Earth's sunscreen – the ozone layer
Activity 7
Can ozone depletion be stopped quickly?
If we were to stop the production of all CFCs and related compounds immediately, why would the destruction of ozone continue?
Teachers notes
Ozone is removed from the atmosphere when an oxygen atom (O) and an ozone molecule (O3 ) meet and react. This reaction is slow. Certain compounds such as chlorine (Cl) and chlorine monoxide (ClO) can catalyse the reaction. The chlorine atoms are catalysts, so they are not consumed during the reaction and can go on to catalyse further reactions. So each chlorine atom introduced into the stratosphere can destroy thousands of ozone molecules before it is removed. (Note that the process is even more dramatic for bromine. It has no stable reservoirs so it can destroy millions of molecules of ozone before it is removed. Fortunately bromine is less abundant than chlorine in the stratosphere.)
There is also a time lag before the chlorine molecules reach the stratosphere. It takes about 5 years for chlorine levels at ground levels in the troposphere to drift up to the stratosphere.
Posted February 1997.