UC San Diego

Atmospheric aerosols are ubiquitous in the atmosphere and can impact climate by scattering or absorbing solar radiation and acting as cloud condensation nuclei (CCN). Sea spray aerosols (SSA) are a major component of primary aerosols given the large ocean coverage of the Earth’s surface. SSA contains a variety of organic species, many of which are surface active, present throughout the ocean that can alter the climate relevant properties of SSA. Therefore, it is crucial to investigate the behavior and properties of these marine relevant species under different environmental conditions.In this dissertation study, the stability of different surface-active organics and biological species, such as palmitic acid, nonanoic acid, other lipids, and proteins at the air/water interface in the presence of a chemically complex underlying bulk phase is investigated. These different organic species are prominent in marine environments and are present within the sea surface microlayer (SSML), the topmost layer of the ocean, and on the surface of SSA. By using surface sensitive techniques such as surface pressure measurements and Infrared Reflectance Absorbance Spectroscopy (IRRAS), we have elucidated that palmitic acid monolayers on air/saltwater interfaces become less stable in the presence of light and a photosensitizer. Similarly, based on surface pressure measurements, model calculations and computational simulation, a thermodynamic cycle for nonanoic acid and its conjugated base between the air/water interface and the bulk phase is established. Furthermore, upon interaction with lipase, negatively charged, neutral and zwitterionic lipid monolayers were found to become disordered as demonstrated by surface pressure measurements, IRRAS measurements, water evaporation measurements, and computational simulations. Moreover, lipase is shown to interact differently depending on the charge of the lipid monolayer. The morphology of fatty acid monolayers with and without the presence of lipopolysaccharide (LPS) was also observed using a Brewster Angle Microscopy (BAM). In addition to studying the stability of surfactants, we have also demonstrated that salt ions, pH and speciation can impact the optical properties and photochemistry of aqueous marine relevant light absorbing molecules, like pyruvic acid and benzoic acid, using Mass Spectrometry, NMR, UV-Vis spectroscopy, and theoretical simulations. Overall, these studies provide insights into environmental factors, such as sunlight and the presence of chemically complex bulk phases, on the marine relevant species that can have important atmospheric implications such as changing SSA reactivity, hygroscopicity and aerosol lifetimes. Furthermore, these detailed measurements coupled with simulations provide insights into the structure, dynamics and photochemistry properties of these important marine atmospherically relevant interfaces and bulk environments.