Vertical distribution and regional transport of air pollution over Northeast China: Insights from an intensive aircraft study

We report an intensive aircraft study of regional air pollution over Northeast China during July and August 2018, unraveling the vertical distributions and regional transport of a variety of trace gases and aerosols. Major air pollutants, including sulfur dioxide (SO2), nitric oxide (NO), ozone (O3), black carbon (BC), aerosol scattering coefficient (Bsc), and volatile organic compounds (VOCs), showed distinct vertical profiles influenced by planetary boundary layer (PBL) dynamics and regional transport processes. Near-surface concentrations of primary pollutants (SO2, NO, BC) generally decreased with altitude, whereas O3 levels increased. Notably, residual layers containing aged BC (300 m-1000 m altitude) were observed during early morning, with subsequent downward mixing to the surface following PBL development. A strong negative correlation between BC and O3 concentrations highlighted their antagonistic behavior in vertically stratified air masses. Vertical VOC distributions were dominated by light alkanes (C2-C4) and halocarbons, with profiles governed by their chemical lifetimes and transport mechanisms. A regional air pollution episode was observed in the high altitude atmosphere, characterized by elevated aerosol loading. WRF-Chem simulations revealed that episode was primarily driven by surface-level emissions from the Beijing-Tianjin-Hebei region. These pollutants were uplifted to the convergence zone and subsequently transported over long distance to Northeast China. Our findings enhance the understanding of vertical pollution profiles and the complex interplay between regional transport and local air quality in Northeast China.