How does hydrocarbon cause pollution? Discuss its harmful effects.

Incomplete combustion of fossil fuel in industry and thermal power plants and the exhaust of automobiles release unburnt hydrocarbons (such as methane, ethylene etc.) constantly into the atmosphere causing pollution.
Harmful effects of hydrocarbons:
(i) Aromatic hydrocarbons irritate various membranes, cause irritation in eyes, nose, lungs etc. Benzene and benzpyrene cause cancer.
(ii) Hydrocarbons react with ozone and oxides of nitrogen to form aldehydes and peroxy acyl nitrate (PAN) which constitute photo- chemical smog.