Atmospheric Sulfur Hexafluoride
Sulfur hexafluoride (SF6) is a very potent chemically stable and almost purely anthropogenic greenhouse gas, which is industrially used mainly in electrical insulation and switching, and for degassing and purifying of molten reactive metals. Destruction of SF6occurs only in the very high stratosphere and in the mesosphere. More than one decade ago we detected from analyses of air samples collected at Neumayer station (Antarctica), Izaña (Tenerife) and subsequent measurements on archived air from Cape Grim (Tasmania) that atmospheric SF6 has been increasing globally (since the 1970s) at a rate of more than 6% per year (Maiss and Levin, 1994). As most SF6 emissions occur in the northern hemisphere, southern hemisphere mole fractions are following those of the northern hemisphere with a delay of about one year. This corresponds to the mean residence time of air in one hemisphere. In the last decade SF6 has been applied as a very valuable tracer to calibrate and evaluate atmospheric transport models. Moreover, the smooth tropospheric increase of SF6 is used for dating of stratospheric air, ground water as well as in oceanographic studies to investigate internal mixing rates of the oceans.
From the global increase of SF6 total emissions can be calculated because virtually all emitted SF6 stays within the atmosphere. Comparison of these top-down estimates with bottom-up reported numbers to UNFCCC suggested significant under-reporting by ANNEX-I countries (Levin et al., 2010). Officially reported numbers have recently been adjusted ( UNFCCC ) and now show better agreement with the ture values derived from the observations.
Distribution of SF6 in the global troposphere (published data available here).
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