Step 2 O + O 2 + M O 3 + M + heat
Step 3 O 3 + hν O 2 + O + heat
1) M is some other particle that can absorb some of the energy released in step 2.
2) The ozone produced in step 2 can also interact with high energy UV light give
molecular oxygen and an oxygen atom in step 3.
3) The oxygen atom formed in step 3 can cause a repetition of step 2, and so forth.
4) The net result of these steps is to convert highly energetic UV light into heat.
- Production of freons or chlorofluorocarbons (CFCs) (chlorofluoromethane and
chlorofluoroethanes) began in 1930 and the world production reached 2 billion
pounds annually by 1974.
- Freons have been used as refrigerants, solvents, and propellants in aerosol cans.
- Typical freons are trichlorofluoromethane, CFCl 3 (called Freon-11) and
dichlorodifluoromethane, CF 2 Cl 2 (called Freon-12).
- In the stratosphere freon is able to initiate radical chain reactions that can upset
the natural ozone balance (1995 Nobel Prize in Chemistry was awarded to P. J.
Crutzen, M. J. Molina, and F. S. Rowland).
- The reactions of Freon-12:
Chain Initiation
Step 1 CF 2 CCl 2 + hν CF 2 CCl• + Cl•
Chain Propagation
Step 2 Cl• + O 3 ClO• + O 2
Step 3 ClO• + O O 2 + Cl•
- In 1985 a hole was discovered in the ozone layer above Antarctica.
- The “Montreal Protocol” was initiated in 1987 which required the reduction of
production and consumption of chlorofluorocarbons.
i).
