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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.

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Presentation on theme: "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."— Presentation transcript:

1 Ozone Depletion 10.4 Chapter 15

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3 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)

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5 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

6 Natural Closed-Loop Cycle

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8 Anthropogenic Ozone Destroying Compounds Chlorofluorocarbons (CFCs) – Refrigeration – Air conditioners – Aerosol propellants – Blowing agents for foam products (Styrofoam) CFCs are stable, inert, nontoxic, nonflammable Others Nitrogen Oxides Bromines (soil fumigation) Carbon tetrachloride

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

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12 Time for Math! A.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? B.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?

13 Time for Math A.2.0x10 7 O 3 molecules/yr B.6.0x10 8 O 3 molecules over 30 years

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

15 Seasonal Ozone Depletion Antarctic Depletion: – August-November (late winter-early spring) Video

16 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

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18 Why an Ozone Hole? Polar winter causes a build-up of ice crystals mixed with nitrogen oxide (NO) Ideal surface for Cl 2 /Br 2 Sun reappears in Spring & UV breaks the Cl 2 down again catalyzing ozone destruction The hole is present in the dark of the polar winter (because it is not being made)

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

20 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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