10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A New Tandem Differential Mobility Analyzer Inversion Routine That Allows Sampling of the Entire Size Distribution in Hygroscopicity Experiments
CHRISTOPHER OXFORD, Brent Williams, Washington University in St. Louis
Abstract Number: 1485 Working Group: Instrumentation
Abstract Tandem Differential Mobility Analyzers (TDMAs) can be used to determine growth factors of aerosols in high relative humidity (90%) environments. Previous TDMA inversion routines assume that the all particles measured by the TDMA are singly charged1,2. This assumption is valid when sampling at diameters larger than the mean of the log-normal size distribution (μ)3. If particles smaller than μ are sampled, the selected aerosol population can be dominated by multi-charged particles. This selection could lead investigators to improper conclusions.
In high growth factor experiments, the total TDMA instrument response can be manipulated by multi-charged particles. For hygroscopicity experiments, the final diameter of multiply-charged particles has a different mobility than their singly charged counterparts. The difference in each population’s mobility will alter the total measured TDMA response. This alteration is exacerbated when sampling diameters are smaller than μ in high growth factor experiments. μ during chamber studies can often exceed 150 nm, and the upper measurement limit of many TDMAs prevent determination of the final diameter of high growth particles larger than a dry diameter of 200 nm. To sample diameters smaller than μ, the size distribution must be considered during inversion.
We created a hygroscopicity inversion routine that includes the original size distribution as an input. We calculate the number of multi-charged particles and assume that all particles sampled have the same growth factor distribution. This inversion routine improves interpretation of TDMA hygroscopicity results and allows analysis of particles across the entire size distribution.
[1] Stolzenburg, M., McMurry, P.H. (University of Minnesota, Department of Mechanical Engineering, 1988). [2] Gysel, M., McFiggans, G. B. & Coe, H. Inversion of tandem differential mobility analyser (TDMA) measurements. Journal of Aerosol Science 40, 134-151, doi:DOI 10.1016/j.jaerosci.2008.07.013 (2009). [3] Rader, D. J. & Mcmurry, P. H. Application of the Tandem Differential Mobility Analyzer to Studies of Droplet Growth or Evaporation. Journal of Aerosol Science 17, 771-787 (1986).