(1) in the stratosphere, CFCs release chlorine free radicals $\require{mhchem}\ce{(Cl)}$ which reacts with $\ce{O3}$ to give chlorine dioxide radicals.
(2) in the stratosphere, it forms a protective shield against UV radiation.
(3) it is a toxic gas and its reaction with $\ce{NO}$ gives $\ce{NO2}$
(4) in the atmosphere, it is depleted by CFCs.