ATMOSPHERE

1.    Introduction to Atmosphere

The surface of the earth is surrounded by a blanket of air and this gaseous sphere surrounding or hanging over the surface of the earth is called the atmosphere. Earth's atmosphere, the blanket of gases surrounding the planet, is the element that, more than any other, enables life to exist. Without its protective insulation, temperature would swing from unbearable cold at night to unbearable heat during the day.

1.2 Composition of the atmosphere

The atmosphere is composed of three elements. They are gases, water vapour and dust particles.

a.  Gas

99% of the atmosphere consists of two gases only- Nitrogen and Oxygen. All other components make less than 1%, while the water vapour content and dust particles differ from place to place, according to temperature conditions.

The gases present in the atmosphere are:

Gases	Percentage
Nitrogen	78.03%
Oxygen	20.99%
Argon	.94%
Carbon Dioxide	.03%
Hydrogen	.01%

b. Water vapour

Other important part of the atmosphere is water vapour. The sources of the water vapour in the atmosphere are sea, lakes, rivers, soil, plants, etc. we can get water vapour in the atmosphere up to the height of 7500 m only. The percentage of the water vapour decreases as one moves from the equator towards the poles. Water vapour is the only one source of clouds, rainfall, due, hell stone, etc.

c. Dust Particles

The third important part of the atmosphere is dust particles. Some of these dust particles are visible while others are quite beyond human sight. These dust particles are responsible for such phenomena as sunsets, twilight and haze. There are the nuclei about which condensation takes place. Besides they are effective in absorbing and diffusing solar energy.