Acid Rain

What is Acid Rain?

Acid rain is the term used to describe the deposition of acidic air pollution. Although some air pollutants fall directly back to Earth, a lot of them return in rain, snow, sleet, hail, mist or fog, hence the term "acid rain".

All rain is slightly acidic as it contains carbon dioxide, a gas found in air. Unpolluted rain usually has a pH of between 5 and 6. Acid rain has been found to have a pH as low as 3 and in some cases even lower.

1   2   3   4   5   6   7   8   9   10   11   12   13   14
       Acid              Neutral                     Alkali

What Causes Acid Rain?

When power stations, factories, houses and cars emit pollution into the air, it contains chemicals like sulphur dioxide and nitrogen oxides. These chemicals may either fall directly back to the Earth due to gravity, these are called dry deposition, or they may mix with water (moisture) in the air to form acids, this is wet deposition. Once acids have formed, they can be transported long distances by the wind before being deposited in rain, snow or hail.  

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In Britain, 90% of sulphur dioxide pollution comes from power stations and industry. Once in the air, sulphur dioxide mixes with moisture to form sulphuric acid, which will later fall as acid rain.

One of the largest sources of air pollution in Britain is transport. The number of vehicles on Britain’s roads is constantly increasing and pollution from them is now a major problem. Today there are about 23 million vehicles on the road in Britain, 20 million of which are cars.  Nitrogen oxides pollution from cars contributes to acid rain. The nitrogen oxides given ...

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