Composition of the Atmosphere

  • The atmosphere is a mixture of many gases. In addition, it contains huge numbers of solid and liquid particles, collectively called ‘aerosols’.
  • Some of the gases may be regarded as permanent atmospheric componentswhich remain in fixed proportion to the total gas volume.
  • Other constituents vary in quantity from place to place and from time to time. If the suspended particles, water vapour and other variable gases were excluded from the atmosphere, then the dry air is very stable all over the earth up to an altitude of about 80 kilometres.
  • The proportion of gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost in negligible quantity at the height of 120 km. Similarly, carbon dioxide and water vapour are found only up to 90 km from the surface of the earth.
  • Nitrogen and oxygenmake up nearly 99% of the clean, dry air. The remaining gases are mostly inert and constitute about 1% of the atmosphere.
  • Besides these gases, large quantities of water vapour and dust particles are also present in the atmosphere. These solid and liquid particles are of great climatic significance.

The details of different gases of the atmosphere are given in the table below.

Structure, Composition of Atmosphere

Different constituents of the atmosphere, with their individual characteristics, are discussed below.

Gases of the atmosphere:

The atmosphere is the mixture of different types of gases, including water vapour and dust particles. Nitrogen and Oxygen are the two main gases of the atmosphere. 99 percent part of it is made up of these two gases. Other gases like organ, carbon dioxide, hydrogen, nion, helium etc. form the remaining part of atmosphere.

  • Nitrogen:
    Nitrogen accounts for 78% of total atmospheric volume. It is a relatively inert gas, and is an important constituent of all organic compounds. The main function of nitrogen is to control combustion by diluting oxygen. It also indirectly helps in oxidation of different kinds.
  • Oxygen:
    Oxygen, although constituting only 21%of total volume of atmosphere, is the most important component among gases. All living organisms inhale oxygen. Besides, oxygen can combine with other elements to form important compounds, such as, oxides. Also, combustion is not possible without oxygen.
  • Carbon dioxide:
    • The third important gas is Carbon Dioxide which constitutes only about 03%of the dry air and is a product of combustion.
    • Green plants, through photosynthesis, absorb carbon dioxide from the atmosphere and use it to manufacture food and keep other bio-physical processes going.
    • Being an efficient absorber of heat, carbon dioxide is considered to be of great climatic significance.
    • Carbon dioxide is considered to be a very important factor in the heat energy budget.
    • With increased burning of fossil fuels – oil, coal and natural gas – the carbon dioxide percentage in the atmosphere has been increasing at an alarming rate.
    • More carbon dioxide in the atmosphere means more heat absorption. This could significantly raise the temperature at lower levels of the atmosphere thus inducing drastic climatic changes.
  • Ozone:
    • Ozone (03) is another important gas in the atmosphere, which is actually a type of oxygen molecule consisting of three, instead of two, atoms.
    • It forms less than 0.00005% by volume of the atmosphere and is unevenly distributed.
    • It is between 20 km and 25 km altitude that the greatest concentrations of ozone are found.
    • It is formed at higher altitudes and transported downwards.
    • Ozone plays a crucial role in blocking the harmful ultraviolet radiationfrom the sun.
    • Other gases found in almost negligible quantities in the atmosphere are neon, helium, hydrogen, xenon, krypton, methane etc.

Water vapour

  • Gaseous form of water persent in the atmosphere is called water vapour.
  • Water vapour present in the atmosphere has made life possible on the earth Water vapour is the source of all kinds of precipitation.
  • Its maximum amount in the atmosphere could be upto 4 percent.
  • Maximum amount of water vapour is found in hot-wet regions and its least amount is found in the dry regions.
  • Generally, the amount of water vapour goes on decreasing from low latitudes to high latitudes.
  • In the same way, its amount goes on decreasing with increasing altitude.
  • Water vapour reaches in the atmosphere through evaporation and transpiration.
  • Evaporation takes place in the oceans, seas, rivers, ponds and lakes while transpiration takes lace from the plants, trees and living beings.

Dust Particles

  • Dust particles are generally found in the lower layers of the atmosphere.
  • These particles are found in the form of sand, smoke and oceanic salt.
  • Sand particle have important place in the atmosphere.
  • These dust particles help in the condensation of water vapour.
  • During condensation water vapour gets condensed in the form of droplets around these dust particles.
  • Due to this process the clouds are formed and precipitation is made possible