1. Ozone Depletion
10.4
Chapter 15

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)

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

8. 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

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

12. 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?

13. Time for Math 2.0x107 O3molecules/yr
6.0x108 O3 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

18. 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)

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