http://www.nytimes.com/library/national/science/072800sci-environ-climate.html


  Note especially paragraphs 6 and 7. As I recall, the author of the
article wrote The Burning Season, about the assassination of
Brasilian eco-activist Chico Mendes.

July 28, 2000

New Greenhouse Gas Identified, Potent and Rare (but Expanding)

By ANDREW C. REVKIN

Scientists have found rising concentrations of a newly identified gas
in the air that traps heat more effectively than all other known
greenhouse gases, the dozens of compounds released by industry and
the burning of fuels that act like a greenhouse roof and may be
warming the global climate.

The synthetic gas is extremely rare, so far reaching concentrations
just over one-tenth of one part per trillion of air, according to a
paper published today in the journal Science.

But it still poses potential problems, the paper's authors say,
because concentrations of the gas are rising quickly, the gas
probably takes more than 1,000 years to break down and its source --
although certainly from human activity -- is a mystery.

"So far, there is far too small a quantity to be of concern," said
William T. Sturges, an atmospheric chemist at the University of East
Anglia in Norwich, England, and the study's principal author. "But I
wouldn't want to see it enormously increased."

The study provides the latest evidence of the global reach of
pollution and the sometimes unintended consequences of industrial
activity, said many chemists familiar with the report. Advance copies
of the paper circulated this week by e-mail.

Some chemists said yesterday that it was possible that the gas was
being used secretly in military equipment. A similar gas, sulfur
hexafluoride, or SF6 , is on lists of chemicals used in electronics,
weapons and for other military purposes.

But they added that the new gas might also be used secretly by some
industry or it could simply be an unintentional byproduct of some
manufacturing process somewhere in the world. The gas could come from
any number of industrialized countries.


The gas was found in samples taken by instrument-laden balloons 21
miles up in the stratosphere and in air trapped under layers of
Antarctic snow. Its name, trifluoromethyl sulfur pentafluoride, is
enough of a tongue twister that chemists prefer to talk about it
using its chemical formula, SF5 CF3 .

Its discoverers found no evidence of the gas in the air before the
1950's, with only a scattering of molecules appearing in the 1960's
and then a steady rise, with concentrations now rising about 6
percent a year. Altogether, the scientists calculated, about 4,000
tons have been released so far, with an additional 270 tons emitted
each year.

That still has resulted in an overall concentration of about 0.12
parts per trillion in air, making the gas exceedingly rare, Dr.
Sturges said.

But because SF5 CF3 is such a potent, and nearly permanent,
heat-trapping gas, he and his colleagues said, they hoped the finding
would serve as a call to industry and governments to find its source.

Molecule for molecule, it is 18,000 times more effective at trapping
heat in the atmosphere than carbon dioxide, the most familiar
greenhouse gas, Dr. Sturges said. And, like the durable
chlorofluorocarbon chemicals, or CFC's, that can erode earth's
protective ozone layer, the gas is extremely long-lived, with
molecules probably persisting for 1,000 years or more once they are
lofted in the air, the study said.

The global warming potential of a greenhouse gas is a measurement
devised by scientists to describe the relative contributions of
different gases to the predicted warming of the climate. It is the
ratio of the amount of heat trapped by a certain quantity of the gas
to the heat trapped by an equivalent quantity of carbon dioxide over
100 years. If the gas traps 10 times as much heat as carbon dioxide,
then the global warming potential for that gas is 10.

Scientists can precisely measure the ability of a gas to trap
infrared energy -- heat in the laboratory.

Yesterday, several chemists who work with similar compounds said that
they were astonished to learn that thousands of tons of the chemical
had infiltrated the atmosphere.

"I nearly fell off my chair," said Gary A. Gard, a chemistry
professor at Portland State University in Oregon, who is an expert in
the properties of compounds containing fluorine, a versatile element
that has helped scientists produce the atom bomb, prevent tooth decay
and make Teflon coatings and refrigerants.

Dr. Gard recalled how SF5 CF3 had first been synthesized more than 40
years ago by one of his mentors, George H. Cady, at the University of
Washington, but had never found much use beyond pure research.

"To the best of my knowledge, no one is using it on an industrial
scale," Dr. Gard said. "It's the kind of research chemical where
you'd buy 100 grams or 50 grams, but you wouldn't buy a ton of this
stuff."

Other chemists said that SF5 CF3 was briefly employed about 30 years
ago as a chemical tag to track the flow of pollution from
smokestacks. The advantages were that it was inert and stood out
clearly in samples taken downwind, said Edward A. Tyczkowski, a
fluorine chemist in Newport, Tenn. who once manufactured about 100
pounds of the material for government scientists. But he said only a
few pounds were used in such tests and he knew of no large-scale
production.


Dr. Gard agreed with a theory proposed by Dr. Sturges that the traces
of the chemical in the air could be some unnoticed byproduct of
industrial processes using fluorine. He also agreed that a search
should be made for the source.

F. Sherwood Rowland, an atmospheric chemist at the University of
California at Irvine, who shared a Nobel Prize in 1995 for
discovering the link between CFC's and the ozone layer, noted that
other greenhouse gases containing fluorine were unintended industrial
byproducts.

Dr. Rowland said the new finding was important because it underscored
the need to give serious consideration to even the atmosphere's most
minor constituents.

In that sense, he said, the new gas is similar to CFC's, which
prompted an international treaty to protect the ozone layer but have
never existed in concentrations higher than 550 parts per trillion.

Dr. Gard said the newly discovered atmospheric gas also served as a
reminder that the atmosphere is not some boundless expanse.

"Not too long ago, people thought we can dump anything we want in the
ocean because it's so vast," he said. "It's the same thing with the
atmosphere. It's just been seen as this huge sink. Now we see it's
not an infinite reservoir. People should realize that and start
taking better care of it."

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