Particle measurement programme : volatile particle remover calibration round robin : final report

A dual ejector system with an intermediate Evaporating Tube was circulated at 11 laboratories to measure the Particle Concentration Reduction Factors (PCRF) at 30, 50 and 100 nm (as required by the legislation). In addition to this "Golden" Volatile Particle Remover (GVPR), a PALAS DNP 3000 graphite spark generator (Golden Aerosol Generator - GAG) and a TSI 3790 Condensation Particle Counter (Golden CPC - GCPC), were also circulated to compare the performance of the different aerosol generators (including CAST, sodium chloride and palladium) and CPCs employed at each laboratory. The study highlighted the importance of controlling and accounting for the pressures in the calibration setup. It also highlighted the difficulties associated with the measurement of the size distribution of the polydisperse aerosols produced by the generators that due to the high number concentrations are prone to significant coagulation. The study also provided evidence that the pre-treatment of sodium-chloride and CAST particles employed in most laboratories is not sufficient, and can lead to inaccuracies in the PCRF measurements at 30 nm if a CPC with a 50% counting efficiency at 23 nm is employed. No significant linearity issues were identified in the 15 in total CPCs that were cross-checked against the GCPC. However, a change of the operating temperature of TSI 3790 CPCs to reduce the cut-off size can lead to significant linearity issues for some units, and therefore such modifications must be accompanied by linearity checks.