UPSC Prelims 2011 · Question 49 of 100

UPSC Prelims 2011 question on Antarctic Ozone Hole

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?

  1. Presence of prominent tropospheric turbulence; and inflow of chlorofluorocarbons
  2. Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
  3. Absence of polar front and stratospheric clouds; and inflow of methane and chlorofluorocarbons
  4. Increased temperature at polar region due to global warming
Show answer

Answer: B. Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons

Verdict

Correct Answer: Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons

Analysis

The Antarctic ozone hole forms due to a combination of CFCs, polar stratospheric clouds and the strong polar vortex/polar front.

Inflow of chlorofluorocarbons — Correct
CFCs released from human activities reach the stratosphere. Under ultraviolet radiation, they release chlorine atoms. These chlorine atoms destroy ozone molecules through chain reactions.

Prominent polar front / polar vortex — Correct
During Antarctic winter, a strong polar vortex forms around Antarctica. It isolates the cold polar air from warmer ozone-rich air of lower latitudes. This allows ozone-depleting reactions to build up.

Polar stratospheric clouds — Correct
In the extremely cold Antarctic stratosphere, polar stratospheric clouds form. These clouds provide surfaces for chemical reactions that convert inactive chlorine compounds into active ozone-destroying forms. When sunlight returns in spring, rapid ozone destruction occurs.

Extra UPSC info

The ozone hole is most severe over Antarctica because of its very cold and stable polar vortex.
The Arctic also faces ozone depletion, but its vortex is weaker and less stable.
Ozone depletion is measured in Dobson Units.
An ozone hole is generally defined when ozone concentration falls below 220 Dobson Units.
The Montreal Protocol, 1987 aimed to phase out ozone-depleting substances like CFCs.
The Kigali Amendment deals with phasedown of HFCs, which do not deplete ozone but are strong greenhouse gases.

How to crack it

The Antarctic ozone hole is caused by CFCs, but it becomes severe because Antarctica has a strong polar vortex and polar stratospheric clouds that accelerate ozone destruction.

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