## 4 Conclusions
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs14051133/s1](https://www.mdpi.com/article/10.3390/rs14051133/s1)]([https://www.mdpi.com/article/10.3390/rs14051133/s1](https://www.mdpi.com/article/10.3390/rs14051133/s1)), Figure S1: Difference of the mean surface CO concentrations and XCO between the DA and SIM experimental results (DA minus SIM); Figure S2: Difference of the mean surface CO concentrations and XCO between the SIM and SIM_anthro experiments (SIM minus SIM_anthro); Figure S3: Difference of the mean surface CO concentrations and XCO between the MOPITT data and the external CAM-Chem datasets (MOPITT minus CAM-Chem); Figure S4: Location of 71 WMO meteorological stations; Figure S5: Map of the 15 Western European countries; Table S1: Information of the ICOS stations used in this study; Table S2: Comparisons of the surface CO concentrations with the MOPITT data; Table S3: Comparisons of the XCO with the MOPPIT data. Conceptualization, Q.G. and Y.H. ; methodology, Y.H., J.W. and Q.G. ; software, [PERSON] and J.J.; validation, [PERSON], J.J. and Q.G. ; formal analysis, Y.H., Q.G. and J.J.; investigation, [PERSON] and [PERSON]; resources, [PERSON]; data curation, [PERSON], [PERSON] and [PERSON]; writing--original draft preparation, [PERSON] and [PERSON]; writing--review and editing, [PERSON] and [PERSON]; visualization, [PERSON], [PERSON] and [PERSON]; supervision, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This research was funded by the Key Research Program of the Chinese Academy of Sciences (ZDRW-ZS-2019-1), the International Partnership Program of the Chinese Academy of Sciences (131211 KYSB20180002), and the Chinese Academy of Sciences Youth Innovation Promotion Association Funding (2018327). Not applicable. The CO concentration and flux data generated and used by this study are openly available in: [[https://github.com/hgrhgy/remote_sensing_2022_CO_FLUX_EU](https://github.com/hgrhgy/remote_sensing_2022_CO_FLUX_EU)]([https://github.com/hgrhgy/remote_sensing_2022_CO_FLUX_EU](https://github.com/hgrhgy/remote_sensing_2022_CO_FLUX_EU)), accessed on 24 February 2022. The authors acknowledge the free availability of the WRF-Chem model [49; 50] provided by NOAA Earth System Research Laboratories, the WRF-Chem preprocess tools [102], the DART system [63], and the Community Atmosphere Model with Chemistry (CAM-Chem) Outputs as Boundary Conditions dataset [86] provided by NCAR, the MOPITT version 8 level 2 CO retrieval data products [76] from NASA Earthdata center, the Final Operational Global Analysis data (FNL) [91] and Global Upper Air and Surface Weather Observations [93] from NCEP, ground-CO concentration observations from ICOS [94], the anthropogenic CO fluxes from the Emissions Database for Global Atmospheric Research part II Air Pollutants gridmaps dataset V4.3.2 [81] and V5.0 [104] and UNFCCC National Inventory Submissions 2021 [46], the input data files [83] needed to calculate the biogenic CO fluxes from the University Corporation for Atmospheric Research, and the biomass-burning CO fluxes from the Fire Inventory from NCAR V1.5 dataset [84]. The authors declare no conflict of interest.