Characterizing the elemental enrichment patterns of fractionated road dust and fluxes in the environment

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Road dust is a sink for a range of metals and metalloids emitted from traffic-related activity in both exhaust (tailpipe) and non-exhaust (wear of street surfaces, automotive components, etc. and their resuspension) forms. As a pollutant sink, road dust is a likely major contributor to local air, water and soil contamination. The evidence to date suggests the finer particle size fractions of road dust have a high potential to be mobilized via resuspension processes and impact local air quality. While the chemical composition of road dust in particle size fractions >63 microns has been well-characterized in a number of studies, there are large data gaps on the following: 1. total traffic-associated particle and metal loadings to roads, 2. elemental enrichment patterns as a function of particle size fraction and associated potential to be mobilized via resuspension processes and, 3. the contribution of specific automotive and street wear sources to road dust particle size fractions capable of being inhaled. This hinders an estimation of road dust-associated elemental fluxes in an urban context and the identification of source emissions as a function of particle size contribution and potential toxicity for management and abatement purposes. In particular, data is lacking regarding the concentrations and road dust enrichment patterns of emerging metals of concern such as rare earths and platinum group elements.***The proposed research will systematically examine the particle size mass distribution and associated metal and metalloid enrichment of road dust collected from a variety of roads with different traffic volumes, fleet composition, etc., in the Greater Toronto Area. The particle size distribution of total road dust samples will be examined to estimate the mass contribution of fine fractions of human and environmental health concern to total amounts deposited on roads of various types. Metal and metalloid concentrations will be determined for unfractionated and fractionated road dust samples for the calculation of elemental loading to streets and flux estimates. The data serve as a basis for development of a model to assess the extent to which mobile fractions of road dust may contribute to urban air pollution and contamination on a wider spatial scale.**