Acid Rain

Acid rain refers to which acids from the atmosphere are deposited on the earth. Acid deposition includes wet and dry deposition. Wet deposition refers to acidic water received through rain, fog, and snow. Dry deposition relates to the wind blown acidic gases and particles in the atmosphere, which settle down on the ground. About half of the acidity in the atmosphere is transferred to earth through dry deposition. Dry deposited gases and particles can also be washed from trees and other surfaces by rainfall.

Nitrogen oxides (NO_N), VOCs and SO₂ and produced during the combustion of coal (in industry) and petroleum (in automobile). Lighting in sky also produces NO_N naturally. These gases are highly reactive in air. They rapidly oxides to acids (sulphuric or nitric), which quickly dissolve in water and are washed out to the ground as acid rain. Normally, rain water is slightly acidic (pH 5.6-6.5) because water and CO₂ combine in air to form a weak acid. The pH of acid rain is less than 5.6, and could be as low as 4 or below. Acid rain damages building materials. Our heritage monuments (such as Taj Mahal at Agra) are threatened by the corrosive action of acid deposition. Acid rain adversely affects terrestrial and aquatic, vegetation. Most planidons, young fish cannot tolerate water having pH below 5.0. Low pH conditions also damage soil microbial community.