Saving the ozone layer

The clear links between CFCs, depletion in stratospheric °3, increased UV radiation reaching the Earth's surface and possible increased incidence of skin cancer in humans have not escaped the media, who have been able, at times during the 1970s and 1980s, to capture the imagination of the general public. It is probably correct that the CFC issue aroused immediate concern because its cause was apparently obvious—in the shape of the aerosol can! Although it is true that aerosol propellant was only a contributor to CFC build up in the atmosphere (refrigerant coolants and industrial uses being other important sources), there is little doubt that the aerosol can became a late 20th-century 'icon' for environmental activism. It is this public awareness that has made the CFC-stratospheric °3 story such a good example of how environmental chemistry research can lead to major international legislation.

Against the odds, the anti-aerosol lobby took on the multimillion-dollar aerosol industry and achieved real success. By the late 1970s, CFCs were at least partially banned in deodorant and hair sprays in the USA; Canada imposed similar controls in the early 1980s. It was, however, the discovery of the Antarctic °3 hole that provoked stronger action. In 1987 a meeting of the United Nations Environment Programme in Montreal resulted in 31 countries agreeing to the so-called 'Montreal Protocol', under which developed countries agreed to a 50% cut in CFCs. Following this agreement, further meetings in Helsinki (1989) and Copenhagen (1992) made the conditions of the Montreal Protocol more stringent, resulting in an agreement to ban production of CFCs in developed countries.

Response to the Montreal Protocol by industry was positive, with agreements to phase out CFC production, resulting in a search for viable safe alternatives; decline in some atmospheric CFCs is now evident (Fig. 3.7). In developed countries, hydrocarbons or alternative means of pressuring containers have largely replaced CFCs in aerosol cans, hydrochlorofluorocarbons (HCFCs)—which are 95% less damaging to °3 than CFCs —are used in the production of polystyrene foams and as refrigerant coolants and a propane/butane mixture is being developed as an alternative refrigerant coolant. Even HCFCs are gradually being phased out and replaced by substances that are less likely to cause ozone deple-

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Fig. 3.7 Concentrations of CFC-11 measured at ground level, Cape Grim, Tasmania. Note that concentrations of CFC-11 have been falling in the 1990s following the rapid increase during the 1980s. Copyright CSIRO Australia, May 2002.

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Fig. 3.7 Concentrations of CFC-11 measured at ground level, Cape Grim, Tasmania. Note that concentrations of CFC-11 have been falling in the 1990s following the rapid increase during the 1980s. Copyright CSIRO Australia, May 2002.

tion. Attention must now turn to assisting developing countries, which still use CFCs to switch to alternate compounds.

In the case of the halons, replacements are also being phased in. For example, halon 1301 (bromotrifluoromethane, CF3Br), widely used as a fire-extinguishing agent to protect sensitive electronic equipment, is being replaced by HFC-227 (CF3CHFCF3), which contains no chlorine or bromine.

It is sobering to remember that despite the recent success in limiting production of CFCs, these stable substances have a long residence time in the atmosphere, between 40 and 150 years. This means their effects on the stratospheric O3 will continue for some time after the bans on their production. Current estimates suggest that the policies in place should see a decline in the stratospheric bromine and chlorine concentrations over the next 50 years, paralleled by a rise in ozone concentrations.

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