In 1982 a team from the British Antarctic Survey working in Antarctica found that much of the ozone overhead had vanished. The report of their findings caused a sensation, as ozone depletion of this scale was totally unforseen. It is now known that a depletion, often termed a hole, of the ozone layer over Antarctica occurs each spring, and lasts for approximately six weeks. The ozone layer was first discovered by Professor Gordon Dobson of Oxford University in 1957. Today ozone concentration is measured in Dobson Units.
Halons release bromine atoms which are even more potent ozone destroyers.
This last property is particularly useful as it means that CFCs do not react chemically with other materials, such as the working parts of refrigerators, the contents of aerosols or plastics. However, when CFCs are released into the atmosphere, they slowly drift up to the ozone rich stratosphere where they break down and release atoms of chlorine. Each chlorine atom may react repeatedly to destroy many ozone molecules. Unfortunately CFCs are very stable, i.e. they do not easily break down or change form. Thus they can remain in the atmosphere for more than 100 years.