Describe the composition of the atmosphere.

Many gases are found in the atmoshere but it can be considered to be composed of mainly nitrogen and oxygen. A rough estimate of the composition of the atmosphere is given in the following Table :

Other rare gases are hydrogen, helium and ozone. Besides water vapour, dust particles, smoke, salts and other impurities are also present in the air, in varying quantities. As a result, the composition of air is never constant. It varies from time to time and place to place. However, if these variable elements are removed from the atmosphere, its make-up would be fairly constant all over the earth, at least in the lower atmosphere.

Fig. 8.3 : Composition of the air

Of the many constituents, carbon dioxide, dust particles, water vapour and ozone are of great importance for the earth’s climatic conditions.

The nitrogen does not easily enters into chemical union with other substances, but gets fixed into the soil. It serves mainly as diluent or dissolver. It regulates combustion. Oxygen on the other hand combines with all the elements and is most combustible. Carbon dioxide is an important gas in the atmospheric processes. It can absorb heat and thus allows the lower atmosphere to be warmed up by the heat radiation coming from the sun and from the earth’s surface. Green plants in the process of photosynthesis utilise carbon dioxide from the atmosphere.