Ozone is a form of oxygen with the formula \(O_3\)

The ozone layer is the part of the stratosphere (upper atmosphere) where ozone is found in the highest concentrations. It absorbs ultraviolet radiation, preventing most of it from reaching the ground.

CFC's are broken down in the stratosphere by ultraviolet light to give highly reactive chlorine atoms known as free radicals.

The ultraviolet light breaks down the carbon-chlorine bond. One electron goes with the chlorine, the other goes with the rest of the molecule. These molecules with unpaired electrons are known as radicals.

\(CCl_3G \rightarrow CCl_2F + \bullet Cl\)

The chlorine free radicals react with ozone but are regenerated after the reaction - meaning they can react several times, damaging a huge numbers of ozone molecules.

CFC's are broken down slowly by the ultraviolet radiation, so they are only slowly removed from the atmosphere. This slow removal, combined with the fact that one chlorine radical can break down many ozone molecules, means that CFC's will continue to harm the environment long after their use has been banned.

CFC's can be replaced with alkanes or hydrocarbons - these will not damage the ozone.