AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Practical Implementation of a New Coincidence Correction Technique
AARON COLLINS, William Dick, Francisco Romay, Lin Li, MSP Corporation
Abstract Number: 133 Working Group: Instrumentation and Methods
Abstract With urban and roadway aerosol concentrations considerably exceeding 20,000 particles/cm^3, it can be a challenge to accurately measure the total particle number concentration using a single-particle counter. A common counter used for ultra-fine particle measurement, the condensation particle counter (CPC), typically has an upper concentration limit of 10^4 to 10^5 particles/cm^3 in the single-particle counting mode. This upper limit is the result of a systematic reduction in counts caused by coincidence.
In this work we introduce a new coincidence correction technique to solve for the theoretical CPC counting rate. Modeling the system as a Poisson process results in a mathematical equation for coincidence that cannot be solved analytically in closed form. Using the Lambert W function to solve this equation allows for real-time correction, as well as post-measurement correction, of CPC count data for coincidence. There is, however, a clearly defined limit to the maximum amount of correction possible because the resulting solution is double-valued.
An experimental verification of this technique was performed using count data collected from MSP 1110, MSP 1120 and TSI 3785 CPCs over their respective valid ranges of correctable concentration. This paper explores the practical limitations of the coincidence correction method as well as issues associated with high concentration measurements. Additionally, correction of CPC count data from the literature demonstrates that this is a suitable method for post-correction of previous experimental data.