Composition of the atmosphere

• consists of a uniform mixture permanent gases called dry air and varying amount of other material including water vapour and both organic and inorganic impurities like dust, smoke, pollen, etc.
• Pure dry air is very stable all over the earth upto an altitude of about 50 km.
• The lower layer, where the chemical composition of air is uniform, is called homosphere and the higher layer is called heterosphere
• Nitrogen and Oxygen constitute about 99% of clean dry air
• Remaining 1% are mostly inert gases.

a) Oxygen:

• It alone contributes about 1/5th of dry air,
• No life without oxygen; plays important role in oxidation (respiration, soil mineralization, soil formation etc.)
• Essential for combustion so called combustible gas.

b) Nitrogen:

• Contribute major component of the atmosphere and attribute more than 78%,
• It is relatively inactive chemically, though many of its compounds are very active.
• Its main function in the atmosphere is to regulate combustion by diluting oxygen.

c) Carbon dioxide:

• It contributes only about 0.03% of the dry air,
• Green plants, in the process of photosynthesis, consume CO2 and in the process of respiration, CO2 is evolved into the atmosphere,
• It is the product of combustion,
• It is one of the greatest contributing gases on atmospheric phenomenon i.e. on climate change,
• % CO2 is increasing in atmosphere, which contribute a vital role in global warming.

d) Ozone:

• Contribute a small percentage of about 0.00006%, found in upper atmosphere and it is not uniformly distributed.
• Mostly concentrates on 30-60 km from earth surface called ozonosphere.
• O3 is an efficient absorber of ultraviolet radiation and help to protect the biosphere.

e) Chemical compounds:

• Ar, Ne, He, Kr, Xe are so inert chemically that they are never found in any chemical compounds.
• Ar is used extensively in electric lamp bulbs because of its inertness. It is also used inflorescent tubes. It flows with blue light.
• Ne is used to fill florescent tubes. It flows with distinctive orange red colour.
• He is the second highest element with a density of 0.177 gm per liter (Hydrogen 0,08988gms /liter). It is used to inflate balloons because it will not burn.
• Kr glows with brilliant green and yellow colour.
• Xe is chemically inert and glows with a blue green colour.

f) Water vapor:

• Absorb long wave length terrestrial radiation and solar radiation
• Source of all clouds & precipitation
• 90% of water vapor lies below 6 km of atmosphere and only1% is above 10 km.

g) Solid particles:

• The air also contains a variable amount of both organic and inorganic impurities such as dust, soot, salts, fungal spores, bacteria and pollen.
• The main source of dust is the arid regions such as deserts and steppes (grassland).
• The industrial regions, forest fires and volcanoes constitute the main source of soot.
• During evaporation from the ocean, the salt remains in the air in the form of minute particles.
• The salt particles from the oceans are most active as condensation nuclei on which the water vapour condenses to form fog or rain.
• Absorb short wave solar radiation
• Determine blue color of sky by absorbing short wave blue color and red & orange color in sun rise and sun set.