AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Photochemical Synthesis of Oligomeric Surfactants at the Ocean-Atmosphere Interface
REBECCA RAPF, Veronica Vaida, University of Colorado Boulder
Abstract Number: 558 Working Group: Aerosol Chemistry
Abstract The synthesis and reactivity of lipid-like molecules, which selectively partition to air-water interfaces, are of interest because of their potential contributions to the formation of secondary organic aerosol (SOA). Sunlight can drive photo-initiated chemistry of organic species at air-water interfaces, such as the sea-surface microlayer (SML). The SML contains high concentrations of amphiphilic organic molecules and, as the boundary layer between the ocean and atmosphere, connects processes at the sea surface with the atmosphere, including the generation of sea spray aerosol. The surface-active molecules found in the SML are often biological in origin, but we show that abiotic photochemical sources may be additional, important contributors. Here, we report on the robust photochemical mechanism by which a class of molecules, α-keto acids, reacts in aqueous solution to form organic radicals, which can recombine to form larger, more complex molecules. The oligomers formed from this photochemistry are amphiphiles, many of which have two or three alkyl chains. The photoproducts generated from these alkyl α-keto acids are more surface-active, and spontaneously self-assemble into monodisperse, spherical aggregates over the course of photolysis. The aqueous photochemistry of α-keto acids also provides radical initiators for the polymerization of non-photoactive molecules. Additionally, the effect of environmental reaction conditions, including oxygen content and solution pH, on the branching ratio of photochemical pathways will be discussed.