July 28, 2000 Scientists at the Max Planck Institute for Chemistry in Mainz, from the School of Environmental Science at University of East Anglia/ UK, Ford Motor Company/USA, University of Reading/UK, University of Frankfurt and British Antarctic Survey, Natural Environment Research Council in Cambridge/UK have detected a previously unreported compound in the atmosphere, trifluoromethyl sulphur pentaflouride (SF5CF3). The increase of this peculiar gas in the atmosphere is coupled with the increase of the very inert gas sulfur hexaflouride (SF6), suggesting a common source (Science, 28 July 2000).
There is no doubt that the new gas SF5CF3 is made by industry, or is produced during certain process involving industrial gases, but its exact source remains a mystery. The scientists speculate that SF5CF3, which is closely chemically related to SF6, originates as a breakdown product of SF6 in high voltage equipment. SF6 is used in electrical switches to suppress sparks, in protecting metals during a melting process, in tennis balls, car tires and even at one stage in running shoes. Due to its good insulation properties it was also used as a noise barrier in double glazed window panes. However, SF6 is a strong greenhouse gas and the molecule is very resistant against attack in the atmosphere. The natural self-cleansing property of the atmosphere is insufficient to deal with such super molecules. Therefore, it has a long lifetime, and being a strong greenhouse gas, its production is now restricted under the Kyoto Protocol.
The new molecule SF5CF3 is even a stronger greenhouse gas. Measurements of its infrared absorption cross-section revealed the largest radiative forcing, on a per molecule basis, of any gas found in the atmosphere to date (0.57 W/m2 ppb). Together with the fact that also this gas has a long lifetime - somewhere between several hundred and a few thousand years - there is good reason to know more about this gas, and to try to stop its increase in the atmosphere.
How do we know the atmospheric increase of this gas? The Max Planck Institute for Chemistry in Mainz has participated in expeditions in Antarctica to extract air samples from the thick firn layers (snow). These layers can be up to 100 meter thick and contain old air, sometimes reaching to the beginning of the last century. This air has been extensively analyzed in our institute and in Norwich, England. The new gas was discovered at extremely low concentrations. At the surface the concentration is the same as in the air at the moment, and amounts to about 0.1 ppt (parts per trillion; one ppt is one part in 1012). At 100 meter depth in the snow its concentration was close to the detection level of 0.01 ppt. This shows the grown of the gas during the second half of the last century. Because the increase of the new gas is very much like that of SF6, we suspect a link between the two gases.
This discovery once again shows that we have to be careful with our atmosphere, and that research is much needed indeed. Without even knowing it, we have been releasing a very potent greenhouse gas for almost 50 years. We have to find the source of this gas and to try to stop its increase. Even though the concentrations are very small, and its implication in climate change is for practical reasons no grave concern, this type of global pollution is unwanted, and most likely unnecessary.
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