First coupled H2-HD inversion with a 3D chemical transport model (TM5): Constraining the global hydrogen budget

Hydrogen (H₂) is expected to become an increasingly important energy carrier during the energy transition. This will likely cause increased levels of atmospheric H₂, due to unavoidable losses during the production, transport, storage, and usage of hydrogen. Multiple studies have shown that through interaction with the hydroxyl radical, global tropospheric and stratospheric composition could be impacted, however, a large uncertainty remains due to a lack of understanding of the global hydrogen budget.

For the first time, we present a comprehensive global hydrogen budget derived using a coupled H₂-HD inversion framework embedded within the three-dimensional chemical transport model TM5. This budget is obtained using a global set of 178,640 H₂ mole fraction measurements and 540 δD(H₂) measurements, which are subsequently supplied to the CarbonTracker data assimilation system. Using its ensemble Kalman filter approach we estimate the magnitude and spatial distribution of monthly global hydrogen emissions, chemical production and losses for 2003–2023. To evaluate the robustness of our results, we compare optimized simulated hydrogen mole fractions with independent observational data from aircraft profiles collected during the IAGOS-CARIBIC, NOAA/ESRL, and ATom campaigns.