Q. 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? (UPSC Prelims 2011)
Answer: Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
Notes: The correct answer is [B] Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons.While Chlorofluorocarbons (CFCs) are present globally, the "hole" specifically forms over Antarctica because of unique atmospheric and meteorological conditions that occur during the southern winter and spring.Why the Antarctic Region?The formation of the ozone hole requires a very specific "chemical kitchen" that only exists in the Antarctic stratosphere:

• The Polar Vortex (Polar Front): During the winter, a strong, circling wind called the "polar vortex" develops over Antarctica. This acts as a barrier, trapping very cold air inside and preventing warmer, ozone-rich air from the tropics from mixing in.
• Polar Stratospheric Clouds (PSCs): The air inside the vortex becomes so cold (below -78°C) that clouds form even in the very dry stratosphere. These are called Polar Stratospheric Clouds.
• The Role of CFCs: These clouds provide a solid surface for chemical reactions. Inactive chlorine compounds (from CFCs) land on these cloud particles and react to become highly reactive chlorine gas.
• Springtime Sunlight: When the sun returns in the spring (September/October), the UV radiation breaks that chlorine gas into free chlorine atoms. A single chlorine atom can destroy thousands of ozone molecules in a rapid chain reaction.

Other Options

• Option [A]: Tropospheric turbulence happens in the lower layer of the atmosphere (the troposphere), whereas the ozone layer is in the stratosphere.
• Option [C]: It is the presence of the polar front and PSCs, not their absence, that creates the conditions for ozone depletion. Also, while methane is a greenhouse gas, it is not the primary driver of the Antarctic ozone hole.
• Option [D]: This is a common misconception. Global warming actually leads to a cooling of the stratosphere (even as the surface warms), which can actually encourage the formation of more Polar Stratospheric Clouds.