Cross-evaluating WRF-Chem v4.1.2, TROPOMI, APEX and in situ NO2 measurements over Antwerp, Belgium

The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) is employed as an intercomparison tool for validating Tropospheric Monitoring Instrument (TROPOMI) satellite NO2 retrievals against high10 resolution Airborne Prism EXperiment (APEX) remote sensing observations performed in June 2019 in the region of Antwerp, a major hotspot of NO2 pollution in Europe. The model is first evaluated using meteorological and chemical observations in this area. Sensitivity simulations varying the model planetary layer boundary (PBL) parameterization were conducted for a 3day period in June 2019, indicating a general good performance of most parameterizations against meteorological data (namely ceilometer, surface meteorology and balloon measurements), except for a moderate overestimation (~1 m s ) of near-surface 15 wind speed. On average, all but one PBL schemes reproduce fairly well the surface NO2 measurements at stations of the Belgian Interregional Environmental Agency, although surface NO2 is generally underestimated during the day (between -4.3 and -25.1% on average) and overestimated at night (8.2-77.3%). This discrepancy in the diurnal evolution arises despite (1) implementing a detailed representation of the diurnal cycle of emissions (Crippa et al., 2020), and (2) correcting the modelled concentrations to account for measurement interferences due to NOy reservoir species, which increases NO2 concentrations by 20 about 20% during the day. The model is further evaluated by comparing a 15-day simulation with surface NO2, NO, CO and O3 data in the Antwerp region. The modelled daytime NO2 concentrations are more negatively biased during weekdays than during weekends, indicating a misrepresentation of the weekly temporal profile applied to the emissions, obtained from Crippa et al. (2020). Using a mass-balance approach, we determined a new weekly profile of NOx emissions, leading to a homogenization of the relative bias among the different weekdays. The ratio of weekend to weekday emissions is significantly 25 lower in this updated profile (0.6) than in the profile based on Crippa et al. (2020) (0.84). Comparisons with remote sensing observations generally show a good reproduction of the spatial patterns of NO2 columns by the model. Both APEX and TROPOMI columns are underestimated on the 27/6, whereas no significant bias is found on the 29/6. The two datasets are intercompared by using the model as an intermediate platform to account for differences in vertical 30 sensitivity through the application of averaging kernels. The derived bias of TROPOMI v1.3.1 NO2 with respect to APEX is https://doi.org/10.5194/egusphere-2022-882 Preprint. Discussion started: 9 September 2022 c © Author(s) 2022. CC BY 4.0 License.