AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Caltech-ADI Portable Scanning Electrical Mobility Spectrometer
STAVROS AMANATIDIS, Changhyuk Kim, Richard Flagan, Steven Spielman, Gregory Lewis, Susanne Hering, California Institute of Technology
Abstract Number: 664 Working Group: Instrumentation and Methods
Abstract The Differential Mobility Analyzer (DMA) is arguably one of the most popular instruments for sub-micron aerosol particle size characterization, serving both as a tool for calibration and size distribution measurement. While DMAs have been traditionally used in the laboratory, there is an increasingly higher interest for size distribution measurements in field applications, where portability and low power consumption are essential.
In this study, we present a highly portable Scanning Electrical Mobility Spectrometer that combines a newly-developed classifier with a self-sustaining water condensation particle counter. The classifier is a compact and lightweight radial-flow DMA developed at Caltech that is designed to operate at low flowrates (on the order of 0.3 L/min aerosol flow) to provide particle sizing in the 10-500 nm range. It operates at relatively low resolution in order to minimize both instrument volume and pumping/power requirements, while enabling size distribution measurement with the precision required for planned atmospheric studies. Particle counting is done with 0.3 L/min, self-sustaining water-based condensation particle counter developed at Aerosol Dynamics that tolerates jostling and tipping, and provides efficient particle counting above 7 nm.
The new DMA differs substantially from prior designs. Because of the low flow operation, aerosol entrance designs such as the tangential inlet previously employed in radial DMAs are no longer efficient for fast and uniform aerosol distribution over the classification region. To overcome this challenge, a novel geometry has been designed and optimized by 3D finite element modelling of flow, electric field and particle trajectories using COMSOL Multiphysics. This design not only allows for uniform aerosol inlet but also results in a narrow residence time distribution within the classification region, facilitating fast voltage scanning operation. This DMA consists of only a few parts, occupies a volume of ~100 cm³ and weighs ~300 g. Higher resolution can be achieved by increasing the sheath flow, although this improved resolution leads to a reduction in the dynamic size range.