The latest generation of internal combustion engines may emit significant levels of sub-23 nm particles. The main objective of the Horizon 2020 “DownToTen” project was to develop a robust methodology and provide policy recommendations towards the particle number (PN) emissions measurements in the sub-23 nm region. In order to achieve this target, a new portable exhaust particle sampling system (PEPS) was developed, being capable of measuring exhaust particles down to at least 10 nm under real-world conditions. The main design target was to build a system that is compatible with current PMP requirements and is characterized by minimized losses in the sub-23 nm region, high robustness against artefacts and high flexibility in terms of different PN modes investigation, i.e. non-volatile, volatile and secondary particles. This measurement setup was used for the evaluation of particle emissions from the latest technology engine and powertrain technologies (including vehicles from other Horizon 2020 projects), different fuel types, and a wide range of exhaust aftertreatment systems. Results revealed that in most cases (non-volatile), PN emissions down to 10 nm (SPN10) do not exceed the current SPN23 limit of 6×1011 p/km. However, there are some cases where SPN10 emissions exceeded the limit, although SPN23 were below that. An interesting finding was that even in the latter cases, the installation of a particle filter could significantly reduce PN emissions across a wide particle size range, fuels, and combustion technology. DownToTen results are being used to scientifically underpin the Euro 7/VII emission standard development in the EU. The method developed and the results obtained may be used to bring in the market clean and efficient vehicle technologies, improve engine and emission control performance with different fuels, and characterize size-fractionated particle chemistry to identify the formation mechanisms and control those in a targeted, cost-effective fashion.
