Just when you thought the Earth's ozone layer was safe from CFC chemicals, there's a new threat. Halon 1202.

And while other damaging chemicals have been identified and banned, Halon 1202 is not only increasing rapidly, we don't even not know where it's coming from.

This is Cape Grim in Tasmania, run by the Bureau of Meteorology, where CSIRO scientists collect what is probably the most pristine air in the world.

From the air collected here, they can determine which pollutants there are in the atmosphere.

Their measurements had indicated that damage to the ozone layer would decline over the next decade, but the discovery of the damaging Halon 1202 has made them reassess that time-table.

Halon 1202 has an ozone depletion potential approximately half that of the common CFC's, but it has increased six fold in the atmosphere since the late 1970's.

In fact, during the past two years the atmospheric concentration of halon 1202 has been growing 17 per cent per year.

"It's present in the atmosphere in quite small amounts currently, but the potential exists that it could rise quite rapidly and it is quite damaging to the ozone layer."

The halon 1202 could be a by-product from the production of other known halons, or it may be being made deliberately for military applications.

"The best way to stop halons increasing in the atmosphere is to have them included in the Montreal Protocol, which is an international agreement designed to limit the release of ozone depleting chemicals to the atmosphere."

When the Montreal Protocol was drawn up in 1987, only three halons were included, Halon 1202 was then unknown. And while the phasing out of CFC's and the known Halons is beginning to show results, the new Halon's growth could set back ozone recovery by up to ten years.

Dr Paul Fraser
CSIRO Marine and
Atmospheric Research
Private Bag 1
Aspendale VIC 3195
Paul.Fraser@csiro.au