This study investigated the chemical characteristics of polycyclic aromatic hydrocarbons (PAHs) and soot particulates emitted from a gasoline direct injection (GDI) engine. The microcosmic morphology of the soot particulate and the correlations between PAH species and the primary carbon particles were studied during dynamometer testing of different engine operating conditions using our purpose-built sampling system. The obtained extracts of PAH samplings and soot samplings were analyzed qualitatively and quantitatively using gas chromatograph-mass spectrometry (GC-MS) and field-emission transmission electron microscopy (FE-TEM). The vapor-phase and particulate-bound PAHs exist in the GDI engine exhaust emissions. PAHs with two and three rings exist nearly entirely in the gas phase, whereas five or more fused rings are predominantly adsorbed on soot particles. The intermediate 4-ring PAHs exist in the two PAH phase. Naphthalene is the most abundant polyaromatic hydrocarbon that was detected in the exhaust vapor-phase PAHs, which was approximately three orders of magnitude higher than the PAHs in the particulate phase. PAHs and soot emissions could be significantly reduced by increasing the injection pressure and by introducing the exhaust gas into the cylinders. Particulate-bound PAHs A4-A6 were suitable for estimating soot emissions from GDI engines. Soot particles are formed by the agglomeration of the quasi-sphere primary carbon particles. Most of the primary carbon particles exhibit an onion-shell nanostructure, with less disordered and amorphous structures. (C) 2015 Elsevier Ltd. All rights reserved.