10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Understanding the Selective Transfer of Carbohydrates from the Ocean to Sea Spray Aerosol
ELIAS HASENECZ, Hansol Lee, Alexei Tivanski, Elizabeth Stone, University of Iowa
Abstract Number: 390 Working Group: Aerosol Chemistry
Abstract The ocean is a globally important source of atmospheric aerosols whose composition and properties are both climate relevant and under-examined. These properties, such as radiative forcing and cloud condensation nuclei activity, are influenced by the diversity of chemicals found in ocean derived aerosol. Surface active species are enriched at the ocean surface in the sea surface microlayer (SSML) and are selectively transferred to sea spray aerosol (SSA) via bubble bursting. Among organic matter enriched in SSA are carbohydrates, or saccharides, that primarily originate from biological sources and can comprise a significant portion of SSA organic mass. The selective transfer of a chemical species is facilitated by their properties and surroundings—for example, carboxylic acids are selectively transferred due to increasing surface activity, which is illuminated by decreases in the surface tension of the water interface. Determining the physicochemical processes that drive selective transfer of saccharides will ultimately improve our understanding of SSA composition and resultant globally relevant properties.
In this study, SSAs were produced with granular glass frit bubblers to determine how increasing the number of saccharide monomer units affects their transfer from bulk seawater to SSA. Sub-surface (bulk), SSML and SSA samples were collected using a 5 stage cascade impactor and analyzed for saccharides and ions via high performance ion exchange chromatography with pulsed amperometry and conductivity detection, respectively. Enrichment factors (EF) were calculated by dividing the saccharide-to-sodium ratio in the SSML or SSA by this ratio in bulk solution. To correlate our chemical speciation measurements to changes in physicochemical properties, solution surface tension was also measured using a force tensiometer. Saccharide monomers through hexamers showed no enrichment (EF = 1), which is consistent with no change in surface tension (73.5 ± 0.3 mN/m) and confirms these species are neither surface active nor enriched in the SSML or SSA. However, alginate, an acidic polysaccharide prevalent in seaweed, shows small enrichment (1.6 ± 0.2) in the smallest aerosol size fraction (Nevertheless, the small polysaccharide enrichment shown here is one to five orders of magnitude smaller than studies containing natural seawater and/or microbes, suggesting surface activity alone is not the main driving force for saccharide transfer. For future studies, microgels that are ubiquitous in the ocean, saccharide-rich, positively buoyant and enriched in SSA, will be studied for their capability to selectively transfer saccharides to SSA.