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Homosphere and Heteroshphere-Atmospheric composition


The atmosphere is a mechanical mixture of different gases. However, among all gases, only three gas are held 99% of the proportion i.e. Nitrogen, Oxygen and Argon.


1. Atmosphere is a gaseous cover around the earth. It covers up to 10000 km. approx.

2. Like the lithosphere and hydrosphere, the atmosphere is also an integral part of the earth that covered the earth due to the earth's (by the core of the earth)gravitation pull.

3. Density of the atmosphere reduces with the increase of height. About 97% of the air is concentrated up to 29 km.

4. Lives are present on the earth because of the earth's atmosphere.

Classification of Atmosphere: 

  According to composition:

1. Homosphere: 

The word 'Homo' means uniform and 'sphere' means region then altogether it means the region of constant. The chemical composition of the atmosphere up to 90 km from the earth's surface is uniform or the proportion of gases, aerosols, water vapour are almost the same throughout. 

This layer comprises of Troposphere, Stratosphere, Mesosphere. However, density decreases increase of height.

2. Heteroshphere: 

The 'Hetero' means varies and 'spere' means region so altogether it means region of varies. Above homosphere i.e above 90 km from the earth's surface gases are distributed in a distinct layer,(rather evenly mixed)   sorted by gravity i.e heavier gaseous elements like oxygen and nitrogen towards earth and helium and hydrogen towards outer space.

This layer comprises of  Thermosphere(Ionosphere), Exosphere, Magnetosphere.

Atmospheric composition- 



Names (present by volume)


a) active-

Nitrogen (N₂)  (78.0%)

Oxygen (O) (20.9%)

Carbon dioxide (Co) (0.033%) {increasing}

Methane (CH4) (0.00017%)

Ozone  (O3) (0.00006%)

Hydrogen  (H) (0.00005%)

b) Inactive-

Argon (Ar) (0.90%)

Neon (Ne) (0.0018%)

Helium (He) (0.0005%)

Krypton (Kr) (0.0011%)

Xenon (Xe) (0.00009%)

Water vapour

.02 % may vary


Ash dust, coal dust, dust particles

Difference between Hompsphere and Hetarophere:

Importance of atmospheric gases:
Nitrogen (N₂)  (78.8%):  It behaves in the atmosphere like a natural filler because it does not easily enter into chemical union with other substances, Very small amount is absorbed by soil bacteria (nitrogen-fixing like Azotobacter, Clostridium) and used by plants. 

Oxygen (O) (20.94%): Oxygen is a highly active gas in the atmosphere chemically and combines readily with other elements in the process of oxidation. Living tissues require oxygen to convert food into energy. Chemical weather also occurs by oxidation. This gas maintains the ecological balance among living bodies.

Carbon dioxide (Co) (0.33%):- This gas has a great ability to absorb heat and thus the lower atmosphere to be warmed by heat radiations coming from the sun (as small wave radiation) and from the earth surface (as longwave radiation). Green plants do photosynthesis (making carbohydrate food) with the help of Carbon dioxide in the daytime. 

Ozone  (O3) (0.00006%): It is produced by the break-up of oxygen molecules by the interaction with ultraviolet radiation with gases present in the middle and upper stratosphere and destroyed by reactions involving nitrogen oxides and chlorine(Cl) later forms CFCs. Ozone protects us from direct exposure to ultraviolet rays by absorbing them.

Methane: It is produced by the anaerobic process by natural wetlands and rice paddies, biomass burning and coal and oil extractions and from landfills. It is a very harmful gas for humans and the biosphere.

Importance of water vapour in the atmosphere:

          The amount of water vapour in the atmosphere is more or less near 5%. In the Tropical humid region amount of water vapour is 2.6% however the amount is very low in 50० - 70० latitude. 90% water vapour presents up to 5km altitude from the sea level.
➤ Plays major roles in forms clouds, fog, due etc and influence precipitations.

➤ Water vapour can absorb long-wave radiation's heat and increase the chances of the greenhouse effect.
➤ At the time of condensation, latent heat produces which increase the atmosphere temperature.

Importance of aerosols in the atmosphere:

➤ When salt particles are floating around in the atmosphere(troposphere) if salt particles absorb water then they act like a hygroscopic nucleus or nucleus of the precepted droplets and plays a major role in precipitation.
➤ The length and density of Dawn and Dusk depend on aerosols.
➤ It can reflect 19% incoming solar radiation.

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