How do polar stratospheric clouds contribute to the Antarctic ozone hole?

Polar stratospheric clouds (PSCs) play a critical role in the formation of the Antarctic ozone hole by facilitating the chemical conversion of chlorine into highly reactive forms.

During the Antarctic winter, the circumpolar vortex isolates the air over the continent, leading to extremely cold temperatures that allow PSCs to form at altitudes of roughly 12 to 22 km. These clouds, which include nacreous clouds composed of water and nitric acid, provide a surface for chemical reactions that transform less-reactive chlorine-containing molecules into more-reactive forms, such as molecular chlorine ($C{l}_2$).12

These reactive chlorine compounds accumulate throughout the dark polar winter. When sunlight returns to Antarctica in the early spring, it breaks the molecular chlorine into single chlorine atoms. These atoms then actively destroy ozone ($O_3$) molecules through a catalytic cycle. This process of ozone depletion continues until the polar vortex breaks up, typically in November.12