Minimizing secondary pollutant formation through identification of most influential volatile emissions in gasoline exhausts: Impact of the vehicle powertrain technology

Abstract

Despite the growing share of hybrid vehicles in worldwide vehicle fleet, the impact of battery/engine switch on secondary pollutant precursors formation remains poorly understood. We herein identify the species to be removed primarily from the exhaust of hybrid vehicles to minimize secondary pollutants formation. Pollutants from a conventional (thermal) and a hybrid vehicle are herein evaluated in a chassis dynamometer bench by using two widely used driving cycles, WLTC and FTP75. Hybrid vehicle exhibits the lowest regulated emissions during all the different tests, except for NOx. The results reveal that low and cold start phases of the cycles contribute mainly to the ozone potential, although methane, butadiene and formaldehyde can be emitted at the tailpipe all along the driving cycle. We evidence for the first time a significant contribution of gas-phase reactions to butadiene and methane production inside the exhaust pipe, especially during warm restarts and accelerations. This study indicates that pollutant traps should target primarily monoaromatics which contribute typically to 40% of photochemical ozone creation and 50% to Secondary Organic Aerosols (SOA). However, the contribution of alkanes to ozone differs markedly for the hybrid vehicle, reflecting a different share of ozone production paths with respect to conventional vehicles.