Developments at the AURA atmospheric simulation chamber to characterize chamber volume, air mixing, and charging

We describe three developments at the AURA atmospheric simulation chamber (made of Teflon and with a volume of ∼5 m³) aimed at an improved understanding of the physical conditions of the chamber to facilitate a better basis for comparisons between experimental data and results from numerical models. First, we demonstrate how the <i>volume</i> of the AURA chamber can be monitored by observing the position of a chamber wall using fixed laser distance sensors. The absolute volume calibration is obtained through a measurement of the relative humidity in the chamber during a controlled dilution experiment. Second, through a direct measurement, we characterize the occurrence, magnitude (∼0 – 80 kV/m), and decay time (∼10 – 20 h) of static <i>electric fields</i> inside the AURA chamber after charging. Further, we confirm directly that the AURA chamber can be significantly discharged and kept in a steady mode of charging with the addition of ion fans to the enclosure where the chamber is suspended. Third, we improve the <i>air mixing</i> capabilities at the AURA chamber by adding two mixing fans that allows efficient mixing of the chamber air within a few minutes. We characterize the effect of the electric field in the chamber and the rate of air mixing by direct measurements of the particle loss rate of injected polydisperse ammonium sulfate particles.