Ion-specific phase behaviors of gluconate aerosols regulated by alkali metal counter-cations: a supramolecular network stiffness perspective

Alkali cations govern the network stiffness of aerosols, thereby influencing phase transitions. • Na + yields a rigid matrix, delaying sulfate efflorescence to the hydration phase. • K + forms a looser matrix, exerting weaker inhibition on sulfate efflorescence. • Ion competition in mixtures facilitates early crystallization. The phase state of highly oxygenated organic aerosols influences their climate and multiphase chemical properties, yet the regulatory role of distinct alkali counter-cations on their supramolecular networks remains insufficiently constrained. We investigated the phase behavior and hygroscopicity of gluconate aerosols mixed with inorganic salts, utilizing macroscopic hygroscopic growth, in situ Raman spectroscopy, and dynamic rheology. We found that counter-cation identity closely correlates with network stiffness and phase-transition trajectories. Specifically, Na + likely promotes more compact ion–organic interactions, yielding a relatively rigid matrix (higher storage modulus) that can kinetically impede sulfate efflorescence. In sodium gluconate/ammonium sulfate mixtures, this resulted in no efflorescence during dehydration; instead, the particles effloresced at 40.1 % RH upon subsequent hydration. In contrast, K + appears less effective in forming compact network associations, leading to a lower-rigidity matrix, enhanced water uptake, and more accessible sulfate efflorescence during dehydration. Furthermore, competitive inter-ionic interactions in mixtures containing potassium gluconate, ammonium sulfate, and sodium sulfate can perturb the organic matrix, facilitating crystallization at a higher relative humidity of 57.1 %. These findings suggest that source-dependent cations can substantially modulate the equilibration kinetics of polyhydroxy aerosols, providing physical insights for improving aerosol phase-state parameterizations in atmospheric models. Download: Download high-res image (323KB) Download: Download full-size image