Atmospheric Structure and Composition | Environmental Science

Atmospheric Composition: Gases, moisture and dust particles are the major constituents of our atmosphere that blanket our earth. It is the gravitational attraction of the earth that holds the atmosphere close to the earth.

Atmospheric Structure and Composition | Environmental Science

Atmospheric Gases: Familiarize the major gases in the atmosphere and their proportionate volume by observing the given table.

Atmospheric Gases

Almost all the gases in our atmosphere support the sustenance of life directly or indirectly. Observe the pictures given. You can notice the importance of gases such as oxygen, carbon dioxide and nitrogen in the existence of life forms.

  • Plants make use of Carbon dioxide for photosynthesis.
  • Man and other organisms make use of oxygen for respiration.
  • Plants make use of nitrogen for their growth through nitrogen fixation.

Water molecules are a major constituent in the lower parts of the atmosphere. As you know, water reaches the atmosphere through evaporation and causes cloud formation and rain. There is spatial and temporal variation in the amount of water present in the atmosphere. Look at the factors influencing the amount of water in the atmosphere.

·        Rate of evaporation will be high at places experiencing higher temperature. So the water content in such places will be high.

·        The amount of water will be high in the atmosphere close to the surface water sources such as oceans, rivers and other water bodies.

The composition of the atmosphere is somewhat uniform up to about 90 Kilometres from the surface of the earth. This part of the atmosphere is called homosphere. Beyond this there is no uniformity in the gaseous composition. So the part of the atmosphere beyond 90 Km from the earth is called as heterosphere. Based on the temperature at different levels, atmosphere can be divided into different layers. From the given diagram.

 you can read the change in temperature with altitude and can identify the layers of the atmosphere. Each layer in the atmosphere has its own indigenous characteristics. Let us see the characteristics of theatmospheric layers as well as their significance on us.


  • This layer extends up to about 90 Km from the surface of the earth and lies close to the earth.
  • The height of the troposphere is more in the equatorial regions because of strong convection here. (about 18 Km)
  • Almost all the weather and climatic phenomena such as cloud formation, rain, snow, wind, thunder and lightning etc. take place in this layer.
  • In the troposphere the temperature decreases at a uniform rate of 1°Celcius for every 165 metres of altitude. This is called Normal Lapse Rate.
  •  The zone of transition above the troposphere is called tropopause.


  • Extends up to a height of about 50 Km from the earth and lies above the tropopause.
  • In the lower parts of the stratosphere there is no change in temperature with altitude. This zone is called isothermal zone. Beyond this there is increase in temperature with altitude.
  • Ozone layer which forms part of this layer absorbs the harmful ultra violet rays from the sun and prevents it from reaching the earth.
  • Allows the free movement of jet aircrafts through clear atmospheric conditions and absence of air gutters.
  • The zone of transition above the stratosphere is called stratopause.


  •  Extends from about 50 to 80 Km altitude from the earth.
  • Temperature decreases with altitude and the lowest temperature of the atmosphere is felt at the mesopause. ( -80°C to -100°C)
  • The meteors on reaching the mesosphere gets burnt out due to friction.
  •   The zone of transition above the mesosphere is called mesopause.

Transition zones: Transition zones are the parts of the atmosphere separating the major atmospheric layers. Tropopause, stratopause and mesopause are the respective transition zones between troposphere, stratosphere, mesosphere and thermosphere.


  • Extends from about 80 to 600 Km altitude.
  • There is considerable increase in temperature with altitude.
  • The lower part of the thermosphere is known as ionosphere.
  • Ionosphere helps in the transmission of radio waves.


  • At an altitude of about 80 to 400 Km in the atmosphere the intense solar rays such as Ultra violet, X-rays etc. react with gaseous molecules to form ions. This process is called ionization and this part of the atmosphere is called ionosphere. Ions conduct electricity.
  • As the radio waves are electromagnetic waves this layer is made use for long distance radio transmission.

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