Constraining the regional and global hydrogen cycle using stable isotope measurements

Atmospheric molecular hydrogen (H2) is increasingly being considered as an important energy carrier in future energy systems. Due to leakages during production, storage, transport, and use of H2, a rise in atmospheric H2 levelsis expected. Such an increase may lead to a prolonged lifetime of methane, enhanced tropospheric ozone concentrations, and increased stratospheric water vapor. Although the major sources and sinks of atmospheric hydrogen are relatively well known, large uncertainties remain in the global hydrogen budget due to limited observational constraints and an incomplete understanding of the underlying processes.Measurements of isotopic signatures of H2 provide a powerful tool to distinguish between different source and sink processes and to better constrain the hydrogen budget, for example by providing improved observational input for atmospheric models. However, recent observations of the hydrogen stable isotope (δD) remain scarce.Here we present new measurements of atmospheric H2 and its stable isotopologue HD, carried out at the Institute for Marine and Atmospheric research Utrecht (IMAU). The system separates the H2 from the air matrix and determines its isotopic composition using isotope-ratio mass spectrometry (IRMS). The dataset includes atmospheric samples from globally distributed sampling networks, including station data and (Atlantic) ship transects, and local sources.These new observations contribute to a better observational basis for understanding the regional and global hydrogen cycle and provide valuable input for future studies of atmospheric hydrogen.