The largest ozone hole in Antarctica occurs in which season?

• A. Early spring
• B. Winter
• C. Summer
• D. Autumn

Answer: (A)

The biggest Antarctic ozone hole shows up in early spring because the destruction of ozone in that region is driven by a seasonal sequence of events tied to sunlight and very cold air. In Antarctic winter, the stratosphere is freezing and the polar vortex isolates the air, allowing polar stratospheric clouds to form. These clouds trap chlorine and bromine in reservoir forms, but without sunlight the chemical reactions that actually destroy ozone can’t run. When spring arrives in the Southern Hemisphere, sunlight returns and photochemical reactions release the active chlorine and bromine from those reservoirs, catalytically destroying ozone rapidly. That combination of returning sunlight and the presence of PSCs leads to the maximum depletion, which is why the hole is largest in early spring (roughly September to October). As conditions warm and PSCs dissipate later in spring and summer, the ozone begins to recover.