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Ozone Depletion

Ozone Depletion. Ozone. O 3 is an unstable molecule formed when O 2 is split by UV making 2 O atoms which then recombine with O 2 in atm to reform O 3 Ozone layer = high concentration of ozone in the lower stratosphere with maximum concentration at ~25 km altitude

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Ozone Depletion

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  1. Ozone Depletion

  2. Ozone • O3 is an unstable molecule • formed when O2 is split by UV making 2 O atoms which then recombine with O2 in atm to reform O3 • Ozone layer = high concentration of ozone in the lower stratosphere • with maximum concentration at ~25 km altitude • 12 ppm concentrations effectively block incoming damaging ultraviolet radiation • naturally shields life from UV’s harmful effects

  3. Not really hole; more of a thinning Defined as concentrations of <200 ppb (<200 DU) 1 ppb of O3 = 1 Dobson unit (DU) Ozone “hole” over Antarctica each spring (Sept.-Nov.) Thinning since 1980s levels over Antarctica had declined by 40-60% Depletion also in Arctic & globally Lets in more UV radiation The Ozone “Hole”

  4. Ozone Depletion • Ozone layer in stratosphere damaged by Ozone Depleting Chemicals (ODCs) • Halons • fire extinguishers • Carbon tetrachloride • solvent • Methyl chloroform • cleaning solvent & propellant • ***CFCs (cholorfluorocarbons)

  5. CFCs • cheap to produce • very stable, nonflammable, & noncorrosive • lasting up to 200 years in the atmosphere • Freons, used in aerosol sprays, ACs, & solvents • 1 million metric tons/year were produced • Releases chlorine atoms that split ozone • A single chlorine atom removes about 100,000 O3 molecules before it is taken out of operation by other substances • In 1988 CFCs were no longer manufactured. • Nevertheless, by 1988 some 320,000 metric tons of CFCs were used worldwide. • Many countries have recently passed laws banning nonessential use of these chemicals.

  6. How to Protect the Ozone • Stop producing ODCs • Substitutes are available for almost all CFCs • Hydrocholorfluorocarbons (HCFCs) • Hydrofluorocarbons (HFCs) • Helium • Hydrocarbons (HCs)

  7. What’s Being Done to Reduce O3 Depletion? • 1987 Montreal Protocol on Substances that Deplete the Ozone Layer • Landmark international agreement • Effective January 1, 1989 • Five revisions • 1990 (London), 1992 (Copenhagen), 1995 (Vienna), 1997 (Montreal), 1999 (Beijing) • Meeting of 36 nations to cut emissions of CFC’s • Aimed to reduce emissions by 35% from 1989-2000 eventually eliminate all ODCs by 2006 • Based on success of treaty ozone levels expected to return to normal around 2050 • Also halons, carbon tetrachloride, & methyl chloroform

  8. The Montreal Protocol is a Success • Today, production & use of ODCs has ↓ 95% • The ozone layer is beginning to recover • Considered biggest enviro. success story • Policymakers included industry in helping to solve the problem • Implementation of the plan allowed an adaptive management strategy that changed strategies in response to new scientific data, technological advances, & economic figures • The Montreal Protocol can serve as a model for international environmental cooperation

  9. Clean Air Act • Motor Vehicle Air Conditioning • CFC’s have been used as a coolant in motor vehicles • Scientists wanted to make sure existing CFC is used efficiently and not wasted • This Act lists provisions for new machines to make sure they meet standards for emissions • Product Labeling • Establishing label requirements for products manufactured with Class I ODCs • Labeling of Class II substances required by 2015 • Made to make public aware of Ozone depletion due to use

  10. Challenges Still Face Us • CFCs will remain in the stratosphere for a long time • Nations can ask for exemptions to the ban

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