Abstract
This study investigates the sources, chemical composition, and vertical transport of particulate matter (PM) at Mt. Gwanak in southeastern Seoul, focusing on differences between surface and elevated altitudes during winter 2021. Using a time-of-flight aerosol chemical species mass spectrometer (ToF-ACSM), PM was measured at 632 m. At this altitude, PM composition was dominated by organics (41.5 %), nitrate (20.5 %), sulfate (17.8 %), and ammonium (13.6 %). Compared to surface-level measurements, nitrate was lower (27.1 %) at the surface. While organic proportions were similar (41.5 % at 632 m vs. 42.7 % at the surface), oxidized organic aerosols (OOA) were more prominent aloft, as shown by Positive Matrix Factorization (PMF) analysis. Despite no direct anthropogenic sources at 632 m, anthropogenic compounds such as nitrate, primary organic aerosols (POA), and black carbon (BC) were detected, peaking at 13:00 with PBL expansion, suggesting surface-level influence.
Two distinct surface haze events were analyzed to understand the influence of upper-layer pollution. The first haze event showed an initial increase in sulfate at high altitudes, which descended to the surface as the PBL expanded. This effect persisted due to the accumulation of nitrate, indicating substantial roles for long-range transport and local accumulation. In contrast, the second haze event was characterized by a marked increase in surface-level NO2, which ascended to higher altitudes and underwent photochemical reactions, resulting in elevated nitrate and O3 levels aloft. These two haze events, coupled with PBL fluctuations demonstrate the complex interactions between atmospheric layers.
Therefore, this study highlights the importance of vertical measurements in understanding surface air pollution and haze events. The findings underscores the need for more comprehensive investigations across different seasons and conditions to gain a more complete understanding of these processes.