Acid rain is the name given to rain, snow or sleet contaminated with acid substances,so that its acidity is greater than the limit expected by normal concentrations of carbon dioxide dissolving in the rain to give carbonic acid.The increased acidity is caused by larger concentrations of a number of contaminants, principally the strong acids,nitric and sulphuric, which arise from industrial effluents containing oxides of nitrogen and sulphur.
It can mark fruit and leaves, and adversely affect soil but its main effect is on aquatic ecosystems especially in regions which cannot naturally buffer acidic inputs such as those with thin soils and granite rocks.Disappearence of fish from amny Scandinavian lakes is largely a result of pollution by acid rain.