Acid rain refers to all types of precipitation--rain, snow, sleet, hail, fog--that is acidic in nature. Acidic means that these forms of water have a pH lower than the 5.6 average of rainwater. Acid rain kills aquatic life, trees, crops and other vegetation, damages buildings and monuments, corrodes copper and lead piping, damages such man-made things as automobiles, reduces soil fertility and can cause toxic metals to leach into underground drinking water sources.

Rain is naturally acidic because carbon dioxide, found normally in the earth's atmosphere, reacts with water to form carbonic acid. While "pure" rain's acidity is pH 5.6-5.7, actual pH readings vary from place to place depending upon the type and amount of other gases present in the air, such as sulphur oxide and nitrogen oxides.

The term pH refers to the free hydrogen ions (electrically charged atoms) in water and is measured on a scale from 0 to 14. Seven is considered neutral and measurements below seven are acidic while those above it are basic or alkaline. Every point on the pH scale represents a tenfold increase over the previous

number. Thus, pH 4 is 10 times more acidic than pH 5 and 100 times more so than pH 6. Similarly, pH 9 is 1O times more basic than pH 8 and 100 times more basic than pH 7.

These toxic metals are bad for human health; high lead levels may harm people who drink such water and people who ingest mercury in tainted fish suffer serious health problems. Most of the frogs and insects also die when the water reaches pH 4.5.

Acid rain harms more than aquatic life. It also harms vegetation. The forests of the Federal Republic of Germany and elsewhere in Western Europe, for example, are believed to be dying because of acid rain. Scientists believe that acid rain damages the protective waxy coating of leaves and allows acids to diffuse into them, which interrupts the evaporation of water and gas exchange so that the plant no longer can breathe. This stops the plant's conversion of nutrients and water into a form useful for plant growth and affects crop yields.

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Approximate Word count = 963
Approximate Pages = 4 (250 words per page double spaced)