Declining, seasonal-varying emissions of sulfur hexafluoride from the United States

[摘要] Sulfur hexafluoride (SF 6 ) is the most potent greenhouse gas (GHG), and itsatmospheric abundance, albeit small, has been increasing rapidly. AlthoughSF 6 is used to assess atmospheric transport modeling and its emissionsinfluence the climate for millennia, SF 6 emission magnitudes anddistributions have substantial uncertainties. In this study, we used NOAA'sground-based and airborne measurements of SF 6 to estimate SF 6 emissions from the United States between 2007 and 2018. Our results suggest a substantial decline of US SF 6 emissions, a trend also reported in the US Environmental Protection Agency's (EPA) national inventory submittedunder the United Nations Framework Convention on Climate Change (UNFCCC), implying that US mitigation efforts have had some success. However, the magnitudes of annual emissions derived from atmospheric observations are 40 %–250 % higher than the EPA's national inventory and substantially lower than the Emissions Database for Global Atmospheric Research (EDGAR) inventory. The regional discrepancies between the atmosphere-based estimate and EPA's inventory suggest that emissions from electric power transmission and distribution (ETD) facilities and an SF 6 production plant that did not or does not reportto the EPA may be underestimated in the national inventory. Furthermore, the atmosphere-based estimates show higher emissions ofSF 6 in winter than in summer. 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 during winter. The results of this study demonstrate the success of past US SF 6 emission mitigations and suggest that substantial additional emission reductions might be achieved through efforts to minimize emissions during servicing or through improving sealing materials in ETD.

[学科分类] 医学（综合）