In this study,three GDI( gasoline direct injection) and one PFI( port fuel injection) light-duty gasoline vehicles were characterized for their particle emission( number concentration and size distributions). Two condensation particle counters( CPC) with different activation efficiencies( 50% cut off diameter) were used. It was found that the number concentration of particles emitted by GDI gasoline vehicle was approximately one order of magnitude higher than that from PFI gasoline vehicle. High emission of...