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class17_w08 - Antarctic Ozone Hole Why is the ozone...

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Antarctic Ozone Hole Why is the ozone depletion so strong at the South Pole? Reactions are catalyzed by chlorine radicals and occur on unique polar stratospheric clouds Ring of rapidly circulating air isolates and freezes out the dark South Pole in the winter Polar Spring then brings intense photons and massive ozone depletion
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Water concentrations in the stratosphere are normally too low to promote cloud formation Condensation of water at low concentration does occur in the polar winter (-80°C). Darkness at the Pole means no hv to release heat via O + O 2 O 3 Low temperature also reduces pressure (PV = nRT), generating a wind vortex that isolates the South Pole Frozen water particles containing sulfuric and nitric acids form in the lower stratosphere : PSC’s
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Catalytically inactive molecules act as reservoirs for chlorine and bromine: HCl, ClONO 2 (chlorine nitrate) HBr, BrONO 2 (bromine nitrate) ClO· + ·NO 2 ClONO All these reactions sequester reactive radicals in inactive form ·NO 2 , an intermediate in ·NO-mediated O 3 depletion, reacts with ·ClO, an intermediate in ·Cl-mediated O 3 depletion ·NO 2 also reacts with ·OH to form nitric acid ·NO 2 + ·OH HNO Cl· + CH 4 HCl + ·CH 3 (·CH 3 is not an “X” catalyst) Also:
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On the surface of the ice crystals in the PSC’s: ClONO 2 (g) + H 2 O (aq) HOCl (g) + HNO 3 (aq) HCl (g) + ClONO
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class17_w08 - Antarctic Ozone Hole Why is the ozone...

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