CFCs were developed by the American engineer Thomas Midgley as a replacement for ammonia (a common refrigerant). The new compound developed had to have a low boiling point, a lack of toxicity and be generally non-reactive. In a demonstration for the American Chemical Association, Midgley flamboyantly demonstrated all these properties by inhaling a breath of the gas and using it to blow out a candle.
Midgley specifically developed CCl2F2. However an attractive feature of CFCs was that there exists a whole family of the compounds, each having a unique boiling point to suit a different application. As well as refrigerants, CFCs have been used as propellants in aerosol cans, cleaning solvents for circuit boards, and as blowing agents for making expanded plastics (such as those used to store fast-foods.)
There has been a movement since the end of the eighties and throughout the nineties to ban CFCs because of their destructive effect on the ozone layer. This effect was, however, first discovered in the seventies, due mainly to the work of scientists [Sherry Rowland]? and [Mario Molina]?. It turns out that one of CFCs most attractive features - its unreactivity - has been instrumental in making it one of our worst pollutants. CFC's unreactivity gives it a lifespan long enough to diffuse up in to the stratosphere?. Here the sun's UV radiation is strong enough to break off the chlorine atom, which on its own is a highly reactive free radical. This catalyses the break up of ozone in to oxygen:
Cl + O3 -> ClO + O2
ClO + O -> Cl + O2
CFCs are such a big problem because they are recreated at the end of these reactions, making them able to keep on reacting with millions of other ozone molecules. The ozone hole produced is able to let through UV light, which causes cancer in humans.
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