The Observations of Phase Separation & Hygroscopicity in Binary Mixtures

NAHIN FERDOUSI, Kotiba A. Malek, Kanishk Gohil, Qishen Huang, Miriam Freedman, Akua Asa-Awuku, University of Maryland, College Park

     Abstract Number: 570
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Aerosol particles can modify the climate by influencing cloud droplets. Aqueous droplets can be composed of both inorganic salts and organic compounds of varying compositions, impacting their water uptake capabilities, also known as hygroscopicity. In this study, we investigated the hygroscopicity of inorganic salt, ammonium sulfate (AS) and organic, 2-methylglutaric acid (2-MGA), mixtures. AS/2-MGA compositions were varied by weight percentage and atomized; hygroscopicity was determined using a hygroscopicity tandem differential mobility analyzer (HTDMA),at a relative humidity of 89% ± 1.5%. Mixtures predominantly composed of AS, up to a 1:1 AS/2-MGA composition, demonstrated κ values close to pure AS at 0.57 ± 0.03. However, as solutions transitioned to being predominantly composed of 2-MGA, hygroscopicity dropped significantly. The results demonstrate non-ideal mixing and is consistent with previous studies that show phase separation behavior can occur for this binary mixture. Ammonium sulfate is prevalent on the surface of the droplet until mixtures become predominantly organic This study can help further enhance understanding of cloud-forming properties of complex aerosol mixtures containing organic and inorganic compounds including phase behaviors.