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A number of people have heard of acid rain. But what is acid rain? Where does it come from? Has it ever rained acid anywhere in any part of the world? And more important, what can we do to minimise its effects?

A hundred years ago in Britain the term acid rain was coined by some residents in the town of Manchester when they realised that the air was not only filthy by also acidic which was attacking vegetation, stones and iron metal. In addition through the years incidents of acid rain have been reported in several industrialised countries.

Acid rain is the rain that contains more than the required amount of acid in it. The culprits in acid are sulphur dioxides, nitrogen oxides and nitric oxides, which reaches the atmosphere in many different ways. Rain is naturally slightly acidic. It reacts with carbon dioxide in the air to produce weak carbonic acid, which has little or no effects on the environment. Without human intervention there would be no acid rain problem.

The gases are introduced into the atmosphere through human activities such as burning of fossil fuels (coal and oil) in industries, power generating stations, residential heating and motor vehicles.

Once these gases reach the atmosphere, then react with moisture in the air to form acids (sulphur dioxide to sulphuric acid, nitric oxides to nitric acid). These gases can travel long distances by wind from point of source before they can come down as acid rain and as a result can transcend national boundaries. Hence acid rain can occur at any place in the world. Here in Malawi samples of rain collected from an air pollution monitoring station at LIA (Lilongwe International Airport) have shown traces of acid.

The most commonly cited environmental effects of acid rain include:

Acidification of lakes, streams and groundwater resulting in destruction to aquatic life, damage to forests and crops and corrosion of man-made materials such as buildings and metal structures.

The way out from this problem is the reduction in the emission of these gases into atmosphere, which can be done by strict enforcement of existing air pollution control measures.

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