6.4.11 (HL)—Polar stratospheric ozone depletion

Very cold polar conditions form polar stratospheric clouds; volcanic aerosols and cloud particles provide active surfaces that convert stored chlorine into forms activated by spring sunlight.

Keep the sequence: polar cold and isolation → PSC or aerosol surface chemistry → active chlorine reservoirs → returning spring sunlight → rapid catalytic ozone destruction.

A warmer polar winter may form fewer PSCs, weakening spring activation even when ODS-derived chlorine remains present.

Spring sunlight activates the prepared chemical system; cold, surfaces and light are jointly required for the strongest seasonal loss.

Cold air stores the setup; sunlight triggers the rapid chemistry. Neither step alone explains the seasonal hole.