Air Pollution

AIr Pollution

Air Pollution can be defined as the occurrence or release of any foreign material or gas into the atmosphere which may be harmful to man, vegetation,, animals or buildings.

Air is a mixture of gases. The air that we breathe is mainly O2 about 20% and N2 about 79% Rest 1% is composed of other constituents like CO2 and water vapour etc. It is in this 1% of air that air pollutants are present which includes gases and particulate matter. Even such a small concentration of pollutants is extremely harmful to life and property.

Air pollution is a serious problem for those living in big, congested and industrialised cities with heavy traffic. The concentration of pollution can vary in different countries and within a country as the mixing and dilution of pollutants is hampered by natural and artificial barriers.

Some Pollutants do not rise above 600 metres. The diffusion  of air is neglegible after about 3000 metres above earth's surface.

AIR POLLUTANTS

A. On the basis of state of the pollutants are emitted, they can be broadly grouped in two categories.

1. Gaseous pollutants

• substances that remain in the gaseous state in atmosphere
• these are vapours of certain compounds with boiling points below 2000C

2. Particulate pollutants

• Substances that remain in the soil or lequid state in atmosphere
• These are in the form of large particles like sand that settle down rapidly or like dust that remains suspended for a long time.

B. On the basis of how the pollutants are released/formed in the environment, they have been put into two categories, namely primary and secondary pollutants.

1. Primary pollutants

• They are harmful substances emitted by the source directly into the atmosphere.

                 Examples: Particulate matter like aerosols, soot, dust, fibres, Carbon monoxide, Sulphur                      

                       dioxide, Nitrous oxides

2. Secondary pollutants

• They are formed during chemical reactions between primary air pollutants like hydrocarbons and nitrogen oxides with atmospheric substances like water vapour

              Examples: Photochemical smog, Acid rain, Per oxyacetyl nitrate(PAN)

Cause of Air Pollution:

The various causes of air pollution are:

(i) Combustion of natural gas, petroleum, coal and wood in industries, automobiles, aircrafts, railways, thermal plants, agricultural burning, kitchens, etc. (soot, flyash, CO2, CO, nitrogen oxides, sulphur oxides).

(ii) Metallurgical processing (mineral dust, fumes containing fluorides, sulphides and metallic pollutants like lead, chromium, nickel, beryllium, arsenic, vanadium, cadmium, zinc, mercury).

(iii) Chemical industries including pesticides, fertilizers, weedicides, fungicides.