10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Effect of Particle Charge on Aerosol Dynamics in Teflon Environmental Chambers
SOPHIA CHARAN, Weimeng Kong, Richard Flagan, John Seinfeld, California Institute of Technology
Abstract Number: 379 Working Group: Aerosol Physics
Abstract Data from environmental chambers are instrumental to understanding the chemistry of the atmosphere and aerosol formation. A common experiment in atmospheric chambers involves determination of the secondary organic aerosol (SOA) yield, the ratio of the mass of aerosol formed to that of a precursor vapor reacted. Since measurements of the amount of aerosol formed in such an experiment can be carried out only on suspended particles, one must account for particles deposited onto the chamber walls throughout the duration of an experiment to obtain an accurate assessment of SOA yield. The effects of particle charge on the aerosol dynamics within a chamber have long been a source of concern.
Here, we provide a procedure for diagnosing the extent to which particle charge contributes to particle dynamics within an environmental chamber. By tracking the preferential deposition of positively charged particles; by comparing experiments carried out under standard, humid, and highly statically charged conditions; and by performing two-parameter optimizations for the chamber eddy-diffusion coefficient and the average magnitude of the electric field, the effect of charge on the rate of particle wall deposition is isolated. A combined experimental and computational method is also developed for determining values for the eddy-diffusion coefficient and the average magnitude of the electric field within a FEP Teflon chamber. To fully account for the effects of charge on particle dynamics, studies of the effect of air ion concentration on the rate of particle coagulation over a typical experiment are performed and demonstrate, in general, that particle charge is negligible for characteristic chamber ion concentrations. Whereas the effect of particle charge on aerosol dynamics in an environmental chamber must be addressed for each specific chamber, we demonstrate experimentally that for the Caltech Environmental Chamber, charge effects on the rate of particle wall deposition are negligible.