Evaluation of Tire Wear Contribution to PM2.5 in Urban Environments

Vehicle-related particulate matter (PM) emissions may arise from both exhaust and non-exhaust mechanisms, such as brake wear, tire wear, and road pavement abrasion, each of which may be emitted directly and indirectly through resuspension of settled road dust. Several researchers have indicated that the proportion of PM2.5 attributable to vehicle traffic will increasingly come from non-exhaust sources. Currently, very little empirical data is available to characterize tire and road wear particles (TRWP) in the PM2.5 fraction. As such, this study was undertaken to quantify TRWP in PM2.5 at roadside locations in urban centers including London, Tokyo and Los Angeles, where vehicle traffic is an important contributor to ambient air PM. The samples were analyzed using validated chemical markers for tire tread polymer based on a pyrolysis technique. Results indicated that TRWP concentrations in the PM2.5 fraction were low, with averages ranging from < 0.004 to 0.10 µg/m3, representing an average contribution to total PM2.5 of 0.27%. The TRWP levels in PM2.5 were significantly different between the three cities, with significant differences between London and Los Angeles and Tokyo and Los Angeles. There was no significant correlation between TRWP in PM2.5 and traffic count. This study provides an initial dataset to understand potential human exposure to airborne TRWP and the potential contribution of this non-exhaust emission source to total PM2.5

Comparison of Tire and Road Wear Particle Concentrations in Sediment for Watersheds in France, Japan, and the United States by Quantitative Pyrolysis GC/MS Analysis

Impacts of surface runoff to aquatic species are an ongoing area of concern. Tire and road wear particles (TRWP) are a constituent of runoff, and determining accurate TRWP concentrations in sediment is necessary in order to evaluate the likelihood that these particles present a risk to the aquatic environment. TRWP consist of approximately equal mass fractions of tire tread rubber and road surface mineral encrustations. Sampling was completed in the Seine (France), Chesapeake (U.S.), and Yodo-Lake Biwa (Japan) watersheds to quantify TRWP in the surficial sediment of watersheds characterized by a wide diversity of population densities and land uses. By using a novel quantitative pyrolysis-GC/MS analysis for rubber polymer, we detected TRWP in 97% of the 149 sediment samples collected. The mean concentrations of TRWP were 4500 (<i>n</i> = 49; range = 62–11 600), 910 (<i>n</i> = 50; range = 50–4400) and 770 (<i>n</i> = 50; range = 26–4600) μg/g d.w. for the characterized portions of the Seine, Chesapeake and Yodo-Lake Biwa watersheds, respectively. A subset of samples from the watersheds (<i>n</i> = 45) was pooled to evaluate TRWP metals, grain size and organic carbon correlations by principal components analysis (PCA), which indicated that four components explain 90% of the variance. The PCA components appeared to correspond to (1) metal alloys possibly from brake wear (primarily Cu, Pb, Zn), (2) crustal minerals (primarily Al, V, Fe), (3) metals mediated by microbial immobilization (primarily Co, Mn, Fe with TOC), and (4) TRWP and other particulate deposition (primarily TRWP with grain size and TOC). This study should provide useful information for assessing potential aquatic effects related to tire service life

Use of a Deuterated Internal Standard with Pyrolysis-GC/MS Dimeric Marker Analysis to Quantify Tire Tread Particles in the Environment

Pyrolysis(pyr)-GC/MS analysis of characteristic thermal decomposition fragments has been previously used for qualitative fingerprinting of organic sources in environmental samples. A quantitative pyr-GC/MS method based on characteristic tire polymer pyrolysis products was developed for tread particle quantification in environmental matrices including soil, sediment, and air. The feasibility of quantitative pyr-GC/MS analysis of tread was confirmed in a method evaluation study using artificial soil spiked with known amounts of cryogenically generated tread. Tread concentration determined by blinded analyses was highly correlated (r2 ³ 0.88) with the known tread spike concentration. Two critical refinements to the initial pyrolysis protocol were identified including use of an internal standard and quantification by the dimeric markers vinylcyclohexene and dipentene, which have good specificity for rubber polymer with no other appreciable environmental sources. A novel use of deuterated internal standards of similar polymeric structure was developed to correct the variable analyte recovery caused by sample size, matrix effects, and ion source variability. The resultant quantitative pyr-GC/MS protocol is reliable and transferable between laboratories