Differentiating winter haze episodes: Assessing the separate impacts of transported air masses and domestic emissions

This research aims to distinguish between winter haze events resulting from long-range transport and those resulting from local atmospheric stagnation in Seoul. Aerosols were monitored using a Time-of-Flight (ToF) Aerosol Chemical Speciation Monitor at Mt. Gwanak (629 m) and a high-resolution ToF Aerosol Mass Spectrometer at the Korea Institute of Science and Technology in Seoul. Corresponding data were collected at the Beijing site in China for comparison. Air-mass observations at Mt. Gwanak revealed distinct diurnal patterns contrasting with the ground-based data from the aerosol mass spectrometer, which successfully distinguish haze episodes driven by long-range transport from those caused by local emissions. Two of three high-concentration episodes were dominated by long-range transport, marked by elevated levels of nitrate, sulfate, and oxidized organic aerosol (OA). The local-emissions-dominated episode exhibited an increased share of primary OAs (cooking OA, biomass-burning OA, and hydrocarbon-like OA). Interestingly, cooking OA exerted a major impact during the nighttime, comprising 31.7 % of the observed NR-PM_1.0 and up to 60 % of OA when local emissions were the primary driver of haze formation. This finding underscores the importance of mitigating cooking OA emissions in the region.