Articles | Volume 15, issue 8
Research article
21 Apr 2015
Research article |  | 21 Apr 2015

Characteristics of trace metals in traffic-derived particles in Hsuehshan Tunnel, Taiwan: size distribution, potential source, and fingerprinting metal ratio

Y.-C. Lin, C.-J. Tsai, Y.-C. Wu, R. Zhang, K.-H. Chi, Y.-T. Huang, S.-H. Lin, and S.-C. Hsu

Abstract. Traffic emissions are a significant source of airborne particulate matter (PM) in ambient environments. These emissions contain an abundance of toxic metals and thus pose adverse effects on human health. Size-fractionated aerosol samples were collected from May to September 2013 by using micro-orifice uniform deposited impactors (MOUDIs). Sample collection was conducted simultaneously at the inlet and outlet sites of Hsuehshan Tunnel in northern Taiwan, which is the second-longest freeway tunnel (12.9 km) in Asia. This endeavor aims to characterize the chemical constituents and size distributions, as well as fingerprinting ratios of particulate metals emitted by vehicle fleets. A total of 36 metals in size-resolved aerosols were determined through inductively coupled plasma mass spectrometry. Three major groups – namely, tailpipe emissions (Zn, Pb, and V in fine mode), wear debris (Cu, Cd, Fe, Ga, Mn, Mo, Sb, and Sn), and resuspended dust (Ca, Mg, K, and Rb) – of airborne PM metals were categorized on the basis of the results of enrichment factor, correlation matrix, and principal component analysis. Size distributions of wear-originated metals resembled the pattern of crustal elements, which were predominated by super-micron particulates (PM1–10). By contrast, tailpipe exhaust elements such as Zn, Pb, and V were distributed mainly in submicron particles. By employing Cu as a tracer of wear abrasion, several inter-metal ratios – including Fe / Cu (14), Ba / Cu (1.05), Sb / Cu (0.16), Sn / Cu (0.10), and Ga / Cu (0.03) – served as fingerprints for wear debris. However, the data set collected in this work is useful for further studies on traffic emission inventory and human health effects of traffic-related PM.

Short summary
In this work, size distributions and chemical compositions of 36 PM metals emitted from traffic emissions are explored by tunnel experiments. Potential sources of tunnel PM are also identified. Importantly, fingerprinting ratios of wear debris and automotive catalysts are established. The ratios will be good tools for apportioning PM sources in the polluted urban atmosphere.
Final-revised paper