Measuring automotive exhaust particles down to 10 nanometres

Current measurement of particle number (PN) emissions from vehicles addresses the particle size range >23nm and has been successful in its aim of enforcing particle filters that virtually eliminate carbon emissions from exhaust emissions. There is minimal understanding, however, of how particles in the sub-23nm region can affect human health and the environment.


DownToTen seeks to enhance the current knowledge of those PN emissions in the size range down to 10nm, or just below. The project focus is on the measurement and emissions of new generations of direct injection gasoline and diesel engines under real world conditions. DownToTen is also considering gas engines, fuel, lubricant factors, and other influences on particle production.

The final objective of the project is a PN-PEMS (Particle Number – Portable Emissions Measurement System) demonstrator for highly effective determination of PN emissions from vehicles in the real world.

Customer Benefit

DownToTen aims to complete the fundamental research necessary to classify and regulate the particle emissions below ~23nm in size. Whilst other projects in the Horizon2020 framework are focusing on developing future combustion engine technologies that might generate <23nm particles, they can only do this effectively if the production mechanisms, chemistry, and measurement approaches for these particles are well understood.

DownToTen will help measure the emissions data and standardise the measurement process for this category of particle emissions across the industry, so that regulators, OEMs, and other manufacturers will have a set of comprehensive measurements and measurement tools to assist their developments.

Exhaust Emission Related Particle Types

DownToTen will also consider the formation of secondary particles in the atmosphere through using specialised accelerated ageing approaches. This will help to assess potential real-world air quality impacts of small particles.


DownToTen aims to assess the presence of particles and magnitude of particle numbers below the size-range that is currently legislated and assist the better understanding of exhaust particle impacts on air quality. The project will complement in-cylinder particle formation, particle filtration research, and the simulation of particle transport and their losses along the exhaust pipe and in the regulatory sampling system. This will allow regulators to link on-road certification measurements to lab-based ones.

Fundamentally, DownToTen will achieve the following:

  • Describe the nature and the characteristics of nanoparticles <23 nm
  • Develop and set up a synthetic aerosol bench and use it for fundamental studies at an instrument level
  • Carry forward favourable measurement techniques from the aerosol lab to chassis-dynamometer and real-world environments for further development.
  • Analyse possible sampling and sample conditioning configurations, and compare with reference methods.
  • Set-up an appropriate PN-PEMS demonstrator
  • Define the particles measured by the new methodology
  • Develop and propose an appropriate sampling and measurement method for the sub 23 nm for both Constant Volume Sampling (CVS) and Real Driving Emissions (RDE) methods
  • Modelling the particle transformation (tailpipe-out to the inlet of the measurement equipment).

Ricardo, specifically, is conducting preliminary testing in order to evaluate sampling conditions, measurement set-ups and appropriate test protocols. The evaluation will include both sample conditioning approaches (thermal and catalytic treatment, CVS vs. raw exhaust etc.) and measurement instruments of different principles and for different size ranges. The developmental equipment will be used to assess the presence of <23nm PN emissions from various vehicle technologies, primarily in CVS-diluted emissions, and indicate the magnitude of PN emissions identified. The findings will be used to guide the transition of the equipment from a lab-based low dilution prototype, to a higher-dilution raw-exhaust PN-PEMS. Additionally, modelling along the exhaust pipe, the sampling and dilution processes is being conducted for the understanding of the relationship between raw (tailpipe) and diluted (CVS) sampling. These data will be employed to understand the relationship between raw and diluted sampling, and the impact this will have on conformity factors between on-road and lab-based methods.

For more information about the project, visit:

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 724085