Development of Measurement Methodology for Sub 23nm Particle Number (PN) Measurements

Abstract

The existing methodology laid down in UNECE regulations to measure vehicle exhaust particle number emission focuses on solid particle emissions (SPN) with a size above 23 nm. The PN emissions are counted with a Particle Number Counter (PNC) having 50% detection efficiency at 23 nm (PN23) after removal of volatile particles in a volatile particle remover (VPR). However, for various vehicle and engine types, notable PN levels are detected in the sub-23 nm particle size range. European Commission announced that sub-23 nm particles will be included in the next regulatory step. The technical development of the measurement method for sub 23nm-range PN regulation is discussed at the UNECE coordinated Particle Measurement Program informal working group (PMP IWG). The current >23 nm PN measurement methodology was chosen as a basis of the sub 23nm-range PN measurement method because the current PN systems should be easily upgradeable. The main topics that were addressed were the counting efficiency of the PNC at 10 nm, the PNC calibration material (emery oil or soot-like), the requirements for the VPR volatile removal efficiency to avoid re-nucleation artefacts and the need of a catalytic stripper. The repeatability and reproducibility of the new sub-23 nm methodology was assessed with an interlaboratory exercise. As a result of the comprehensive work of the PMP group, a proposal of the sub 23nm PN measurement methodology was developed.