Question

Define the term “acid rain”, and explain how it occurs.

Answer 1

Normal rainfall has pH just less than 7. This small acidity is caused by the presence of carbonic acid in rain when rain drops absorb CO2 in air. If however air is polluted with primary pollutants like Sulphur dioxide SO2 and oxides of nitrogen NOx dain water becomes more acidic due to formation of acids like Sulphuric acid (H2SO4) and Nitric acid (HNO3) which is termed as acid rain. It is specified that when rain pH drops below 5.4 it is termed as acidic.

Effects of acid rain:

1. Conversion of forest land to waste lands.

2. Death of aquatic life.

3. Acidification of water in lakes , ponds, canals which makes it undrinkable for human beings.

The causes of acid rain can be natural or man-made. The main pollutants responsible for acid rains are SO2 and NOx. SO2 is responsible for twoo third of acid rains and NOx is responsible for one third of the acid rains.

SO2 is produced by burning of fossil fuels in thermal power plants. Use of petrol and diesel in motor vehicles also produces SO2.

Nox is produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures like in thermal plants, nuclear plants, smelting operations etc.

HCL is also found to have caused acid rains but to a very small scale.