Composition of air

Air is a mixture of gasses mainly containing nitrogen, about 78% by volume oxygen, about 21% by volume other gasses, about 1% by volume consisting mainly of Argon and about 0.9% by value carbon dioxide,0.3 by volume and small quantities of other gasses.  Varying quantities of dust, smoke and water vapor are also present.The amount of these in the air varies from place to place and from time to time.Besides oxygen, the other gasses in the air are also important.Carbon dioxide is used by plants to prepare food.Nitrogen is important for the growth of plants