The pH of natural rain is found to be in the range from 5 to 7. The term acid rain is customarily applied to precipitation with a pH below 5. Such low pH values are generally possible only in the presence of large amounts of anthropogenic pollution.
Sulphuric acid and nitric acid is considered as the principal agents responsible for acid rain. But the major culprit are human beings. Smokes emitted from the industries is the major source of sulphur dioxide whereas smokes emitted from the motor vehicle is the major source of nitrogen oxide. These emissions mixed with atmospheric moisture form the sulphuric acid and nitric acids which, sooner or later precipitate on earth in various form.
It has been known since the 1960s that the high concentrations of H2NO3 and H2SO4 in acid rain are due to atmospheric oxidation of NO and SO emitted by fossil fuel combustion.
The harmful effects of Acid Rain includes the following:
- The soil may turn acidic adversely affecting plant growth;
- The fertility status of the soil may be reduced or totally lost.
- The forests and other vegetation may also be badly affected by acid rain.
- It may cause skin and eyes diseases in Humans.