How free chlorine in the atmosphere destroys ozone.
  1. Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (ClO) and O2.
  2. Two ClO molecules react, forming chlorine peroxide (Cl2O2).
  3. Sunlight causes Cl2O2 to break down into O2 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.