What are the different layers of the atmosphere?

The thin sheet of gaseous mixture which envelops the planet earth is called atmosphere (Greek: Atmos means vapor). Content of water vapor, density of the air mass and atmospheric pressure decreases rapidly with the increase in altitude.

The rate of change of temperature with the altitude is called lapse rate. The atmosphere has been stratified into major four layers where temperature decreases (negative lapse rate) or increases (positive lapse rate). Brief description of atmospheric layers is as follows:

Troposphere

The altitude of this layer varies from 16 km at equator to 8 km at poles. Largest percentage of the air mass found in this region. The upper layer is called tropopause. Temperature decreases with increase in altitude (-6.4 °C per km) in this layer and varies from 15 °C (ground Level) to – 56 °C (tropopause).

Stratosphere

Temperature starts rising in this layer from tropopause (-56 °C) to stratopause (-2 °C) as ozone (O3) layer in the upper stratosphere absorbs solar radiation and temperature rises. Ozone layer in this region absorbs harmful UV radiation, particularly UV-B radiation (280 nm to 315 nm), because of which life is possible on earth’s surface. However, the ozone layer is depleting at a fast pace due to the presence of ozone depleting substances (like chlorofluorocarbons- CFCs). Ozone holes are the places in the upper stratosphere where the concentration of ozone has depleted drastically.

Mesosphere

Temperature starts decreasing again and reaches at -96 °C at the upper boundary of the layer i.e. mesopause. Density of air is very low and important chemical species found in this region are O2+ and NO+ which do not absorb much solar radiation. This causes the decline in ambient temperature in this region.

Thermosphere

Ionic oxygen atoms and other ions in this layer absorb short wave solar radiation which increases the temperature in this layer rapidly from -96 °C (lower boundary) to 1200 °C (upper layer).