Comparison of Three Particle Number Concentration Calibration Standards Through Calibration of a Single CPC in a Wide Particle Size Range

Abstract

We carried out a set of experiments to compare three particle number concentration standards (NCSs) by calibrating the same condensation particle counter (CPC) unit (Model 3772, TSI Inc., Shoreview, MN, USA). The standards were, in the order of operation size range, the primary NCS of the National Institute of Advanced Industrial Science and Technology (AIST, Japan), the Single Charged Aerosol Reference (SCAR) (Finland), and the Inkjet Aerosol Generator (IAG) of AIST. The results obtained with the 3 standards were found to agree at all overlapping particle sizes within the uncertainty limits. The relative expanded uncertainties varied between 0.6% and 2.6%, depending on the size and standard, while the overall agreement between the standards was within 0.5%. The observed consistency of the results is an important step toward establishing internationally coherent particle NCSs. As a result, the CPC 3772 was successfully calibrated in a particularly wide size range, approximately from 10 nm to 10 μm. The results indicate that the CPC can be considered as a practical tool for calibrating particle number concentration up to 1 μm. In general, the particle number concentration can be measured up to 2.5 μm without a significant decrease of the detection efficiency. By attaching an appropriate size-classifying inlet, the CPC could be used even for measuring the total number concentration for particles smaller than 2.5 μm, in parallel with the PM2.5 mass measurement. Above this particle diameter, the detection efficiency gradually decreased and reached 50% at about 10 μm.