Quantifying the change of brake wear particulate matter emissions through powertrain electrification in passenger vehicles

William Hicks; David C Green; Sean Beevers

doi:10.1016/j.envpol.2023.122400

Quantifying the change of brake wear particulate matter emissions through powertrain electrification in passenger vehicles

Environ Pollut. 2023 Nov 1:336:122400. doi: 10.1016/j.envpol.2023.122400. Epub 2023 Aug 16.

Authors

William Hicks¹, David C Green², Sean Beevers²

Affiliations

¹ MRC Centre for Environment and Health, Environmental Research Group, Imperial College London, UK. Electronic address: w.hicks@imperial.ac.uk.
² MRC Centre for Environment and Health, Environmental Research Group, Imperial College London, UK; NIHR HPRU in Environmental Exposures and Health, Imperial College London, UK.

PMID: 37595730
DOI: 10.1016/j.envpol.2023.122400

Abstract

With vehicle fleets transitioning from internal combustion engines (ICE) to electric powertrains, we have used friction brake power simulations, for different vehicle classes and driving styles, to predict the impact of regenerative braking systems (RBS) on brake wear particulate matter emissions (PM₁₀ and PM_2.5). Under the same powertrain, subcompact (SC) vehicles were predicted to require between 38 and 68% less friction brake power than heavier sports utility vehicles (L-SUV). However, despite electric and hybrid vehicles being heavier than ICE vehicles, the results show that RBS would reduce brake wear by between 64 and 95%. The study highlights the effect of aggressive braking on the amount of friction brake power required, with electric powertrains more likely to require friction braking to perform short, but aggressive braking compared with longer, slower braking events. Brake wear reductions varied under different driving conditions, as the level of mitigation depends on the complex interaction of several variables, including: vehicle speed, deceleration rate, regenerative braking technology and vehicle mass. Urban brake wear emission factors for electric powertrains ranged from 3.9 to 5.5 mg PM₁₀/km and 1.5-2.1 mg PM_2.5/km, providing an average reduction in PM emission factors of 68%. Rural and motorway driving conditions had lower brake wear emission factors, with plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV) emitting negligible PM₁₀ and PM_2.5 brake wear. Although electric powertrain uptake, vehicle mileage driven and driving styles are dependent upon national policies and strategies, by 2035, we project that total UK brake wear PM emissions would reduce by up to 39% compared with 2020 levels. This analysis supports the transition towards electric and hybrid vehicle fleets to reduce brake wear emissions, however increases in tyre wear, road wear, and resuspension due to increased vehicle mass may offset these benefits.

Keywords: Brake wear; Electrification; Non-exhaust emissions; PM(10); PM(2.5).

MeSH terms

Air Pollutants* / analysis
Environmental Monitoring / methods
Motor Vehicles
Particulate Matter* / analysis
Vehicle Emissions / analysis

Substances

Particulate Matter
Air Pollutants
Vehicle Emissions