The answer is; chlorine
When CFC (Chlorofluorocarbons) and HCFC is exposed to UV light for a long time they slowly decompose to chlorine radicals as shown the chemical reaction below;
CCl3F → CCl2F+ + Cl-
This CL is not a molecule but rather a radical and hence behaves differently from CL2. Cl- reacts with ozone (O3) and reduces it to oxygen (O2) hence depleting ozone in the stratosphere that protects life on earth.
