Environmental & Climate Sciences Department Seminar

"Improved Tandem Measurement Techniques for Gas Phase Nanoparticle Analysis"

Presented by Vivek Rawat, University of Minnesota

Wednesday, April 20, 2016, 11:00 am — Conference Room, Bldg 815E

Non-spherical, chemically inhomogeneous nanoparticles are encountered in a number of natural and engineered environments, including combustion systems, reactors used in gas-phase materials synthesis, and in ambient air. To better characterize these complex nanoparticles, tandem measurement techniques are well suited, in which analytes are characterized by two orthogonal properties (e.g. size and mass). Tandem measurement techniques have been applied in a number of situations; however, there are still a considerable number of fundamental developments needed to advance these approaches. Specifically, new instrument combinations (with existing instruments) and appropriate data inversion routines need to be developed to determine combined two-dimensional mass-size distribution functions, pure mass distribution and for mobility-mass analysis for sub 2-nm clusters (ions).

With this motivation, we first develop and apply a data inversion routine to determine the number based size-mass distribution function (two dimensional distribution) from tandem differential mobility analyzer-aerosol particle mass analyzer (DMA-APM) measurements, while correcting for multiple charging, instrument transfer functions and other system efficiencies. This two dimensional distribution can be used to calculate the number based size distribution or the mass based size distribution. We employ this technique to analyze various spherical and non-spherical nanoparticles and examine the validity of this approach by comparing the calculated size distribution functions and mass concentrations with direct measurements of these quantities. In a second study, we utilize a transversal modulation ion mobility spectrometer (TMIMS) coupled with a mass spectrometer (MS) to study vapor dopant induced mobility shifts of sub 2 nm ion clusters. Isopropanol vapor is introduced into the TMIMS, shifting the mobilities of ions to varying extents depending on ion surface chemistry, which provides an improved separa

Hosted by: Jian Wang

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