Why the ozone layer is depleted by chlorofluoro-carbons (CFC's) which have been used as aerosol propellants and refrigerants? Illustrate with example.

Explanation

Chlorofluorocarbons or freons are stable compounds. They diffuse into the stratosphere where they undergo photochemical dissociation to produce chlorine radicals. These chlorine radicals react with ozone and thereby decrease the concentration of ozone at a rate much faster than its formation from `O_(2)` . In this way, the ozone layer in the stratosphere is depleted by the freons. In the case of `CF_(2)Cl_(2)` (Freon -12), the following reactions take place.
`CF_(2)Cl_(2)(g)overset(hv)tocdotCl(g)+cdot"CC"lF_(2)(g)`
`cdotCl(g)+O_(3)(g)toClOcdot(g)+O_(2)(g)`
`ClOcdot(g)toClcdot(g)+Ocdot(g)`
`ClOcdot(g)+Ocdot(g)tocdotCl(g)+O_(2)(g)`