Abstract
Traffic is a significant pollution source in cities and has caused various health and environmental concerns worldwide. Therefore, an improved understanding of traffic impacts on particle concentrations and their components could help mitigate air pollution. In this study, the characteristics and sources of trace elements in PM2.5 (fine), and PM10-2.5 (coarse), were investigated in dense traffic areas in Toronto and Vancouver, Canada, from 2015–2017. At nearby urban background sites, 24-h integrated PM samples were also concurrently collected. The PM2.5 and PM10-2.5 masses, and a number of elements (i.e., Fe, Ba, Cu, Sb, Zn, Cr), showed clear increases at each near-road site, related to the traffic emissions resulting from resuspension and/or abrasion sources. The trace elements showed a clear partitioning trend between PM2.5 and PM10-2.5, thus reflecting the origin of some of these elements. The application of positive matrix factorization (PMF) to the combined fine and coarse metal data (86 total), with 24 observations at each site, was used to determine the contribution of different sources to the total metal concentrations in fine and coarse PM. Four major sources were identified by the PMF model, including two traffic non-exhaust (crustal/road dust, brake/tire wear) sources, along with regional and local industrial sources. Source apportionment indicated that the resuspended crustal/road dust factor was the dominant contributor to the total coarse-bound trace element (i.e., Fe, Ti, Ba, Cu, Zn, Sb, Cr) concentrations produced by vehicular exhaust and non-exhaust traffic-related processes that have been deposited onto the surface. The second non-exhaust factor related to brake/tire wear abrasion accounted for a considerable portion of the fine and coarse elemental (i.e., Ba, Fe, Cu, Zn, Sb) mass at both near-road sites. Regional and local industry contributed mostly to the fine elemental (i.e., S, As, Se, Cd, Pb) concentrations. Overall, the results show that non-exhaust traffic-related processes were major contributors to the various redox-active metal species (i.e., Fe, Cu) in both PM fractions. In addition, a substantial proportion of these metals in PM2.5 was water-soluble, which is an important contributor to the formation of reactive oxygen species and, thus, may lead to oxidative damage to cells in the human body. It appears that controlling traffic non-exhaust-related metals emissions, in the absence of significant point sources in the area, could have a pronounced effect on the redox activity of PM, with broad implications for the protection of public health.
Highlights
Air pollution continues to be one of the most pressing problems in urban areas because of the increased risk for a number of adverse health effects [1,2]
The amount of crustal material (CM) in PM2.5 and PM10-2.5 was calculated based on the concentrations of the oxides of the major elements i.e.,: Al, Si, Ca, K, Ti and Fe, following a widely used approach [49] given by Equation (1)
Than in Toronto (13%; 0.26 μg m−3 ). This suggests that frequent stop-and-go driving, and the low speed of the vehicles at the major intersection on a heavily used trucking route in Vancouver, in addition to less dilution compared to the NR-TOR, may, in part, result in the greater emissions of mechanically generated brake/tire wear and, greater contributions to the PM10-2.5 element concentrations [7,58]
Summary
Air pollution continues to be one of the most pressing problems in urban areas because of the increased risk for a number of adverse health effects [1,2]. Traffic-generated particulate matter arises from vehicular exhaust and non-exhaust sources [7,8,9,10,11] The former is related to fuel combustion, and the latter are due to the wear of brake systems (pads and discs), tires, road surface abrasion, and the resuspension of road dust particles. A number of recent studies have shown that ambient metal elements (in their soluble and insoluble forms) have been extensively associated with the generation of reactive oxygen species (ROS), which has been postulated to be an important mechanism leading to PM-induced toxicity and the associated adverse health effects [16,17,18,19,20,21]. FPM- and CPM-bond metal concentrations, at both near-road urban sites, were identified using the positive matrix factorization (PMF) model
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