THE ATMOSPHERE

THE ATMOSPHERE

Atmosphere is defined as an envelope of gaseous mixtures covering the earth held to it by gravitational forces. Atmosphere is essential for the life on earth. The principal constituents of the lower atmosphere are Nitrogen (78.08%by volume), Oxygen (20.94%), Argon (0.93%), and Carbon dioxide (0.033%). Besides there are minute proportions of other gases.

Oxygen is the most important component among atmospheric gases. Nitrogen which is an important constituent of all organic compounds is relatively inert. The main function of nitrogen is to control combustion by diluting oxygen, thus it acts as a dilutant.
The amount of carbon dioxide varies from place to place, being greatest around the cities and smallest in the country side. Green plants during photosynthesis absorb carbon dioxide from the atmosphere and use it to manufacture food and keep other bio-physical processes going. Ozone consisting of three oxygen atoms chemically linked is another variable constituent of the atmosphere. In the lowest layers, the proportion of ozone is very low (less than 0.00005 by volume of atmosphere). At levels above 32 km, it increases forming what is known as the ozone belt.
Between 20km and 40 km altitude greater concentrations of ozone are found. It plays a crucial role in blocking the harmful ultraviolet radiation from the sun.

Water vapor is one of the most variable gaseous substances present in the atmosphere, constituting between 0.02% and 4% of the total volume (in cold dry and humid tropical climates respectively). 90% of moisture content in the atmosphere exists within 6km on the surface of earth.

Atmosphere also contains huge numbers of solid and liquid particles called "aerosols". In addition negligible quantities of other gases such as argon, neon, helium, hydrogen, xenon, krypton, methane etc were also present in the atmosphere. The earth's atmosphere is made up of a series of layers on the basis of the vertical distribution of temperatures. Atmosphere can be classified into troposphere, mesosphere, thermosphere, stratosphere, exosphere and the Ionosphere.

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