10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Hygroscopic Behaviours of Inorganic/Organic Mixtures Including Ammonium sulfate, Dicarboxylic Acid and Oligomer
HICHEM BOUZIDI, Andreas Zuend, Jakub Ondrácek, Jaroslav Schwarz, Vladimír Ždímal, Institute of Chemical Process Fundamentals of the CAS
Abstract Number: 806 Working Group: Aerosol Chemistry
Abstract Aerosol particles are an important atmospheric constituent, influencing global climate. The hygroscopic growth behaviour of aerosol particles is one of the important parameters controlling these climate effects. Atmospheric aerosol particles are generally complex mixtures of a diversity of inorganic constituents and organic compounds. In many regions, organic aerosol dominates the ambient aerosol mass. It is well established that high-molecular-weight organic compounds like oligomer with molecular masses ranging from 200 to 1600 gmol-1 [1], represent an important fraction in atmospheric aerosols, but their interactions with other inorganic/organic, and atmospheric water vapour are not well understood. Moreover, single particle measurements suggest that organic and inorganic constituents are internally mixed in particulate matter [2]. Therefore, Non-ideal interactions between the organic and inorganic aerosol fractions affect water uptake and solubility, may induce Liquid-liquid phase separation (LLPS) into an organic-rich and an aqueous electrolyte phase (phase separation), may affect efflorescence and deliquescence behaviour, and alter the gas/particle partitioning of semi-volatile compounds [3-4]. The presence or absence of LLPS in aqueous mixtures can be computed using a liquid-liquid equilibrium model [3].
Here, the hygroscopic properties of submicron particles under subsaturated relative humidity (RH), composed of ammonium sulfate, dicarboxylic acids including oxalic acid (OA), malonic acid (MA), and oligomer Poly(Ethylene-Glycol) (PEG-300 (-CH2OCH2-)n ) with various mixtures and mass ratios are investigated in a laboratory study using a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA). Those constituents correspond to materials found in the atmosphere in great abundance and, therefore, particles prepared in this study should mimic atmospheric mixed-phase aerosol particles.
The experimental data are compared with predictions from Zdanovskii-Stokes-Robinson (ZSR) mixing rule and Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients (AIOMFAC). In addition, particle-phase behaviour, including the prevalence of liquid–liquid phase separation (LLPS), was also modelled with AIOMFAC.
By comparison with HTDMA data, it was also found that the model was capable of capturing the behaviour of different mixtures of AS/PEG/dicarboxylic acids at high RH. Therefore, experimental data could be used for models to improve the estimation of interaction parameter for PEG group (CH2OCH2) with the carboxyl group (COOH).
The work was supported from ERDF "ACTRIS-CZ RI" (No. CZ.02.1.01/0.0/0.0/16_013/0001315).
Reference [1]: N.Hodas et al. (2016), Atmos. Chem. Phys., 16, 12767-12792. [2]: D. Murphy et al. (2006), J. Geophys. Res. Atmos., 111, D23S32. [3]: C. Marcolli et Krieger. (2006), J. Phys. Chem. A , 110, 1881-1893. [4]: A. Zuend et al.(2010), Atmos. Chem. Phys., 10, 7795-7820.