A bilateral comparison of particle number concentration standards via calibration of an optical particle counter for number concentration up to ∼1000 cm−3

The first bilateral comparison of particle number concentration (PNC) standards via calibrating the counting efficiency (CE) of an optical particle counter (OPC) at high concentration of 1000 cm-3 is reported. An OPC (GRIMM 11-D) has been used as the transfer standard between NMC and NMIJ, with its CE being calibrated using monodisperse polystyrene latex (PSL) particles around 0.3 µm by the Faraday Cup Aerosol Electrometers (FCAE) of both metrology institutes. The CE of the OPC has been evaluated for a series of increasing concentrations to determine the highest concentration level which is free from coincidence loss. The OPC was also calibrated at 0.5 µm using an inkjet aerosol generator (IAG) and FCAE to compare its CE at different concentration levels. We have analysed the CE’s stability at decreasing concentration levels from 1228 to 0.5 cm-3 to derive the evidence for the equivalence of CE at different concentration levels. The CE values of the OPC around 0.3 and 0.5 µm measured by two institutes have agreement within 1.5% (normalized error En