Traffic vehicles,many of which are powered by port fuel injection (PFI) engines,are major sources of particulate matter in the urban atmosphere.We studied particles from the emission of a commercial PFI-engine vehicle when it was running under the states of cold start,hot start,hot stabilized running,idle and acceleration,using a transmission electron microscope and an energy-dispersive X-ray detector.Results showed that the particles were mainly composed of organic,soot,and Ca-rich particles,with a small amount of S-rich and metal-containing particles,and displayed a unimodal size distribution with the peak at 600 nm.The emissions were highest under the cold start running state,followed by the hot start,hot stabilized,acceleration,and idle running states.Organic particles under the hot start and hot stabilized running states were higher than those of other running states.Soot particles were highest under the cold start running state.Under the idle running state,the relative number fraction of Ca-rich particles was high although their absolute number was low.These results indicate that PFI-engine vehicles emit substantial primary particles,which favor the formation of secondary aerosols via providing reaction sites and reaction catalysts,as well as supplying soot,organic,mineral and metal particles in the size range of the accumulation mode.In addition,the contents of Ca,P,and Zn in organic particles may serve as fingerprints for source apportionment of particles from PFI-engine vehicles.