Targeted brake emissions investigations undertaken within the Department for Transport’s Non-Exhaust Emissions programme are described in this paper. The non-exhaust emissions study aimed to improve understanding of particulate mass and particle number emissions from friction braking, and to quantify the influence of component selection, vehicle technology, operating conditions, and emissions control measures. A brake enclosure and sampling methodology, developed in an earlier project phase, was refined to improve airflow control, reduce leakage, and minimise artefacts. The updated system incorporated MPEC (hot and cold), APC10, DMS500, and eFilter instruments, enabling simultaneous measurement of volatile and non-volatile PN10, plus PM2.5.
Nine brake pad formulations and two disc types were evaluated using a common C-segment platform during chassis dynamometer and on-road drive cycles, and under specific controlled braking events. Speed, deceleration and temperature effects on PM2.5 and PN10 emissions were investigated. The common platform testing included ICE, PHEV, and EV variants to capture test mass and regenerative braking influences, together with assessments of aged components.
Results showed clear, repeatable differences between pad formulations, with low dust/ceramic pads yielding the lowest PM2.5 and PN10 emissions. Disc type effects were minimal, while component ageing/conditioning reduced emissions and improved repeatability. Brake temperature and energy input dominated emissions behaviour: dynamic braking produced the highest emissions, these increasing with road speed and disc temperature. Regenerative braking reduced EV and PHEV PM2.5 versus ICE, but PN10 remained comparable due to the dominance of non-volatile PN emissions during friction braking events. Increased vehicle mass led to proportionally higher emissions.