UPSC Prelims 2011 Q9: Environment & Ecology – Pollution & Waste Management
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?
- (a) Presence of prominent tropospheric turbulence; and inflow of chlorofluorocarbons
- (b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
- (c) Absence of polar front and stratospheric clouds; and inflow of methane and chlorofluorocarbons
- (d) Increased temperature at polar region due to global warming
Answer: (b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons
Explanation
Why the ozone hole forms over Antarctica
The ozone hole needs a special combination of cold and chemistry found mainly over the Antarctic.
| Option | Verdict | Reason |
|---|---|---|
| (a) Tropospheric turbulence and CFCs | Incorrect | The reaction happens in the stratosphere, not the troposphere |
| (b) Polar front and stratospheric clouds; inflow of CFCs | Correct | The polar vortex (front) isolates Antarctic air; Polar Stratospheric Clouds provide surfaces for reactions that release chlorine from CFCs, which destroys ozone |
| (c) Absence of polar front/clouds; inflow of methane and CFCs | Incorrect | It is the presence, not absence, of the polar front and clouds that matters; methane is not the key gas |
| (d) Increased temperature due to global warming | Incorrect | The hole forms due to extreme cold, not warming |
Mechanism in brief:
| Step | What happens |
|---|---|
| 1. Winter | Polar vortex traps extremely cold air over Antarctica |
| 2. Clouds form | Polar Stratospheric Clouds provide surfaces for chemical reactions |
| 3. Spring sunlight | Releases chlorine from CFCs, which destroys ozone molecules |
Answer: (b) Presence of prominent polar front and stratospheric clouds; and inflow of chlorofluorocarbons.
Why each option is right or wrong
- (a) Incorrect. The destructive reactions occur in the stratosphere, not the troposphere.
- (b) CORRECT. The polar front, stratospheric clouds and CFC inflow together cause the ozone hole.
- (c) Incorrect. It is the presence, not absence, of the polar front and clouds that drives ozone loss; methane is not the main culprit.
- (d) Incorrect. The hole forms because of extreme cold, not rising temperature from global warming.
Key point
Antarctic ozone hole: polar vortex (front) + Polar Stratospheric Clouds + CFCs, reacting in the stratosphere during extreme cold, not warming.
Remember
Ozone hole: polar vortex + stratospheric clouds + CFCs, in extreme cold.
Common mistakes
- Placing the chemistry in the troposphere instead of the stratosphere.
- Reversing 'presence' and 'absence' of the polar front and clouds.
- Blaming global warming/heat for a phenomenon that actually needs extreme cold.
Exam tip
The ozone hole is a cold-weather, stratosphere phenomenon. Any option invoking heat or the troposphere is wrong.
Sources
- NASA Ozone Watch — How the Antarctic ozone hole forms
- World Meteorological Organization / UNEP — Scientific Assessment of Ozone Depletion