title: Physicochemical characterization of airborne particulate matter at a mainline underground railway station.
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.
authors.affiliation: The Brooke Laboratory, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, University Hospital Southampton, Tremona Road, Southampton, SO16 6YD, United Kingdom. m.loxham@soton.ac.uk
authors.forename: Matthew
authors.initials: M
authors.lastname: Loxham
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Cooper
authors.forename: Miriam E
authors.initials: ME
authors.lastname: Gerlofs-Nijland
authors.forename: Flemming R
authors.initials: FR
authors.lastname: Cassee
authors.forename: Donna E
authors.initials: DE
authors.lastname: Davies
authors.forename: Martin R
authors.initials: MR
authors.lastname: Palmer
authors.forename: Damon A H
authors.initials: DA
authors.lastname: Teagle
mesh_terms: D000838:Anions / Q000032:analysis; D001980:Bronchi / Q000166:cytology; D055598:Chemical Phenomena; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005452:Fluoresceins; D005453:Fluorescence; D006801:Humans; D008670:Metals / Q000032:analysis; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D052638:Particulate Matter / Q000737:chemistry* / Q000633:toxicity; D017382:Reactive Oxygen Species / Q000032:analysis; D014186:Transportation
chemical_list: C110400:2',7'-dichlorodihydrofluorescein diacetate; D000838:Anions; D005452:Fluoresceins; D008670:Metals; D052638:Particulate Matter; D017382:Reactive Oxygen Species