Acid rain:
Rain water has PH 5.6 approximately due to fromation of H+ by CO2 . When PH falls below 5.6 it becomes acidic. Acid rains is caused by oxides of nitrogen and sulphur. Oxides of sulphur are released by the combustion of fossil fuels, roasting of sulphur ores, petroleum refining, sulphur based industries. Oxides of nitrogen are released from combustion of fossil fuels and exhaust of automobiles. Acid rain is toxic to vegetation and aquatic life. It damages buildings and statues. Acid rain corrodes water conduct pipes thus releasing ions of iron, copper, lead into drinking water.