Emissions of SF6 in China inferred from atmospheric observations

Sulfur hexafluoride (SF₆) is the most potent non-CO₂ Greenhouse Gas currently incorporated in the Paris Agreement, with a global warming potential of around 25,000 over a 100-year time horizon and lifetime of around 1,000 years. Global mole fractions and emissions of SF₆ have increased substantially since the 2000s. The increasing SF₆ emissions worldwide are thought to originate from its growing emissions in Kyoto Protocol non-Annex-I countries, where China is a major contributor. 

Top-down emission estimates provide evaluation of national bottom-up inventories, based on information from atmospheric observations. Previous top-down emissions of SF₆ in China were determined by observations made outside of China (e.g., in Korea and Japan), which lack sensitivity to emissions in regions far from the measurement sites (like the western or southern parts of China). In this study, emissions of SF₆ in China over 2011-2020 were derived using observations of SF₆ from 9 sites within China, coupled with a Lagrangian transport model and a hierarchical Bayesian inference algorithm. Analysis of the sensitivity maps (footprints) of these measurement sites suggest broad sensitivity to the major emission areas in China. The emissions in China show a substantial increase throughout the study period and contribute substantially to the rise in global emissions. The spatial distribution of SF₆ emissions in different regions or provinces in China and their changes are further analyzed. Finally, the potential industrial drivers behind the changes in emissions in China, and the necessity of continuous atmospheric observations in some key regions like in the northwest of China are discussed.