Domestic and Transboundary Impacts of High-Concentration PM_2.5 Generated by Large-Scale Wildfire in South Korea

In March 2025, a series of large-scale wildfires that broke out across central and southeastern regions of South Korea rapidly burned vast areas of forest and released substantial amounts of combustion products and fine particulate matter (PM_2.5) into the atmosphere. This study comprehensively analyzed the spatiotemporal characteristics of air pollutant concentrations, focusing on PM_2.5 emitted from wildfires, as well as the domestic and transboundary impacts of wildfire smoke, by utilizing satellite imagery, ground-based monitoring networks, and atmospheric models. According to real-time PM_2.5 monitoring data from South Korea, extremely high concentrations exceeding 246 μg m⁻³ were observed in areas near the wildfire originating between 25 and 26 March. High concentration events were observed for SO₂ (sulfur dioxide) and CO (carbon monoxide), with peak values of 0.0066 ppm and 1.38 ppm, respectively. The elevated air pollutant concentrations originating from South Korea were weakened when reaching Japan, yet high concentration levels were still detected. Elevated PM_2.5 concentrations were also detected across western Japan. Analysis of VIIRS satellite-based active fire data and wind vector fields indicated that the wildfires spread rapidly over a wide area within a short time. Furthermore, AOD (aerosol optical depth) data from the GK-2B satellite and RGB/false-color imagery from Himawari-8 visually confirmed that wildfire smoke containing high aerosol concentrations had reached Japan. HYSPLIT backward trajectory and dispersion analysis also suggested that the air masses arriving in western Japan likely originated from the wildfire-affected areas in southeastern Korea within 24 hours. This study demonstrates that large-scale wildfires can significantly deteriorate regional air quality across national borders in a short period. It highlights the urgent need for enhanced cooperation among East Asian countries and the development of an integrated satellite-ground-based monitoring system to effectively address transboundary air pollution caused by extreme wildfire events.