Condensation Particle Counter Proportionality Calibration from 1 Particle·cm−3 to 104 Particles·cm−3

This article presents a process to calibrate a condensation particle counter (CPC) over the concentration range from 1 particle·cm −3 to 10 4 particles·cm −3 with traceability to SI units as realized by the National Institute of Standards and Technology (NIST). The process combines two independent steps: a proportionality assessment over the range of the CPC using a consistent diluter and an absolute calibration of the CPC with an aerosol electrometer (AE) at high concentrations. The proportionality assessment, which is the focus of the article, is analogous to the attenuation method for testing the proportionality of high-power laser detectors. This procedure tests the proportionality of one CPC by itself and does not require the use of a calibrated reference CPC. The primary calibration of the CPC with the AE at high concentrations allows for an absolute calibration with NIST traceability, resulting in a simple one-parameter correction to the measured CPC data. The proportionality test enables uncertainties to be assigned to the CPC over an extended range of concentration beyond the lower detection limit of the AE, thereby establishing measurement traceability for low concentrations. The relative expanded uncertainty of the CPC with a coverage factor of k = 2 is 2.8% over the range of about 1 particle·cm −3 to 10 4 particles·cm −3 .