A thousand inversions to determine European SF₆ emissions from 2005 to 2021

Abstract. We determine European emissions of sulfur hexafluoride (SF₆) from 2005 to 2021 using a large ensemble of atmospheric inversions. To assess uncertainty, we systematically vary key inversion parameters across 986 sensitivity tests and apply a Monte Carlo approach to randomly combine these parameters in 1,003 additional inversions. Our analysis focuses on high-emitting countries with robust observational coverage — UK, Germany, France, and Italy — while also examining aggregated EU-27 emissions.

SF₆ emissions declined across all studied regions except Italy, largely attributed to EU F-gas regulations (2006, 2014), however, national reports underestimated emissions: (i) UK emissions dropped from 65 (±13) t yr⁻¹ in 2008 to 20 (±6) t yr⁻¹ in 2018, aligning with the reports from 2018 onward; (ii) French emissions fell from 88 (±37) t yr⁻¹ (2005) to 51 (±28) t yr⁻¹ (2021), exceeding reports by 73 %; (iii) Italian emissions fluctuated (31–67 t yr⁻¹), surpassing reports by 88 %; (iv) German emissions declined from 166 (±41) t yr⁻¹ (2005) to 95 (±11) t yr⁻¹ (2021), aligning reasonably well with reports; (v) EU-27 emissions decreased from 484 (±213) t yr⁻¹ (2005) to 255 (±58) t yr⁻¹ (2021), exceeding reports by 40 %. A substantial drop from 2017 to 2018 mirrored the trend in southern Germany, suggesting regional actions were taken as the 2014 EU regulation took effect.

Our sensitivity tests highlight the crucial role of dense monitoring networks in improving inversion reliability. The UK system expansions (2012, 2014) significantly enhanced result robustness, demonstrating the importance of comprehensive observational networks in refining emission estimates.