10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Using a Differential Mobility Analyzer and an Electrostatic Precipitator in Tandem for Determining Physicochemical Properties of Airborne Particles
SPYRIDON BEZANTAKOS, Maria Katergi, George Biskos, The Cyprus Institute, Nicosia, Cyprus
Abstract Number: 1245 Working Group: Instrumentation
Abstract Tandem differential mobility analyzer systems (TDMAs) are commonly employed for determining some of the key physicochemical properties of aerosols such as hygroscopicity and volatility. TDMAs are, however, bulky and costly, limiting their employability in cases that require high mobility and/or concurrent spatially distributed measurements. To address these limitations we have developed and tested a cylindrical precipitator which can be used as a replacement of the second DMA in TDMA systems. This approach, namely the tandem DMA-precipitator (TDMA-P), reduces significantly the bulkiness complexity and cost of a tandem system, since the precipitator is compact and does not require a sheath flow and consequently all the necessary peripherals for controlling it. Its classification zone (approx. 8cm in our design) consists of a central metallic rod, on which high voltage (HV) is applied. This rod is concentrically placed within a metallic cylinder that is always grounded. Penetration of charged particles through the cylindrical precipitator is dictated by the applied HV on its central electrode and the sample flow rate. Measurements of the relative penetration (i.e., the penetration of particles when the central electrode is at HV divided by their penetration when the central electrode is at 0V) of the sampled particles is related to their size at a specific and constant sample flow rate.
A tandem system consisting of a DMA (for selecting monodisperse particles), the cylindrical metallic precipitator and a condensation particle counter (CPC), was used for measuring the relative penetration of monodisperse ammonium sulfate (AS) particles, sizing from 10 to 400 nm through the precipitator at voltages varying from 5 to 1400 V, and at flow rates of 0.3 and 1.5 lpm. The measured relative penetration curves could be thereafter used for calculating the apparent electrical mobility diameter of an unknown aerosol population, providing information on its size. The performance of the TDMA-P was characterized using laboratory-generated ammonium sulfate particles, and the system is currently being deployed in the field.