Final answer:
Chlorine in the stratosphere primarily comes from chlorofluorocarbons (CFCs) used in aerosols and refrigerants, which decompose under UV light, releasing chlorine that destroys ozone molecules.
Step-by-step explanation:
According to the EPA, chlorine in the stratosphere is believed to come primarily from the CFCs rather than from volcanoes because chlorofluorocarbons (CFCs), once used extensively as aerosol propellants in spray cans and as refrigerants, release chlorine atoms upon breakdown. These chlorine atoms are produced when ultraviolet (UV) light causes CFCs to decompose, leading to the destruction of ozone molecules through a specific chemical process. The reaction can be summarized by the reaction: Cl + O3 → ClO + O2, where the chlorine atom acts as a catalyst, meaning that it can destroy many ozone (O3) molecules over a considerable amount of time before it is removed from the stratosphere. The persistence and stability of CFCs allow them to contribute to ozone depletion for years. Consequently, this leads to a net removal of O3 from the stratosphere, contributing to the thinning of the protective ozone layer and the creation of the ozone hole. As a result, international efforts have been made to reduce CFC emissions, leading to a decline in atmospheric concentrations of atomic chlorine and a gradual recovery of the ozone layer.