Improving PM_2.5 simulation in the stable boundary layer over eastern China through parameterized minimum eddy...

Weak turbulence often occurs during heavy pollution events in eastern China (EC). However, existing mesoscale meteorology models cannot accurately simulate turbulent diffusion under weakened turbulence, particularly under the nocturnal stable boundary layer (SBL), often leading to significant turbulent diffusivity underestimation and surface aerosol overestimation. In this study, a new parameterization of minimum turbulent diffusivity coefficient (Kz_min) was tested and applied to PM_2.5 simulations in EC under SBL conditions in WRF-Chem. The original model overestimated the PM_2.5 simulation and the simulation performance can be improved by adding Kz_min. Sensitivity experiments revealed different ranges of available Kz_min values over the northern (0.8 to 1.2 m²/s) and southern (1.0 to 1.5 m²/s) regions of EC. The geographically related Kz_min was parameterized by sensible heat flux (H) and latent heat flux (LE), which also exhibited regional differences related to the climate and underlying surface. Furthermore, we assign physical significance to the parameterized formula Kz_min and found that our proposed Kz_min scheme can reasonably yield dynamic Kz_min values over EC. The revised Kz_min scheme (EXP_NEW) enhanced the turbulent diffusion (north: 0.93 m²/s, south: 1.10 m²/s on average) in the SBL, simultaneously improving the PM_2.5 simulations on the surface (north: 65.78 to 0.67 µg/m³; south 30.48 to 12.86 µg/m³) and upper SBL. A process analysis showed that vertical mixing was the key process for improving PM_2.5 simulations on the surface in EXP_NEW. This study highlighted the importance of improving turbulent diffusion in current mesoscale models under SBL and has great significance for aerosol simulation.