This paper summarises targeted brake emissions investigations undertaken as part of the Department for Transport’s Non Exhaust Emissions programme. The work was carried out to improve understanding of particulate mass and particle number emissions from friction braking and to assess the influence of component selection, vehicle technology, operating conditions, and control measures on those emissions. Starting from a pre-developed brake enclosure and sampling system methodology, these were further refined to improve airflow management, reduce leakage, and minimise sampling artefacts. The updated system was integrated with a suite of particulate measurement instruments, including MPEC (hot and cold), APC10, DMS500, and eFilter, enabling simultaneous measurement of volatile and non volatile PN10 plus PM2.5.
A matrix of nine brake pad formulations and two disc types was tested on a common C segment vehicle platform across chassis dyno and on road cycles, together with controlled braking events designed to explore the effects of speed, deceleration rate, and brake temperature. Tests were repeated across ICE, PHEV, and EV variants to assess the influence of regenerative braking on friction brake emissions. Additional evaluations were undertaken with aged pad and disc sets. The results showed clear and repeatable differences between pad formulations, with the low dust/ceramic pads consistently achieving the lowest PM2.5 and PN10 levels. Disc type showed minimal influence within the tested range, whereas pad and disc ageing reduced emissions, improving stability and repeatability.
Brake temperature and energy input were found to be the primary factors affecting emission magnitude. Dynamic braking generated the highest PM2.5 and PN10 emissions across all vehicles, with emissions increasing with speed and temperature. Although regenerative braking substantially reduced PM2.5 for the PHEV and EV relative to the ICE baseline, PN10 emissions remained similar because the non volatile fraction arises during the friction braking events. Increases in vehicle test mass produced proportionally higher PM and PN emissions, consistent with increased brake work.
A brake mounted particle capture system (Tallano TAMIC) was also assessed, and this demonstrated meaningful reductions in PM2.5 and non volatile PN under continuous extraction. Overall, the results provide a comprehensive characterisation of brake wear emissions under controlled and representative driving conditions and project outputs inform both technology development and future regulatory approaches.