Freons or chlorofluoro carbons are responsible for depletion of the ozone layer in the upper strata of the atmosphere. They are used as propellants, aerosol spray caps, refrigerents, fire fighting reagents etc. They are stable and chemically inert compounds. They absorb UV-radiation and break down liberating free atomic chlorine which causes decomposition of ozone through free radical reaction. This results in the depletion of the ozone layer.

Freons are mainly Freon-1 (CFCl3) and Freon-12 (CF2Cl2). They form free radical of chlorine in presence of UV-radical decomposes O3 as follows :

Cl • + O3 ClO • + O2

ClO • + O3 + 2O2