Global Emissions of Tetrafluoromethane (CF4) Hexafluoroethane (C2F6) Determined by Inverse Modeling

We determined global emissions of the perfluorocarbons (PFC) tetrafluoromethane (CF₄) and hexafluoroethane (C₂F₆) from 2004 to 2023 using an inverse modeling approach. These PFCs are characterised by their exceptionally long atmospheric lifetimes (~50.000y for CF₄ and ~10.000y for C₂F₆) and strong infrared absorption, making them some of the most potent greenhouse gases. Emissions of these gases are almost entirely anthropogenic, originating primarily from aluminium smelting and semiconductor manufacturing. Previous studies have highlighted significant discrepancies between bottom-up inventories, based on activity and industry data, and top-down estimates derived from atmospheric measurements. In this study, we use continuous and flask measurements combined the Bayesian inversion algorithm FLEXINVERT+ and the Lagrangian particle dispersion model FLEXPART to estimate global emissions of CF₄ and C₂F₆ and their regional distribution. Our findings indicate a decline in emissions until approximately 2009, followed by an increase in subsequent years, contrasting with bottom-up inventories, which show a steady decrease over the study period. The largest emissions are located primarily in East Asia, with substantial potential emissions in South and Southeast Asia, followed by North America and Europe. India and Malaysia, with their growing aluminium (India) and semiconductor (Malaysia) industries, emerge as significant sources of uncertainty in our emission estimates due to limited observational coverage in these regions. While emission reduction measures in the aluminium industry appear to be effective, the impact of mitigation efforts by semiconductor manufacturers are likely overestimated.