Chemical Characterization of Outdoor and Subway Fine (PM2.5–1.0) and Coarse (PM10–2.5) Particulate Matter in Seoul (Korea) by Computer-Controlled Scanning Electron Microscopy (CCSEM)

Outdoor and indoor (subway) samples were collected by passive sampling in urban Seoul (Korea) and analyzed with computer-controlled scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (CCSEM-EDX). Soil/road dust particles accounted for 42%-60% (by weight) of fine particulate matter larger than 1 µm (PM(2.5-1.0)) in outdoor samples and 18% of PM2.5-1.0 in subway samples. Iron-containing particles accounted for only 3%-6% in outdoor samples but 69% in subway samples. Qualitatively similar results were found for coarse particulate matter (PM(10-2.5)) with soil/road dust particles dominating outdoor samples (66%-83%) and iron-containing particles contributing most to subway PM(10-2.5) (44%). As expected, soil/road dust particles comprised a greater mass fraction of PM(10-2.5) than PM(2.5-1.0). Also as expected, the mass fraction of iron-containing particles was substantially less in PM(10-2.5) than in PM(2.5-1.0). Results of this study are consistent with known emission sources in the area and with previous studies, which showed high concentrations of iron-containing particles in the subway compared to outdoor sites. Thus, passive sampling with CCSEM-EDX offers an inexpensive means to assess PM(2.5-1.0) and PM(10-2.5) simultaneously and by composition at multiple locations.