Composition of the Atmosphere: The atmosphere mainly consists of a mixture of gases in a fairly constant composition.

The atmosphere is composed of the following three elements :

1. Gases: Nitrogen and Oxygen are the two major gases found in the atmosphere. In pure dry air, Nitrogen occupies 78% and Oxygen occupies 21% by volume. The remaining 1% is composed of a number of gases like Hydrogen, Argon, Ozone, Helium, Carbon dioxide. The proportions of the gases remain constant.

Active gases: Oxygen, Nitrogen, Hydrogen, Carbon dioxide, Ozone are active gases. Oxygen is the most vital gas for sustaining life. Nitrogen and Carbon dioxide are essential for plant life and help in the process of Photosynthesis.

Inert Gases: Argon, Neon, Helium, Krypton are inert gases which are not so effective.

Atmosphere Composition:

It shows that Nitrogen (N₂) alone occupies about four-fifths of air by volume and oxygen (O₂) one-fifth. In addition to the above, other gases like Neon, Methane, Krypton and Radon are also present in the atmosphere. The atmoshpere is odourless, colourless and tasteless. It is mobile, elastic, both compressible and expandable. It is invisible but, it has weight and pressure.

2. Water Vapour: Water vapour represents 2% of the air by volume. It is mostly found in the lower layers of the troposphere. About half the water vapour in the air lies below an altitude of 2000 metres. It is of primary importance to man. It absorbs insolation. It is the source of all condensation and precipitation on the earth. Water vapour, an unstable element is obtained from oceans, lakes, rivers and other water bodies.

3. Dust Particles: The atmosphere holds in suspension many dust particles whose sizes vary. The major source of dust particles are deserts, lake beds, beaches and dry river beds. These are found in the lower layer of the atmosphere. These affect sun rays by scattering and absorbing insolation. These are responsible for the formation of clouds, fog and smog. Solid particles like carbon, salt, pollen grains, etc. are also found in the lower layers of the atmosphere.