The Influence of Internal Mixing of Organic Acids and Sea Salt on Size-Resolved Aerosol Refractive Index and Hygroscopicity

MIGUEL HILARIO, Eva-Lou Edwards, Cassidy Soloff, Kayla Preisler, Armin Sorooshian, University of Arizona

     Abstract Number: 94
     Working Group: Aerosol Chemistry

Abstract
Internal mixing of sea salt with organic acids impacts ambient aerosol optical and hygroscopic properties, which has implications for radiative effects, cloud droplet formation, and remote sensing. In this study, we used the Differential Aerosol Sizing and Hygroscopicity Spectrometer Probe (DASH-SP) to understand the influence of five organic acids (oxalic, malonic, succinic, glutaric, adipic) and methanesulfonic acid on the hygroscopic growth factor (GF) and the real part of the refractive index of sea salt. The analysis was performed on binary mixtures of NaCl and each acid for six dry particle sizes (200 – 1000 nm), a wide range of subsaturated relative humidities (20 – 95%), and five molar ratios (NaCl only, 2:3, 1:1, 3:2, acid only). The resulting GFs were greatly influenced by the particle dry size, with larger particles exhibiting higher GFs. Mixture properties such as the specific species mixed with NaCl and their molar ratio resulted in notable differences in the extent of particle growth upon deliquescence but did not significantly affect the relative humidity at which deliquescence occurred. This presentation will also discuss results of size-resolved real refractive index measurements in relation to composition. Understanding the impact of internal mixing on ambient aerosol hygroscopic and optical properties is critical for climate-sensitive regions such as the Arctic, which experiences periodic smoke transport rich in organic aerosol that can mix with the Arctic’s naturally abundant sea salt. These results also inform future sampling campaigns involving the DASH-SP such as the NASA Arctic Radiation-Cloud-Surface-Aerosol-Interaction Experiment (ARCSIX) occurring during May – August 2024.