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.