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Inter-comparison of Particle Wall Loss Among UCR Chambers and Caltech Chamber
CHEN LE, Don Collins, David R. Cocker III, University of California, Riverside
Abstract Number: 273
Working Group: Aerosol Physics
Abstract
Understanding particle wall loss mechanisms is critical in environmental chamber studies because accurate wall loss corrections minimize uncertainty in measured aerosol yield. The driving forces of particle wall loss are Brownian motion, gravitational settling and the Electrostatic effect (McMurry and Rader, 2007). Supported by a general comparison of reported particle wall loss patterns from several laboratories (McMurry and Rader, 2007; Nah et al., 2017; Charan et al., 2018; UC Davis, personal communication), it is found that chambers from different research groups have varied particle wall loss patterns as a function of particle size. The Electrostatic effect among the chambers is believed to vary significantly due to different physical chamber designs leading to sometimes extreme variations in the size-dependent wall-loss behaviors observed.
This study evaluates the particle wall loss characteristics in three typical types of chambers: i) CE-CERT’s collapsible chamber (EPA chamber) which holds a constant pressure, ii) Caltech’s suspended chamber with minimal volume change and iii) CE-CERT’s naturally suspending chamber (Mez chamber) where neither pressure nor volume is controlled. Separate wall-loss characterization experiments were conducted injecting monodisperse or poly-disperse ammonium sulfate particles and monitoring their size dependent concentration decay over several hours. Losses due to the electrostatic effect were observed to be greater in the CE-CERT EPA chamber than in the Caltech chamber. These findings are further supported by comparing the Caltech chamber with the CE-CERT Mez chamber, which has less contact with external materials and is, therefore, expected to have a reduced source of static charge. The acquired size-dependent wall loss pattern for the CE-CERT EPA chamber was applied to historical data, which was originally treated using an observed average particle size independent loss rate from each experiment, to evaluate the sensitivity from different wall-loss correction methods. Evaluation of the chamber and particle dynamics increases our understanding of differences observed between facilities. Mitigation strategies for particle wall loss within environmental chambers will be suggested.