Quantification of the SF₆ lifetime based on mesospheric loss measured in the stratospheric polar vortex

Abstract

Abstract Sulfur hexafluoride (SF 6 ) is a greenhouse gas with one of the highest radiative efficiencies in the atmosphere as well as an important indicator of transport time scales in the stratosphere. The current widely used estimate of the atmospheric lifetime of SF 6 is 3200 years. In this study we use in situ measurements in the 2000 Arctic polar vortex that sampled air with up to 50% SF 6 loss to calculate an SF 6 lifetime. Comparison of these measurements with output from the Whole Atmosphere Community Climate Model (WACCM) shows that WACCM transport into the vortex is accurate and that an important SF 6 loss mechanism, believed to be electron attachment, is missing in the model. Based on the measurements and estimates of the size of the vortex, we calculate an SF 6 lifetime of 850 years with an uncertainty range of 580–1400 years. The amount of SF 6 loss is shown to be consistent with that of HFC‐227ea, which has a lifetime of 670–780 years, adding independent support to our new SF 6 lifetime estimate. Based on the revised lifetime the global warming potential of SF 6 will decrease only slightly for short time horizons (<100 years) but will decrease substantially for time horizons longer than 2000 years. Also, the use of SF 6 measurements as an indicator of transport time scales in the stratosphere clearly must account for potential influence from polar vortex air.