Constraining the Hydrogen Soil Sink and Photochemical Source: Insights from Atmospheric H₂ Inversions (2003–2023)

Abstract. Hydrogen (H₂) is expected to become an increasingly important energy carrier during the energy transition, likely leading to higher atmospheric H₂ levels due to losses during production, transport, storage and usage of hydrogen. Multiple studies have shown this could impact atmospheric composition through interactions with the hydroxyl radical. However, the magnitude of this impact remains uncertain due to large uncertainties in the global H₂ budget, particularly in the soil sink and photochemical source. To address this, we present a spatiotemporally resolved H₂ budget derived using atmospheric inversions with the TM5 chemical transport model. With this approach, we infer a global mean soil sink of 52.8 [47.8–56.7] Tg yr⁻¹ and a photochemical source of 34.6 [29.2–38.2] Tg yr⁻¹ over 2003–2023. Relative to Ouyang et al. (2025), we estimate a soil sink that is 45 % and 35 % weaker in the Middle East and Oceania, and 45 % and 70 % stronger in South America and Russia, respectively. Our results further suggest that variability in the observed H₂ growth rate between 2003–2023 was primarily driven by changes in the photochemical source from CH4 oxidation, together with a declining global soil sink at a mean rate of 0.23 Tg yr⁻² . Finally, we infer a sensitivity of the soil sink to the El Niño–Southern Oscillation, strongest over diffusion-limited soils in tropical South America, with increased uptake during drier El Niño conditions and reduced uptake during wetter La Niña conditions.