Impact of vehicle electrification on brake wear particle (BWP) emissions under real-world driving conditions

Brake wear particle (BWP), a significant source of non-exhaust emissions, have gained increased regulatory attention with their inclusion in the Euro 7 standards. Regenerative braking in hybrid electric vehicles (HEVs) and pure battery electric vehicles (PEVs) can reduce BWP emissions, but real-world validation of its effectiveness and of the UN GTR No. 24 c-factor estimation method remains limited. We aimed to assess real-world BWP emission factors of internal combustion engine vehicle (ICEVs), HEVs, and PEVs, and evaluate the predictive accuracy of UN GTR No. 24 c-factors. On-road measurements of BWP emissions and friction braking energy were conducted across urban, rural, and motorway routes. Emission estimates using UN GTR No. 24 c-factors were compared to measured values. HEVs and PEVs showed BWP emission reductions of 61–82 % and 96–98 %, respectively, compared to ICEVs. The lowest regenerative braking rates and the highest BWP emissions were observed in urban driving, where braking frequency was highest. Conversely, rural and motorway conditions showed lower friction braking energy and proportionally lower BWP emissions. The application of UN GTR No. 24 c-factors provided reasonable estimates but tended to overestimate BWP emissions in PEVs and HEVs. Regenerative braking significantly reduces BWP emissions, with real-world reductions closely linked to decreased friction braking.