An investigation into brake wear particle emissions from various pad materials used in heavy-duty vehicles

Non-exhaust particulate emissions from brake and tyre wear have become a growing air-quality concern and are now regulated under EU emission standards. Brake system manufacturers are adapting their products to meet the new Euro 7 regulations aimed at reducing non-exhaust emissions from brake wear. While passenger vehicle brake emissions have been extensively studied, data for heavy-duty vehicles (HDVs) remain limited. This study addresses this gap by investigating brake wear emissions from three commercial HDV brake pad materials (P1, P2, P3) tested against a grey cast iron disc under low- and high-temperature sliding conditions using a pin-on-disc tribometer. Friction, wear, temperature, and particle emissions (PM 10 , PM 2.5 , PM 1 , and particle number concentration) were measured. Additionally, we analysed worn surfaces and collected particles using SEM/EDS and ICP-MS. At low temperature, the three pads showed comparable tribological and emission behaviour. At high temperatures, the pads responded differently. P1 was the most sensitive, shifting from the lowest to the highest wear and particle number emitter, with Cu- and Sn-enriched particles. P2 was the least sensitive but remained the highest PM emitter under both conditions, with the strongest enrichment in Zn and Sb at high temperature. P3 showed intermediate behaviour despite reaching the highest disc temperatures. Particle number followed wear, whereas particle mass did not, indicating that pad formulation governs the size and composition of emitted particles beyond wear quantity alone. The findings highlight the complex interplay among material properties, operating conditions, and emission behaviour, underlining the need for further research on brake emissions from HDVs.