Natural and human-related sources of ozone-forming trace gases in southern Africa

Abstract

Nitric oxide (NO) reacts with hydrocarbons and carbon monoxide (CO) in the presence of sunlight to form ozone in the lower atmosphere. Tropospheric ozone can be harmful to plants and animals, and is usually regarded as a symptom of industrial or vehicular pollution. The cloud of tropospheric ozone which forms over southern Africa every spring probably has its main origin in natural emissions of the ozone-forming trace gases, including CO from vegetation fires, emissions of NO from soils, and hydrocarbons from plants. The observed levels of ozone are not dangerous to humans, but form a high background level to which pollutants of human origin are added.