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acid rain — English
Rainwater is normally more acidic than pure, clean water. Pure, clean water has a neutral pH of 7,0 but rainwater normally has a lower pH; the average pH of rainwater is 5,6. The reason why rainwater is more acidic than pure water is because rainwater contains small amounts of dissolved natural particles as well as some anthropogenic (human-made) pollutants that act as condensation nuclei. The atmosphere is never devoid of natural substances like dust, smoke, ash and pollen and these dissolve in the rainwater as the raindrops travel through the atmosphere. Hence, all rainwater contains small volumes of carbon, sulphur and nitrous compounds which turn the rainwater into very weak, diluted carbonic, sulphuric and nitric acids. Human activities release huge volumes of pollutants, such as carbon dioxides, sulphur dioxides and nitrogen oxides into the atmosphere. This is called air pollution (see “air pollution”). All of these pollutants could dissolve in the moisture in the atmosphere or in the raindrops, with the result that the rain falling from a heavily polluted atmosphere is more acidic than what rainfall normally is. Rain that contains more than normal the concentrations of these acids – especially carbonic and sulphuric acids – becomes “acid rain”. Acid rain has pH values of 5,2 to as low as 5,0 and is a far more corrosive solution than normal rainwater. Vegetation dies when it receives acid rain for a lengthy period. Millions of hectares of cypress, spur, spruce, pine and birch forests in Northern Europe and Canada have already been lost as a result of acid rain caused by industrial airpollution in Southern European countries and the USA. From a geographical point of view it is very important that air pollution caused in one region, might result in acid rain in another region since winds convey the pollutants. In the Eastern and South-Eastern Highveld of South Africa (mainly Mpumalanga and Limpopo) a wide variety of problems might possibly be ascribed to the acid rain caused by air pollution from coal-burning power stations in the Eastern Highveld and the petrochemical industry in Sasolburg and Secunda. These problems range from respiratory diseases in children, to sluggish growth and die-off of pine forests, to decreasing soil productivity (through soil acidification), but no irrefutable cause and result relationships have yet been established.
