Acid deposition, commonly termed acid rain, results from a complex chemical and atmospheric phenomenon that occurs when emissions of sulfur dioxide, nitrogen oxides, and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either wet or dry form. The wet forms can fall to earth as rain, snow, or fog. The dry forms are acidic gases or particulates.
Acid deposition can damage crops, forests, and ecosystems, kill fish, and cause a deterioration of water quality affecting human health directly or indirectly through affecting livestock consumed by humans. Acid deposition can also cause damage to valued statues and buildings.
More information on Acid Rain:
EPA Acid Rain Overview.
Information on Federal Regulations of Acid Rain.