Evaluation of simulated CO 2 power plant plumes from six high-resolution atmospheric transport models

. Global anthropogenic CO 2 sources are dominated by power plants and large industrial facilities. Quantifying the emissions of these point sources is therefore one of the main goals of the planned constellation of anthropogenic CO 2 monitoring satellites (CO2M) of the European Copernicus program. Atmospheric transport models may be used to study the capabilities of such satellites through observing system simulation experiments and to quantify emissions in an inverse modelling framework. How realistically the CO 2 plumes of power plants can be simulated and how strongly the results may depend on 5 model type and resolution, however, is not well known due to a lack of observations available for benchmarking. Here, we use the unique data set of aircraft in-situ and remote sensing observations collected during the CoMet measurement campaign downwind of the coal-ﬁred power plants at Bełchatów in Poland and Jänschwalde in Germany in 2018 to evaluate the simulations of six different atmospheric transport models. The models include three Large-Eddy-Simulation (LES) models, two mesoscale numerical weather prediction (NWP) models, and one Lagrangian particle dispersion model (LPDM) and cover a 10 wide range of model resolutions from 200 m to 2 km horizontal grid spacing. At the time of the aircraft measurements between late morning and early afternoon, the simulated plumes were slightly (at Jänschwalde) to highly (at Bełchatów) turbulent, consistent with the observations, and extended over the whole depth of the atmospheric boundary layer (ABL, up to 1800 m a.s.l. in the case of Bełchatów). The stochastic nature of turbulent plumes puts fundamental limitations to a point-by-point comparison between simulations and observations. Therefore, the evaluation focused on statistical properties such as plume 15 amplitude and width as a function of distance from the source. LES and NWP models showed similar performance and sometimes remarkable agreement with the observations when operated at comparable resolution. A resolution of 1 km or better, however, appears to be necessary to realistically capture turbulent plume structures. At coarser resolution, the plumes disperse too quickly especially in the near ﬁeld (0-8 km from the source) and turbulent structures are increasingly smoothed out. Total vertical columns are easier to simulate accurately than the vertical distribution of CO 2 , since the latter is critically affected by 20 proﬁles of vertical stability, especially near the top of the ABL. Cross-sectional ﬂux and integrated mass enhancement methods applied to synthetic CO2M data generated from the model simulations with a random noise of 0.5 ppm – 1.0 ppm suggest that emissions from a power plant like Bełchatów can be estimated with an accuracy of about 20% from single overpasses. Estimates of the effective wind speed are a critical input for these methods. Wind speeds in the middle of the ABL appear to be a good approximation for plumes in a well-mixed ABL as encountered during CoMet. The present study complements their analysis by focusing speciﬁcally on emissions from power plants rather than on surface emissions. runs, AK, AW and PP the EULAG runs, and RH, MPA and CV the ARTM runs. AF, AnF, AR, CK, SK, KG, HB, MG and CG conducted the CoMet campaign in 2018 and processed the measurements used in this study. AnF was PI of the CoMet campaign and contributed to the measurements of DLR. AF and AR performed the DLR-Cessna in-situ measurements and MG and CG the HALO in-situ measurements. CK and SK performed and analyzed the CHARM-F measurements. JB conducted the FUB-Cessna MAMAP 645 and in-situ measurements. SK performed the analysis of the MAMAP remote sensing data. All authors contributed to the interpretation of the results and to the writing and improvements of the article. Acknowledgements. We acknowledge support by the EU project CoCO2 funded through the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 958927 and by the project SMARTCARB funded by the European Space Agency 650 (ESA). We also acknowledge funding for the CoMet campaign by the BMBF (German Federal Ministry of Education and Research) through AIRSPACE (FK 01LK1701B), the State of Bremen, and the Max Planck Society. The work was further supported by the German Research Foundation (DFG) within the Priority Program (SPP 1294) Atmospheric and Earth System Research with the Research Aircraft HALO (High Altitude and Long Range Research Aircraft) under grant BO 1731/1-1. Simulations with COSMO-GHG were supported by a grant from the Swiss National Supercomputing Centre (CSCS) under project ID s1091 and by the Center for Climate Systems Modelling (C2SM). We thank 655 ECMWF and for providing operational analysis and forecast data as initial and boundary conditions for the high-resolution models.