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Ozone Depletion

Ozone Depletion. 10.4 Chapter 15. Ozone Layer and the UV Spectrum. UV-A: unabsorbed, starting of skin cancer UV-B & UV-C (99% absorbed) Damage to tissues Damage to DNA (especially amphibians). Ozone Depletion in Stratosphere. Ozone Protects earth from UV radiation

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Ozone Depletion

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  1. Ozone Depletion 10.4 Chapter 15

  2. Ozone Layer and the UV Spectrum • UV-A: unabsorbed, starting of skin cancer • UV-B & UV-C (99% absorbed) • Damage to tissues • Damage to DNA (especially amphibians)

  3. Ozone Depletion in Stratosphere • Ozone Protects earth from UV radiation • Part of the electromagnetic spectrum with wavelengths just shorter than visible light The Ozone Layer is an implicit global ecosystem service

  4. Natural Closed-Loop Cycle

  5. Anthropogenic Ozone Destroying Compounds • Chlorofluorocarbons (CFC’s) • Refrigeration • Air conditioners • Aerosol propellants • Blowing agents for foam products (Styrofoam) CFC’s are stable, inert, nontoxic, nonflammable • Others • Nitrogen Oxides • Bromines (soil fumigation) • Carbon tetrachloride

  6. Chlorine is a Catalyst 1 Cl atom can destroy 100,000 ozone molecules

  7. Time for Math! • Suppose that 200 CFC molecules entered the stratosphere. If one chlorine atom destroys 100,000 ozone molecules, how many ozone molecules would be destroyed by 200 CFC molecules? • If the same number of CFC molecules entered the stratosphere each year for the next 30 years how many total ozone molecules would be destroyed?

  8. Time for Math • 2.0x107 O3molecules/yr • 6.0x108 O3 molecules over 30 years

  9. Ozone Depletion in Stratosphere • Ozone thinning/hole • First identified in 1985 over Antarctica • Caused by • human-produced bromine and chlorine containing chemicals • Ex: CFCs

  10. Seasonal Ozone Depletion • Antarctic • Depletion: • August-November (late winter-early spring) Video

  11. Hole over Antarctica Requires Two Conditions • (1)Sunlight just returning to polar region • (2)Circumpolar vortex- a mass of cold air that circulates around the southern polar region • Isolates it from the warmer air in the rest of the planet • Polar stratospheric clouds form • Enables Cl and Br to destroy ozone

  12. Why an Ozone Hole? • Polar winter causes a build-up of ice crystals mixed with nitrogen oxide (NO) • Ideal surface for Cl2/Br2 • Sun reappears in Spring & UV breaks the Cl2 down again catalyzing ozone destruction • The “hole” is present in the dark of the polar winter (because it is not being made)

  13. Increased UV-so What! • marine phytoplankton (food webs) • amphibian populations • skin cancer (melanoma) • Cataracts • damage to crops & forests

  14. Recovery of Ozone Layer • Montreal Protocol (1987) • Reduction of CFCs • Started using HCFCs (greenhouse gas) • Satellite pictures in 2000 indicated that ozone layer was recovering • Full recovery will not occur until 2050

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