Ozone Depletion

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  • Created on: 14-04-12 11:50
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Ozone Depletion
It has been established that the ozone layer has been substantially depleted, especially
around the poles and one of the group of chemicals responsible for this depletion is
chlorofluorocarbons (CFCs). They produce chlorine radicals (Cl·) which catalyse the
breakdown of ozone.
When UV radiation strikes a CFC molecule on the stratosphere, a C-Cl bone breaks, producing a Cl·.
Eg,
CFCl Cl· + ·CFCl Initiation
The breakdown of ozone takes place in two propagation steps:
Cl· + O ClO· + O Propogation Step 1
ClO· + O Cl· + O Propogation Step 2
The two propagation steps above repeat in a cycle, many thousands of times, with each
cycle removing another ozone molecule.
Overall: O + O 2O
Antoher radical that destroys ozone is nitrogen oxide, ·NO, from lightning or aircraft
engines.
As with the chlorine radicals, the breakdown of ozone proceeds in two propogation steps:
·NO + O ·NO + O Propogation Step 1
·NO + O ·NO + O Propogation Step 2
Overall: O + O 2O
Restrictions in the Montreal Protocol aimed at preserving the ozone layer:
Production of CFCs stopped by 2000
Production of tetrachloromethane (used as a solvent) stopped by 2000
Production of halons (used in fire extinguishers) phased out by 2000
Production of 1,1,1-trichloroethane (used as a solvent) phased out by 2005
The use of HCFCs to replace CFCs in about 15% of applications.
HCFCs and HFCs are now thought to contribute to global warming.

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