서울 PM2.5 내 2차 유기탄소의 기여도와 주요 생성 요인 = Contribution and Major Factors of Secondary Organic Carbon Formation in PM2.5 in Seoul

다국어 초록 (Multilingual Abstract)

This study quantified the fraction of secondary organic carbon (SOC) within organic carbon (OC) in fine particles (PM2.5) and investigated the characteristics of SOC formation and spatial origins of both SOC and primary organic carbon (POC) in PM2.5 in Seoul using hourly resolved atmospheric monitoring data in 2023. While PM2.5 and its major components such as NO3 - and elemental carbon (EC) exhibited typical winter-high and summer-low seasonal patterns, OC maintained elevated levels across all seasons. Using the minimum R-squared (MRS) method, the annual average POC and SOC concentrations were estimated at 2.3 and 1.9 μg m-3, respectively, with SOC accounting for 45% of the total OC and peaking at 3.7 μg m-3 in July. During summer, SOC showed strong correlations with O3 and Ox (i.e., sum of O3 and NO2) under high temperatures, indicating the dominant photochemical oxidation. In contrast, winter SOC was linked to elevated CO, NO2, and high relative humidity, which suggests the importance of aqueous-phase reactions and the accumulation of primary emissions. Spatial analyses, including bivariate polar plots and concentration weighted trajectory (CWT) modeling, confirmed that summer SOC was dominantly formed locally from domestic precursors under stagnant conditions. In contrast, elevated winter and spring carbonaceous aerosol concentrations were significantly influenced by the long-range transport of pollutants from northeastern China across the Yellow Sea, coupled with regional aqueous chemistry. These findings highlight that effective mitigation of OC in PM2.5 in Seoul requires season-specific strategies: controlling local VOCs and oxidant levels to reduce summer photochemical SOC while addressing both regional transport and local precursor emissions in winter.