Instrumentation Challenges for Measuring Sub-23 nm Particle Number Emissions from Transportation Sources

Particle number exhaust emissions from diesel – and recently – from gasoline direct injection engines have already been regulated for particle sizes larger than 23 nm. However, interests have been extended to different applications and also to particles smaller than 23 nm. The UNECE Particle Measurement Programme (PMP) group is currently evaluating the feasibility to measure the sub-23 nm particle emissions by modifying the existing methodology. This paper focuses on the associated challenges of particle number measurement instruments in terms of sampling and diluting the emissions as well as of counting the sub-23 nm particles.