Aircraft observations of black carbon over the Yellow Sea and Seoul Metropolitan Area: Vertical profiles and air mass origin influence

초록

Black carbon (BC) is a climate-relevant aerosol whose atmospheric effects depend on its microphysical properties, including core size, mixing state, and coating thickness. However, vertical and regional variability in BC aging across Northeast Asia remains poorly constrained, particularly during winter when emissions are high and boundary layer development is suppressed. This study presents aircraft-based observations of BC over the Yellow Sea (YS) and Seoul Metropolitan Area (SMA) during winter 2023-2024, using a single particle soot photometer to measure refractory BC (rBC) mass and number concentrations, mass and count median diameters (MMD, CMD), the fraction of thickly coated particles (Fthick), and coating thickness. Despite similar rBC mass concentrations (similar to 0.30 mu g/m3 for YS, similar to 0.24 mu g/m3 for SMA), BC properties differed markedly. YS exhibited larger rBC core sizes (MMD similar to 160 nm; CMD similar to 88 nm) and higher Fthick (similar to 0.32), suggesting more aged, internally mixed BC from long-range transport. In contrast, SMA showed smaller sizes and lower Fthick (similar to 0.23), consistent with fresher, local emissions. Coating thickness was similar (similar to 67-68 nm). Air masses were classified into four transport types using 72 h back trajectories, revealing distinct microphysical signatures by source. The observed contrasts emphasize the interplay between emission regime, transport history, and BC aging. These results highlight the value of trajectory-informed, vertically resolved BC measurements in constraining climate and air quality impacts in East Asia.

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