Insoluble lipid film mediates the transfer of soluble saccharides from the sea to the atmosphere: the role of hydrogen bonding

Abstract. Saccharides are a large group of organic matter in sea spray aerosol (SSA). Although they can affect climate-related properties of SSA, the mechanism through which saccharides are transferred from bulk seawater to the ocean surface and ultimately into SSA is still debated. Here, the transfer of small soluble saccharides was validated and quantified using a controlled plunging jet sea spray aerosol generator to better understand the wide range of particle properties produced by natural seawater mixed with model organic species, glucose and trehalose. Data show that both soluble saccharides can promote the production of SSA particles. Conversely, the role of the insoluble fatty acid film on the surface greatly reduced the production of SSA. The resulting inorganic-organic mixed particles identified by the transmission electron microscope (TEM) showed typical core-shell morphology. Langmuir model was used to parameterize the adsorption and distribution of saccharide into SSA across the bubble surface, while infrared reflection-absorption spectroscopy (IRRAS) combined with Langmuir isotherms were undertaken to examine the effects of aqueous subphase soluble saccharides on the phase behavior, structure and ordering of insoluble lipid monolayers absorbed at the air/water interface. Changes in alkyl chains and headgroups structure of mixed fatty acid monolayers under different saccharide concentrations in aqueous phase were reported. In seawater solution, the effects of dissolved saccharides on the ordering and organization of fatty acid chains were muted. Hydrogen bond analysis implied that soluble saccharide molecules displaced a large amount of water near the fatty acid polar headgroups. Saccharide-lipid interactions increased with increasing complexity of the saccharide in the order glucose < trehalose. Our results indicate that the interaction between soluble saccharides and insoluble fatty acid molecules through hydrogen bonds is an important component of the sea-air transfer mechanism of saccharides.