Multi-method approach for analysis of road dust particles: elemental ratios, SP-ICP-TOF-MS, and TEM

Abstract

Road dust particles including nanoparticles (NPs), with heterogeneous composition, are significant carriers of metals/metalloids and can be further transported into the atmosphere or surface runoff. However, their elemental composition remains poorly defined. In this study, seven road dust samples were collected from different areas in Shanghai, China and were analyzed for total metal concentrations, particle elemental composition and ratios, morphology, composition, and crystalline phases. Overall, the road dust particles were characterized by high concentrations of Fe, Ti, Al, Cr, Ci, V Ni, Cu, Zn, Sn, and Sb, which varied among the samples. Four potential sources of metals were identified using PCA analysis including natural sources, exhaust and non-exhaust emissions, and vehicle electronics. The bulk elemental ratios of Ti/Nb, Ti/Al, Ti/Fe, Pb/Nb, Sn/Nb and W/Nb in the road dust samples were higher than the corresponding reference ratios indicating that the road dust was contaminated with Ti, Pb, Sn, and W. Anthropogenic Ti, Pb, Sn and W were estimated by mass balance calculation and varied between 0.25 and 1.48 × 10⁶ μg kg⁻¹, 0.19 and 1.21 × 10⁵ μg kg⁻¹, 0.98 and 4.22 × 10⁴ μg kg⁻¹, and 0.12 and 1.01 × 10⁴ μg kg⁻¹, respectively. The number concentration of NPs was determined by SP-ICP-TOF-MS and was 0.66–3.3 × 10¹⁰ particles per g for Ti-containing NPs, 0.23–1.51 × 10¹⁰ particles per g for Pb-containing NPs, 0.28–3.10 × 10⁹ particles per g for Sn-containing NPs, and 1.34–9.38 × 10⁸ particles per g for W-containing NPs, respectively. TEM analysis further confirmed the occurrence of both natural and anthropogenic Ti- and W-containing NPs and the contamination of Pb- and Sn-containing NPs in Shanghai road dust. These NPs could originate from the non-exhaust emission of vehicles and coal combustion. Overall, this study provides a reliable comprehensive approach for the characterization of road dust particles and new insights into the nature of Ti-, Pb-, Sn-, and W-containing particles in dust samples.