AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Water-Based Fast Integrated Mobility Spectrometer
STEVEN SPIELMAN, Chongai Kuang, Jian Wang, Susanne Hering, Aerosol Dynamics Inc.
Abstract Number: 350 Working Group: Instrumentation and Methods
Abstract The Fast Integrated Mobility Spectrometer (FIMS), developed by Kulkarni and Wang (2006), can capture an aerosol mobility distribution with 1-second time resolution. As with a conventional scanning mobility particle spectrometer, FIMS uses an electric field to separate particles by electrical mobility. However, rather than counting only those particles within a scanned mobility window, FIMS uses a camera to detect every particle, deducing the mobility by its position in the channel. The separator sheath flow is saturated with butanol vapor which condenses on the positioned particles in a cold condenser. The droplets are illuminated by a laser.
We have modified FIMS to use water as the growth condensate. Elimination of butanol will allow operation of FIMS in environments that cannot tolerate the solvent or its vapor. Also, butanol in the sheath flow can potentially affect the sizes of some particles before they are size-separated, whereas with the water method, the separator sheath air composition could match that of the sampled air.
We constructed a parallel-plate water condensation growth cell and incorporated it into the existing FIMS system. To prevent condensation on the optics, the dew point of the outflow was controlled by a new two-stage condenser design. The wicks forming the walls were wetted by a new water-feed system that eliminates the need for overflow barriers in the air channel, which would disrupt the laminar flow.
Stand-alone tests of the growth cell, operating at flow rate of 13 L/min with a 31 C temperature jump, showed ambient particles growing to become 5 to 6 micron droplets. Operating under similar conditions, the assembled water-FIMS system was tested with monodisperse and ambient aerosols. It measured concentration spectra with a size range of 30-100 nm.
P. Kulkarni, J. Wang, J. Aerosol Science 37 (2006) 1303-1325