Ion-molecule interactions enable unexpected phase transitions in organic-inorganic aerosol.

Atmospheric aerosol particles are commonly complex, aqueous organic-inorganic mixtures, and accurately predicting the properties of these particles is essential for air quality and climate projections. The prevailing assumption is that aqueous organic-inorganic aerosols exist predominately with liquid properties and that the hygroscopic inorganic fraction lowers aerosol viscosity relative to the organic fraction alone. Here, in contrast to those assumptions, we demonstrate that increasing inorganic fraction can increase aerosol viscosity (relative to predictions) and enable a humidity-dependent gel phase transition through cooperative ion-molecule interactions that give rise to long-range networks of atmospherically relevant low-mass oxygenated organic molecules (180 to 310 Da) and divalent inorganic ions.

Dual-Balance Electrodynamic Trap as a Microanalytical Tool for Identifying Gel Transitions and Viscous Properties of Levitated Aerosol Particles.

The formation of gelatinous networks within an aerosol particle significantly alters the physicochemical properties of the aerosol material. Existing techniques for studying gel transitions rely on bulk rheometry, which is limited by contact with the sample, or microrheological techniques such as holographic optical tweezers, which rely on expensive equipment and high-powered lasers that can degrade light-absorbing aerosol. Here, we present a new technique to probe the microrheological characteristics of aerosol particles and explore gel formation under atmospheric conditions in a contactless environment without the need for high-power light sources.