Thursday, March 4, 1999 Published at 13:42 GMT
Ozone hole recovery slows
Antarctic science laid the foundations of ozone layer knowledge
By Environment Correspondent Alex Kirby
Scientists working at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia have discovered a major obstacle to the recovery of the Earth's ozone layer.
The scientists are from CSIRO's division of atmospheric research and from two British centres of ozone expertise - the company ICI, and the University of East Anglia.
The team has found that global emissions of one of the worst ozone-depleting gases are 50% greater than had been thought until now.
The gas is halon-1211 (bromochlorodifluoromethane), used as a fire retardant.
Halon-1211's ozone depletion potential (ODP) is 3.0, compared with 1.0 or less for CFCs (chlorofluorocarbons), the gases which originally triggered the concern about damage to the ozone layer.
Halons the greatest threat
Two other halons are even more damaging. Halon-2402 has an ODP of 6.0, while halon-1301's is 10.0. But they are far less widely used.
The international agreement on protecting the ozone layer is the Montreal Protocol.
That is based on calculations which assume that halon-1211 emissions had peaked in 1988.
But the CSIRO team says emissions have in fact risen by about 25% since then.
They measured the halon levels in CSIRO's archive of pristine air collected at the Cape Grim air pollution station in north western Tasmania.
The station is located in the path of the "roaring forties", strong winds which blow unpolluted air across the southern ocean.
The measurements show that emissions of halon-1211, far from having stabilised, are increasing at about 200 tonnes a year.
Dr Paul Fraser of CSIRO says: "The continued growth of halon-1211 could be due to increased legal manufacture and release in China".
China is responsible for about 90% of the world's production of the gas, and as a developing country it has until 2010 before it must stop all halon production.
Developed countries were required under the Montreal Protocol to phase out halons at the beginning of 1994, except for essential uses.
Halons phase out
Dr Fraser says he expects China to begin reducing halon production soon. "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."
The ozone layer protects all life on earth against harmful ultra-violet radiation from the sun.
That can cause cataracts and skin cancer, and there are fears that it could even affect plankton, the microscopic organisms at the base of the marine food chain.
The US Environmental Protection Agency estimates that if ozone depletion continues until only 40% of the original amount is left, there would be an additional 154 million cases of skin cancer.