10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Rapid Measurement of Sub-micrometer Aerosol Size Distribution Using a Fast Integrated Mobility Spectrometer
YANG WANG, Tamara Pinterich, Jian Wang, Brookhaven National Laboratory
Abstract Number: 137 Working Group: Instrumentation
Abstract Rapid measurement of sub-micrometer particle size distributions enables the characterization of aerosols with fast changing properties, and is often necessary for measurements onboard mobile platforms (e.g., research aircraft). Aerosol mobility size distribution is commonly measured by a scanning mobility particle sizer (SMPS), which relies on voltage scanning or stepping to classify particles of different sizes, and may take up to several minutes to obtain a complete size spectrum of aerosol particles. The recently developed fast integrated mobility spectrometer (FIMS) with enhanced dynamic size range classifies and detects particles from 10 to ~ 600 nm simultaneously, allowing sub-micrometer aerosol mobility size distributions to be captured at a time resolution of 1 second. The FIMS consists of a parallel plate mobility separator, a condenser, and a CCD camera. Inside the separator, an electric field separates charged particles based on their electrical mobilities. The spatially separated particles then pass through a condenser, where particles as small as 7 nm grow to above 1 μm through water or heptanol condensation. Finally, the grown particles are illuminated by a laser sheet and imaged onto a CCD array. The images provide both aerosol concentration and position, which directly relate to the aerosol size distribution.
In this study, we present a detailed data inversion routine for deriving aerosol size distributions from FIMS measurements. The inversion routine takes into consideration the FIMS transfer function, particle penetration efficiency in the FIMS, and multiple charging of aerosols. The accuracy of the FIMS measurement is demonstrated by comparing parallel FIMS and SMPS measurements of stable aerosols with a wide range of size spectrum shapes, including ambient aerosols and aerosols classified by a differential mobility analyzer (DMA). The FIMS and SMPS-derived size distributions agree well for all aerosols tested, showing differences within 5% in average particle size and total number concentration. In addition, total number concentrations of ambient aerosols were integrated from 1 Hz FIMS size distributions, and compared with those directly measured by a condensation particle counter (CPC) operated in parallel. The integrated and measured total particle concentrations agree well within 5%.