This study introduces the method to evaluate the counting efficiencies of optical particle counters ( OPCs), g, at particle diameter greater than 1 lm by using an inkjet aerosol generator ( IAG). This study demonstrates the evaluations at 5 and 10 lm in volume equivalent diameter. The chemical composition of the particles is either sodium chloride or lactose monohydrate. The aerosol flowrate of the IAG is set at 0.3 L/ min, and the aerosol is delivered to an OPC with sampling flowrate 6 L/ min ( Omron, ZN- PD50S). The mismatch of the flowrates is compensated for by adding particle- free air in a laminar flow chamber. In order to simulate the sampling of uniformly mixed aerosol from a real environment, the particles are delivered to different points over the inlet plane of the isokinetic probe attached to the OPC. Particle flux into the isokinetic probe is proportional to the gas- velocity into the probe; however, the true velocity distribution is usually unknown. It is assumed that the true velocity distribution is bounded by two flow models: the plug and parabolic flows. A set of delivery points are prepared to simulate the particle flux under each flow model. Experimental results show that the choice of flow model influences the value of g at 10 lm indicating g is potentially different from the true value since the true value can be evaluated only if the true velocity distribution is known. The potential bias in g is considered as a source of systematic error in our uncertainty analysis.
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