Comprehensive particulate matter characterization study from Brake wear due to brake temperature under real-world driving test

Recent research indicates that brake wear from EURO VI vehicles is a primary contributor to non-exhaust Particulate Matter (PM) emissions. As brake temperature significantly influences friction mechanisms, it remains a critical factor in brake pad design. This study investigates the impact of brake temperature—specifically 'cold' (< 130°C) and 'hot' (> 130°C) conditions—on brake wear PM characteristics under real-world driving conditions. Using a sedan equipped with semi-metallic brake pads and an on-board sampling system, PM samples were collected and analyzed for mass concentration, chemical composition, and morphology via Light Scattering Laser Photometry, IC/OC analysis, and SEM-EDS. Braking conditions were categorized into 'hot' and 'cold' using a threshold of 130°C, the point at which PM emissions significantly escalate. This threshold, however, remains sensitive to vehicle specifications and driving cycle conditions. Results showed that hot braking emitted 6–8 times more PM than cold braking, with PM₁ constituting approximately 64% of total emissions. While both conditions shared chemical signatures of oxygen, carbon (primarily organic), and nitrogen from binders and reinforcements, hot braking triggered the release of additional metallic elements such as Fe, Si, Al, Mg, Zn, and Pt. The presence of Pt and Zn specifically points to increased wear from the brake disc. Furthermore, SEM analysis revealed a morphological shift: particles from cold braking were predominantly smooth and spherical, whereas those from hot braking exhibited rougher surfaces due to metal deposition. These findings suggest a critical temperature threshold that alters the underlying particle generation mechanisms.