Field Evaluation of a Community Condensation Particle Counter for Ultrafine Particle Monitoring

SUSANNE HERING, Arantzazu Eiguren-Fernandez, David Pariseau, Judith Chow, John Watson, Xiaoliang Wang, Aerosol Dynamics Inc.

     Abstract Number: 535
     Working Group: Instrumentation and Methods

Abstract
With the increasingly widespread monitoring of air pollutants at the community level, there is a growing need for accurate and reliable data at a reasonable cost. Especially challenging are measurements of ultrafine or nanometer sized particles, as these are too small to be detected directly by optical sensors. Reported here is the field evaluation of a new, community condensation particle counter (cCPC) that targets this community measurement need. It utilizes quasi-adiabatic expansion coupled to single particle counting to monitor particle number concentrations in the 5-2500 nm size range. An air sample is captured in a Nafion-walled cell, humidified at the cell temperature due to water transport across the Nafion membrane, and then temporarily cooled by rapid evacuation of the chamber to approximately 80% of the initial pressure. The expansion of the humidified air sample creates a region of supersaturation within the central region of the cell, leading to the condensational growth of the particles. The droplets formed are counted individually as they exit the cell, while the sample volume is determined from the concurrent measurement of the chamber pressure. This yields a 'first principles' measurement of ultrafine particle concentrations. The only parameters entering the derivation of the particle concentration are the total particle count, the change in pressure, and the physical volume of the cell. Laboratory evaluation with size-selected aerosol show the counting efficiency is above 50% at 5nm, and above 95% for particles larger than 30nm.

Reported here are results from the field evaluation of these new cCPCs. Three cCPCs were deployed over a four-month period, from November 2023 to March 2024, at the Reno4 air quality monitoring station. This site, located near downtown Reno, NV, is part of the U.S. EPA NCore Monitoring Network. A research-grade condensation particle counter (CPC, Model 200, Aerosol Dynamics Inc.) was used as a reference. The coefficient of variation among the three collocated cCPCs was 3%. Comparisons with the reference CPC yielded coefficients of determination R² >0.99, and the ratio of the mean cCPC to that of the reference CPC concentration ratios was 0.95–1.00. At the highest concentrations of ~40,000 particles/cm3, the cCPC data were 15% lower than the reference, an effect attributed to condensational heating. Additional field evaluations are planned for summer 2024, and results from these studies will also be presented.

This work was supported by NIH under Grant number R44-ES031458, and through in-kind support from Particles Plus Inc.