Improved simulation of atmospheric hydrogen using Eulerian and Lagrangian models

Renewably produced hydrogen will contribute to climate change mitigation for hard to abate emission generating sectors, if leakage rates are minimised. Despite this benefit, leakage of hydrogen into the atmosphere is well documented to cause indirect climate effects such as depletion of hydroxyl radical and changes in different greenhouse gases, such as increases in methane lifetime, tropospheric ozone and stratospheric water vapor. Therefore accurate earth system modeling of hydrogen budget changes, especially in the upper troposphere and lower stratosphere (UTLS), is an important tool to quantify climate change impacts, induced by changes due to different hydrogen budgets. It has been shown, that Lagrangian transport improves the simulation of water vapour in the UTLS, by reducing climate model moist biases by a factor between 2 and 3 in the lowermost stratosphere (Charlesworth et. al., 2023).

Following this approach, we investigate the atmospheric distribution of hydrogen using a similar model setup, which faciliates an improved estimation of the hydrogen-induced water vapor climate effect. We show simulations of two model versions, the Eulerian EMAC model and the Lagrangian coupled model EMAC-CLaMS. Emissions of hydrogen and methane as well as the soil sink are prescribed from previous work by Surawski et al. (2025) The model has a resolution corresponding to a horizontal grid of 1.87° * 1.87° (≈ 180-190 km) up to a model top height of 80 km. Another major model improvement is the change from a default to an improved radiation scheme. To ensure that the new Lagrangian transport scheme only affects the stratosphere, the entire troposphere in the Lagrangian EMAC-CLaMS simulation is set to the EMAC simulation data.
For model evaluation and comparison between the Eulerian and Lagrangian frameworks, the simulation results are compared with NOAA ground-based hydrogen measurements as well as balloon-borne stratospheric measurements by the University of Frankfurt cryosampler BONBON between 1998 and 2005.