Chemistry and Human Environment_Ridge_Date__030410

Chemistry and Human Environment_Ridge_Date__030410 - Ozone...

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Ozone III Ozone Destruction Ozone destruction is greatest in Antarctica The Chapman Cycle 1. O 2 2O (UV-C radiation) 2. O + O 2 O 3 3. O + O 3 2O 2 4. O 3 O 2 + O (UV-B radiation) Ozone concentration increases/decreases with solar flux (step 1) Solar flux changes with latitude and time of year (ex: maximum in summer in northern hemisphere) Solar flux varies on 12-year cycle (sun spots) Stratospheric winds (dilution) “Natural” mechanisms of ozone destruction o Ex: : H 2 O + UV-C radiation → H• + •OH (these decompose ozone) o H 2 O concentration varies with thunderstorms, etc.; Volcanoes release HCl which can destroy ozone similar to CFCs Chlorofluorocarbon characteristics o 1. Efficient, nonreactive, nontoxic refrigerants and propellents o 2. Photodissociate with UV-C radiation (not UV-A, B) Stratospheric Ozone Destruction Initiation: CF 2 Cl 2 + UV-C radiation → CF 2 Cl• + •Cl UV-C radiation exists only in the stratosphere; for this reason, the above reaction
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Chemistry and Human Environment_Ridge_Date__030410 - Ozone...

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