A man can live without food for a month, without water for two or three days, but he cannot live without breathing even for a minute. According to research, it is estimated that an average adult male breathes in 15 kg of air a day, in comparison to about 1.5 kg of the food consumed and 2.5 kg of water intake. Hence it is obvious that the quantum of pollutants that enter our body through respiration would be manifold in comparison to those taken in through polluted water or contaminated food.Air is a mixture of gases comprising 78 per cent nitrogen, 21 per cent oxygen and a little less than 1 per cent argon, together with 0.03 per cent carbon dioxide. These elements make upto 99.9 per cent of dry air. As long as this composition is maintained, the air is pure.
Smog is the visible gaseous and particular matter concentrating near the earth's surface particularly in the cities due to SO2, CO2, factory and traffic emission and meteorological conditions. Acid rain may be defined as any precipitation such as rain, fog, mist or snow which is more acidic than the normal i.e. having a lower pH than that of normal rain water. The term acid rain was first referred by Robert Angus in 1872.Acid rain is due to presences of various pollutants like oxides of nitrogen, carbon, sulphur, and halogens radicals or molecules in the atmosphere have become the serious problem in most industrialized countries.
The presences of unwanted matters in dissolved state, colloidal state and sediment states make the water unsuitable for ingestion. Contamination in water which hinders the natural growth and existence of living things (human, animals and aquatic life) are called water pollutants. Natural water from all the sources is useful for living things but water from a source by environmental degradation may become unsuitable for the survival of aquatic life and others.