Gaseous Brake Wear Emissions from Heavy-Duty and Light-Duty Vehicles

A few studies have identified gaseous emissions from brake wear, yet their quantification so far remains limited. With the goal to quantify gases emitted from brake wear, this study utilizes a high-resolution proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) for measurements. Four commercially available brake pad materials were tested on a pin-on-disc tribometer against gray cast iron. The results reveal that emissions of volatile organic compounds (VOCs) strongly depend on braking intensity and the material composition of the brake pads, with light-duty brake pads emitting more gases compared to heavy-duty formulations under comparable braking conditions. Laboratory emission factors for total VOCs were estimated at around 2.20 to 19.20 mg km–1 vehicle–1 by upscaling pin-on-disc emissions to vehicle scale emissions, while more environmentally relevant emission factors were estimated at around 1.58 to 15.26 mg VOC km–1 vehicle–1 using measured VOC/PM10 ratios and published emission factors for primary particles. The chemical composition is dominated by oxidized VOCs and nitrogen-containing organics. Because urban areas can experience elevated brake wear emissions due to high traffic density, these findings highlight the need for further study to determine realistic emission factors and assess the contribution of brake wear gases to air pollution and human health.