The answer is ; deplete the stratosphere ozone layer and allow harmful ultraviolet radiation from the sun to reach the earth.
CFCs and HCFCs decompose over years to release CL- radical. When these radicals reach the atmosphere, they react with ozone as shown in the equations below. They reduce the ozone to oxygen hence depleting the protective layer.
Cl(g) + 03(g) ---- ClO(g) + 02(g) (1)
ClO(g) + O(g) ---- Cl(g) + 02(g) (2)
