Destruction of the ozone layer by CFC radicals

The high reactivity of free radicals and the multiplicative nature of radical chain reactions can be useful in the synthesis of materials such as polyethylene plastic – but these same factors can also result in dangerous consequences. You are probably aware of the danger posed to the earth’s protective stratospheric ozone layer by the use of chlorofluorocarbons (CFCs) as refrigerants and propellants in aerosol spray cans.  Freon-11, or CFCl₃, is a typical CFC that was widely used until fairly recently.  It can take months or years for a CFC molecule to drift up into the stratosphere from the surface of the earth, and of course the concentration of CFCs at this altitude is very low.  Ozone, on the other hand, is continually being formed in the stratosphere.  Why all the concern, then, about destruction of the ozone layer – how could such a small amount of CFCs possibly do significant damage?  The problem lies in the fact that the process by which ozone is destroyed is a chain reaction, so that a single CFC molecule can initiate the destruction of many ozone molecules before a chain termination event occurs.