Introduction to Acid Rain

In simple words, Acid Rain is acid mixed with rain water. Some acidic gases mixed in air, such as sulphur dioxide, some oxides of nitrogen etc. On prolonged reaction with oxygen and moisture of air produce various acids. When there is rain, these acids (along with some suspended particulate substances) being dissolved in rain water come down on the earth and may render the soil or water of surface water bodies acidic. Acid rain is thus an outcome of air pollution.

Generally rain water is slightly acidic; carbon dioxide of air gets dissolved to some extent in this water forming carbonic acid. Such slight acidity of rain-water is not detrimental because the acidity is practically neutralized by the basic dust particles suspended in air.

But if there are acidic oxides such as sulphur dioxide, oxides of nitrogen etc. in relatively large amounts in the air, the rain water may become sufficiently acidic for causing the harmful effects mentioned above. Therefore, control of Acid rain has been a matter of great concerns to environmentalists all over the world.

Harmful Effects

There may be some harmful effects of acid rain on the

• Flora and fauna;
• Buildings and monuments of archeological importance.

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.

The forests in North America, Canada, Europe and Japan were affected by acid rain. Production of some vegetables, such as peas and beans, potato, reddish etc, may be reduced by acid rain, growth of pine; eucalyptus etc. may also be impeded.

There may be harmful effects of acid rain on some animals also. It has been observed that breeding of moths is impeded by acid rain. In many places of the world, acid rain has reduced the number of different types of birds. In India, the water of the lake of Bharatpur Bird Sanctuary is turning acidic in contact with sulphur dioxide gas of the air; as a result the migratory birds are coming to this place in fewer numbers.

Acid rain may turn acidic the water of ponds, rivers, lakes etc. In such acidic water the eggs of the fishes may be destroyed, the physiological processes of the fishes may also be affected and as a result the water reservoir may be fishless ultimately. If the soil below the water and at the sides of the water sources (lake, pond etc.) be basic in nature, the effects of acid rain on the aquatic animals may not be that much serious, but if such soil contains some acid soluble metals which are detrimental to the fishes and other aquatic animals, the effects may be fatal. For example Manganese or Aluminium form the soil may dissolve in acidic water and may be harmful to the fishes. Mercury compounds may also mix with acidic water and may thus cause danger to the aquatic animals. In fact, many lakes have become fishless as a result of acid rain.

The effects of acid rain on the public health and on the animals may be dangerous. Acid rain contains mainly two acids - sulphuric acid and nitric acid – which are harmful to the lungs and the respiratory system; they may cause lung cancer, and damage the digestive and nervous systems. There may be several other dangerous air pollutants other than acid in the acid rain which may also be harmful to public health.

Due to Acid rain, some heritage buildings and monuments of architectural and historical importance are in danger in different parts of the world. Acid of the Acid rain attack marble, limestone etc. of which such architectures are made of. In India a few years back, signs of corrosion on the walls of Taj-Mahal were observed. According to environmentalists this was due to the presence of sulphur dioxide in high concentrations in the air of Agra which would react with the moisture of air form sulphuric acid and corrode the marble of the walls of Taj-Mahal. Sulphur dioxide emitted from the petroleum refinery situated on the other side of the Jamuna River was held primarily responsible for such corrosion. This ‘stone-cancer’ of Taj-Mahal has since been checked through adoption of suitable control measures. As the concentration of sulphur dioxide is increasing in the air of Delhi, there may be danger of corrosion of Red Fort and similar other historical buildings and monuments made up of stones. In Calcutta also, architectures such as the marble-built Victoria Memorial Hall may be in similar danger in the near future.