Britannica Sources used in this answer

How can one chlorine atom destroy many ozone molecules?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

organohalogen compound Vinyl chloride is an organohalogen compound that has important industrial applications. When treated with certain catalysts, vinyl chloride monomers undergo polymerization and form the larger compound known as polyvinyl chloride, or PVC. PVC is used in the manufacture of numerous products, including packaging films and water pipes.

A single chlorine atom can destroy thousands of ozone molecules through a continuous catalytic cycle in the stratosphere.1

The process begins when ultraviolet radiation causes chlorofluorocarbons (CFCs) to dissociate, releasing a free chlorine atom. This chlorine atom reacts with an ozone molecule ( $O_{3}$ ), stripping away one oxygen atom to form chlorine monoxide ( $C l O$ ) and leaving behind an oxygen molecule ( $O_{2}$ ).12

The cycle continues as the chlorine monoxide reacts further in a sequence of steps that cleaves a second ozone molecule. Crucially, this process regenerates the original chlorine atom, allowing it to repeat the destruction cycle over and over again. Because the chlorine atom is not consumed in the reaction but rather acts as a catalyst, one atom can facilitate the destruction of extensive amounts of ozone before it is eventually removed from the atmosphere. This mechanism is a primary driver of ozone depletion, which poses significant risks to human health, such as an increased incidence of skin cancer.12