Biological and Anthropogenic Influences on the Organic Composition of Coastal Sea Spray Aerosol

Abstract:

During periods of intense marine biological activity, the majority of submicron sea spray aerosols consist of a salty core coated by an organic exterior, which is supported by many previous observations. These surface organic compounds play an important role in regulating the cloud and ice formation properties of sea spray aerosols, yet a significant fraction of this organic coating remains uncharacterized. In a recent 2019 mesocosm experiment, SeaSCAPE [Sea Spray Chemistry and Particle Evolution], a facilitated phytoplankton bloom in coastal seawater was used to study various aspects of marine volatile gases, secondary marine aerosol, and primary sea spray aerosol. In this experiment, coastal water from the Scripps Pier was brought into an environmentally controlled 30-meter wave tank, where mechanically generated breaking waves generate realistic sea spray aerosols. Quartz fiber filters were used to collect submicron aerosol throughout the course of an 18-day phytoplankton bloom cycle. These filters were subsequently analyzed for organic composition using thermal desorption two-dimensional gas chromatography coupled with high resolution mass spectrometry. Results indicate significant transfer of known anthropogenic coastal contaminants, in particular benzothiazole, benphenone, and their related compounds, from the bulk water into the atmosphere. Common proxies for the organic content in marine aerosols, namely sugars, amino acids, and fatty acids, make up a significant fraction of organic sea spray aerosol coating. However, less commonly considered constituents, including halogenated and cyclic compounds of both biological and anthropogenic origin also make up a significant fraction. A speciated understanding of organic coating of sea spray aerosols, with complementary analyses of marine dissolved organic matter (m-DOM) and sea surface microlayer (SSML) organics, provide insights into how marine organics are transferred to the atmosphere, a key step in unraveling how aquatic pollution and biological activity in the ocean influence atmospheric chemistry and climate.