AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Hygroscopic Properties of Alkyl Aminium Sulfates at Low Relative Humidities (RH)
YANGXI CHU, Meike Sauerwein, Chak K. Chan, Hong Kong University of Science and Technology
Abstract Number: 312 Working Group: The Role of Water in Aerosol Chemistry
Abstract Alkyl aminium sulfates (AAS) can affect the physicochemical properties of atmospheric aerosols such as hygroscopicity. Previous laboratory experiments have shown that water contents in AAS bulk solutions are higher than in aqueous ammonium sulfate solution in the range of 60–95% RH. Furthermore, amine was found to evaporate from the solution during the preparation of AAS from the parent amine and sulfuric acid solutions. Here we report the hygroscopicities of deposited particles of four AAS at different aminium-to-sulfate mole ratios (A/S) in the range of <3–90% RH using air-flow cells coupled with in situ micro-Raman spectroscopy. Normalized areas of O–H stretching peaks in the Raman spectra were converted to water-to-solute mole ratios (WSR) at various RH. Amine evaporation was also observed and the exact A/S of sample particles or solutions were determined by ion chromatography. Mono-methylaminium sulfate (MMAS) and mono-ethylaminium sulfate (MEAS) particles were stable at A/S=2.0 but di-methylaminium sulfate (DMAS) and tri-methylaminium sulfate (TMAS) suffered from DMA and TMA evaporation and eventually equilibrated to A/S of 1.5 and 1.0, respectively. Besides, an approach to estimate the hygroscopicities of DMAS and TMAS particles at initial A/S larger than that of the stable compositions was presented. In the range of 60–95% RH, the WSR of all the studied AAS particles were consistent with a previous study based on experimental values and the extended Zdanovskii-Stokes-Robinson equation. In general, all the studied AAS were more hygroscopic than their corresponding ammonium counterparts within the studied RH range therefore they can enhance the water uptake of aerosols if they exist in appreciable amounts in the particle phase.