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 PM_2.5 mass measurement. Above this particle diameter, the detection efficiency gradually decreased and reached 50% at about 10 μm.

Copyright 2012 American Association for Aerosol Research

Acknowledgments

Publication of this article does not imply recommendation or endorsement of any commercial products by the National Institute of Advanced Industrial Science and Technology (AIST).The work related to the SCAR was supported by the project “MESTAN—Traceable measurement of nanoparticles” funded by Tekes—the Finnish Funding Agency for Technology and Innovation, Dekati Ltd., Ecocat Oy, and Gasmet Technologies Oy, and also by the Cluster for Energy and Environment (CLEEN Ltd., MMEA, WP 4.5.1). The authors truly acknowledge Mr. Richard Högström and Dr. Martti Heinonen from Mikes—Centre for Metrology and Accreditation (Finland) for providing traceable, high-quality instrumentation for the measurements. The work with the Inkjet Aerosol Generator in this study was supported by the Environment Research and Technology Development Fund (RF-1001) of the Ministry of the Environment, Japan. The authors would like to thank Ms. Emiko Ohnuma for her assistance in carrying out the measurements.

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Notes

Note that the derivation and uncertainty evaluation of the CPC detection efficiency from 10-repetition measurements in regular CPC calibrations at AIST (Wang et al. 2010) differ from the procedure presented in Section 3. In the regular calibration at AIST, the ratios of the CPC concentration to the FCAE concentration for each repetition were averaged to calculate the mean CPC efficiency. If the particle generation operated in a stable manner during the 10 repetitions, the two methods would result in very similar efficiency and uncertainty values. The method applied in this article has the advantage of revealing differences in evaluated uncertainties between SCAR and the AIST primary NCS, which will be discussed in Section 4.