Trends in rain quality data from the South African interior

Acidity in rain has several natural origins, such as biomass burning, and a gricultural and maritime sources. Emissions from power-station stacks and i ndustry are of concern. The economic cost of fitting control technologies t o limit the emissions of acid precursors such as sulphur dioxide and oxides of nitrogen to the atmosphere is potentially very large. It is thus essent ial that the need for controls be adequately demonstrated before industry c ommits itself to this action. Such demonstration requires a detailed unders tanding of the mechanisms involved in acidification and the time it will ta ke for ecosystem responses to develop. This needs to be seen within the con text of continuing progress towards fundamentally cleaner technologies and the fact the South Africa is a relative latecomer as an industrialized coun try. Rain quality has been monitored by Eskom (the national electricity sup plier) since the mid-1980s, end this paper analyses trends over time for se ven sites with data for seven or more years. Trends in volume-weighted conc entrations are evident for several parameters, with chloride, potassium, hy drogen and sodium increasing over time, and acetate, magnesium and formats decreasing at almost all sites. Total anions are increasing at three sites, and decreasing at one, while total cations are increasing at six sites. Th e ratio of total anions to total cations is decreasing significantly at all but one site. The major trend is related to biomass burning, and appears t o have been affected by drought over this period. Fossil fuel-derived acidi ty is increasing only at Warden.