Interfacial Enrichment of Lauric Acid Assisted by Long-Chain Fatty Acids at Sea Spray Aerosol Surfaces Intrigues Climate-Relevant Properties

MICKEY ROGERS, Abigail Dommer, Kimberly Carter-Fenk, Nicholas Wauer, Patiemma Rubio, Aakash Davasam, Heather Allen, Rommie Amaro, Pacific Northwest National Laboratory

     Abstract Number: 260
     Working Group: Aerosol Chemistry

Abstract
Surfactant monolayers at sea spray aerosol (SSA) surfaces regulate various atmospheric processes including gas transfer, cloud interactions, and radiative properties. Most experimental studies of SSA employ a simplified surfactant mixture of long-chain fatty acids (LCFAs) as a proxy for the sea surface microlayer (SSML) or SSA surface. However, medium-chain fatty acids (MCFAs) make up nearly 30% of the FA fraction in nascent SSA. Given that LCFA monolayers are easily disrupted upon the introduction of chemical heterogeneity (such as mixed chain lengths), simple FA proxies are unlikely to represent realistic SSA interfaces. Integrating experimental and computational techniques, we characterize the impact that partially-soluble MCFAs have on the properties of atmospherically-relevant LCFA mixtures. We explore the extent to which the MCFA lauric acid (LA) is surface stabilized by varying acidity, salinity, and monolayer composition. We also discuss the impacts of pH on LCFA-assisted LA retention, where the presence of LCFAs may shift the surface-adsorption equilibria of laurate—the conjugate base—towards higher surface activities. Molecular dynamic simulations suggest a mechanism for the enhanced surface retention of laurate. We conclude that increased FA heterogeneity at SSA surfaces promotes surface activity of soluble FA species, altering monolayer phase behavior and impacting climate-relevant atmospheric processes.