Earth is completely surrounded by thick envelope of gases called atmosphere.
Atmosphere is sub divided into different layers depending upon the distance from the sea level.
The nearest layer which extends to the height of about 10 km from sea level is called troposphere. It almost contains about 80% of total mass of air and almost all the water vapours.
The layer above the troposphere between 50 km is called stratosphere.
Atomspheric pollution is generally studied under the two heads.
(a) Tropospheric pollution
(b) Stratospheric pollution