As most people living in urban area spend more than 85% of their time in a variety of indoor locations, information regarding their exposure routes of pollutants is crucial in human health.
The contaminants originated from indoor pollution sources as well as various outdoor sources are easily accumulated in indoor environment. Note that the natural ventilation is nearly impossible in the subway system. Hence, its pollution status can be worsened if pollutants are constantly produced and circulated inside the station due to the repetitive operation of subway trains. Therefore, the concentration levels and associated elemental composition of PM in an indoor environment (e.g., subway station, cabin, and tunnel) can be used as a practical barometer of indoor air quality, IAQ.
In this dissertation, the first chapter presents the analytical summary of seasonal PM2.5 data collected at a subway platform in Daejeon, Korea. The PM2.5 concentrations were 36.9 ± 12.4 μg/m3 that fell below the guideline set by the Korean Indoor Air Quality Control Act. Fe was identified as the predominant element (22% of PM2.5), which generally occurred in the form of magnetite (Fe3O4). Four sources at the subway platform were identified, and the contribution of each source was quantified by PMF receptor model; rail dust (50%), secondary aerosol (19%), soil-road dust (19%), and vehicle exhaust (12%). Except for the rail dust generated by the friction of a rail and wheel, the PM2.5 at the subway platform is expected to be originated from outdoor pollution sources (e.g., secondary aerosol, soil-road dust, and vehicle exhaust). Thus, the quantity of PM2.5 infiltrated from outdoor PM2.5 sources was estimated to be about 50% at the subway platform.
The second chapter presents the analytical summary of PM10 data collected from a subway cabin. In order to assess the pollution status and distribution characteristics of PM10 and PM-bound species in the subway cabin, PM10 samples were collected using mini-volume air sampler during the time of subway operation. The measurements of up to about 30 elements including toxic metals in PM10 were made by INAA and WD-XRF. The average PM10 concentration was 59.3 ± 14.5 μg/m3, while the associated elemental concentrations varied in the range of 10-3 to 105 ng/m3. It was found that the concentrations of Fe (12.5 μg/m3) and S (1.89 μg/m3) were substantially higher than all the other elements measured from the subway cabin. In those PM10 samples, Ba and Fe were highly enriched probably due to mechanical wearing and friction of subway brake system, rail, and wheels in the tunnel. The results of factor analysis indicated that there were no more than six sources in the cabin (e.g., brake-nonferrous metal particle, resuspended rail dust, fuel combustion, vehicle exhaust, black carbon, and Cr-related), which can cover as much as 80.2 % of total variance.
In the third chapter, the chemical composition and distribution of Fe-containing particles were explored from subway particles collected from platform, cabin, and tunnel. PM10 concentrations in the subway tunnel (243 ± 56.0 μg/m3) were 4 times higher than those measured in the cabin. At the subway platform, coarse particles mainly consisted of major crustal elements (25% of coarse particles: such as Al, Ca, K, Mg, and Si), while it was not for fine particles. If the PM10 results at the platform are compared across seasons, the concentrations of metals originated from subway environments (e.g., Ba, Cu, Fe, and Mn) were significantly lower in winter than other seasons, which was similar to PM2.5. In the subway system, the concentrations of certain metal species (e.g., Ba, Cu, Fe, and Mn) were elevated especially about 5~400 times than those in ground-level offices. These elements were well correlated statistically between cabin and tunnel regardless of differences in measurement period.