Abstract View
Next Generation UCR Chamber Minimizes Effect of Electrostatics on Particle Wall-loss
CHEN LE, Qi Li, Don Collins, David R. Cocker III, University of California, Riverside
Abstract Number: 278
Working Group: Aerosol Physics
Abstract
Minimal particle wall loss along with accurate particle wall-loss correction is critical for an environmental chamber to be used to determine true aerosol yield. It has been concluded by experimental observations over the previous years that the UCR dual 90-m³ collapsible chambers particle wall-loss behavior was dominated by electrostatic deposition and was significant enough to overwhelm Brownian motion and gravitational settling, which are the other two main driving forces of particle wall-losses (Le et al., 2021; McMurry and Rader, 1985). Possible explanations for the existence of electrostatic effect were speculated to be: 1) the Teflon chamber walls rubbing against each other in the dual-chamber design due to our external mixing system (air handlers) being on during experiments; 2) the Teflon chamber walls rubbing the reflective aluminum surfaces of the chamber enclosure (Le et al., 2021). Understanding the shortcomings of our previous chamber design and operation, a next generation 120-m³ indoor chamber has been recently constructed at UCR to minimize the effect of electrostatics and to lower its particle wall-loss rate. An extra supporting structure for the Teflon chamber was implanted, physically separating the chamber wall and the metal groundings. In addition, a set of soft x-ray external enclosure neutralizing devices was deployed and tested (Hamamatsu Photonics).
A high-flow mono-dispersed particle injection system and a dual-SMPS measurement technique were utilized in the earlier study to characterize the size-dependent particle wall-loss behaviors in the previous generation environmental chamber (Le et al., 2021). In the current study, an identical experimental set-up was applied to the new generation of chamber with or without the using of the additional external neutralizing system. It was observed that the new construction design reduced particle wall loss rate and that the particle wall loss rate became more size dependent. Further neutralization of the chamber walls using the soft x-ray system further reduced particle wall loss rate and also further increased the dependence of particle wall loss rate on size. Particle wall loss correction used for aerosol yield measurement was reduced from 85-90% to ~20% for a 12-hour experiment. Evaluation of the potential side-effects of using these external neutralizing devices on aerosol generating processes during experiments provides guidance for the standard operation processes of the new chamber and provides insights for the future chamber designs.