▬ The envelope of air that completely surrounds the carth is known as atmosphere.
▬ The atmosphere extends to about 1000 km from the surface of the earth. But 99% of the total mass of the atmosphere is found within 32 km.
▬ This is because the atmosphere is held by the gravitational pull of the earth.
Composition of the Atmosphere:
(i) Nitrogen-78% (ii) Oxygen-21% (iii) Argon-0.93% (iv) Carbon dioxide 0.03% (v) Neon-0.0018% (vi) Helium-0.0005% (vii) Ozone-0.0006% (viii) Hydrogen-0.00005%.
▬ Carbon dioxide is present in small quantity in the atmosphere.
▬ It is an important constituent of air because it has the ability to absorb heat and thus keep the atmosphere warm, thereby, balancing the heat of the earth.
▬ Water vapour is the most significant component of the atmosphere as far as its effect on weather is concerned although its quantity varies considerably from practically none (0) to up to about 4% by volume.
▬ Water vapour is the source of all clouds and precipitation (rain, hail, storm etc.). Water vapour, like carbon dioxide, has the ability to absorb heat energy. It also regulates the hydrological cycle.
▬ Dust intercepts and reflect incoming insolation.
▬ The polluted particles present in the air not only absorb larger amount of Insolation but also greatly absorb the terrestrial radiation.
▬ Dust in the atmosphere contributes to the red and orange colour of Sunrise and sunset.
Layers of the Atmosphere
There are five distinct layers of the atmosphere-(a) Troposphere (b) Stratosphere (c) Mesosphere (d) Thermosphere and (c) Exosphere.