Air is a mixture of gases in varying amounts. It consists of 78% nitrogen, 21% oxygen, argon and other inert gases to the extent of about 1.0%. In addition, carbon dioxide is another important constituent of the atmosphere which varies in amount from 0.1% to 0.3%. The variation is mainly due to combustion photosynthetic processes. The other gases, e.g., sulphur dioxide, nitrogen dioxide, ozone, etc. are found in very small quantities. Water vapor is also an important constituent which varies from region to region.