O 3 zone Story Terry Deshler, Atmospheric Science Formation Importance Loss –Before 1985Before 1985 –After 1985After 1985 Recovery Relationship to global warming The end

Relationship to Global Warming Peripheral Ozone has a slight greenhouse effect, but Loss of ozone over Antarctica may have intensified the polar vortex and reduced the warming expected in Antarctica CFCs are a significant green house gas Reduction of CFCs largest single human action mitigating the current warming

The End? No, we have to limit the release of CFCs into the atmosphere from now on. The good news - the atmosphere will cleanse itself of present atmospheric chlorine. The bad news - it will take another 50 years to see the ozone hole above Antarctica disappear.

Ozone Formation O 2 + h  O + O Then, O + O + M  O 2 + M orO + O 2 + M  O 3 + M (Ozone created) – Where will this primarily occur? Also, O 3 + h ( > 310 nm )  O 2 + O and O 3 + h ( < 310 nm)  O 2 * + O* (UV absorption) O 2 * + O 2  2O 2 + thermal energy (Excess energy dumped O 2 *  O 2 + h ( = 1.3  m) in ozone layer)

Importance of ozone Absorbs DNA damaging UV radiation –This UV affects both animals and plants SH/NH differences - In summer UV radiation is 50% more intense in SH than NH. Australia - world leader in skin cancer –Reasons –10% - Earth is closer to sun in SH summer than NH summer –20% - Antarctic ozone loss/clearer atmosphere –20% - Unknown

Food Preservation 100 BC s, Early methods: Drying, Salting, Cool cellars/Spring houses, Pickling, Fermenting, Canning. Cooking -> could eat spoiled food - spices to hide the flavor Ice Boxes - Thomas Moore invented the insulated box, with ice was in a separate container above the food storage area. Relied on stores of natural ice from frozen lakes and rivers. 1850s - Methods to artificially produce ice were developed Warm weather/rain lead to a shortage of natural ice. Spurred the development of mechanical refrigeration.

Refrigeration Kelvinator, First refrigerator introduced to American market. 1920s - Refrigerators used ammonia (NH 4 ), sulfur dioxide (SO 2 ), (toxic, odorous), and methyl chloride (CH 3 Cl), (toxic, no odor) - silent killer Thomas Midgley, Fridgidaire, dichlorodifluoromethane (CCl 2 F 2 ) Fridgidaire and DuPont joined to produce CCl 2 F 2, and CFCl 3 as Freon.

Molina and Rowland - simple question - What happens to CFCs released into the atmosphere? (awarded Nobel prize Chemistry 1995) CCl 3 F (F-11) + h ( O 3 layer)  CCl 2 F + Cl CCl 2 F 2 (F-12) + h ( O 3 layer)  CClF 2 + Cl Then Cl + O 3  ClO + O 2 ClO + O  Cl + O 2 Net: O 3 + O  O 2 + O 2 This would occur above ozone layer altitudes above 30 km

Reservoir molecules – Predicted ozone losses above 30 km were not observed. Reservoir molecules discovered. – Cl + CH 4  HCl + CH 3 –ClO + NO 2  ClONO 2 –HCl and ClONO 2 are reservoir species – Models predict 10% ozone loss in 100 years for current CFC production rates.

Ozone Profiles McMurdo Station, Antarctica

Late winter spring During Winter

Catalytic Cycle Polar Stratosphere – PSC particle + HCl + ClONO 2  Cl 2 – Cl 2 + h  Cl + Cl – 2 [ Cl + O 3  ClO + O] – ClO + ClO + M  ClOOCl + M ( M=N 2 or O 2 ) – ClOOCl + h  Cl + ClOO – ClOO + M  Cl + O 2 + M –h = Sun’s return Net2O 3 + h  3O 2 A single Cl atom can destroy more than100,000 ozone molecules. This cycle will continue until the NO 2 and OH lost in the form of HNO 3 in polar stratospheric clouds is replenished by mid latitude air, thus converting Cl back to its reservoir species.

Nitric acid/water Ice Nitric acid/water Ice

Molina & Rowland, 1974 Reservoir Molecules Discovered Montreal Protocol, and amendments Antarctic ozone hole discovered

Refrigerants Foam Expansion Solvents Propellants Fire Extinguishants 1974 Ozone Depletion Hypothesis 1986 Base Year for Montreal Protocol 1996 CFC Phaseout Complete in Developed Countries CFCs HCFCs HFCs Refrigerants Other Thousands of tonnes An Industry in Transition

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