Acid rain refers to any precipitation hence a pH value less than that of normal rain water, when pH value is around 5 or 6. Normal rain water is weakly acidic, because atmospheric carbon dioxide combines with rain water to form weak carbonic acid.
The severe acidic nature of water occurs due to massive pollution caused by industrialization. Oxides of sculpture, nitrogen and hydrocarbons are the major contributing factors to acid rain.
The gases and aerosols accumulate high up in the atmosphere, water vapors condense on aerosol surface and form a fine film providing suitable level as catalysts for the oxide of sculpture and nitrogen to dissolve in water and react to form corresponding acids which form salts such as nitrates and sulphates when come in contact with basic aerosols. As water vapors continue to condense on these aerosols, large droplets of water are produced which rain down as acid rains.
Sulphuric acid, nitric acid and various sulphates and nitrates are the major chemical constituents of acid rain, small amount of hydrochloric acid and its salt may also be present.
ADVERTISEMENTS:
Most areas are susceptible to acid rain. The buffering capacity of water or soil determines its susceptibility. In general, lower the buffering capacity of soil or water is produced which rain down as acid rains.
Oxides of sulphur mainly sulphur dioxide with second most important pollutant of the atmosphere is obtained from burning of organic matter, fossil fuels and from industries – usually oxides of sulphur dissolve in the water and are carried out down the earth with rain.
The pressure of sulphur dioxide in the* atmosphere causes a wide variety of harmful effects on plants and animals. Plants when exposed for a long time, sulphur damage to chloroplasts.