere by natural processes and anthropogenic activities. Substantial changes are taking place in the troposphe- ric ozone abundance. In this paper, an overview is given of the chemical processes that lead to ozone fo~mation and destruction in the troposphere, emphasizing human impact on the global scale. In the northern hemisphere, anthropogenic emissions of NOx clearly lead to high ozone concentrations du~ing photochemical pollution episodes. However, also in the background free troposphere, pronounced ozone concentra- tion increases have occurred, which are here confirmed by a review of measurements that were made in the 1930's - 50's in Europe. The potential for tropospheric ozone production from carbon monoxide and hydrocarbon oxidation, with NOx acting as catalyst, is enormous. At this stage, only at most 10% of this does actually occur, due to insufficient NO x in the background troposphere. Future human developments that lead to increasing NO emissions may, therefore, lead to further ozone increases, especially in the tropics.