IAS 2011 — Environment & Ecology Environment & Ecology

2011mcqmedium

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 ?

Official previous-year question

Verified 2 Aug 2026.

Options

APresence of prominent tropospheric turbulence; and inflow of chlorofluorocarbons
BPresence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
CAbsence of polar front and stratospheric clouds; and inflow of methane and chlorofluorocarbons
DIncreased temperature at polar region due to global warming

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Solution

Correct Option (B)

The formation of the ozone hole in the Antarctic region is primarily attributed to a specific combination of meteorological and chemical conditions:

During the Antarctic winter, extremely low temperatures lead to the formation of Polar Stratospheric Clouds (PSCs). These clouds provide surfaces for heterogeneous chemical reactions.
Chlorofluorocarbons (CFCs) and other ozone-depleting substances, which accumulate in the stratosphere, are activated on the surface of PSCs. These reactions convert inactive chlorine and bromine compounds into highly reactive forms (e.g., Cl₂, HOCl).
With the return of sunlight in the Antarctic spring, these reactive chlorine and bromine species are photolyzed, releasing free radicals (e.g., Cl, Br) that catalytically destroy ozone molecules.
The prominent polar front and the strong polar vortex isolate the air mass over Antarctica, preventing mixing with ozone-rich air from lower latitudes and allowing the ozone-depleting reactions to proceed extensively.

Incorrect Options

Option 1: Ozone depletion primarily occurs in the stratosphere, not the troposphere. While CFCs do enter the troposphere before rising to the stratosphere, tropospheric turbulence is not the direct meteorological factor causing the ozone hole.
Option 3: The presence, not absence, of polar front and stratospheric clouds is crucial for the formation of the ozone hole. Methane is a greenhouse gas and can indirectly influence stratospheric chemistry, but it is not a primary direct cause of ozone depletion in the same manner as CFCs.
Option 4: Ozone depletion in the Antarctic is enhanced by extremely cold temperatures, which facilitate the formation of Polar Stratospheric Clouds. Increased temperatures would generally inhibit PSC formation and thus reduce ozone depletion, contrary to the observed phenomenon.

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Correct Option (B)

The formation of the ozone hole in the Antarctic region is primarily attributed to a specific combination of meteorological and chemical conditions:

During the Antarctic winter, extremely low temperatures lead to the formation of Polar Stratospheric Clouds (PSCs). These clouds provide surfaces for heterogeneous chemical reactions.
Chlorofluorocarbons (CFCs) and other ozone-depleting substances, which accumulate in the stratosphere, are activated on the surface of PSCs. These reactions convert inactive chlorine and bromine compounds into highly reactive forms (e.g., Cl₂, HOCl).
With the return of sunlight in the Antarctic spring, these reactive chlorine and bromine species are photolyzed, releasing free radicals (e.g., Cl, Br) that catalytically destroy ozone molecules.
The prominent polar front and the strong polar vortex isolate the air mass over Antarctica, preventing mixing with ozone-rich air from lower latitudes and allowing the ozone-depleting reactions to proceed extensively.

Incorrect Options

Option 1: Ozone depletion primarily occurs in the stratosphere, not the troposphere. While CFCs do enter the troposphere before rising to the stratosphere, tropospheric turbulence is not the direct meteorological factor causing the ozone hole.
Option 3: The presence, not absence, of polar front and stratospheric clouds is crucial for the formation of the ozone hole. Methane is a greenhouse gas and can indirectly influence stratospheric chemistry, but it is not a primary direct cause of ozone depletion in the same manner as CFCs.
Option 4: Ozone depletion in the Antarctic is enhanced by extremely cold temperatures, which facilitate the formation of Polar Stratospheric Clouds. Increased temperatures would generally inhibit PSC formation and thus reduce ozone depletion, contrary to the observed phenomenon.