Acid Deposition,also known as "Acid Rain" is a major environmental issue in this day and time. The term "Acid Rain" was coined by a british chemist in 1872. One hundred years after the term was coined acid rain became an important scientific and political issue. The acidity in acidic rain is measured by a pH scale. The pH scale is 0 (very acidic) to 14 (very basic) and 7 is neutral. If the rain and snow had no pollutants in them it would be naturally acidic. The pH of natural rainfall is between 5.0 and 5.6. Any substance in the atmostphere that produces a pH of lower then natural rainfall is acid rain.