16Gasoline vehicles greatly contribute importantly to urban particulate matter (PM) pollution. Gasoline direct 17 injection (GDI) engines, known as their higher fuel efficiency than that of port fuel injection (PFI) engines, have 18 been increasingly employed in new gasoline vehicles. However, the impact of this trend on air quality is still poorly 19 understood. Here, we investigated both primary emissions and secondary organic aerosol (SOA) formation from 20 GDI and PFI vehicles under urban-like condition, using combined approaches involving chassis dynamometer 21 measurement and environmental chamber simulation. The PFI vehicle emits slightly more volatile organic 22 compounds, e.g., benzene and toluene, whereas the GDI vehicle emits more particulate components, e.g., the total 23 PM, elemental carbon, primary organic aerosols and polycyclic aromatic hydrocarbons. Strikingly, a much higher 24 SOA production (by a factor of approximately 2.7) is found from the exhaust of the GDI vehicle than that of the 25 Atmos. Chem. Phys. Discuss., https://doi