Evaluating ICON-ART’s Performance in Simulating Methane: A Benchmark Against aircraft observations, CAMS, and WRF Models

Methane (CH₄), a potent greenhouse gas, is a key player in atmospheric chemistry and climate forcing. Its spatial and temporal variability is driven by emissions, atmospheric transport, and chemical loss processes. Accurate modelling of CH₄ is essential for understanding its sources, sinks, and role in Earth’s energy budget. In this study, we evaluate the skill of forward methane simulations of ICON-ART (ICOsahedral Nonhydrostatic - Aerosols and Reactive Trace gases) implementation established at Max Planck Institute for Biogeochemistry in Jena. The ICON-ART model represents a cutting-edge atmospheric modelling system jointly developed by the consortium of German and Swiss institutes. Its proven capability to realistically simulate trace gases, aerosols, and chemical interactions makes it a versatile tool for regional-to-global atmospheric studies focusing on improving flux estimates of a variety of atmospheric compounds, including methane. This work was conducted within the framework of the ITMS project (Integrated Greenhouse Gas Monitoring System for Germany), designed to enable Germany to operationally monitor the source and sinks of the most import long-lived greenhouse gases.

In the study, we evaluate the performance of the ICON-ART simulations set over the ICON-EU domain at 7 km horizontal resolution and compare their results other, more established modelling systems, including CAMS (Copernicus Atmosphere Monitoring Service) inversion optimized product (v21r1), CAMS reanalysis (EGG4) and the WRF-GHG (Weather Research and Forecasting with GHG module) model run at 5 km horizontal resolution. Both ICON-ART and other models include realistic realizations of anthropogenic emissions, natural fluxes, and boundary conditions that allow for realistic representation of atmospheric methane. We further compare all model results to in-situ airborne observations performed with HALO (High Altitude and LOng Range) during CoMet Campaign in May-June 2018, providing high-resolution CH₄ measurements, including vertical profiles spanning from the planetary boundary layer (PBL) to the low stratosphere (LS). The comparability of the models was ensured through collocated data analysis and performance metrics. These methodological frameworks minimize biases arising from resolution differences, enabling a fair assessment of the models’ capabilities.

The results reveal that ICON-ART is able to capture uplift transport and strong vertical mixing processes with remarkable fidelity. Displaying only 1.8 ppb mean bias error (MBE) for CH₄, it outperforms both WRF and global CAMS products, across the used metrics. In the PBL, ICON-ART resolves small-scale CH₄ variability better than CAMS and WRF. Similarly, in the free troposphere, ICON-ART successfully simulates CH₄ transport and mixing, aligning closely with aircraft observations. Notably, ICON-ART shows better agreement in the LS, which is linked to improved stratosphere-troposphere exchange processes, but also underlines the importance of realistic lateral boundary conditions.