| 12 May 2025
Global atmospheric hydrogen chemistry and long-term source-sink budget simulation with the EMAC v2.55 model
Abstract. In this study, we use an earth system model with detailed atmospheric chemistry (EMAC v2.55.2) to undertake simulations of hydrogen (H2) atmospheric dynamics. Long-term simulations were performed globally with a horizontal resolution of 1.9 degrees with results being compared with observational data from 56 stations in the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Laboratory (GML) Carbon Cycle Cooperative Global Air Sampling Network. We introduced H2 sources and sinks, the latter through a soil uptake scheme, that accounts for bacterial consumption. The model thus accounts for detailed H2 and methane (CH4) flux boundary conditions. Results from the EMAC model are accurate and predict the magnitude, amplitude and interhemispheric seasonality of the annual hydrogen cycle at most observational stations. Time series comparison of EMAC and observational data produces Pearson correlation coefficients in excess of 0.9 at eight stations that experience well-mixed air masses free from direct anthropogenic perturbation. A further 23 stations yielded correlation coefficients between 0.7–0.9 in remote tropical or mid-latitude locations. The quality of model predictions is reduced in anthropogenically highly polluted stations in east Asia and the Mediterranean region and stations impacted by peat fire emissions in Indonesia, as local and incidental emissions are difficult to capture. Our H2 budget corroborates bottom-up estimates in the literature in terms of source and sink strengths and overall atmospheric burden. By realistically simulating hydroxyl radicals in the atmosphere, we show that the EMAC model is a capable tool for undertaking high accuracy simulation of H2 at global scale. Future research applications could target the impact of potentially significant natural and anthropogenic H2 sources on air quality and climate, reducing uncertainties in the H2 soil sink and impacts of H2 release on the future oxidising capacity of the atmosphere.
Competing interests: We declare that two of the co-authors hold an editorial board position with Geoscientific Model Development. The authors have no other competing interests to declare.
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