Calibration of Condensation Particle Counters for Legislated Vehicle Number Emission Measurements

Light duty vehicle emissions legislation requires calibration and validation of Condensation Particle Counters (CPCs). A workshop was organized at the European Commission's Joint Research Centre (JRC, Ispra, Italy) to study the effect of test aerosol materials (of their chemical composition) on CPC calibration results. The counting efficiencies of Combustion Aerosol STandard (CAST) particles at 23 nm (steep part of the counting efficiency curve) were found to be similar (0.53) to those of heavy duty diesel engine particles (0.57), the counting efficiencies of Emery oil were either similar (0.53) or higher (0.72), while those of tetracontane (C40H82) particles were much higher (0.86). However, tests performed at JRC after the workshop found much lower counting efficiencies for tetracontane particles (almost 0 at 23 nm) and variable results for NaCl (0.6 or lower for 23 nm) indicating the importance of the generation method and the thermal treatment of the generated aerosol. Measurement issues including calibration against an electrometer or a reference CPC, the effect of multiply charged particles on counting efficiencies, stability, repeatability, reproducibility and comparability of CPCs and electrometers of different manufacturers were also investigated.