AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Real-time Elemental Characterization of Polydisperse Aerosol Particles Using a DMA Coupled with an Inductively Coupled Plasma-Mass Spectrometer
VIVEK RAWAT, Thaseem Thajudeen, Christopher Hogan Jr., University of Minnesota
Abstract Number: 82 Working Group: Instrumentation and Methods
Abstract We have interfaced a differential mobility analyzer (DMA) with an Inductively Coupled Plasma- Mass Spectrometer (ICP-MS), and developed a corresponding “Elemental distribution function” inversion routine to determine the elemental composition of aerosol particles in near-real time. The measurement system consists of a Po-210 bipolar ion a source followed by a TSI long DMA operated with an open-loop Argon sheath flow coupled to both a condensation particle counter (CPC), and Perkin-Elmer Elan 6100 ICP-MS. With the ICP-MS calibrated, the ratio of ICP-MS signal to CPC measured number concentration yields the average mass of each element within DMA-selected particles. While this instrument combination has been utilized previously, its application to polydisperse, chemically complex aerosol particles has been hindered by the fact that the influence of multiply charged particles on ICP-MS signal has not been addressed. These effects are considerable, as the mass of a doubly charged particle of the same electrical mobility as a single charged particle, is significantly higher, and the ICP-MS measured signal intensity is proportional to sample particle mass flow rate. Therefore, without correcting for multiply charged particle influences, the average mass of each element within DMA selected particles cannot be linked directly to the chemical composition of particles at the selected “mobility” size. To this end, we utilize an inversion routine with the Twomey-Markowski method to obtain the actual elemental distribution function. The kernel function for the inversion includes the DMA transfer function, the steady-state bipolar charge distribution determined from a recently developed Brownian dynamics approach, the CPC transport efficiency, and the ICP-MS calibration curve. The DMA-ICP-MS and inversion routine have both been tested using atomizer produced cesium and rubidium iodide salt clusters. The extension of this instrument combination to chemically diverse aerosol particles is also discussed here.