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

Abstract

Abstract. Saccharides are a large portion 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 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. We showed that both soluble saccharides can promote the production of SSA particles, and the presence of trehalose could increase the SSA number concentration by 49.4 %. Conversely, the role of the insoluble fatty acid film on the seawater 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. A 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 was undertaken to examine the effects of aqueous subphase soluble saccharides with various concentrations on the phase behavior, structure, and ordering of insoluble lipid monolayers adsorbed at the air/water interface. We found that the adsorption of glucose and trehalose on the fatty acid monolayer led to the expansion of the mean molecular area. Saccharide–lipid interactions increased with increasing complexity of the saccharide in the order of glucose < trehalose. In a seawater solution, the effects of dissolved saccharides on the ordering and organization of fatty acid chains were muted. The enhancement of the carbonyl band to the low wavenumber region implied that soluble saccharides can form new hydrogen bonds with fatty acid molecules by displacing large amounts of water near the polar headgroups of fatty acids. 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.