Air is a mixture of various gases contributing to the earth's atmosphere. In general, air consists of molecular Nitrogen (N2) with a volume count of 78%, molecular oxygen (O2) with a volume count of 20%. There are also small amounts of Argon (Ar) with a volume of 1.9%, Neon (Ne), Helium (He), Methane (CH4), Krypton (Kr), Hydrogen (H), Nitrous Oxide (N2O) and Xenon (Xe). Other gases and elements like water vapour (H2O), Ozone (O3), Carbon-dioxide (CO2), Sulphur dioxide (SO2) and Nitrogen dioxide (NO2) are found in variable concentration. The ammonia and hydrogen sulphide are also common constituent of air. Water vapour is the source of all forms of precipitation of water and it acts as an absorber as well as emitter of infrared radiation. Carbon dioxide (in general air concentration level is 20%) is a necessary component for photo-synthesis. Ozone is primarily located in the Stratosphere and is an effective absorber and emitter of infrared radiation.
