Explain the differences between pure air and polluted air.

Pure air has 78% nitrogen, 21% is oxygen and carbon dioxide, argon, methane, ozone and water vapour are also present in very small quantities. Pure air has balanced quantity of all its constituent gases and it is free from harmful gasesand is fit for breathing.
On the other hand polluted air has unwanted gases and other suspended impurities like dust and smoke. It is unfit for breathing and has a harmful effect on both the living and the non-living. 

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