Ensemble-Based Source Attribution of Fine Particulate Matter over South Korea during the ASIA-AQ/SIJAQ Campaign

Fine particulate matter (PM2.5) remains a major challenge for air quality management in South Korea, driven by transboundary transport and domestic emissions. While the Korea-United States Air Quality (KORUS-AQ) campaign offered valuable insights into springtime sources, wintertime pollution has yet to be well characterized. The Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) and Satellite Integrated Joint Monitoring of Air Quality (SIJAQ) campaigns (February-March 2024) provided a unique opportunity to quantify winter PM2.5 sources using coordinated ground-based, airborne, and satellite observations across East Asia. Here, we present a regional source attribution analysis of surface PM2.5 during the campaign, employing seven chemical transport model configurations and three source attribution approaches, all driven by the updated East Asian anthropogenic emissions inventory (ASIA-AQ v3.0). The model ensemble mean reproduced observed PM2.5 variability at ground sites in China and South Korea with strong correlations (R = 0.79 in China; R = 0.86 in South Korea) and low normalized mean biases (-6.4% and -7.0%, respectively), supporting its robustness for source attribution. Results indicate that continental outflows contributed 57-84% of surface PM2.5 in South Korea, whereas domestic sources accounted for up to 43% under less influence of transboundary transport. The ensemble-based approach provides useful evidence to guide targeted mitigation strategies. These estimates are representative of the specific meteorological conditions during the ASIA-AQ/SIJAQ winter period rather than a climatological mean state.