- A It is sometimes mistakenly thought to form with exactly equal intensity and at precisely the same time of year across every latitude band of the globe, stretching continuously from the tropics to both poles during normal conditions
- B It forms over Antarctica in spring because polar stratospheric clouds form in Antarctic winter, providing surfaces for CFC photolysis reactions that spring sunlight then activates into ozone-destroying chlorine radicals
- C It is sometimes mistakenly thought to be caused mainly by rising atmospheric carbon dioxide concentrations alone, with halogenated chlorine compounds playing little measurable destructive role in this process as generally observed
- D The ozone hole is sometimes mistakenly thought to persist at a perfectly constant size throughout the entire calendar year, showing little detectable seasonal variation in its overall extent in typical laboratory settings
Correct answer: B. It forms over Antarctica in spring because polar stratospheric clouds form in Antarctic winter, providing surfaces for CFC photolysis reactions that spring sunlight then activates into ozone-destroying chlorine radicals
Explanation: Antarctic ozone hole forms in September-October (southern spring). Mechanism: (1) Winter darkness cools stratosphere to below -78C, forming PSCs; (2) CFC reservoir species (ClONO2, HCl) react on PSC surfaces, releasing Cl2 and HOCl; (3) Spring sunlight photolyes these to reactive Cl atoms; (4) Cl catalytically destroys O3 in intense bursts; (5) Polar vortex traps depleted air. Montreal Protocol is working: hole slowly recovering.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.