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Sulfur hexafluoride (SF6) is the most potent greenhouse gas (GHG), and its atmospheric abundance, albeit small, has been increasing rapidly. Although SF6 is used to assess atmospheric transport modeling and its emissions influence 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 United States between 2007 and 2018. Our results suggest a substantial decline of US SF6 emissions, a trend also reported in the US Environmental Protection Agency's (EPA) national inventory submitted under 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 SF6 production plant that did not or does not report to the EPA may be underestimated in the national inventory. Furthermore, the atmosphere-based estimates show higher emissions of SF6 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 SF6 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.

Sulfur hexafluoride (SF6) is the most potent greenhouse gas (GHG), and its atmospheric abundance, albeit small, has been increasing rapidly. Although SF6 is used to assess atmospheric transport modeling and its emissions influence 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 United States between 2007 and 2018. Our results suggest a substantial decline of US SF6 emissions, a trend also reported in the US Environmental Protection Agency's (EPA) national inventory submitted under 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 SF6 production plant that did not or does not report to the EPA may be underestimated in the national inventory. Furthermore, the atmosphere-based estimates show higher emissions of SF6 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 SF6 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.

The perfluorocarbons (PFCs), tetrafluoromethane (CF4) and hexafluoroethane (C2F6), are potent greenhouse gases with very long atmospheric lifetimes. They are emitted almost entirely from industrial sources, including the aluminum and rare earth metal smelting industries that emit them as by-products, and the semiconductor and flat panel display manufacturing industries that use them and vent unutilized amounts to the atmosphere. Despite extensive industrial efforts to quantify and curb these emissions, “top-down” PFC emission estimates derived from atmospheric measurements continue to rise and are significantly greater than reported process- and inventory-based “bottom-up” emissions. In this study, we estimate emissions of CF4 and C2F6 from East Asia, where PFC emitting industries are heavily concentrated, using a top-down approach (a Bayesian inversion) with high-frequency atmospheric measurements at Gosan (Jeju Island, South Korea) for 2008–2019. We also compile and analyze the available bottom-up CF4 and C2F6 emissions in East Asia from industrial and government reports. Our results suggest that the observed increases in global PFC emissions since 2015 are driven primarily by China's aluminum industry, with significant contributions from Japan's and Korea's semiconductor industry. Our analysis suggests that Chinese emissions occur predominantly from the aluminum industry, although their emissions per production ratio may be improving. Our results for Japan and Korea find significant discrepancies between top-down and bottom-up emissions estimates, suggesting that the effectiveness of emission reduction systems (abatement) used in their semiconductor industries may be overestimated. Overall, our top-down results for East Asia contribute significantly to reducing the gap in the global PFC emission budgets.

Under the Greenhouse Gas Reporting Program (GHGRP), the US Environmental Protection Agency (EPA) receives reports of production, imports and exports of SF6 in bulk and inside of electrical equipment. EPA also receives reports of SF6 emissions, consumption and/or related parameters from users of SF6, including manufacturers and users of electrical transmission and distribution equipment, semiconductor manufacturers, and magnesium producers and processers. Based on these reports, EPA estimates the consumption of SF6 by each industry, including facilities that do not report to the GHGRP. In this paper, we compare the consumption estimated based on reports from SF6 suppliers (producers, importers and exporters) to the consumption estimated based on reports from SF6 users, discussing differences and possible reasons for them. We find that in the one year studied, 2012, consumption based on reports from users accounted for 59% of the consumption based on reports from suppliers. We conclude that the unce...

Atmospheric concentrations of HFCs, PFCs, and SF6 have been growing rapidly over the last 100 years, and they have the potential to continue growing rapidly, given the high growth rates of some emitting industries and the role of HFCs and PFCs as replacements for ozone-depleting substances. This analysis estimates global emissions of HFCs, PFCs, and SF6 from twelve source categories for the years 1990, 1995, 2000, 2010, and 2020, and provides guidance for projecting emissions beyond 2020. It also presents 2010 and 2020 marginal abatement cost curves (MACs) for the same source categories. To address issues unique to the fluorinated gases, the analysis accounts for the impact of international industry agreements to voluntarily reduce emission rates, and it aggregates emissions and MACs by gas lifetime as well as economic sector. Results indicate the availability of large, low-cost reductions, especially in developing countries, and the importance of better characterizing these reductions in future analysis.