Aerosols play an important role in our atmosphere by scattering and absorbing solar radiation, serving as cloud condensation nuclei (CCN), acting as substrates for chemical reactions, as well as affecting air quality and human health. The hygroscopicity of aerosol is characteristic of its composition, and the compositions of aerosols globally are diverse and still being elucidated. The hygroscopic behavior of aerosol particles governs their size, viscosity, phase morphology, diffusional and reaction rates, and optical properties. A linear quadrupole electrodynamic balance (LQ-EDB) is used to levitate and analyze aerosol particles. The LQ-EDB is a contactless approach that allows particles to be analyzed free of surface interactions encountered in other methods. Mie spectroscopy is used for time-resolved determination of the sizes and refractive indices of studied particles and their responses to changes in relative humidity (RH). Measurements of RH-dependent processes such as hygroscopic growth, deliquescence, efflorescence, and phase separations require accurate knowledge of the in-situ RH, which is determined through the hygroscopic response of a probe particle. Two particles of different composition are simultaneously trapped (a probe NaCl or LiCl particle, and a sample particle) and the size response of the probe is used to determine the RH. The hygroscopic growth properties of model chemical systems using atmospherically relevant compounds will be explored. Of particular interest is the hygroscopic behavior of 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.

Dual-droplet approach for measuring the hygroscopicity and phase morphology of aqueous aerosol in linear quadrupole electrodynamic balance (LQ-EDB)

ACS Spring 2022

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