LAUSR

Abstract Partly due to the lack of fine-resolution measurements of the planetary boundary layer (PBL), the impacts of PBL on the aerosol pollution in the densely populous Shandong province were not well understood. On the basis of long-term PM2.5 measurements, fine-resolution radiosonde data, and meteorological reanalysis from April 2016 to March 2019, the aerosol pollution in Jinan and Qingdao and its complex relationships with the multi-scale meteorological conditions were investigated in this study. During an annual cycle, prominent seasonal variations of PM2.5 concentrations can be observed in both cities, with heaviest pollution in the heating season and relatively low concentrations in summer. Significant positive correlationwas found between the monthly PM2.5 concentrations and thermal stability of the lower troposphere, indicating that the seasonal shifts of PBL play an important role in regulating the variations of aerosol pollution, in addition to the seasonal changes in the emissions. In the heating season, influenced by unfavorable synoptic patterns, heavy pollution often simultaneously happened in Jinan and Qingdao. Utilizing an objective synoptic classification approach with reanalysis data, two dominant synoptic types led to heavy pollution in Jinan and Qingdao were identified, which were featured by 900-hPa warm advections from the west or southwest with weaker prevailing winds. These synoptic types not only strengthened the elevated thermal inversion and inhibited the vertical dilution of pollutants locally, but also caused the regional transports of pollutants to Jinan and Qingdao from high-emission upstream regions, such as the Beijing-Tianjin-Hebei region, Henan province and Jiangsu province. Therefore, to prevent heavy pollution in Jinan and Qingdao, regional joint measures should be implemented with full consideration of synoptic impact.