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 SO4
2– 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.