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Evolution of the Molecular Composition and Physicochemical Properties of Sea Spray Aerosol in the Presence of OH Radicals
SAMANTHA KRUSE, Paul Tumminello, Allison Kawasaki, Kathryn Mayer, Jon Sauer, Christopher Cappa, Timothy Bertram, Vicki Grassian, Kimberly Prather, Jonathan Slade, University of California, San Diego
Abstract Number: 283
Working Group: Aerosol Chemistry
Abstract
Sea spray aerosol (SSA) is the largest contributor by mass of aerosols to the atmosphere annually, with an average yearly flux of 6.8 billion metric tons. SSA particles can act as cloud condensation nuclei and ice nuclei, thereby affecting the hydrological cycle. However, this is heavily dependent on their composition and hygroscopicity, which may change due to atmospheric oxidation processes. In this work, we report on the molecular-level composition and transformations of nascent SSA (nSSA) in the presence of OH radicals and marine-derived gases generated from a phytoplankton bloom in a laboratory mesocosm with controlled wave breaking. We utilize an extractive electrospray ionization high-resolution time-of-flight mass spectrometer to study the evolving molecular composition of the extractable components of nSSA. This method enables real-time analysis of aerosol molecular composition by soft ionization with no detectable interference from inorganic salts. Our results compare well to more established ESI mass spectrometry of nSSA collected onto filters. Our analysis shows an apparent correlation between the average molar mass of the organic components in nSSA with biological activity in the water, while the average O:C ratio does not change as significantly with age of the bloom. With increasing OH exposure in the presence of marine-derived gases, the average molar mass of nSSA first increases at low levels of oxidation due to functionalization, then decreases significantly due to molecular fragmentation and volatilization at higher OH exposures. In comparison with particle bounce factor measurements, we demonstrate that the decrease in the average molar mass of aged SSA correlates with an increase in liquid-like particles resulting from smaller, more water-soluble organics present in the SSA. This work contributes to better understanding of the fundamental processes affecting the age and growth of SSA following emission from the ocean surface.