U.S. and European researchers have discovered minute traces of a new, extremely potent greenhouse gas in the upper atmosphere. The gas, trifluoromethyl sulfur pentafluoride (SF5CF3), is at least 17,500 times better than carbon dioxide at preventing radiated heat from escaping the Earth, and is almost certainly of human-made origin.
The strength of a greenhouse gas depends on its ability to absorb infrared radiation that would otherwise disappear into space, as well as how long it remains in the atmosphere. Researchers think they have identified most of these gases; some occur naturally, like carbon dioxide (CO2), and some are exclusively human-made, like SF6, an insulating gas used in electrical transformers and other high-voltage equipment.
Bill Sturges, an atmospheric scientist at the University of East Anglia, U.K., tracks these greenhouse gases. He collects samples from different levels of the atmosphere and from air found in deep-packed snow in Antarctica, which provide glimpses into the atmosphere years or even decades ago. Several years ago, Sturges decided to investigate an unidentified peak in the gas chromatography and mass spectrometry analysis of his stratospheric samples.
The gas turned out to be SF5CF3, the team reports in this week's issue of Science. Sturges and his colleagues suspect the gas may be a breakdown product of SF6 because both began to appear in air samples in the early 1970s. SF5CF3's current contribution to global warming is insignificant, says Sturges, but the gas is accumulating at a rate of 6% a year; if that trend continues, it could pose a problem--although not for at least a thousand years.
"It's not surprising that [SF5CF3] is a potent greenhouse gas," says Don Blake, an atmospheric scientist at the University of California, Irvine. The molecule contains sulfur-fluor bonds that would be expected to absorb heat. "But it is a surprise that it's in the atmosphere."