L1 /
8
CH3041
CFC’s II
• By 1972 only 25% of the “Cl” crossing the
tropopause into the stratosphere came
from CH3Cl the remainder came from CFCs.
tropopause into the stratosphere came
from CH3Cl the remainder came from CFCs.
• The CFCs migrate upwards in 3 - 10
years.
• Gradual
Photolysis in the Stratosphere
UV l 190- 220 nm
CF2Cl2 + hn ®
CF2Cl. + Cl.
Catalytic
Destruction of Ozone
Cl. +
O3 ® ClO. + O2 (chlorine monoxide)
ClO. + O3 ®
Cl.
+ 2O2 (net loss of O3)
• CFCs increase the amount of Cl. and their
overall rate of decomposition is slow. t 110y
overall rate of decomposition is slow. t 110y
1 Cl. Destroys around
100 000 O3 molecules
