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. 2013 Apr 16;47(8):3614-22.
doi: 10.1021/es304481m. Epub 2013 Apr 2.

Physicochemical characterization of airborne particulate matter at a mainline underground railway station

Matthew Loxham  1 , Matthew J Cooper, Miriam E Gerlofs-Nijland, Flemming R Cassee, Donna E Davies, Martin R Palmer, Damon A H Teagle
Affiliations

Physicochemical characterization of airborne particulate matter at a mainline underground railway station

Matthew Loxham et al. Environ Sci Technol. .

Abstract

Underground railway stations are known to have elevated particulate matter (PM) loads compared to ambient air. As these particles are derived from metal-rich sources and transition metals may pose a risk to health by virtue of their ability to catalyze generation of reactive oxygen species (ROS), their potential enrichment in underground environments is a source of concern. Compared to coarse (PM10) and fine (PM2.5) particulate fractions of underground railway airborne PM, little is known about the chemistry of the ultrafine (PM0.1) fraction that may contribute significantly to particulate number and surface area concentrations. This study uses inductively coupled plasma mass spectrometry and ion chromatography to compare the elemental composition of size-fractionated underground PM with woodstove, roadwear generator, and road tunnel PM. Underground PM is notably rich in Fe, accounting for greater than 40% by mass of each fraction, and several other transition metals (Cu, Cr, Mn, and Zn) compared to PM from other sources. Importantly, ultrafine underground PM shows similar metal-rich concentrations as the coarse and fine fractions. Scanning electron microscopy revealed that a component of the coarse fraction of underground PM has a morphology indicative of generation by abrasion, absent for fine and ultrafine particulates, which may be derived from high-temperature processes. Furthermore, underground PM generated ROS in a concentration- and size-dependent manner. This study suggests that the potential health effects of exposure to the ultrafine fraction of underground PM warrant further investigation as a consequence of its greater surface area/volume ratio and high metal content.

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Figures

Figure 1
Figure 1
Concentrations of Fe, Cu, Cr, Mn, Zn, and K in PM of coarse (C), fine (F), and ultrafine (UF) fractions collected from a woodstove (WS), a roadwear generator (RW), an underground station (UG), and a road tunnel (RT). Values expressed as single values (RT) or mean ± 1 SE of two (WS, RW) or three (UG) individual samples.
Figure 2
Figure 2
Concentrations of SO42– (left panel), Cl– (center panel), and NO3– (right panel) in coarse (C), fine (F), and ultrafine (UF) fractions of PM collected from a woodstove (WS), a roadwear generator (RW), an underground station (UG), and a road tunnel (RT). Values expressed as single values (RT) or mean ± 1 SE of two (WS, RW) or three (UG) individual samples. (*) p < 0.05 and (**) p < 0.01, analyzed by one-way repeated measures ANOVA.
Figure 3
Figure 3
SEM micrographs showing morphology of coarse (C; ×5000), fine (F; ×5000), and ultrafine (UF; ×30 000) underground PM. Flakelike particulates in the coarse fraction are indicated by arrowheads. Scale bars represent 10 μm (C and F) or 2 μm (UF).
Figure 4
Figure 4
DCF fluorescence induced by 3 h incubation of PBECs with coarse, fine, or ultrafine underground PM. Values expressed as mean ± 1 SE, n = 3–5. (***) p < 0.001 vs control; (#) p < 0.05 for fine or ultrafine vs respective concentration of coarse PM. (##) p < 0.01 and (###) p < 0.001, analyzed by one-way repeated measures ANOVA.
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