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

Fine particulate matter (PM_2.5) 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 PM_2.5 sources using coordinated ground-based, airborne, and satellite observations across East Asia. Here, we present a regional source attribution analysis of surface PM_2.5 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 PM_2.5 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 PM_2.5 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.