Atmosphere is a blanket of air surrounding the earth. It is composed of different gases. Among the gases nitrogen and oxygen are the main gases which comprise 78.08 % and 20.95% by volume respectively. The carbon dioxide is another important gas which consists of 0.036%. In the atmosphere water vapor is 0 to 4% but its concentration varies in the atmosphere near different regions, for example the highest concentrations is near the equator over the oceans and tropical rain forests.