The gas is used for soil fumigation, termite treatment and post-harvest insect control on fruits, nuts, and grains. But because sulfuryl fluoride production has not yet reached high levels there is still time to nip this potential contributor in the bud, the scientists said.
Researchers at the Massachusetts Institute of Technology, the Scripps Institution of Oceanography and other institutions are reporting the results of their study of the gas this month in the "Journal of Geophysical Research."
The scientists have measured sulfuryl fluoride levels in the atmosphere, and determined its emissions and lifetime to help gauge its potential future effects on climate.
Originally developed by the Dow Chemical Company, sulfuryl fluoride, SO2F2, is in widespread use as a structural fumigant insecticide to control drywood termites, particularly in warm weather portions of the southwestern and southeastern United States and in Hawaii.
Soil fumigation before planting (Photo courtesy Society of Nematologists and APSnet)
More recently, sulfuryl fluoride has been introduced as a replacement for methyl bromide, a widely used fumigant that is being phased out under the Montreal Protocol because of its ozone-destroying chemistry. Methyl bromide has been used for insect control in grain storage facilities, and in intensive agriculture in arid lands where drip irrigation is combined with covering of the land with plastic sheets to control evaporation.
The U.S. Department of Agriculture is assessing fumigation with sulfuryl fluoride as a quarantine treatment for exotic wood boring insects in merchantable logs and timber, the agency said in a December 2008 report.
"Such fumigants are very important for controlling pests in the agricultural and building sectors," says Ron Prinn, director of MIT's Center for Global Change Science and a co-author of the new paper. But with methyl bromide being phased out, "industry had to find alternatives, so sulfuryl fluoride has evolved to fill the role," he says.
Until the new study, nobody knew accurately how long sulfuryl fluoride would last in the atmosphere after it leaked out of buildings or grain silos.
"Our analysis has shown that the lifetime is about 36 years, or eight times greater than previously thought, with the ocean being its dominant sink," Prinn says. So it would become "a greenhouse gas of some importance if the quantity of its use grows as people expect."
Houses tented for termite treatment with sulfuryl fluoride are a common sight in Honolulu. (Photo courtesy Aloha Termite @ Pest Control)
Its newly reported 36-year lifetime, along with studies of its infrared absorbing properties by researchers at the National Oceanic and Atmospheric Administration, "indicate that, ton for ton, it is about 4,800 times more potent a heat-trapping gas than carbon dioxide," says Prinn.
Fortunately, though, "we've caught it very early in the game," says Prinn, the TEPCO Professor of Atmospheric Science in MIT's Department of Earth, Atmospheric and Planetary Sciences.
The sulfuryl fluoride detection was made through a NASA-sponsored global research program called the Advanced Global Atmospheric Gases Experiment, or AGAGE.
"In AGAGE, we don't just monitor the big greenhouse gases that everybody's heard of," said Prinn. "This program is also designed to sniff out potential greenhouse and ozone-depleting gases before the industry gets very big."
He describes the team's approach as "a new frontier for environmental science." They are trying eliminate potential dangers to the global climate as early as possible, rather than waiting until the industries that produce damaging gases are mature with lots of capital and jobs at stake.
The lead author of the research paper is Jens Muhle of Scripps, and besides Prinn, the co-authors include Jin Huang, a research scientist at MIT's Center for Global Change Science, Ray Weiss of Scripps, who co-directs AGAGE with Prinn, and eight others from Scripps, the University of Bristol in the United Kingdom and the Centre for Australian Weather and Climate Research.
"Unfortunately, it turns out that sulfuryl fluoride is a greenhouse gas with a longer lifetime than previously assumed," says Muhle. "This has to be taken into account before large amounts are emitted into the atmosphere."
Sulfuryl fluoride fumigation notice (Photo by Landruc)
Sulfuryl fluoride is currently marketed by three manufacturers under four different brand names.
Vikane, marketed by Dow, has been commercially available since the early 1960s, with Zythor, marketed by competitor EnSystex II of North Carolina, being more recently introduced as its use is approved by individual states.
Dow has begun marketing sulfuryl fluoride as a post-harvest fumigant for dry fruits, nuts, and grains under the trade name ProFume.
Most recently Drexel Chemical Company has registered Master Fume for the structural market, competing against Vikane and Zythor.
Prinn says that "fumigation is a big industry, and it's absolutely needed to preserve our buildings and food supply."
But identifying the greenhouse risks from this particular compound, before many factories have been built to produce it in very large amounts, would give the industry a chance to find other substitutes at a time when that is still a relatively easy change to implement, he says.
"Given human inventiveness," said Prinn, "there are surely other alternatives out there."
The Kyoto Protocol establishes legally binding commitments for the reduction of four greenhouse gases - carbon dioxide, methane, nitrous oxide, sulphur hexafluoride - and two groups of gases - hydrofluorocarbons and perfluorocarbons.
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