Measurement of Automotive Nonvolatile Particle Number Emissions within the European Legislative Framework: A Review

In 2011 the European Commission introduced a limit for non-volatile particle number (PN) emissions >23 nm from light-duty vehicles and the stated intent is to implement similar legislation for on-road heavy-duty engines at the next legislative stage. This paper reviews the recent literature regarding the operation-dependent emission of PN from light-duty vehicles and heavy-duty engines, and the measurement procedure used for regulatory purposes. \nThe repeatability of the PN method is of the order 5% and higher scatter of the results could easily be explained by the effect of the vehicles or the aftertreatment devices on the PN emissions (e.g. the fill state of the diesel particulate filters). Reproducibility remains an issue since it may exceed 30%. These high variability levels are mainly associated with calibration uncertainties of the PN instruments and drifts of the PN systems (especially those of the Particle Number Counters - PNCs) over time. \nCorrelation measurements between the full dilution tunnels (Constant Volume Samplers - CVS) and the proportional Partial Flow Dilution Systems (PFDS) showed agreement within 15% for the PN method down to 1x1011 p/kWh. At lower concentrations, the PN background of the CVS and/or the PFDS can result in larger inconsistencies.\nThe filter-based Particulate (matter) Mass (PM) and the PN emissions correlate well down to 1-2 mg/km for light-duty vehicles and also 2-3 mg/kWh for heavy-duty applications. The correlation improves when only elemental carbon mass is considered: It is relatively good down to 0.1-0.3 mg/km or mg/kWh; one order of magnitude below the PM levels.