AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Glass Forming Properties of Secondary Organic Aerosol and Surrogates Examined by Thin Film Dielectric Relaxation Spectroscopy
YUE ZHANG, Andrew Lambe, Timothy Onasch, Wen Xu, Lindsay Renbaum-Wolff, William Brooks, Wade Robinson, Manjula Canagaratna, Paul Kebabian, Andrew Freedman, Shachi Katira, David Chandler, Paul Davidovits, John Jayne, Douglas Worsnop, Charles Kolb, Boston College; Aerodyne Research, Inc.
Abstract Number: 403 Working Group: Aerosol Chemistry
Abstract Glass transitions from a liquid to semi-solid and solid phase state have important implications for the reactivity, growth, and cloud forming (cloud condensation nuclei and ice nucleation) capabilities of secondary organic aerosols (SOAs). The small size of SOA makes it challenging to measure glass transitions using conventional methods. This study examined the glass forming properties of various SOA surrogates and their tracers by measuring the dielectric behavior of their thin films on interdigitated electrodes (IDEs). Organic aerosol particles were deposited onto the IDE substrates using electrostatic precipitation and were observed to form uniform thin films. The thin films were then analyzed by dielectric spectroscopy, which provides dipole relaxation about the organic material, such as the motion of the molecules, as a function of temperature. This information was used to calculate the glass transition temperature of single compound surrogates for SOA, simple mixtures, and complex SOA generated in an oxidation flow reactor. Dielectric spectra were obtained as a function of various operating conditions, and the correlations between SOA chemical composition and glass forming properties were examined.