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1 Ozone depletion module prepared by Eugene C. Cordero Lesson 2: "The Antarctic Ozone Hole"

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2 Ozone depletion module prepared by Eugene C. Cordero Learning objectives To develop an understanding for the history of ozone depletion To develop an understanding for what the ozone hole is. To understanding how the ozone hole is produced.

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3 Ozone depletion module prepared by Eugene C. Cordero Early concerns about ozone depletion

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4 Ozone depletion module prepared by Eugene C. Cordero History of Ozone Depletion CFCs developed in 40s and 50s Refrigerants, propellants, fire retardants 1970s CFCs detected in atmosphere. Many of these have long atmospheric lifetimes (10s to 100s of years) 1974 Rowland and Molina propose that CFCs can destroy ozone in the stratosphere. CFCs broken apart by UV radiation forming chlorine which can destroy ozone quickly: O 3 +Cl ClO+ O 2 (Catalytic Reaction) ClO+O Cl+O 2

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5 Ozone depletion module prepared by Eugene C. Cordero History of ozone depletion 1970s Supersonic Aircraft fleet under review. 1978: CFCs used in aerosols banned. 1985: British Antarctic Survey reports 40% loss of ozone over Antarctica during spring. (NASA confirms) 1987: Signing of the Montreal Protocol International agreement to reduce CFC use Later agreements agreed to completely phase out CFC and halons. 1996 Complete ban on industrial production of CFCs goes into effect.

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6 Ozone depletion module prepared by Eugene C. Cordero The Ozone Hole First discovered in 1985: observations from Antarctica extend back into 1950s. Characterized as a rapid depletion of ozone over Antarctica during spring. Ozone hole season, Spring (August October) Ozone hole located over mainly over Antarctica. Ozone hole recovers by late December Ozone hole caused by human chemicals (CFCs) Ozone hole not present in early 1970s

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7 Ozone depletion module prepared by Eugene C. Cordero Total Ozone: October 14, 1997

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8 Ozone depletion module prepared by Eugene C. Cordero Where is the ozone hole? Ozone hole largely restricted to areas over Antarctica Ozone hole may pass over tip of South America Ozone hole seldom comes near Australia. Northern Hemisphere (NH) has no ozone hole like the Southern Hemisphere However, recently NH has experienced the occurrence of ozone mini holes.

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9 Ozone depletion module prepared by Eugene C. Cordero Satellite Total Ozone from 70s and 90s

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10 Ozone depletion module prepared by Eugene C. Cordero Ozone observations over Antarctica

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11 Ozone depletion module prepared by Eugene C. Cordero Is the ozone hole getting worse?

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12 Ozone depletion module prepared by Eugene C. Cordero Animation

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13 Ozone depletion module prepared by Eugene C. Cordero Ozone Hole Recipe Ingredients: Chlorine gas Cold Temperatures (~-80C) Instructions: Allow cold temperatures to form Polar Stratospheric Clouds (1-2 weeks). Allow time for polar stratospheric clouds to convert chlorine gas into ozone destroying chemicals. (1 month) Bake ingredients with sunlight. Presto, a delicious ozone hole! Science interpretation Chlorine gas is abundant in atmosphere due to CFCs Cold Temperatures (~-80C) only occur over Antarctica during the cold winter. Polar Stratospheric Clouds allow ozone friendly chlorine to be transformed into ozone destroying chlorine. Ozone depletion then starts when sun returns to Antarctica in the spring Ozone hole grows from late August through till October.

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Chlorine gas Cold Temperatures T~-80C Polar Stratospheric Clouds Ozone destroying chemicals Everywhere in Atmosphere Sunlight Ozone Hole produces and produces Ozone Hole Formation

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15 Ozone depletion module prepared by Eugene C. Cordero Summary The Ozone hole develops during spring over Antarctica. The Ozone hole is produced by unique combination of weather (cold temps) and chemistry (chlorine). Global ozone trends are negative except in the tropics.