Emission characterization of particle number as well as particle mass from three diesel passenger cars equipped with diesel particulate filter (DPF),diesel oxidation catalyst (DOC) and exhaust gas recirculation (EGR) under the vehicle driving cycles and regulatory cycle.Total particle number emissions (PNEs) decreased gradually during speed-up of vehicle from 17.3 to 97.3 km/hr.As the average vehicle speed increases,the size-segregated peak of particle number concentration shifts to smaller size ranges of particles.The correlation analysis with various particulate components such as particle number concentration (PNC),ultrafine particle number concentration (UFPNC) and particulate matter (PM) mass was conducted to compare gaseous compounds (CO,CO2,HC and NOx).The UFPNC and PM were not only emitted highly in Seoul during severe traffic jam conditions,but also have good correlation with hydrocarbons and NOx influencing high potential on secondary aerosol generation.The effect of the dilution temperature on total PNC under the New European Driving Cycle (NEDC),was slightly higher than the dilution ratio.In addition,the nuclei mode (Dp:≤13 nm) was confirmed to be more sensitive to the dilution temperature rather than other particle size ranges.Comparison with particle composition between vehicle speed cycles and regulatory cycle showed that sulfate was slightly increased at regulatory cycle,while other components were relatively similar.During cold start test,semivolatile nucleation particles were increased due to effect of cold environment.Research on particle formation dependent on dilution conditions of diesel passenger cars under the NEDC is important to verify impact on vehicular traffic and secondary aerosol formation in Seoul.