Revaluating the effects of regenerative braking on brake particle emissions using real-world braking characteristics

With vehicle electrification, regenerative braking (RB) is widely used to reduce brake emissions, although its effectiveness may vary across driving conditions. In this study, OBD data from two hybrid vehicles were extracted to reconstruct the real-world regenerative braking characteristics, which were subsequently reproduced on a brake dynamometer to quantify particle emissions with and without RB activation. Event-level analysis showed that PN emissions could increase during some braking events, possibly due to prior braking history. At the cycle level, PN emissions reached up to 1.2 × 10¹⁰ #/km under RDE cycles, approximately two orders of magnitude higher than under the WLTP-Brake cycle. RB reduced PN emissions by up to 98%, while PM₁₀ emissions and RB-related emission ratios varied substantially across cycles, with measured ratios ranging from 2% to 83%. Brake emission reduction was not proportional to friction braking energy reduction, and different particle-size fractions showed different reduction responses. These results suggest that braking energy alone may not fully represent the variability in RB-related emission reductions. The combined effects of vehicle electrification, i.e., increased vehicle mass and RB, were also assessed. Compared with size-equivalent gasoline vehicles, tested PHEVs emitted fewer brake particles than their gasoline counterparts, with a maximum reduction of 92%.