A toxic substance, living or non-living, at an undesirable limit is called a pollutant. Such a substance when present in air is called a<r pollutant. The process of polluting the air and making it unsafe for living is called pollution of air.
Air is precious and life cannot be sustained on this planet without it. In the troposphere, it provides oxygen for respiration, nitrogen to synthesize amino acids and proteins, carbon dioxide for carbohydrates through photosynthesis by plants, which is ultimately consumed by animals. Water vapours are required to form clouds leading to the formation of rain and snow.
Carbon dioxide absorbs infrared radiations to keep the earth warm. Thus, troposphere controls the weather conditions.
In the stratosphere, the dense layer of ozone and oxygen acts as a policeman to protect living beings from the harmful UV rays coming from the sun.
An alteration of the composition of the atmosphere by the introduction of potentially harmful substances will cause pollution and affect life on the earth severely.
The major cause of air pollution is the result of emissions of high concentrations of sulphur oxides, nitrogen oxides, carbon oxides and particulate matter. The excessive amount of sulphur oxide and nitrogen oxide is due to the burning of fossil fuels, especially coal used in power plants. The sulphur oxides form sulphurous smog.
On the other hand, the oxides of carbon, oxides of nitrogen, volatile organic compounds react with each other in the presence of sunlight to form photochemical smog. This major problem is also closely associated with motor vehicles.
There is a set of six substances, called criteria pollutants which have, contributed in the formation of sulphurous and photochemical smog.
We are also getting exposed to hazardous air pollutions at home and workplace, where we spend most of our time. In the rural area people cooking with kerosene, cow dung and wood in closed conditions are severely affected.
In India, about 100 million tons of pollutants are poured into the atmosphere and the amount is increasing every year.