Impact of urbanized atmosphere-land processing to the near-ground distribution of air pollution over Central Liaoning Urban Agglomeration

Urban heat island effect and local atmospheric boundary layer circulation caused by urbanization are important factors affecting the transport and spatial and temporal distribution of atmospheric particulate matter in cities and surrounding areas. To analyze the local atmospheric circulation and its influence on the temporal and spatial characteristics of PM_2.5 concentration over the Central Liaoning Urban Agglomeration, a heavy haze process was selected. The atmospheric chemistry model WRF-Chem was applied for numerical simulations with sensitivity experiments of urban canopy physical processes. The experiment case (EXP) was set up by coupling an improved urban canopy model with WRF-Chem, in which more details of inhomogeneous wind and diffusion in the complexed street canyon were fully and reasonably considered. Compared with the control case (CTR) by the original WRF-Chem, the deviation of the simulated and observed near-surface temperature and atmospheric boundary layer height was significantly improved in EXP: the error during the daytime was reduced from −1.30% and −48.39% in CTR to −0.78% and −33.68% in EXP, respectively, while during the nighttime it was reduced from −1.15% and −48.98% to 0.05% and −24.42%. The simulation accuracy of the near-surface PM_2.5 concentration in EXP was also significantly higher: the deviation during the daytime was 18.24% in CTR and 3.28% in EXP, while it was reduced from 40.69% in CTR to 28.88% in EXP during the nighttime. Thus, the EXP improved significantly in meteorological simulation during the nighttime, and then particulate matter concentrations in EXP during the nighttime were obviously improved. This study shows that improving the wind profiles and diffusion mechanism in urban canopy schemes in the air quality model can effectively improve the simulation ability of the model on the transport and diffusion processes of atmospheric pollutants in cities and surrounding areas, thus improving the simulation ability of urban near-surface air pollution concentration.