15 Sep 2022
15 Sep 2022
Status: this preprint is open for discussion.

Declining, seasonal-varying emissions of sulfur hexafluoride from the United States point to a new mitigation opportunity

Lei Hu1,2, Deborah Ottinger3, Stephanie Bogle3, Stephen Montzka2, Phil DeCola4,5, Ed Dlugokencky2, Arlyn Andrews2, Kirk Thoning2, Colm Sweeney2, Geoff Dutton1,2, Lauren Aepli5, and Andrew Crotwell1,2 Lei Hu et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado-Boulder, Boulder, CO, USA
  • 2Global Monitoring Laboratory, US National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 3Climate Change Division, US Environmental Protection Agency, Washington D.C., USA
  • 4University of Maryland, College Park, MD, USA
  • 5Gist.Earth LLC, College Park, MD, USA

Abstract. Sulfur hexafluoride (SF6) is the most potent greenhouse gas and its atmospheric abundance, albeit small, has been increasing rapidly. Although SF6 is used to assess atmospheric transport modeling and influences the climate for millennia, SF6 emission magnitudes and distributions have substantial uncertainties. In this study, we used NOAA’s ground-based and airborne measurements of SF6 to estimate SF6 emissions from the U.S. between 2007 and 2018. The substantial decline in U.S. SF6 emissions derived from atmospheric observations agrees with the reported trend in the U.S. Environmental Protection Agency (EPA)’s national inventory submitted under the United Nations Framework on Climate Change, suggesting mitigation efforts have had some success. However, the magnitudes of derived annual emissions are 40–250 % higher than the EPA national inventory and substantially lower than the Emissions Database for Global Atmospheric Research inventory. The regional discrepancies between atmosphere-based estimate and EPA’s inventory suggest that emissions from electric power transmission and distribution (ETD) facilities and an SF6 production plant that did not or do not report to EPA may be underestimated in the national inventory. Furthermore, the atmosphere-based estimates show higher winter than summer emissions of SF6. These enhanced wintertime emissions may result from increased maintenance of ETD equipment in southern states and increased leakage through aging brittle seals in ETD in northern states in winter. These results demonstrate the success of past U.S. SF6 emission mitigations, and suggest substantial additional emission reductions might be achieved through efforts to minimize emissions during servicing or through improving sealing materials in ETD.

Lei Hu et al.

Status: open (until 27 Oct 2022)

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Lei Hu et al.


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Short summary
Effective mitigation of greenhouse gas (GHG) emissions relies on an accurate understanding of emissions. Here we integrate inventory- and atmosphere- based approaches for estimating US emissions of SF6, the most potent GHG known over a 100-year time-horizon. The results suggest a large decline in US SF6 emissions, shed light on the possible processes causing the differences between the independent estimates, and identify opportunities for substantial additional emission reductions.