Volcanoes aren't a big source of CFCs.
An international team of researchers collected and analyzed gas samples from four volcanoes in Japan and Italy. They identified more than 300 organic substances, but only one of them was a CFC. Halocarbons such as CFCs and methyl bromide trigger chemical reactions that break down Earth's stratospheric ozone (SN: 10/14/95, p. 245).
The researchers, from the Max Planck Institute for Aeronomy in Germany, the National Scientific Research Center in Gif sur Yvette, France, and the Geological Survey in Tsukuba, Japan, will report their findings in an upcoming ENVIRONMENTAL SCIENCE AND TECHNOLOGY.
Previous studies, notably a 1990 report from V.A. Isidorov of St. Petersburg University in Russia and his colleagues, suggested that volcanoes account for a large proportion of the CFCs in the atmosphere. "Those reports have been utilized by some people to claim exaggerated natural contributions to the atmospheric budget of CFCs," says Armin Jordan, a coauthor of the new study and now at the Max Planck Institute for Biogeochemistry in Jena. CFCs were once widely used as refrigerants and solvents but are being phased out worldwide.
Out of the 300 chemicals identified in the volcanic emissions, 134 are halocarbons. Most halocarbons don't survive long in the atmosphere, says James H. Butler of the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo. CFCs, though, have a half-life of 50 to 100 years, so they stick around long enough to accumulate and reach the stratosphere.
From their data, Jordan and his colleagues estimate that the only detected CFC--trichlorofluoromethane, known as CFC-11--provides less than 1 part per quadrillion of the emission. "This volcanic source would be trivial compared with the [human-made] atmospheric CFC load," Jordan says. The results support recent findings by Butler's group.
Butler and his colleagues measured halocarbons in air trapped by yearly snows in Antarctica and Greenland. This provided a record of halocarbons back to the late 19th century. No CFCs appeared in the samples from the years before the chemicals were used industrially.
The volcanoes tested by Isidorov may indeed produce higher concentrations of CFCs than the Japanese and Italian volcanoes studied, says Jordan. However, "Isidorov's extrapolation of his results to 75 percent of the world's volcanoes is not justified," he asserts.
When sampling gas, scientists have to be especially careful about contamination from the equipment they use, Butler says. A Teflon stopper, for example, can absorb CFCs from the air, which then show up in a detector. The higher CFC concentrations seen in earlier studies "could have been a methods issue, or it could be that the volcanoes were different," Butler says. "The work needs to be replicated."
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|Article Type:||Brief Article|
|Date:||Feb 19, 2000|
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