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...