Source identification of particulate matter collected at underground subway stations in Seoul, Korea using quantitative single-particle analysis

Subway particle samples collected at four underground subway stations in Seoul, Korea were characterized by a single-particle analytical technique, low-Z particle electron probe X-ray microanalysis. To clearly identify indoor sources of subway particles, four sets of samples collected in tunnels, at platforms, near ticket offices, and outdoors were investigated. For the samples collected in tunnels, Fe-containing particles predominate, with relative abundances of 75–91% for the four stations. The amounts of Fe-containing particles decrease as the distance of sampling locations from the tunnel increases. In addition, samples collected at the platform in subway stations with platform screen doors (PSDs) that limit air-mixing between the platform and the tunnel showed marked decreases in relative abundances of Fe-containing particles, clearly indicating that Fe-containing subway particles are generated in the tunnel. PM10 mass concentration levels are the highest in the tunnels, becoming lower as the distance of sampling locations from the tunnel increases. The extent of the decrease in PM10 in stations with PSDs is also larger than that in stations without PSDs. The results clearly indicate that Fe-containing particles originating in tunnels predominate in the indoor microenvironment of subway stations, resulting in high indoor PM10 levels, and that PSDs play a significant role in reducing Fe-containing particles at platforms and near ticket offices.