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

• Published in: International journal of environmental research and public health Vol. 15; no. 11; p. 2534
• Main Authors: Lee, Yongil, Lee, Young-Chul, Kim, Taesung, Choi, Jin Seok, Park, Duckshin
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 12-11-2018; MDPI
• Subjects: Air conditioning; Air Pollutants - analysis; Air pollution; Air quality; Airborne particulates; Arc discharges; Calcium carbonate; Carbon; Cellulose acetate; Chemical analysis; Electric arcs; Environmental Monitoring - methods; Ferric oxide; Hematite; Image transmission; Inductively coupled plasma; Interfaces; Iron oxides; Morphology; Mortality; Organic carbon; Particulate emissions; Particulate matter; Particulate Matter - analysis; Pollutants; Railroads; Republic of Korea; Scanning electron microscopy; Seoul; Silicon dioxide; Spectroscopy; Subway tunnels; Traffic congestion; Transmission electron microscopy; Tunnels; Ventilation; Wire; X-ray diffraction; Seoul; Republic of Korea; New York; United States > US; Japan; Finland; particulate matter; characteristics; source identification; air quality; subway tunnel
• ISSN: 1660-4601; 1661-7827; 1660-4601
• DOI: 10.3390/ijerph15112534

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 PM
and PM
concentrations (
= 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 PM
and PM
. 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 (
-Fe₂O₃) and maghemite-C (
-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.