Geography

Composition of Atmosphere

The composition of Atmosphere is said to be a mixture of different gases. It envelops around the Earth. 99% of total mas of atmosphere is confined to highest of 32 km from the Earth’s surface.

composition of atmosphere

Permanent gases of the Atmosphere

  • Atmosphere is consists of various gases, water vapour and dust particles.
  • The presence of oxygen becomes negligible at the height of 120 km from the surface of earth with regards to the composition of atmosphere.
  • Carbon dioxide and water vapour occur only upto 90 km.
  • Carbon dioxide is meteorically very important as it is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation. It is also responsible for greenhouse effect.
  • Ozone gas: 10-50 km above earth surface and acts as filter, absorbing ultraviolet rays from the sun. Ozone prevents the rays from reaching the surface of earth.
  • Water vapour is variable gas, decreases with altitude.
  • It also decreases from equator towards the poles.
  • Acts like blanket allowing the earth to neither to become too cold nor too hot. Also contributes to the stability and instability in the air.
  • Dust particles: are in higher concentration in subtropical and temperate regions due to dry winds in comparison to equatorial and polar regions.
  • Dust particles act as a hygroscopic nuclei over which water vapour of atmosphere condenses to produce clouds.

The composition of atmosphere varies with local environmental factors also.

 Structure of Atmosphere:

There are five layers in the structure of atmosphere depending upon temperature.structure of atmosphere

I. Troposphere:

  • It is the lowermost layer.
  • 13 km height average with 8 km at poles and 18 km at equator (lesser at poles and greater at equator).
  • The thickness is 18 km at equator because heat is transported to great heights by strong convectional currents.
  • This layer has adult particles and water vapour.
  • Climate and weather changes occur here.
  • Temperature decreases at rate of 1 degrees celcius for every 165 m of height.
  • Zone separating troposphere from stratosphere is called tropopause.
  • Temperature at tropopause is minus eighty degrees celcius over equator and minus forty five degrees celcius over the poles. This remains constant through the year.

II. Stratosphere

  • It is found above the troposphere.
  • extends upto 50 km of height.
  • Has ozone layer – absorbs ultraviolet radiation and shields life on earth from harmful energy.

III. Mesosphere:

  • Above stratosphere
  • reaches till 80 km height.
  • Temperature decreases with altitude  here, by 80 km it reaches minus hundred structure of atmosphere degrees celcius .
  • The upper limit is called mesopause.

IV. Ionosphere or Thermosphere:

  • 80 to 400 km above mesopause.
  • Ionosphere consists of electrically charged particles known as ions.
  • Radio waves which are transmitted from the earth are reflected back by this layer.
  • Temperature here increases with height.

VExosphere:

  • It is the outermost layer.
  • Not much is known about this layer.
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