Evaluation of PM Emissions from Internal Combustion Engines, Electric and Plug-In Hybrid Vehicles by Using Emission Factors

To pursue the target of the “net-zero” emission by 2050 and to reduce the most harmful pollutant emissions from road traffic, more specifically of particulate matter (PM), the transportation sector is subject to significant changes. A transition from internal combustion engine passenger cars (ICEVs) to hybrid vehicles (HEVs) and battery-electric vehicles (BEVs) is taking place. This transition, however, must be carefully examined from different perspectives, as hybridization/electrification may not reduce the levels of PM and CO₂ as much as expected. In this work, exhaust and non-exhaust PM emissions of a vehicle powered with an internal combustion engine, and of the same vehicle in plug-in hybrid and electric configurations is carried out, by using the emission factors approach. The main objective is the evaluation of the impact of vehicle weight, of percentage of regenerative braking and of energy management strategy (for hybrid configuration), on tire, wear and road surface wear, which are the most important non-exhaust PM sources. In particular, as most of the studies focus on a comparison between ICEs and BEVs, the current analysis aims at evaluating if the plug-in hybrid configuration, which is half-way between ICE and BEV, can overcome the limitations of electrification and of ICEs in terms of PM emissions. Results for gasoline engine show that a weight increase of 31% and 40% for the hybrid and electric configurations, respectively, with respect to the ICE version, contributes to increase the total PM₁₀ of about 16% and PM_2.5 of 9% for PHEV. For BEV, these values amount to 20% for PM₁₀ and to 4% for PM_2.5. Adoption of regenerative braking significantly contributes to counteract the effects of a higher weight, so that overall, for PHEV and BEV, total PM emissions are reduced with respect to the ICE versions. In particular, total PM emissions (both PM₁₀ and PM_2.5) are reduced of about 3% for PHEV and of 13% for BEV. For the diesel engine, where the weight difference between the ICE and PHEV and BEV versions are more limited (+8% for PHEV and +36% for BEV), higher beneficial effects related to regenerative braking are achieved, so that total PM emissions are reduced of 13% for PHEV and of 14% for BEV, with respect to ICE.