10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Characterization and Performance of the Caltech-ADI Portable Scanning Electrical Mobility Spectrometer
STAVROS AMANATIDIS, Huajun Mai, Changhyuk Kim, Richard Flagan, Steven Spielman, Gregory Lewis, Susanne Hering, California Institute of Technology
Abstract Number: 589 Working Group: Instrumentation
Abstract In this study, we present the detailed characterization and preliminary performance of the Caltech-ADI Scanning Electrical Mobility Spectrometer(SEMS), a newly developed and highly portable particle sizer designed primarily for planned atmospheric studies.
The instrument combines a novel, compact radial-flow Differential Mobility Analyzer (DMA) developed at Caltech, and a self-sustaining, motion-tolerant, water-based condensation particle counter (WCPC) designed by Aerosol Dynamics Inc. The system operates at low flowrates (0.6 – 0.9 L/min, and 0.3 L/min for sheath and aerosol flows, respectively), and provides particle sizing in the 10-500 nm range with resolving power on the order of 2-3; this resolution and these flow rates are sufficient to attain the precision and counting statistics required for atmospheric measurements. The reductions from traditional operating parameters in SEMS measurements has enabled dramatic reductions in the volume, weight, pumping, and power requirements (<5kg, <50W).
The transfer function of the radial-DMA has been determined over the operating range of sheath/aerosol flows and voltage using highly monodisperse NaCl particles in the 10-500nm range. Moreover, we have explored the effect of voltage scan time to determine the extent to which the transfer function is smeared due to the delay time distributions in the plumbing and WCPC. This is especially important for Unmanned Aerial Vehicles (UAV) measurement applications where fast scans (<30s) are required to attain good spatial resolution of the atmospheric aerosol properties. The results are compared to theoretical transfer functions, as well as simulated ones calculated using COMSOL 3D finite element modelling. Further, based on the experimentally determined transfer functions, we compare the Caltech-ADI SEMS to a benchtop Scanning Mobility Particle Sizer (SMPS) in measuring ambient aerosol particle size distributions.