Previous Year Question
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?
Correct Answer: B
Detailed Solution
Three major conditions operate together to produce the Antarctic ozone hole:
Strong polar vortex: During the Antarctic winter, strong westerly winds form a polar vortex around the pole. It isolates polar air from the relatively warmer air of the middle latitudes.
Polar stratospheric clouds: The isolated Antarctic stratosphere becomes extremely cold. At temperatures of approximately –78°C or below, polar stratospheric clouds form. Their ice and nitric-acid particles provide surfaces for important chemical reactions.
Chlorine derived from CFCs: Chlorofluorocarbons reach the stratosphere, where ultraviolet radiation breaks them down and eventually releases chlorine. Reactions on polar stratospheric cloud particles convert inactive chlorine compounds into more active forms.
When sunlight returns during the Antarctic spring, active chlorine is released. It destroys ozone through catalytic reactions:
Cl + O3 → ClO + O2
ClO + O → Cl + O2
The chlorine is regenerated and can therefore destroy many ozone molecules.
Examination of the options:
Option (a) is incorrect: The ozone hole is not caused by tropospheric turbulence; it results from chemical reactions in the stratosphere.
Option (b) is correct: Polar circulation, stratospheric clouds and chlorine derived from CFCs together produce severe ozone depletion.
Option (c) is incorrect: The presence—not absence—of the polar vortex and stratospheric clouds is essential. Methane is not the principal cause.
Option (d) is incorrect: Severe Antarctic ozone loss is associated with extremely cold stratospheric conditions, not a general increase in polar temperature.