Stabilization of Low Solubility Brown Carbon at the Air-Water Interface by Stearic Acid

ANNABEL EDWARDS, Elizabeth Lyon, Denison University

     Abstract Number: 403
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
Our work is motivated by the stabilization of low aqueous solubility secondary brown carbon at the air-water interface by simple fatty acids. We use stearic acid and laboratory-produced brown carbon as model compounds to explore if interactions among organic components in aqueous aerosols affect surface composition and surface tension. We collect and resolubilize particulates synthesized from iron-catalyzed reactions in acidic guaiacol solution. We then spread dilute methanol solutions of polyguaiacol at the air-water interface. Pure polyguaiacol films are unstable upon surface area compression in a Langmuir-Blodgett trough. At dilute concentrations, polyguaiacol partitions into the water subphase and minimally impacts water's surface tension. Jointly depositing stearic acid and polyguaiacol on the water surface results in mixed films with distinct behavior. In comparison to pure stearic acid films, gas-liquid and liquid-solid film packing transitions occur in polyguaiacol-stearic acid mixed films at larger surface areas. Because mixed films show changes at larger surface areas, models that rely on fatty acid concentrations and packing alone likely underpredict the effect of surface tension lowering in more complex aqueous aerosol mixtures. After full compression of the mixed film, visual inspection suggests the formation of multilayer stearic acid – polyguaiacol structures that remain at the air-water interface. Ongoing work will investigate the surface stability, structure and composition of these multilayers. These preliminary results underscore the need to investigate the role of secondary products of biomass burning on surface composition in addition to bulk aerosol properties.