ACID-RAIN AND BELOW-CLOUD SCAVENGING IN SOUTH-WESTERN CHINA

Major urban areas in south-western China exhibit unique air pollution problems due to increasing use of high sulphur-content fuels in an env ironment of unfavourable topography and climate. Ambient levels of sul phur dioxide exceed the air quality objectives, and this gas is the ma jor precursor of acid rain. Cloudwater chemistry studies are reported for urban, suburban and countryside locations, during the period 1985- 1989. Although cloudwater acidity was found to increase towards the cl oud base, the acidity was much greater for rainwater samples collected simultaneously, and was more pronounced in urban rather than neighbou ring suburban or countryside regions. The main contribution to the aci dity arises from below-cloud scavenging of gas and aerosol and model c alculations are able to simulate this behaviour.