Enrichment and Chemical Transformations of Marine Organic Matter in Sea Spray Aerosol

Organic matter is enriched at the oceans surface and is further enriched in sea spray aerosol (SSA). This enrichment exhibits size-dependence, with submicronic SSA particles increasing in organic matter relative to salt with decreasing particle size by up to five orders of magnitude relative to seawater. Among the enriched species are long-chain fatty acids, alcohols, saccharides, and anthropogenic surfactants. Measurements of organic species across SSA, the sea-surface microlayer, and seawater during controlled laboratory studies and biologically-active mesocosm experiments reveal that the magnitude of this enrichment depends upon a molecules surface activity, the surrounding sample matrix, and the biological activity of the seawater. Compared to the sea-surface microlayer, enrichment increases in persistent whitecap foam, revealing that organic matter is further enriched as bubble films mature at the ocean surface. Chemical reactions alter the composition of organic matter in SSA through secondary marine aerosol formation and heterogeneous chemistry. These transformation processes were examined using oxidative flow reactors in the Sea Spray Chemistry and Particle Evolution (SeaSCAPE) experiment conducted within the NSF Center for Aerosol Impacts on Chemistry of the Environment. The molecular characterization of nascent and aged SSA indicated the presence of organosulfates that contain a sulfate ester functional group. Among these were alkyl sulfates, which are common anthropogenic surfactants that likely entered the ocean by run off and were enriched during SSA production due to their high surface activity. Functionalized organosulfates indicated that acidic sulfate contributed to the formation of low-volatility SOA products by aging biological molecules, such as unsaturated fatty acids and volatile organic compounds including monoterpenes. Together, these studies provide a deeper understanding of primary and secondary marine SSA composition, as well as the properties and processes that determine the extent of organic matter enrichment.