Role Of Land–Atmosphere Process In The PM Simulation Of A River Valley City With Complex Topography

Realistic representation of land–atmosphere processes（LAPs）plays a significant role in meteorology and consequent air quality simulations.In this study,15series setups,different combinations of five planetary boundary layers（PBL）with compatible surface layer（SL）schemes,and three land surface models（LSMs）were designed in the WRF-Chem model to perform a sensitivity study assessing the influence of LAPs on simulations.Sensitivity tests were conducted over the river valley city at 1 km resolution under synoptically quiescent conditions on December 1–6,2019.The results were evaluated via comparison with 5 meteorological and 29 air quality stations.Statistical indicators were used to understand the physical mechanisms of various LAPs which impact air pollution diffusion and to identify the preferred configuration.（1）All land-atmosphere configuration sensitivity test results can reproduce the characteristics of the meteorological field and changes in air quality,but there are significant differences between different configurations,indicating that the land-atmosphere configuration has a great impact on the numerical simulation.Adequate representations of physical processes occurred in lower atmosphere play a more significant role in both meteorological and air quality predictions than those of moderate and upper atmosphere characteristics.（2）The simulation performance on temperature is better than relative humidity and wind speed.The inability to characterize the nature of the underlying surface at the subgrid scale is the main reason for the generally high simulated surface wind speed.Compared with other configuration,the 2-meter temperature simulated by the coupling of Noah MP model and different boundary layer schemes is closest to the actual atmospheric temperature,and the 10-m height wind speed simulated by this configuration is more consistent with the observed characteristics.（3）The land-atmosphere process has an important impact on the air quality simulation,and the correlation coefficients between different land-atmosphere configurations are quite different.The correlation coefficients of PM₁₀ and PM_2.5simulated by MYN＿N are respectively 0.69 and 0.66,while MYJ＿R was 0.37 and 0.33,respectively.Statistical analysis results show that the combination of Noah MP land surface model and MYNN boundary layer scheme（MYN＿N）has the best simulation performance,which can significantly improve the accuracy of particle simulation.（4）Judging from the influence of average wind speed,boundary layer height,and ventilation coefficient,the simulation characteristics of particle concentration and average wind speed are basically consistent.The non-locally closed YSU scheme and the locally closed Boulac scheme have little difference in the near-surface meteorological fields.The main reason is that the two boundary layer schemes use the same surface layer scheme,which shows that the simulation results are more sensitive to the near-surface layer scheme.（5）Judging from the radiative flux and surface flux simulated by different land-atmosphere schemes,when the land surface model is Noah MP,the distribution of snow cover simulated by the model is more consistent with actual situation.Better temperature simulation can help reproducing the local circulation induced by thermal inhomogeneity.The comparison and evaluation of the 10-meter wind field can further verify this conclusion,which is also the main reason of best air quality simulation by Noah MP scheme.