The two chlorofluorocarbons, CFC-11 and CFC-12, are used in fridges, air conditioners and the manufacture of aerosols and plastic foams. They account for half the ozone-destroying chemicals that come from man-made sources.
Manufacturers have promised to phase out the production of the two gases and, according to scientists at the United States National Oceanic and Atmospheric Administration in Boulder, Colorado, this already shows in a slowing down of the increase in atmospheric levels. If the growth rates in the atmosphere continue to slow in line with predicted changes in industrial emissions, global levels of the two gases 'will reach a maximum before the turn of the century and then begin to decline', the US scientists say.
Because of the relatively long time CFCs spend in the atmosphere, they pose a considerable long-term threat to the ozone layer, which protects the planet from harmful ultraviolet radiation from the Sun.
Governments undertook to cut production of CFCs following the signing of the Montreal protocol in 1987 which, with its subsequent amendments, called for the elimination of CFC production by 1996.