Nanoparticle emissions continue to catch the attention because of their adverse health effects and their impact on the environment. Internal combustion engines are the major source of particle emissions in urban areas. The legislation proposes a stronger restriction for both diesel and gasoline engines. In particular, the European particle measurement program (PMP) has introduced particle number regulation for both diesel and gasoline engines. Great efforts are then devoted to the reduction of the particle emissions; nonetheless, the mechanisms governing particle formation are still not fully understood, neither for diesel nor for gasoline engines. The aim of the paper is the experimental characterization of particles emitted from a Port Fuel Injection (PFI) gasoline engine in steady state operating conditions. In particular, the impact of engine control variables (i.e. injection time and spark advance) and emissions control technologies (i.e. exhaust gas recirculation-EGR) on particle size and number was deeply investigated. Moreover, the effect of the dilution conditions was also analyzed. The investigation was carried out at the exhaust of a 1242 cc PFI spark ignition (SI) engine. The engine test bench was equipped with a full-pass engine control system dSPACE MicroAutoBox and a scanning mobility particle sizer (SMPS) for particle counting and sizing. (C) 2013 Elsevier Ltd. All rights reserved.