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Stratospheric
Ozone
Depletion
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• Ozone: 3 oxygen atoms in
stratosphere that absorbs UV radiation
• Protects us from UV B and UVC
radiation: sunburns and cancer
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Strat. O3 Formed?
O2 + UV (light) O + O
O + O2 Stratospheric O3
O3 + UV O + O2
**The Cycle Continues**
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With your partner,
describe the series
of chemical
reactions just
presented to you!
Then, switch!
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Cause of Ozone
Depletion
•Chlorofluorocarbons, CFC’s:
Cpds w/ Cl, F, & C
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Very stable not rained out from
troposphere, traveled up into
stratosphere.
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DuPont gave them the
brand name Freon
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Disposal of
CFC’s
• Currently a problem…old fridges, AC’s,
and Styrofoam still contain CFCs!
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• UV rays broke down CFC’s so Cl-
interacted w/ O3: Cl- + O3 ClO + O2
• 1 Cl- can break down 1000’s of O3
molecules. (Br- also)
CFC’s in Stratosphere
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• Rowland and Molina (1974)- UCI
• Chlorine atoms are removed
from CFCl3 by UV light
• CFCl3 + UV -------> CFCl2 + Cl
• Cl + O3 --------> ClO + O2
• 2ClO + UV -------> 2Cl + O2
I guess there is a reason to
go to UCI…!
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Rowland
and Molina
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No hole…just thinning (40-70%) of
O3 layer over Antarctica
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Why Antarctica?
• In Antarctic winter icy clouds
form sites for CFCs to react and
produce Cl2 atoms
• Cl2 stay attached to clouds until
spring
• In spring, ice crystals melt,
releasing Cl2 into air react to
remove O3
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Largest hole during
Antarctic spring
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Skin Cancer!
Effects of Ozone Depletion
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Cataracts (blindness)
increases
Effects of Ozone Depletion
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Effects of Ozone Depletion
Amphibian egg
mutation
Effects of Ozone Depletion
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Reduction in crop productivity
Effects of Ozone Depletion
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Mutates/ kills phytoplankton
(base of aquatic food chain)
Effects of Ozone Depletion
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Effects of Ozone Depletion
More UV radiation in will melt
polar ice caps.
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Protecting Ozone Layer
• 1978 - U.S. banned use of CFC’s
• 1987 - Montreal Protocol: gradually
phased out use of CFC’s
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Alternatives
HFCs: Hydrofluorocarbons: No Cl!
Groundwater pollutant as it breaks
down