acid rain
Acid rain is a term which is used to describe a variety of processes which might more accurately be referred to as acidic deposition. Natural rainfall is slightly acidic due to dissolved carbon dioxide, picked up in the atmosphere. Organisms and ecosystems all over the planet have adapted to the slightly acidic nature of normal rain, and thus it poses no environmental problems. It is an increase in the acidity of rain, caused by human activities such as the combustion of fossil fuels, that has turned acid rain into a problem. Highly acidic rain can damage or destroy aquatic life, forests, crops and buildings, as well as posing a threat to human health.
The actual term "acid rain" was first used over one hundred years ago by British chemist Robert Angus Smith. At that time, he realized that smoke and fumes from human activities could change the acidity of precipitation. Unfortunately his awareness was not considered an environmental concern until the 1950's. Around this time, increased levels of acidity were discovered in lakes in both Canada and Scandinavia. At first, this was looked at as an interesting situation, rather than a growing problem. Since that time, much research has gone into identifying the sources of acid rain and the damage that it causes. As research continued, the situation reached catastrophe proportions in the late 1970's. By this time, thousands of lakes in Canada and Scandinavia had been declared dead, devoid of life, while emissions of acid gasses continued to rise.
As mentioned earlier, the term acid rain is used to describe a variety of different types of acidic deposition. These include "wet" deposition such as rain, snow and fog, as well as "dry" deposition in the form of acidic gases and dust. The term acid rain is only used to describe deposition which is more acidic than normal. Acidity is measured on the pH scale, a scale which runs from zero to 14, distilled water, which contains no carbon dioxide, has a neutral...
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