American Association for Aerosol Research - Abstract Submission

AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA

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Application of a Drift tube Ion Mobility Spectrometer (DTIMS) for Aerosol Particle Size Distribution and Vapor Uptake Measurements

DEREK OBERREIT, Peter McMurry, Christopher Hogan Jr., University of Minnesota

     Abstract Number: 49
     Working Group: Instrumentation and Methods

Abstract
Described in this presentation, we have developed a prototype drift tube ion mobility spectrometer (DTIMS) which provides modest to high resolution measurements of aerosol particle electrical mobility distributions. This device differs from traditional drift tube devices in that it is able to sample pre-charged aerosol particles and has sufficient sensitivity to be used at the concentration levels typically found in ambient aerosols. Laboratory tests show that the resolving power of the device approaches 10 and that it is able to obtain size distribution measurements in less than 5 seconds. The measurement speed and resolution of the device make it an ideal candidate for investigating vapor uptake by small aerosol particles, particularly those formed during new particle formation events in the atmosphere. Traditionally, such uptake measurements have been performed with two differential mobility analyzers in tandem. However, due to poor transmission efficiency in these systems along with degrading resolving power with increasing particle mobility, the measurements have been limited to particle sizes greater than 5 nm. Measurements of water vapor uptake by hygroscopic aerosol particles using the DTIMS in tandem with a DMA have been made under laboratory and field conditions for particle diameters ranging from 3nm to 7nm. The results show the degree of water vapor uptake has a strong dependence on size and composition of the particles and is dependent on the water activity of a saturated solution of the particle material. Finally, we demonstrate that through the use of non-linear electric fields in the DTIMS drift region, either instrument resolution or transmission can be optimized.