Friday, May 19, 2017

Composition and structure of the Atmosphere




·         The air is a mixture of several gases and it encompasses the earth from all sides.
·         The air surrounding the earth is called the atmosphere.
·         Nitrogen and oxygen are the two main gases in the atmosphere and 99 percentage of the atmosphere  is made up of these two gases.


Chemical Constituents of the Atmosphere:
1. Nitrogen (N2) - 78% (by volume).
2. Oxygen (O2) - 21%.
3. Argon (Ar) - 1%.
4. Carbon Dioxide (CO2) - 0.038% (376 ppm) and rising.




Structure of the Atmosphere:

Troposphere:
·         It is the lowermost layer.
·         Average height is 13 km with 16-18 km at the equator and 6-8 km at the poles.
·         75-80% of total mass.
·         Temperature generally decreases with height; Average lapse rate is 6.5°/km.
·         Referred to as the "weather layer".
·         Climate and weather changes occur here.
·         Zone separating troposphere from stratosphere is called tropopause.

Stratosphere:
        It extends up to a height of 50 km.
        Temperature is constant with height initially, then it increases with height, known as an inversion (temperature increases with height).
        One important feature of stratosphere is that it contains a layer of ozone gas.
        This layer is almost free from clouds and associated weather phenomenon,
making conditions most ideal for flying aeroplanes.
·         So aeroplanes fly in lower stratosphere, sometimes in upper troposphere where weather is calm.
·         Sometimes, cirrus clouds are present at lower levels in this layer.

Ozonosphere:
        It lies at an altitude between 30 km and 60 km from the earth’s surface.
        This layer reflects the harmful ultraviolet radiation.
        The ozonosphere is also called chemosphere.

Mesosphere (from the Greek meso meaning middle):
        It extends up to a height of 80 km.
        The temperature gradually falls to -100°C at 80 km altitude.
        Meteorites burn up in this layer on entering from the space.
Thermosphere (from the Greek therme meaning heat):
        In thermosphere temperature rises very rapidly with increasing height.
        It extends between 80-400 km.
        Ionosphere is a part of this layer.
        This layer helps in radio transmission.
        The International Space Station and satellites orbit in this layer.
        Aurora’s are observed in lower parts of this layer(Aurora Borealis and Aurora Australis).
        Topped by exosphere.

Ionosphere:
        This layer is located between 80 km and 400 km and is an electrically charged layer.
        This layer is characterized by ionization of atoms.
        Because of the electric charge, radio waves transmitted from the earth are reflected back to the earth by this layer.
        Temperature again starts increasing with height because of radiation from the sun.

Exosphere:
        Light gases like helium and hydrogen float into the space from here.
        It is the outermost layer.
        This layer coincides with space.

Vertical Structure of Composition:

1.Homosphere:(homo means same):
        Well mixed, the chemical composition is constant.
        This layer extended up to 80 km from the surface.
        This part of the atmosphere continually circulates, so that the principal atmospheric gases are well mixed.
2.Heterosphere:(hetero means different):
        Settling of gases according to weight above 80 km.





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  2. Amazing information about the Composition and structure of the Atmosphere. It gives me the knowledge of the composition of various types of gases present in the atmosphere including nitrogen gas, Oxygen gas, argon gas, neon, helium gas and so on.

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