Optimization of vertical grid setting for air quality modelling in China considering the effect of aerosol-boundary layer interaction

Abstract

The feedback between ambient aerosols and planetary boundary layer (PBL) meteorology has been proven to play a critical role in the enhancement of haze pollution. Vertical distribution of aerosols as well as temperature stratification are vital to understand aerosol – boundary layer interaction (ABI) and its impact on air quality deterioration. In current regional air quality models, the default vertical grid setting is relatively coarse and decreases progressively with altitude. However, the ABI is sensitive to aerosol layer at specific altitudes, i.e. around the top of PBL. This work aims to explore optimized vertical grid setting for better characterizing ABI and its role in air quality degradation. A single column model (SCM) is used for sensitivity tests considering the balance between model performance and computational cost. This optimized grid setting is then applied in three-dimensional air quality modelling in eastern China. Compared with default configuration, the optimized one is demonstrated to perform much better in characterizing temperature stratification and extreme fine particle (PM2.5) concentration as well as its diurnal variation during haze episodes. Specifically, the averaged decrease in PBL height and increment in surface PM2.5 concentration are about 5% and 20% while applying optimized setting, thereby reducing the mean bias from 30 to 5 μg/m3 in PM2.5 concentration. The improvements could be attributed mainly to more accurate profiles of aerosol and its heating effect, and thus stabilized lower atmosphere. The optimization of vertical grid setting could be applied to areas with high concentration of absorbing aerosols such as eastern China and India, which could help better predict extreme near-surface pollution episodes.