Impacts of LULC, FDDA, Topo-wind and UCM schemes on WRF-CMAQ over the Beijing-Tianjin-Hebei region, China

In this study, the impacts of land use and land cover (LULC) change, four-dimensional data assimilation (FDDA), Topo-wind and urban canopy module (UCM) schemes on meteorology and air quality were investigated with the latest LULC data in Weather Research and Forecasting Model-Community Multiscale Air Quality (WRF-CMAQ) by scenarios analysis. Results showed that LULC change had significant effects on meteorological conditions and air quality at urban stations, which was attributed to the increasing surface roughness and impervious surface caused by the significant growth of urban land use. Considering the fraction of impervious surfaces and thermal and radiative processes related to urban geometry, UCM improved simulation of 2-m temperature (T2) and relative humidity (RH) in comparison to LULC change at urban stations. Topo-wind scheme slowed down surface wind speed domain-widely especially at valley stations in the nighttime. Based on the Final Operational Global Analysis data, the effects of FDDA varied with stations and layers. FDDA scheme had significant impacts on surface wind speed and aloft wind speed in the vertical range of 60-3500 m obviously. Meanwhile, the simulation results of O-3 in FDDA scheme was better than other schemes. Moreover, the combination of LULC change, FDDA, Topo-wind and UCM schemes showed the best simulation performance of surface wind speed, pressure, SO2 and PM2.5 among scenarios, and the distributions of days under different pollution levels of O-3 and PM2.5 were much closer to observed data than other scenarios, especially for stations with severe air pollution.