The thermal power plants, industries and vehicles release nitrogen oxides and sulphur dioxide into atmosphere because of burning of coal and oil. These gases produce acid rain. If these gases react with water vapour in the atmosphere, they form acids and descend on to earth as acid rain, through rain water.
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The acid rain brings about severe damage to the plant and animal life. Because of the drifting of these gases in the atmosphere by the wind, their presences are felt as far as 2000 kilometers.
The air pollution of one nation could cause acid rain for another nation. Population growth too aggravates acid rain problem. With more people, the developmental activities and the transport facility are increased resulting in great emission of nitrogen and sulphur oxides.
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Recently Acid Rain as an environmental problem received much attention. This problem has become a threat to water bodies like pods, rivers, dams, lakes and to terrestrial ecosystems like grasslands and forests.
The term acid rain was first referred by Robert Angus in 1872. This acid rain has become a problem in U.S.A., U.K., Germany, Norway, Sweden, Russia and Canada. We have experienced Acid Rain in Agra, were acid rain is destroying the greatest monument Taj Mahal.
In Agra, the acid rain is caused due to Mathura Oil Refinery, an industry discharging poisonous gases into the atmosphere that react with water vapour or rain droplets to form different types of acids like sulphuric acid, nitric acid and hydrochloric acid. These acids are stronger acids, when compared to naturally occurring carbonic acid.
In cities like Calcutta, New Delhi, Bombay, Kanpur and heavily industrialized areas experienced acid rain in the initial phases of monsoon rain. In later period of monsoon, the pH slightly increases showing the decrease in acids content in rain water.
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Acid rain is nothing but a mixture of sulphuric acid, nitric acid and hydrochloric acid in higher quantities and Carbonic acid in lower quantities.
Sulphuric and Nitric acid enjoy the major share in acid rain, when compared to Hydrochloric acid and Carbonic acid. Substantial amounts of sulphur and nitrogen oxides are released into the atmosphere by several natural processes and industrial activities. Chlorine gas released from industries or naturally, reacts with water vapour to produce hydrochloric acid.
All these three acids with naturally occurring carbonic acid form ACID with rain water and pH falls to 4.0, at times the pH can also fall to 2.0. The pH of normal rain water is around 5.65 and presumed to be weakly acidic.