Counting efficiency of a TSI environmental particle counter monitor model 3783

In this study, we present our investigations on the counting efficiency of a TSI Environmental Particle Counter (EPC) Monitor Model 3783. The operation of the instrument is based on activation of sampled particles by water condensation, thus making it essentially a water-based condensation particle counter (WCPC). The counting efficiency was measured and simulated using different temperature settings on the conditioner and the growth tube, as well as using hygroscopic and water-soluble ammonium sulfate and sodium chloride particles, and insoluble and hydrophobic silver particles. The parameter that best describes the performance of the instrument is the cut-off diameter, or the diameter where 50% of sampled particles are activated and detected. In this study, the cut-off diameter for silver particles varied from 5.2 nm to 7.4 nm as a function of the temperature difference between the conditioner and the growth tube. The chemical composition and, specifically, the water solubility of particle components, had a significant effect on the counting efficiency. Using the standard operation settings of the EPC, the cut-off diameter for silver particles was 6.4 nm, and for ammonium sulfate and sodium chloride particles it was 4.8 nm and 4.3 nm, respectively. The simulations made with Comsol Multiphysics 3.5a simulation software gave the silver-water contact angle in the range of 29-45° depending on the temperature difference between the conditioner and the growth tube, and the effective contact angles of 25° and 21° for ammonium sulfate and sodium chloride particles.