Structure and Functions of Atmosphere

Structure of Atmosphere

• The multilayered gaseous envelope that surrounds the earth is called air or atmosphere.

• The physio-chemical structure of atmosphere consists of five concentric layers. 

These layers are :

1. Troposphere (10 km above earth)

2. Stratosphere (18 to 50 km)

3. Mesosphere (51 to 85 km)

4. Thermosphere / Ionosphere (upto 500 km)

5. Exosphere

1. Troposphere:

• Troposphere is the lowest layer of the atmosphere. It extends from 10 to 18 kms.

• It contains 75 % of the atmospheric mass. It also contains moisture.

• There is gradual reduction in temperature within troposphere from 15 to - 56 °C.

• The chemical constituents of troposphere are : O₂, CO₂, H₂O and N₂.

2. Stratosphere :

• Stratosphere extends from 18 to 50 kms above earth's surface.

• Stratosphere is characterized by temperature range of - 55 °C to 5 °C.

• Stratosphere is rich in ozone (O₃) gas and free from moisture and clouds.

• Stratosphere prevents earth from ultraviolet radiation of the sun.

3. Mesosphere :

• Mesosphere extends from 50 to 85 kms above earth's surface.

• The mesosphere possesses characteristics of low temperature - 92 °C and reduced atmospheric pressure.

• Mesosphere contains N₂ and less ozone gas.

4. Thermosphere

• The thermosphere extends upto 450 to 500 kms above earth surface.

• The thermosphere possesses characteristic of gradual increase in temperature upto 1200 °C.

• Thermosphere contains charged particles like O⁺₂, O₊ and NO⁺ . 

5. Exosphere

• The exosphere extends from 1600 km to 3000 kms above earth's surface.

• The exosphere possesses characteristic of very high temperature because of direct solar radiation.

• The exosphere contains H-, and He only.

• Fig. 1.3.1 illustrates vertical structure of earth's atmosphere.

1. Functions of Atmosphere

• Important functions of atmosphere are

1. Atmosphere absorbs Infra-red (IR) radiations thereby maintaining heat balance on earth.

2. Atmosphere contains several gaseous such as oxygen, carbon-dioxide and nitrogen, which are very important for sustaining life on earth.