Particle measurement programme (PMP) light-duty inter-laboratory exercise: comparison of different particle number measurement systems

The particle measurement programme (PMP) used a particle measurement system (reference system (RS)) to quantify the particle number emissions of several vehicles. The RS was circulated around several laboratories to represent an internal standard. During the exercise dilution factors, losses and volatile removal efficiencies of the RS were regularly checked. In parallel with the RS, some labs employed their own particle measurement systems (lab systems (LS)) to determine the emissions of the same test vehicles. Comparisons between results from the RS and the LS showed that several different instruments were capable of measuring particle number emissions to within +/- 15% across an emission range of four orders of magnitude. Real-time emission patterns also correlated well in most cases. However, larger differences were observed when dilution factors and losses were not accurately determined and subjected to correction. Equivalence between measurement systems can be achieved once calibration and validation procedures are standardized for both manufacturers and users.