Variation of Particles in the Exhaust Plume of Gasoline Direct Injection Vehicles Based on a Multipoint Sampling System: Concentrations, Components, and Numbers

To grasp the primary particulate matter (PM) emissions and the corresponding secondary evolution of gasoline direct injection (GDI) vehicles, an innovative combination system of chassis dynamometer and multipoint sampling (up to 4.5 m) was constructed. The exhaust plumes in the area near the exhaust gas discharge outlet were successfully captured. There were intense secondary formation processes. With the increase of dilution factors, the PM mass concentrations and particle number emissions of secondary particles gradually exceeded that of primary particles. Component analysis explored that the formation of both secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) occurred in the exhaust plume and SIA played a leading role. Secondary inorganic ions contributed 65.15 +/- 7.94% to PM2.5 at 4.5 m under 60 km/h, of which NH4+ and SO42- comprised the largest proportion. The contribution of secondary organic carbons was 20.89 +/- 2.90% in this case. Particle size distribution displayed that an additional peak appeared in the nucleation mode with the aging of exhaust plume. The generation of nucleation and Aitken mode particles dominated the increase of particle number emissions. The study is expected to modify the overestimation of primary PM and bridge the gap between observed and modeled SOA.