A large proportion of the total number of particles emitted from direct injection engines are below 23 nm and although the EUaims to regulate those emissions and impose limits for new light duty vehicles, this is not yet possible due to the absence ofaccurate quantification methods, especially under real driving conditions. The main reason for this is the absence ofadequate knowledge regarding the nature of sub-23 nm particles from different engine/fuel combinations under differentoperating conditions. SUREAL-23 aims to overcome such barriers by introducing novel measurement technology forconcentration/size/composition measurements. The recently established supercontinuum laser technology will be coupled tophotoacoustic analysis and will also be employed for photoelectric ionization aerosol charging to achieve real-time,composition size-specific analysis of the particles. In parallel, state of the art aerosol measurement techniques will beadvanced for better compatibility with sub-23 nm exhaust particles as well as on-board use. The developed instrumentationwill assess sub-23 nm particle emissions from both Diesel and GDI vehicles accounting for effects of the fuel, lubricants,aftertreatment and driving conditions for existing and near-future vehicle configurations. The most suitable concepts will bedeveloped for PN-PEMS applications and evaluated accordingly. The project will provide measurement technologies that willcomplement and extend established particle measurement protocols, sustaining the extensive investments that have alreadybeen made by industry and regulation authorities. The project will deliver systematic characterization of sub 23-nm particlesto facilitate future particle emission regulations as well as to assess any potential trade-off between advances in ICEtechnology towards increased efficiency and emissions. The consortium consists of European and US organisations, whichare leaders in the field of aerosol and particle technology.