Fluoride Action Network

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

Source: The New York Times | July 28th, 2000 | by Andrew C. Revkin
Industry type: Greenhouse/Ozone Gases

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.”