How  free  chlorine in the atmosphere
   destroys ozone.
<Li> Chlorine  from  CFCs interacts with ozone (O[3]), forming chlorine
monoxide (ClO) and O[2].
<Li> Two ClO molecules react, forming chlorine peroxide (Cl[2]O[2]).
<Li> Sunlight  causes  Cl[2]O[2]  to  break  down  into  O[2]  and free
chlorine atoms.

   The chlorine atoms can begin the cycle again.

   The  destruction  of  atmospheric  ozone  can lead to depletion of the
   ozone layer in the stratosphere.