Spatiotemporal Characterization and Transfer Patterns of Aerosols and Trace Gases over the Region of Northeast China

This study examined air quality data collected from 2015 to 2023 across Shenyang, Dalian, Changchun, and Harbin to assess interannual and monthly variations in PM2.5, PM10, SO2, NO2, and O3, along with their correlations, seasonal meteorological influences, and potential source regions. Annual mean concentrations of PM2.5, PM10, SO2, and NO2 declined substantially (by 39.9–79.3%), whereas O3 showed a fluctuating pattern, remaining persistently high in the coastal city of Dalian. Seasonally, PM2.5, PM10, SO2, and NO2 concentrations peaked in winter and decreased in summer, while O3 displayed the opposite trend. Particulate levels in Liaoning rebounded earlier in spring than in Jilin and Heilongjiang. Correlation analysis revealed strong positive relationships among particulate and gaseous pollutants, but O3 generally exhibited negative correlations with other species. Haze events occurred mainly in winter, whereas complex pollution episodes were more frequent in summer. Meteorological analysis indicated that relative humidity was negatively correlated with PM2.5, PM10, SO2, and NO2 in summer but positively correlated in winter. Elevated temperatures outside the winter months promoted NO2 dispersion and enhanced O3 formation. Strong winds in spring and winter markedly reduced PM2.5 and SO2 levels, though this effect was less evident in Shenyang. WPSCF results identified significant cross-regional transport from the southwest contributing to PM2.5, PM10, and NO2 during spring and winter, while O3 was primarily affected by long-range transport in spring and only marginally in winter. In Dalian, sea–land breeze circulation further intensified transport processes in summer and autumn. Overall, this work provides an integrated, multi-year, and multi-city assessment of pollution dynamics, meteorological drivers, and transboundary transport in Northeast China, offering new insights into regional air quality improvement and its spatial heterogeneity relative to other regions of China.