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Why did chlorofluorocarbons contribute to ozone-layer depletion?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — halogen Modern version of the periodic table of the elements.

Chlorofluorocarbons (CFCs) contribute to ozone-layer depletion because they act as a significant source of chlorine in the stratosphere.1

When CFCs are released into the atmosphere, they accumulate in the stratosphere, where they are exposed to ultraviolet radiation. This radiation causes the CFC molecules to dissociate, liberating chlorine atoms and reactive radicals. These free chlorine atoms then react with ozone molecules, breaking them apart by stripping away an oxygen atom.21

This process is catalytic; a single chlorine atom can initiate a cycle that converts thousands of ozone molecules into oxygen, thereby thinning the ozone layer that shields Earth from harmful radiation. Because this depletion poses a severe risk to human health and the environment, international efforts such as the Montreal Protocol were established to phase out the production and use of these ozone-depleting chemicals.23