Brake and tire particles measured from on-road vehicles: Effects of vehicle mass and braking intensity

Abstract

Vehicle exhaust emissions have been decreasing due to stricter regulations and advancements in control strategies. However, non-exhaust emissions from brake and tire wear have not been extensively regulated in the past, and their relative contribution to particulate matter (PM) in urban areas is increasing. We examined the effect of a vehicle's mass and braking intensity on brake and tire particles based on on-road data collected from three different types of vehicles under real-world driving conditions. PM 2.5 and PM 10 concentrations and particle size distributions were measured near the center and rear of the right front wheel, respectively. During the braking, the highest peaks in brake PM 2.5 (520–4280 μg/m 3 ) and PM 10 (950–8420 μg/m 3 ) concentrations were observed from the heaviest vehicle, while the lowest peaks in brake PM 2.5 (250–2440 μg/m 3 ) and PM 10 (430–3890 μg/m 3 ) concentrations were observed from the lightest vehicle. Similarly, the observed peaks in tire PM 2.5 (340–4750 μg/m 3 ) and PM 10 (810–8290 μg/m 3 ) concentrations of the heaviest vehicle were shown to be the highest among the test vehicles, while the peaks in tire PM 2.5 (220–2150 μg/m 3 ) and PM 10 (370–3840 μg/m 3 ) concentrations of the lightest vehicle were lower than other vehicles. A statistically significant difference in the peak values of PM 2.5 and PM 10 concentrations was observed between the heaviest and lightest vehicles for both brake and tire particles. The braking deceleration rate was found to be an important factor in predicting the peaks in PM 2.5 and PM 10 concentrations during major braking events for all three test vehicles. Brake particles showed a unimodal mass size distribution with a mode diameter of 3–4 μm, while tire particles showed a slightly larger mode diameter of 4–5 μm. The finding of this study provides insight into the effects of driving conditions and vehicle mass on brake and tire emissions. • Brake and tire particles were measured from three vehicles tested on-road. • Heavier vehicles emit higher levels of brake and tire particles. • Heavy braking can lead to elevated brake and tire PM concentrations.