CFCs are released by refrigerators and air conditioners.  CFCs are very harmful to the atmosphere as they deplete the ozone layer. They are discharged in the lower layer of the atmosphere from where they move upwards towards the stratosphere. In the stratosphere they release chlorine atoms on reaction with UV rays. This Cl act as catalysts and degrade ozone releasing molecular oxygen.  Cl atoms are not consumed in the reaction and thus have permanent and cotinuing effect on ozone levels.