Interactive Simulation of Methane and Hydrogen Soil Deposition Using the Newly Implemented BIODEP Submodel of the ECHAM5/MESSy Atmospheric Chemistry Model (EMAC) v2.55

Methane (CH₄) and molecular hydrogen (H₂) are key components of atmospheric composition with important implications for climate processes. Methane acts as a strong greenhouse gas, whereas hydrogen affects climate indirectly by modifying the atmosphere’s oxidative capacity. The primary atmospheric removal pathway for methane is its reaction with hydroxyl radicals, while hydrogen is mainly removed through microbial consumption in soils. In addition to atmospheric oxidation, roughly 6% of global methane emissions are taken up by soils, making this pathway a meaningful contributor to the overall methane budget. The efficiency of soil uptake depends on a range of environmental and soil-related factors, including soil texture, temperature, moisture content, and -for methane- nitrogen availability. Accurately representing these controls requires an integrated description of atmospheric conditions alongside land surface characteristics and soil hydrological processes.

In this work, we present BIODEP, a newly developed biogenic deposition module implemented within the Modular Earth Submodel System (MESSy). BIODEP is coupled to the ECHAM5/MESSy atmospheric chemistry model (EMAC) and the JSBACH land surface and vegetation model, which includes a detailed five-layer soil hydrology scheme. The performance of the model including the newly implemented BIODEP submodel is evaluated by comparing simulated methane and hydrogen atmospheric mixing ratios with measurements from more than 50 stations of the NOAA GML Carbon Cycle Cooperative Global Air Sampling Network covering the period 2009–2019. In addition, the column-averaged methane mixing ratio is compared with observations from the Greenhouse Gases Observing Satellite (GOSAT). For present-day conditions, the model captures observed spatial distributions and seasonal variability of soil uptake fluxes.

By explicitly connecting soil characteristics with meteorological drivers and atmospheric composition, BIODEP enhances EMAC’s capability to represent trace gas dynamics across a range of climate conditions. This development advances the understanding of soil–atmosphere exchange mechanisms and provides a robust modeling framework for assessing future methane and hydrogen cycles, which is essential for climate mitigation strategies and the planning of a sustainable hydrogen economy.