Fingerprinting metals in urban street dust of Beijing, Shanghai, and Hong Kong

Street dust samples were taken between July and December 2005 at 25 locations in Shanghai, Beijing, and Hong Kong and sieved to 63 mu m particle size before elemental analyses by CHN analyzer, XRF and ICP-MS. About 60% of the particles from the Beijing and Shanghai sieved samples were <10 mu m mean diameter, and similar to 20% were <2 mu m mean diameter, so that they are readily resuspendable and respirable with increased risk of adverse health impacts. The optical size distributions determined, by electron microscopy were reasonably similar to the mass size distributions of total suspended particulate matter (TSP) at these two megacities. Hong Kong street dust particles were coarser with only about 3% of the sieved samples being <10 mu m. The elemental composition profile of Hong Kong street dust differs considerably from those of Beijing and Shanghai, being more abundant in C, S, Cr, Cu, Ce, and Zn due to higher traffic density. In particular,the vehicle contribution to Hong Kong street dust is shown by order-of-magnitude relative enhancements of Fe and Cr compared with those in TSP sampled nearby, attributed to vehicle iron and stainless-steel wear and tear and rusting contributing to street dust in the street canyons. The concentrations of Cr in Hong Kong street dust, measured from Cr-52 and Cr-53 by ICP-DRC-MS after a modified three-stage microwave-assisted acid digestion, are higher than those reported elsewhere.