"Green" chemicals harming ozone laye

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Green" chemicals harming ozone layer


11:40 17 October 01


Four chemicals being marketed as harmless to the ozone layer may be nothing of the sort, new research suggests. As evidence grows that the ozone hole over the Antarctic is not healing as expected, an international coalition of governments will discuss this week whether to ban them.

Top of the list is n-propyl bromide, a new solvent approved in 1997 by the US Environmental Protection Agency as an acceptable substitute for ozone-depleting substances such as CFCs. The chemical was known to be a potential ozone-eater, but it survives in the environment for less than a fortnight, so regulators assumed it could not reach the ozone layer.

But Donald Wuebbles of the University of Illinois, Urbana-Champaign, and others have since warned that when the substance is released in the tropics, the dynamic weather systems there can launch it into the stratosphere within days.

Even if the chemical breaks down in the lower atmosphere, they say, it could still be churning out by-products that react with ozone-depleting bromine and help transfer it into the stratosphere.


Chinese opposition


The Montreal Protocol limits emissions of ozone-destroying chemicals. This week, a scientific panel will tell a meeting of signatories in Colombo, Sri Lanka, that n-propyl bromide's potential for depleting ozone is 30 times more in the tropics than at northern latitudes. But some countries are questioning the research and may oppose a ban. China, for example, says it does not believe that n-propyl bromide depletes ozone.

UN scientists estimate that up to 10,000 tonnes of the chemical, often marketed as "environmentally friendly", are made each year. That could rise to 50,000 tonnes a year by 2010, they say.

Three other chemicals may also be banned this week.

Hexachlorobutadiene is a solvent and by-product of the manufacture of PVC. Tens of thousands of tonnes are made each year. Halon-1202 is an older chemical still used to fight fires in military aircraft and tanks, and 6-bromo-2-methoxy-naphthalene is used in the manufacture of the agricultural fumigant methyl bromide.


Delayed healing


There are growing fears that there could be many other as-yet unidentified ozone- destroying chemicals in widespread use. "Relatively small amounts of these new substances are being produced, but the levels of some of them are growing rapidly in the atmosphere," says John Pyle of the Centre for Atmospheric Science at the University of Cambridge.

"We cannot be complacent. If enough of these new chemicals are manufactured, we will delay the recovery of the ozone layer quite significantly," warns Mario Molina of the Massachusetts Institute of Technology, who won the chemistry Nobel Prize in 1995 for his work on the thinning ozone layer.

Predictions that the Antarctic ozone hole would begin to heal in the late 1990s have been proved wrong. Last week the British Antarctic Survey reported that this year's hole covered 24 million square kilometres, more than twice the size of Europe. This equals the hole that opened up in 1999 - only the holes in 1998 and 2000 have been bigger.


Fred Pearce

http://www.newscientist.com/news/news.jsp?id=ns99991438