Atmospheric aerosol are complex chemical mixtures with physiochemical properties dependent on their composition and morphology. Aerosol interact with incoming and outgoing solar radiation, act as substrates for chemical reactions, serve as nuclei for cloud droplet and ice particle formation, and impact air quality and human health. The hygroscopicity of aerosol is characteristic of its composition, and the hygroscopicity of an aerosol will determine its equilibrium size, viscosity, phase morphology, diffusion and reaction rates, and their optical properties. In this work, we use a linear quadrupole electrodynamic balance (LQ-EDB) to levitate single aerosol particles and probe their response to change in relative humidity. Mie spectroscopy is used for time-resolved determination of the size and refractive indices of particles and to determine the onset of phase separation. The objective of this work is to explore the connections between the hygroscopicity, phase morphology, and viscosity of model chemical systems containing atmospherically relevant compounds. Of particular interest are systems containing mixtures of inorganic salts (e.g. NaCl, (NH4)2SO4, and NH4NO3) and oxygenated organic compounds, such as carboxylic acids and sugar-alcohols. The chemical systems and methods discussed here will form the basis for the interpretation of more complex mixtures that better represent real aerosol.

Exploring the role of composition on the water uptake, viscosity, and phase morphology of mixed organic-inorganic aerosol

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