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Hygroscopic Growth and Water Transport in Mixed Organic-Inorganic Aerosol Particles
JAMES F. DAVIES, Jack Choczynski, Ravleen Kaur Kohli, Craig Sheldon, Chelsea Price, University of California, Riverside
Abstract Number: 90
Working Group: Aerosol Chemistry
Abstract
Recent measurements have revealed unique physical and chemical characteristics associated with mixtures of organic and inorganic molecules in aqueous aerosol particles [1,2]. Relative to their individual components, these mixtures may exhibit increased viscosity, slowed water transport, and phase transitions to liquid-liquid phase separated states and gels as a function of relative humidity (RH). Characterizing the RH response of these particles is important for exploring their role in atmospheric processes, such as cloud formation and heterogeneous reactions, and in disease transmission via respiratory aerosol.
In this work, we describe a new experimental approaching using a linear-quadrupole electrodynamic balance to levitate two aqueous particles [3]. Mie resonance spectroscopy is used to probe the size and refractive index of both particles, and to identify changes in phase state [4]. One particle acts as a fast-responding and accurate in-situ probe of the RH, while the response of the other particle is measured to elucidate its hygroscopic growth, condensed-phase diffusivity, and phase state as a function of RH. Through these measurements we will characterize the hygroscopic properties of mixtures of ammonium sulfate and organic molecules, such as citric acid, and directly measure both the rate of water diffusion and the aqueous concentration across the whole RH range. We will compare our results to predictions based on simple mixing rules and established thermodynamic models to validate their use in predicting the dynamics of mixed organic-inorganic particles.
[1] Wallace, B. J.; Price, C. L.; Davies, J. F.; Preston, T. C. Multicomponent Diffusion in Atmospheric Aerosol Particles. Environ. Sci.: Atmos. 2021, 1 (1), 45–55. https://doi.org/10.1039/D0EA00008F.
[2] Richards, D. S.; Trobaugh, K. L.; Hajek-Herrera, J.; Price, C. L.; Sheldon, C. S.; Davies, J. F.; Davis, R. D. Ion-Molecule Interactions Enable Unexpected Phase Transitions in Organic-Inorganic Aerosol. Science Advances 2020, 6 (47), eabb5643. https://doi.org/10.1126/sciadv.abb5643.
[3] Choczynski, J. M.; Kaur Kohli, R.; Sheldon, C. S.; Price, C. L.; Davies, J. F. A Dual-Droplet Approach for Measuring the Hygroscopicity of Aqueous Aerosol. Atmospheric Measurement Techniques Discussions 2021, 1–24. https://doi.org/10.5194/amt-2021-108.
[4] Price, C. L.; Bain, A.; Wallace, B. J.; Preston, T. C.; Davies, J. F. Simultaneous Retrieval of the Size and Refractive Index of Suspended Droplets in a Linear Quadrupole Electrodynamic Balance. J. Phys. Chem. A 2020, 124 (9), 1811–1820. https://doi.org/10.1021/acs.jpca.9b10748.