Smog is a type of air pollution. It is a blend of smoke and fog. Smog is classified into classical smog and photochemical smog.Classical smog occurs in a cool, humid climate. Its components include smoke, fog and sulphur dioxide. It is reducing in nature.Photochemical smog occurs in a dry, sunny climate. Its components are PAN, acrolein, ozone, formaldehyde, nitric oxide. It is oxidizing in nature.