The Antarctic ozone hole usually reaches its greatest extent during which month?

Concept

The Antarctic ozone hole is a seasonal stratospheric phenomenon governed by very low temperatures, polar stratospheric clouds, reactive chlorine and bromine, sunlight, and the isolation created by the polar vortex.

Halogen compounds are activated on cloud particles during the cold winter, but rapid ozone destruction begins when sunlight returns in austral spring. Later warming and vortex breakup end the event.

Application

1. During Antarctic winter, the cold polar vortex permits polar stratospheric clouds to form and converts halogen compounds into ozone-destroying forms.

2. As sunlight returns in August and September, photochemical cycles rapidly destroy ozone while the vortex is still cold and isolated.

3. NASA describes the hole as growing in August and reaching its largest area and depth from mid-September to early October.

Contrast and cross-check

• March is early austral autumn, before the wintertime chemical preparation and springtime ozone-loss phase.

• April is austral autumn, when the cold-season vortex is developing rather than reaching the springtime depletion maximum.

• November is late austral spring; the hole may persist, but the vortex commonly weakens and ozone-rich air begins mixing into the region.

Therefore, among the offered choices, September is the standard best-supported month.