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Acid rain

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Acid rain can make the leaves fall off trees.
A gargoyle that has been damaged by acid rain

Acid rain is rain that is unusually acidic. In other words, it is rain that has high levels of hydrogen ions (low pH). Acid rain can have harmful effects on plants, animals and humans. Acid rain is caused when gaseous compounds of ammonium, carbon, nitrogen, and sulphur are released into the atmosphere. The wind carries the gases high into the sky. There the compounds react with the water in the atmosphere and acids are made. The expression "Acid Rain" was first used by Angus Smith in 1872.


Acid rain is caused by acids mixing with air. The largest source of acid is sulfur dioxide. Carbon dioxide and various oxides of nitrogen also make acid in the atmosphere. These chemicals are both natural and artificial.

Scientists have realised that humans are responsible for giving out most of the compounds that cause acid rain. People started producing more acidic gases when they started building factories and power stations. These buildings as well as houses and vehicles burn coal or oil as fuel. This releases gases into the air that produce acid rain.[1] Governments have tried since the 1970s to reduce the amount of sulfur being released into the Earth's atmosphere, and have had good results so far. However, it is expensive to clean the smoke from factories and power stations. In 2001 Great Britain still produced about five million tonnes of these gases every year; China produced eighteen million tonnes, and the United States of America produced more than twenty million tonnes.[1]

Acid rain can also be caused naturally. For example, acids can be made by nitrogen compounds made by lightning, and volcanic eruptions can release sulfur dioxide into the atmosphere.


Acid rain has been shown to have a bad impact on forests, freshwater and soil. It kills insect and aquatic life-forms as well as causes damage to buildings and having impacts on human health.

Acid rain poisons rivers and lakes. Fish and other animals cannot live in acid water.[1] It is also bad for buildings as the acid damages calcium carbonate stone. The acid makes it erode away (crumble away.) Many of the world's oldest and most famous buildings and monuments are in danger because of acid rain.[1]


  1. 1.0 1.1 1.2 1.3 Border, Rosemary (2001). Pollution. Great Clarendon Street, Oxford OX2 6DP: Oxford University Press. ISBN 0 19 422868 1 .