The global SF₆ source inferred from long-term high precision atmospheric measurements and its comparison with emission inventories

Abstract. Emissions of sulphur hexafluoride (SF₆), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (estimated as 800 to 3200 years), the accumulation of SF₆ in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF₆ observations shows an increase in SF₆ abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF₆ decreased after 1995, most likely due to SF₆ emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF₆ source leaves a surprisingly large gap of more than 70–80% of non-reported SF₆ emissions in the last decade. This suggests a strong under-estimation of emissions in Annex I countries and underlines the urgent need for independent atmospheric verification of greenhouse gases emissions accounting.