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.
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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
doesn’t 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.
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.