Recovery of the ozone layer is likely to take years longer than expected, CSIRO scientists warn. Latest research shows that global emissions of a key ozone-depleting halon are 50 per cent greater than previously supposed, says Dr Paul Fraser of CSIRO Atmospheric Research.
Emissions of halon-1211, a fire retardant, are increasing at the rate of approximately 200 tonnes per year, based on measurements in the atmosphere made in Tasmania.
Until now, Montreal Protocol calculations assumed that halon-1211 had peaked in 1988. In fact, emissions have since risen by about 25 per cent. Halon-1211 is one of the three ozone-destroying halons that the Protocol seeks to control. Current emissions make it the most damaging of the halons.
The finding on halon-1211 has been made by Dr Paul Fraser from CSIRO Atmospheric Research and UK colleagues. The team measured the halon levels in CSIRO's unique archive of pristine air collected at the Cape Grim baseline air pollution station in north-western Tasmania.
"Halons are now responsible for about 20 per cent of global ozone destruction. The continued growth of halon-1211 could be due to increased legal manufacture and release in China," says Dr Fraser.
China is responsible for about 90 per cent of the world's production of halon-1211. Under the Montreal Protocol, designed to protect the ozone layer, developing countries such as China have until the year 2010 before they must completely phase out halon production.
"I anticipate that China will begin reducing halon production soon," says Dr Fraser. "Montreal Protocol calculations based on production data indicate that halon levels in the air will stabilise during the next few years. Unfortunately, growth of halon-1211 is likely to delay this stabilisation by years."
While concentrations of most of the ozone-damaging CFCs are either steady or falling, halon levels continue to rise.