Machine Learning Assessment of Aerosol and Meteorological Impacts on Atmospheric Boundary Layer Height in Eastern China: Highlighting the Role of Aerosol Hygroscopicity

Abstract The planetary boundary layer height (PBLH) regulates air pollutant dispersion, yet the combined effects of aerosols and meteorology remain insufficiently quantified. Here, an interpretable XGBoost SHAP framework is applied to daytime (08:00–20:00 BJT) PBLH across the Beijing–Tianjin–Hebei (BTH) and Yangtze River Delta (YRD) regions using ERA5 and MERRA‐2 reanalysis data for 2013–2023. The mean PBLH in BTH (812 m) is about 125 m higher than in YRD (687 m), largely due to contrasting humidity conditions (46.3% vs. 68.6%). Meteorology dominates PBLH variability, with surface net solar radiation (SSR) and near‐surface wind speed correlating positively, whereas relative humidity (RH) is the opposite. Among aerosol factors, single‐scattering albedo (SSA) exerts the strongest influence (10.9% in BTH; 10.8% in YRD). In BTH, absorbing aerosols are associated with lower PBL more strongly than scattering aerosols, whereas in YRD neither type exerts dominant control. High RH enhances the hygroscopic growth of scattering aerosols, increasing the extinction efficiency and SSA and weakening the positive SSA–PBLH relationship, especially in YRD. Component‐specific analysis shows that hygroscopic components are identified as the major contributors to scattering extinction, with the sulfate effect markedly amplified under humid conditions. Seasonal analysis shows that thermal variables (SSR, RH) dominate the model in summer, while dynamic factors are more influential in winter, especially over BTH. These findings provide quantitative evidence for the coupled impacts of aerosols and meteorology, especially hygroscopic growth, on boundary layer dynamics, offering a scientific basis for region‐specific air quality management in eastern China.