10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Size-Resolved Physicochemical Properties of Organic Salt Nanoparticles
Sabrina Chee, Michael Lawler, Kelley Barsanti, Bryan Wong, JAMES SMITH, University of California, Irvine
Abstract Number: 1027 Working Group: Aerosol Chemistry
Abstract The volatility and hygroscopicity of atomized alkylaminium carboxylate particles have been previously studied in laboratory experiments. However, these properties have not been measured for nanoparticles formed from the acid-base reaction between gas-phase alkylaminium bases and organic acids. To study this, gas-phase acetic acid (CH3COOH) and dimethylamine (DMA) were introduced into a flow tube reactor to nucleate and grow nanoparticles (defined here as < 50 nm) under dry and elevated relative humidity conditions. A Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) was used to measure the size-resolved chemical composition of the nanoparticles formed, and volatility and hygroscopicity measurements were taken by using Volatility and Hygroscopicity Tandem Differential Mobility Analyzers (H- and V-TDMAs, respectively).
Acid:base ratio measurements from TDCIMS are presented. Size-resolved volatility measurements suggest that dimethylaminium acetate nanoparticles are less volatile than ammonium sulfate nanoparticles of comparable sizes and temperatures. These results are combined with thermodynamic modeling to explore the limits of bulk thermodynamic properties of acids and bases, such as pKa, in determining the size-dependent acid:base ratio of the dimethylaminium acetate nanoparticles formed. The implications of these modeling observations on alkylaminium carboxylate nanoparticle volatility are also discussed.