Pinpointing optimized air quality model performance over the Beijing-Tianjin-Hebei region: Mosaic approach

Mosaic approach, with certain number of tiles representing land use (LU) types in each grid cell, had been implemented into WRF-Noah model. Previous studies found mosaic approach had a better performance on meteorological parameters than only considering dominant LU in dominant approach. In this study, the impacts of mosaic approach on meteorological parameters and air quality were investigated in WRF-CMAQ over Beijing-Tianjin-Hebei (BTH) region in China in 2020. Results showed that mosaic approach improved the simulation results of WS10 (surface wind speed at 10 m), T2 (temperature at 2 m), and RH (relative humidity) especially in nighttime in winter and were available for all stations with different percent of urban area. "MOS_TOPO" scenario, which coupled with mosaic approach and "topo-wind" schemes, obtained best simulation results of WS10 and T2 in January among six scenarios, with the lower average Root Mean Square Error of WS10 (1.18 m/s) and Mean Bias of T2 (0.55 degrees C) for all stations. Meanwhile, mosaic approach obtained lower vertical bar NMB vertical bar of PM2.5 than dominant approach in more than 69% cities in BTH region. Cities in southern Hebei province, especially Xingtai city, were identified as the most sensitive area for PM2.5 simulation affected by mosaic approach. Although the mosaic approach has improved the simulation results of meteorological parameters, especially the nighttime simulation results of WS10, there is still some deviation in the simulation results of PM2.5. Accurate emission inventory, suitable physics option in numerical weather model and rational chemical mechanism in air quality model are the important factors for WRF-CMAQ.