Incorporating Droplet Growth in Simulating the Performance of Condensation Particle Counters
MARCUS BATISTA, Weixing Hao, Michel Attoui, Yang Wang,
University of Miami Abstract Number: 575
Working Group: Instrumentation and Methods
AbstractThe measurement of airborne particles with sizes below 3 nm is critical for the understanding of atmospheric nucleation and elucidating important particle synthesis mechanisms in the gas phase. Condensation particle counters (CPCs) have been widely used to measure the concentration of aerosols. However, due to the insufficient activation and condensational growth of particles, it is difficult for the CPC to measure particles below 3 nm. Methods have been proposed to increase the saturation ratio of the condensing vapor to promote the detection efficiency of sub-3 nm particles in the CPC, as shown by our recent work the influence of CPC operating conditions on particle activation efficiency (Hao et al., 2021).
Existing models simulating CPC particle detection focus primarily on particle activation. However, upon activation, vapor condensation affects the size of the grown droplets, which, in turn, influences their detection efficiency depending on the performance of the photodetector. Adjusting the detection efficiency is crucial to CPC detection limits and increases the chances of counting sub-3 nm particles. Here, using COMSOL and MATLAB, we introduced a probability function to incorporate droplet growth and simulate the size-dependent particle detection efficiency in a sheathed laminar flow CPC. We defined a critical detectable droplet size (D
d,c) that is associated with the performance of the photodetector. Our simulation demonstrates that the particle size corresponding to 50% detection efficiency (D
p,50) increases from 2.9 to 3.4 nm when Dd,c increases from 10 µm to 15 µm for the CPC 3025A design. Also, the detection efficiency is not sensitive to size when D
d,c is below 10 µm. Our results demonstrate that improved optical component design can enhance sub-3 nm particle detection. The influence of working fluids and temperature will be further discussed.
Hao et al., 2021, J. Aerosol Sci., 158: 105841.