Newfound gas is greenhouse powerhouse

Scientists have detected in the atmosphere a gas that traps heat more effectively than any other previously found there. Laboratory measurements show that, pound-for-pound, it absorbs about 18,000 times as much infrared radiation as carbon dioxide does.

The researchers find the gas, trifluoromethyl sulfur pentafluoride (SF5CF3), only at trace levels—about 0.12 parts per trillion in 1999—in the atmosphere, but their analysis shows that concentrations are rising at about 6 percent per year. The research, led by scientists at the University of East Anglia in Norwich, England, is reported in the July 28 Science.

The newly detected gas is chemically similar to sulfur hexafluoride (SF6)—another strong absorber of solar radiation—which manufacturers put into gas-insulated electrical switches, transformers, and other high-voltage equipment. S6 is also commonly used in magnesium smelting and the manufacture of semiconductors (SN: 7/15/00, p. 45: An Ounce of Prevention).

Samples of air trapped in Antarctic ice show that SF5CF3 first began to appear in the atmosphere in the late 1960s, says William T. Sturges, lead author of the report. Concentrations of this gas have risen in tandem with those of S6, which suggests a link between the two, he adds.

Sturges and his colleagues say they don’t believe that SF5CF3 is a manufacturing byproduct because they haven’t been able to detect it in freshly made batches of S6. Instead, the researchers surmise that the newly identified gas forms when S6 breaks down inside high-voltage equipment and then reacts with perfluorinated carbon compounds commonly included there.

If the gas does indeed form inside the high-voltage equipment, Sturges says, substantial amounts of SF5CF3 may already be present in those devices. Although the sources of SF5CF3 haven’t been identified, they are almost certainly not natural processes, Sturges says. Therefore, he’s optimistic that scientists can develop ways to curtail the emissions.

“It would behoove us to discover the source of this gas so that we can make better-informed decisions about what to do,” agrees Stephen A. Montzka, an atmospheric research chemist at the National Oceanic and Atmospheric Administration in Boulder, Colo.

Measurements on air samples collected by high-altitude balloons launched from France in 1999 and Sweden in 1997 suggest that SF5CF3 doesn’t easily break down into compounds that are more benign, Sturges says.  Instead, the data suggest that the gas slowly builds up in the atmosphere. By drawing an analogy with nitrous oxide measurements, the researchers estimate that SF5CF3 has a lifetime of at least several hundred years.

The newfound gas joins a growing group of atmospheric trace compounds, many humanmade, that strongly absorb infrared radiation and threaten to exacerbate the greenhouse effect. Sturges and his colleagues recently reported the presence of fluoroform (CHF3), and he says he’s convinced that other greenhouse gases in low concentrations are yet to be identified. The researchers are now calculating the collective warming effect of these compounds, which Sturges says will be significant in terms of the Kyoto protocol. That international agreement seeks to substantially reduce greenhouse-gas emissions from industrial nations by the year 2012.

There’s clearly a need to identify long-lived, potent greenhouse gases well before their industrial production and use becomes widespread, Sturges told Science News. “Together, these gases are not very abundant, but they can make a difference,” he says. “[SF5CF3] is not a present-day threat, but it’s one to be vigilant of.”

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