When the cfcl3 in the atmosphere is hit by UV rays from the sun, it decomposes to Cl atoms. These Cl atoms then react with the ozone producing O2 and ClO. The ClO bombard with O atoms splitting the ClO up and the free Cl atom again bonds to another O3 molecule hence reducing it. One ClO can reduce several O3 molecules (up to 100,000) creating an ozone hole.
