The formation of ozone hole in the Antarctic region has been a cause of concern. What could be the reason for the formation of this hole?

Answer: (b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons.

The polar vortex (polar front) isolates cold air; polar stratospheric clouds form, and on their surfaces stored chlorine becomes active, destroying ozone in spring sunlight.

The idea

CFCs are spread over the whole globe, yet the hole opens over Antarctica. The reason is cold. The Antarctic winter is colder and longer than the Arctic winter, so ice clouds form more regularly in its stratosphere, and the surface of those clouds is where harmless chlorine compounds change into the active form that destroys ozone.

Polar night: a ring of wind (polar vortex) seals off Antarctic air → Temperature falls below about −78°C → Polar stratospheric clouds form → On the cloud surface chlorine becomes active → Sunlight returns in spring → Chlorine destroys ozone: the hole, September–October

Why the others are wrong

(c) The clouds are present, not absent; methane is not the cause.

(d) The Antarctic stratosphere is extremely cold — that is the point.

The trap

(d) links two big climate stories, but ozone loss needs cold, not heat.

Also know

The Arctic is warmer and its vortex is weaker, so the loss there is smaller and irregular. The hole was reported in 1985 by scientists of the British Antarctic Survey. Ozone is measured in Dobson units, and the “hole” is the area below 220 units. In summer the vortex breaks up and ozone-rich air flows back in.