stratospheric ozone depletion - willis'...

Stratospheric

Ozone

Depletion

• Ozone: 3 oxygen atoms in

stratosphere that absorbs UV radiation

• Protects us from UV B and UVC

radiation: sunburns and cancer

ozone_creation.mov

ozone_creation.mov

Strat. O3 Formed?

O2 + UV (light) O + O

O + O2 Stratospheric O3

O3 + UV O + O2

**The Cycle Continues**

With your partner,

describe the series

of chemical

reactions just

presented to you!

Then, switch!

Cause of Ozone

Depletion

•Chlorofluorocarbons, CFC’s:

Cpds w/ Cl, F, & C

Very stable not rained out from

troposphere, traveled up into

stratosphere.

DuPont gave them the

brand name Freon

Disposal of

CFC’s

• Currently a problem…old fridges, AC’s,

and Styrofoam still contain CFCs!

• 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

• 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…!

Rowland

and Molina

No hole…just thinning (40-70%) of

O3 layer over Antarctica

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

Largest hole during

Antarctic spring

Skin Cancer!

Effects of Ozone Depletion

Cataracts (blindness)

increases



Amphibian egg

mutation


Reduction in crop productivity


Mutates/ kills phytoplankton

(base of aquatic food chain)



More UV radiation in will melt

polar ice caps.

Protecting Ozone Layer

• 1978 - U.S. banned use of CFC’s

• 1987 - Montreal Protocol: gradually

phased out use of CFC’s

Alternatives

HFCs: Hydrofluorocarbons: No Cl!

Groundwater pollutant as it breaks

down

stratospheric ozone depletion - willis'...

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