The linearity of a condensation particle counter (CPC) (3760A, TSI, Inc.) for a monodisperse aerosol has been previously evaluated by comparison to an aerosol electrometer (AE) (Fletcher et al., 2009). The comparison of the CPC to the AE is an absolute calibration of the CPC with traceability to SI units. However, due to the limitations of the AE, accurate measurements of aerosol concentration cannot be performed below approximately 1000 particlescm-3 for typical CPCs. Furthermore the linear model fit to the AE CPC calibration data results in a statistically significant intercept (Fletcher et al., 2009), which causes discrepancies between the linear model and the CPC reading when extrapolated to lower concentrations. The presence of the intercept also introduces some reluctance to assume a proportional fit and extrapolate to zero. This creates problems for laboratories that require legal calibrations of CPCs at concentrations below 103 particlescm-3. In this work a proportional statistical model for the CPC concentration is proposed, and an experimental method to verify the model and quantify the uncertainty of the fit over a wide range of concentrations is described. Traceability to SI units is achieved by comparing the CPC to an AE at high concentrations, fixing the constant of proportionality. The result is a CPC calibrated with traceability to SI units and uncertainties assigned to concentrations from 1 particlecm-3 to 104 particlescm-3.
Citation: Journal of Aerosol Science
Pub Type: Journals
condensation particle counter calibration, proportionality calibration, traceability to SI units, diluter independent of concentration, sampling bias, flow calibration for condensation particle counter, wide concentration range, gas mask leakage, uncertainty analysis