Viscosity and physical state of sucrose/ammonium sulfate/H2O droplets 

<p>To explore aerosol chemistry and climate change, information of the physical state of aerosol particles is essential. Herein, we measured viscosities of binary mixtures of sucrose/H₂O and ammonium sulfate (AS)/H₂O, and ternary mixtures of sucrose/AS/H₂O with different organic-to-inorganic dry mass ratios. For sucrose droplets, the viscosity gradually enhanced from ~4 &#215; 10^-1 to > ~1 &#215; 10⁸ Pa&#8231;s as the relative humidity (RH) decreased from ~81% to ~24%. This corresponds from liquid to semisolid or solid state. For AS droplets, the viscosity dramatically enhanced at ~ 50% RH upon dehydration; to be < 10² Pa&#8231;s for RH > ~50% (liquid state), and > ~1 &#215; 10¹² Pa&#8231;s for RH &#8804; ~50% (solid state). In case of the ternary mixtures, remarkable enhancement in viscosity was observed as the inorganic ratio increased at a given RH. All particles studied in this work were observed to exist as a liquid, semi-solid or solid depending on the organic-to-inorganic dry mass ratios and RH. Moreover, the measured viscosities of the binary and ternary mixtures were compared with the calculated viscosities using the Aerosol Inorganic&#8211;Organic Mixtures Functional groups Activity Coefficients Viscosity model (AIOMFAC-VISC) predictions with the Zdanovskii&#8211;Stokes&#8211;Robinson (ZSR)-style organic&#8211;inorganic mixing model. It showed excellent model&#8211;measurement agreement. The result will be discussed.</p>