History of atmospheric SF<sub>6</sub> from 1973 to 2008

Abstract. We present atmospheric sulfur hexafluoride (SF6) mole fractions and emissions estimates from the 1970s to 2008. Measurements were made of archived air samples starting from 1973 in the Northern Hemisphere and from 1978 in the Southern Hemisphere, using the Advanced Global Atmospheric Gases Experiment (AGAGE) gas chromatographic–mass spectrometric (GC-MS) systems. These measurements were combined with modern high-frequency GC-MS and GC-electron capture detection (ECD) data from AGAGE monitoring sites, to produce a unique air history of this potent greenhouse gas. Atmospheric mole fractions were found to have increased by more than an order of magnitude between 1973 and 2008. The 2008 growth rate was found to be the highest recorded, at 0.29 ± 0.02 pmol mol−1 yr−1. A three-dimensional chemical transport model and a minimum variance Bayesian inverse method was used to estimate annual emission rates using the measurements. Consistent with the mole fraction growth rate maximum, global emissions during 2008 were also found to be highest in the 1973–2008 period, reaching 7.5 ± 0.4 Ggyr−1 and surpassing the previous maximum in 1995. The 2008 values follow an increase in emissions of 50 ± 25% since 2000. A second global inversion which also incorporated National Oceanic and Atmospheric Administration (NOAA) flask measurements and in situ monitoring site data was found to agree well with the emissions derived using AGAGE measurements alone. By estimating continent-scale emissions using all available AGAGE and NOAA surface measurements covering the period 2004–2008, we find that it is likely that much of the global emissions rise during this five-year period originated primarily from Asian countries that do not report emissions to the United Nations Framework Convention on Climate Change (UNFCCC). We also find it likely that SF6 emissions reported to the UNFCCC were underestimated between at least 2004 and 2007.