An Ultrafine, Water-Based Condensation Particle Counter and its Evaluation under Field Conditions

Abstract

An ultrafine, water-based condensation particle counter (U-WCPC, TSI Model 3786) has been compared to a butanol-based ultrafine counter (U-BCPC, TSI Model 3025) for measurement of atmospheric and freeway-tunnel aerosols. The U-WCPC utilizes a warm, wet-walled growth tube to activate and grow particles through water condensation in a laminar-flow. It has an aerosol sampling rate of 0.3 L/min, and a nominal detection limit near 3 nm. Several field comparisons were made to the butanol-based instrument with the same nominal detection limit. For measurements of size-selected aerosols with diameters of 5 nm and larger the two instruments generally agreed, with a mean response within 5%. At 3 nm particle size differences were observed, and these differences varied with the data set. Measurements of ambient aerosol in Boulder, Colorado showed higher counting efficiency at 3 nm with the U-BCPC, while in a California freeway tunnel the opposite trend was observed, with higher counting efficiencies at 3 nm observed by the U-WCPC. For direct measurement of atmospheric aerosols, the two types of instruments yielded equivalent concentrations, independent of particle number concentration.

Acknowledgments

The authors gratefully acknowledge the financial support of the Office of Science (BER), U.S. Department of Energy, grant DE-GF-02-05ER63997, the National Science Foundation Award No. ATM-0506674, and the California Air Resources Board ICAT program Contract No. 04-03. We extend special thanks to TSI Inc. for the loan of equipment, to Matthew J. Dunn of NCAR for assistance with the measurements in Colorado, and to Paul Ziemann of the University of California, and to Ken Docherty and Jose Jimenez of the University of Colorado for hosting the SOAR study.