Tandem differential mobility analyzer studies and aerosol volatility
"This thesis contains three main contributions: the derivation of a parameter which characterizes the performance of a Differential Mobility Analyzer (DMA) for diffusing particles; the first measurements of the transfer function for a specific type of cylindrical DMA used extensively at the University of Missouri-Rolla (UMR); and the application of a tandem DMA (TDMA) to characterize the performance of a thermal discriminator. Stolzenburg's DMA theory is employed to derive the universal diffusion parameter Γ which is the characteristic parameter for the deterioration of DMA resolution due to particle diffusion. For the first time, this new parameter Γ, allows the quantitative characterization of the regime for which diffusion effects are negligible in a universal sense, i.e. independent of DMA type and flow conditions. The transfer function of the UMR DMA is measured over a wide range of particle sizes and flow conditions. Comparison with Stolzenburg's DMA theory shows that the UMR DMA exhibits almost ideal performance for ß > 0.2 and Γ < 0.198 (non-diffusion regime), where ß is the ratio of sample and sheath flow rates. For ß < 0.2, additional broadening, possibly due to flow instabilities, limits the apparent half width of the transfer function to ßapp > 0.16. The thermal discriminator is a widely used device, which exploits differences in aerosol volatility to discriminate between particles of different chemical composition. The performance of this device is characterized and a method is developed for the measurement of the volatile volume fraction (ratio of volatile and total aerosol volume) of polydisperse aerosols with a thermal discriminator. For the first time, this method quantitatively includes effects due to both particle loss and partially volatile aerosols"--Abstract, page iii.
Missouri University of Science and Technology
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