How did chlorofluorocarbons contribute to ozone-layer depletion?

Chlorofluorocarbons (CFCs) contributed to the depletion of the ozone layer by acting as a source of chlorine in the stratosphere.12

When these human-produced molecules—which contain carbon, fluorine, and chlorine—reach the stratosphere, they are exposed to ultraviolet radiation from the Sun. This radiation causes the CFC molecules to dissociate, liberating free chlorine atoms.12

These chlorine atoms then react with ozone ($O_3$) molecules, stripping away one oxygen atom and breaking the ozone apart. This process is highly destructive; a single chlorine atom can initiate a catalytic cycle that converts thousands of ozone molecules into oxygen gas. Because stratospheric ozone is essential for shielding life on Earth from harmful ultraviolet radiation, the widespread industrial use of CFCs as refrigerants, propellants, and solvents created a significant environmental threat that led to international efforts to phase out their production.12