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 Acid rain is caused by the release of the gases SO2 (sulphur dioxide) and NOX (nitrous oxides). The main sources of SO2 in South Africa are coal-fired power stations and metal working industries. The main sources of NOX emissions are vehicles and fuel combustion.

Sulphur dioxide reacts with water vapour and sunlight to form sulphuric acid. Likewise NOX form nitric acid in the air. These reactions takes hours, or even days, during which polluted air may move hundreds of kilometres. Thus acid rain can fall far from the source of pollution.