Comparison of primary aerosol emission and secondary aerosol formation from gasoline direct injection and port fuel injection vehicles

Abstract. Gasoline vehicles significantly contribute to urban particulate matter (PM) pollution. Gasoline direct injection (GDI) engines, known for their higher fuel efficiency than that of port fuel injection (PFI) engines, have been increasingly employed in new gasoline vehicles. However, the impact of this trend on air quality is still poorly understood. Here, we investigated both primary emissions and secondary organic aerosol (SOA) formation from a GDI and a PFI vehicle under an urban-like driving condition, using combined approaches involving chassis dynamometer measurements and an environmental chamber simulation. The PFI vehicle emits slightly more volatile organic compounds, e.g., benzene and toluene, whereas the GDI vehicle emits more particulate components, e.g., total PM, elemental carbon, primary organic aerosols and polycyclic aromatic hydrocarbons. Strikingly, we found a much higher SOA production (by a factor of approximately 2.7) from the exhaust of the GDI vehicle than that of the PFI vehicle under the same conditions. More importantly, the higher SOA production found in the GDI vehicle exhaust occurs concurrently with lower concentrations of traditional SOA precursors, e.g., benzene and toluene, indicating a greater contribution of intermediate volatility organic compounds and semi-volatile organic compounds in the GDI vehicle exhaust to the SOA formation. Our results highlight the considerable potential contribution of GDI vehicles to urban air pollution in the future.