Effect of particle charge on aerosol dynamics in Teflon environmental chambers

Abstract

The contribution of particle charge to the rate of particle wall deposition has been a persistent source of uncertainty for experiments performed in environmental chambers. 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 (k_e) and the average magnitude of the electric field (E), 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 k_e and E within a FEP Teflon chamber. To fully account for the effects of charge on particle dynamics in environmental chambers, studies of the effect of air ion concentration on the rate of particle coagulation over a typical 20 h experiment are performed and demonstrated, in general, that particle charge is negligible for characteristic chamber ion concentrations. While 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 19 m^3 Environmental Chamber, charge effects on the rate of particle-wall deposition are negligible.