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Open AccessArticle

Sources and Characteristics of Particulate Matter in Subway Tunnels in Seoul, Korea

Korea Railroad Research Institute (KRRI), 176 Cheoldobakmulkwan-ro, Uiwang-si 16105, Korea
Mechanical Engineering, Sungkyunkwan University, 2066 Seobu-ro, Suwon-si 16419, Korea
Department of BioNano Technology, Gachon University, 1342 seongnamdae-ro, Seongnam-si 13120, Korea
Analysis Center for Research Advancement, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon-si 34141, Korea
Author to whom correspondence should be addressed.
Int. J. Environ. Res. Public Health 2018, 15(11), 2534;
Received: 27 September 2018 / Revised: 29 October 2018 / Accepted: 31 October 2018 / Published: 12 November 2018
(This article belongs to the Special Issue Indoor Environmental Quality)
PDF [5724 KB, uploaded 12 November 2018]


Hazards related to particulate matter (PM) in subway systems necessitate improvement of the air quality. As a first step toward establishing a management strategy, we assessed the physicochemical characteristics of PM in a subway system in Seoul, South Korea. The mean mass of PM10 and PM2.5 concentrations (n = 13) were 213.7 ± 50.4 and 78.4 ± 8.8 µg/m3, with 86.0% and 85.9% of mass concentration. Chemical analysis using a thermal–optical elemental/organic carbon (EC–OC) analyzer, ion chromatography (IC), and inductively coupled plasma (ICP) spectroscopy indicated that the chemical components in the subway tunnel comprised 86.0% and 85.9% mass concentration of PM10 and PM2.5. Fe was the most abundant element in subway tunnels, accounting for higher proportions of PM, and was detected in PM with diameters >94 nm. Fe was present mostly as iron oxides, which were emitted from the wheel–rail–brake and pantograph–catenary wire interfaces. Copper particles were 96–150 nm in diameter and were likely emitted via catenary wire arc discharges. Furthermore, X-ray diffraction analysis (XRD) showed that the PM in subway tunnels was composed of calcium carbonate (CaCO3), quartz (SiO2), and iron oxides (hematite (α-Fe2O3) and maghemite-C (γ-Fe2O3)). Transmission electron microscopy images revealed that the PM in subway tunnels existed as agglomerates of iron oxide particle clusters a few nanometers in diameter, which were presumably generated at the aforementioned interfaces and subsequently attached onto other PM, enabling the growth of aggregates. Our results can help inform the management of PM sources from subway operation. View Full-Text
Keywords: characteristics; particulate matter; source identification; subway tunnel; air quality characteristics; particulate matter; source identification; subway tunnel; air quality

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Lee, Y.; Lee, Y.-C.; Kim, T.; Choi, J.S.; Park, D. Sources and Characteristics of Particulate Matter in Subway Tunnels in Seoul, Korea. Int. J. Environ. Res. Public Health 2018, 15, 2534.

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