E9: Ozone Depletion HL (UNMODIFIED)

Factors Encouraging more ozone depletion over Polar Regions:Winter: Severe drop in stratosphere temperatures = strong circular winds will form (aka polar vortex) Vortex prevents warmer air from entering Total Darknesses at the poles (keeps temperature extremely low and maintains the polar vortex) Polar Vortex + Extremely cold conditions promote formation of polar stratospheric clouds over the poles (formation of ice crystals, compounds with Cl (HCl and ClONO2) trapped inside the crystals Surfaces of ice crystals act as catalysts for the formation of Cl2 Spring: More sunlight available in spring Therefore: Cl2 molecules start to photo-dissociate from CFCs in the stratosphere Rate of ozone depletion increases Summertime: Warmer air over the poles in the summer Polar stratospheric clouds disappear Ozone Depletion slows (or even stops)

Key Points: Large scale depletion of the ozone layer forms the ozone hole over Antarctica (only possible with extremely cold conditions that produce polar stratospheric clouds) Seasonal Variation in the ozone layer over poles - dependent on extremely cold temperatures Ozone Depletion over the Arctic is less than the Antarctica (due to higher temperature)

Ozone Depletion in Polar Regions