| Abstract: | The effects of aerosol–radiation interactions (ARI) are not only important for regional and global climate, but they can also drive particulate matter (PM) pollution. In this study, the ARI contribution to the near-surface fine PM (PM2.5) concentrations in the Guanzhong Basin (GZB) is evaluated under four unfavorable synoptic patterns, including "north-low", "transition", "southeast-trough", and "inland-high", based on WRF-Chem model simulations of a persistent heavy PM pollution episode in January 2019. Simulations show that ARI consistently decreases both solar radiation reaching down to the surface (SWDOWN) and surface temperature (TSFC), which then reduces wind speed, induces sinking motion, and influences cloud formation in the GZB. However, large differences under the four synoptic patterns still exist. The average reductions of SWDOWN and daytime TSFC in the GZB range from 15.2％ and 1.04°C in the case of the"transition" pattern to 26.7％ and 1.69°C in the case of the "north-low" pattern, respectively. Furthermore, ARI suppresses the development of the planetary boundary layer (PBL), with the decrease of PBL height (PBLH) varying from 18.7％ in the case of the "transition" pattern to 32.0％ in the case of the "north-low" pattern. The increase of daytime near-surface PM2.5 in the GZB due to ARI is 12.0％, 8.1％, 9.5％, and 9.7％ under the four synoptic patterns, respectively. Ensemble analyses also reveal that when near-surface PM2.5 concentrations are low, ARI tends to lower PM2.5 concentrations with decreased PBLH, which is caused by enhanced divergence or a transition from divergence to convergence in an area. ARI contributes 15％–25％ toward the near-surface PM2.5 concentrations during the severe PM pollution period under the four synoptic patterns. |
