Greg J. Evans

As exhaust emissions (EE) from motor vehicles decline, non-exhaust emissions (NEE) from brake wear (BW), tire wear, and road dust (RD) are becoming a major source of traffic-related particulate matter (PM). Hence, there is a pressing need to characterize the resulting exposures and health burden. Here we examine the factors affecting NEE concentrations in ambient fine and coarse PM (PM2.5 and PM10–2.5) using speciated PM measurements conducted near a highway and an arterial road in Canada. Receptor model source apportionment analysis showed BW and RD combined contributed 28–49% of traffic-derived PM2.5, with associated near-road concentrations being 4–8 times higher for PM10–2.5 than PM2.5. Copper and iron, primarily contributed by BW, were 2–5 times higher than background levels. Multiple linear regression analysis showed NEE concentrations are affected by meteorology, traffic volume, and fleet composition. Emission factor (EF) calculations showed copper emission per vehicle-kilometer traveled declined at a rate of 7–9% year–1 (p < 0.001), cautioning against its use as a stable BW marker as brake pad formulations evolve. While the EFs for EE were comparable across both sites due to similar heavy-duty vehicle (HDV) shares, BW and RD EFs were 3–4 times higher at the highway site, highlighting driving conditions as key determinants of NEE emissions. Light-duty vehicles (LDVs) dominated BW and RD contributions in PM2.5 due to their much higher traffic volume, yet HDVs became important in PM10–2.5 with their higher EFs for coarse particles. This work highlights the need to account for size-resolved characteristics and real-world driving conditions, in addition to vehicle fleet composition, to accurately quantify NEE contributions.

Ultrafine particles (UFP) and black carbon (BC) are key markers of combustion-related air pollution, yet disentangling their sources remains a challenge in complex urban environments. Using a hybrid mobile and fixed-site monitoring campaign, we investigated a marginalized northwest Toronto neighbourhood downwind of Toronto Pearson International Airport and a freight distribution corridor. Results reveal a divergent spatial footprint for the two pollutants. UFP concentrations correlated strongly with flight activity (r = 0.58, p < 0.05 at 3.5 km), with 1.7- to 3.3-fold enrichment downwind of the airport, measured as the ratio of the IQR of UFP concentrations under downwind versus other wind conditions, reaching 3.2-fold at residential sites ∼8 km away. BC was instead driven by roadway proximity and freight activity, with weak correlations with flight counts. BC–UFP correlations were strong during northerly winds (Mean r = 0.62), but weak downwind of the airport (Mean r = 0.1), indicating shared traffic and industrial sources versus independent sources downwind. Random Forest models (R2 = 0.79 for UFP, R2 = 0.87 for BC) identified industrial land-use and a highway as dominant drivers for both pollutants, airport proximity as a UFP-specific driver, and freight trucking as a BC-specific driver. These findings demonstrate that airport emissions can contribute to increased community UFP exposure several kilometers downwind, while local freight activity drives elevated BC concentrations.

Oxidative potential (OP) of atmospheric particulate matter (PM) is a metric of increasing scientific interest because it potentially links chemical particle properties to particle health effects. OP has been recently introduced as a recommended monitoring metric in the European Air Quality Directive. However, inconsistent protocols in the existing literature make it difficult to compare results across studies. Following a 2023 inter-laboratory comparison that focused on PM OP measured using the dithiothreitol (DTT) assay, this paper presents the findings and lessons learnt from a second inter-laboratory study focused on the ascorbic acid assay (OP-AA). In this study, twenty-six laboratories worldwide quantified OP of four PM filter samples and of one chemical compound to evaluate the entire analytical chain, including the extraction step, using a simplified OP-AA protocol. While most laboratories produced repeatable internal results when applying the simplified protocol, significant discrepancies between participants highlight the need for each laboratory to carefully evaluate deviations from the simplified OP-AA protocol. Over half of the 26 participants achieved satisfactory results, suggesting that the protocol is suitable for large-scale implementation. Beyond assessing performance, this work investigates technical, analytical, and mathematical refinements to measurement protocols. Building on the first DTT assay study, this second inter-laboratory comparison represents a significant step toward harmonizing OP assays, and provides specific recommendations to ensure consistent future measurements, ready to be applied in the new air quality directive EU 2024/2881.

Oxidative potential (OP) of atmospheric particulate matter (PM) is a metric of increasing scientific interest because it potentially links chemical particle properties to particle health effects. OP has been recently introduced as a recommended monitoring metric in the European Air Quality Directive. However, inconsistent protocols in the existing literature make it difficult to compare results across studies. Following a 2023 inter-laboratory comparison that focused on PM OP measured using the dithiothreitol (DTT) assay, this paper presents the findings and lessons learnt from a second inter-laboratory study focused on the ascorbic acid assay (OP-AA). In this study, twenty-six laboratories worldwide quantified OP of four PM filter samples and of one chemical compound to evaluate the entire analytical chain, including the extraction step, using a simplified OP-AA protocol. While most laboratories produced repeatable internal results when applying the simplified protocol, significant discrepancies between participants highlight the need for each laboratory to carefully evaluate deviations from the simplified OP-AA protocol. Over half of the 26 participants achieved satisfactory results, suggesting that the protocol is suitable for large-scale implementation. Beyond assessing performance, this work investigates technical, analytical, and mathematical refinements to measurement protocols. Building on the first DTT assay study, this second inter-laboratory comparison represents a significant step toward harmonizing OP assays, and provides specific recommendations to ensure consistent future measurements, ready to be applied in the new air quality directive EU 2024/2881.

Oxidative potential (OP) of atmospheric particulate matter (PM) is a metric of increasing scientific interest because it potentially links chemical particle properties to particle health effects. OP has been recently introduced as a recommended monitoring metric in the European Air Quality Directive. However, inconsistent protocols in the existing literature make it difficult to compare results across studies. Following a 2023 inter-laboratory comparison that focused on PM OP measured using the dithiothreitol (DTT) assay, this paper presents the findings and lessons learnt from a second inter-laboratory study focused on the ascorbic acid assay (OP-AA). In this study, twenty-six laboratories worldwide quantified OP of four PM filter samples and of one chemical compound to evaluate the entire analytical chain, including the extraction step, using a simplified OP-AA protocol. While most laboratories produced repeatable internal results when applying the simplified protocol, significant discrepancies between participants highlight the need for each laboratory to carefully evaluate deviations from the simplified OP-AA protocol. Over half of the 26 participants achieved satisfactory results, suggesting that the protocol is suitable for large-scale implementation. Beyond assessing performance, this work investigates technical, analytical, and mathematical refinements to measurement protocols. Building on the first DTT assay study, this second inter-laboratory comparison represents a significant step toward harmonizing OP assays, and provides specific recommendations to ensure consistent future measurements, ready to be applied in the new air quality directive EU 2024/2881.