Sugar Hitches a Ride on Organic Sea Spray
Sticky organic molecules hop aboard oily floaters and may influence the amount of sunlight reflected by marine clouds.
Sugar molecules (saccharides) are normally soluble in water. Yet, somehow, they make their way into sea-spray particles that are tossed into the atmosphere by breaking waves, eventually helping to seed low-lying marine clouds. Researchers found that a “sticky” strategy binds sugar-like molecules to floating fatty molecules on the sea surface, shielding them from their soluble nature. These molecules are then flung into the atmosphere by bursting bubbles. This mechanism appears to explain the discrepancies between models that predict sea spray’s organic enrichment and actual measurements of sea spray aerosol composition.
By solving the mechanistic mystery by which sugars and other organic matter in sea spray aerosol are emitted to the atmosphere, scientists will be able to better simulate the impact of sea-spray particles on climate.
Scientists are interested in the composition of particles tossed into the atmosphere by sea spray, a large source of water vapor that helps to form clouds. Researchers who analyze sea spray samples collected onboard ships found that they contain a large amount of saccharides (sugar-like molecules). Because saccharides easily dissolve in water, however, researchers were unclear as to how these molecules could survive to enter the spray. In a recent study, scientists from Pacific Northwest National Laboratory (PNNL), Environmental Molecular Sciences Laboratory (EMSL), Montana State University, and Los Alamos National Laboratory (LANL) discovered the mechanism by which these molecules are incorporated into sea spray. The team conducted spectroscopy experiments at EMSL, a Department of Energy Office of Science user facility, and showed that saccharides can adsorb to the bottom of a layer of fatty acids that coat the water surface. This adsorption causes an increased amount of saccharide molecules to be present at the surface. When the layer of fatty acids was not present, the saccharide molecules dissolved in the water. Because sea spray aerosol forms from the surface layer of ocean water, this finding suggested that similar mechanisms could increase the amount of organic matter emitted in sea spray. The team also found that this “sticky” strategy not only shields these molecules from their soluble nature, it explains the discrepancies between models that predict sea spray’s organic enrichment and actual measurements of sea spray aerosol composition.
Using a model developed at PNNL and LANL, the researchers tested the sensitivity of modeled sea spray composition to this mechanism and found that if the molecules adsorb strongly enough, the amount of organic matter emitted in sea spray could be substantially increased. These organic matter emissions could potentially impact the amount of sunlight reflected by sea-spray seeded clouds, which has a cooling effect on Earth’s climate.
Pacific Northwest National Laboratory
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility; and the National Science Foundation.
Burrows, S. M., E. Gobrogge, L. Fu, K. Link, S. M. Elliott, H. Wang, and R. Walker. 2016. “OCEANFILMS-2: Representing Co-Adsorption of Saccharides in Marine Films and Potential Impacts on Modeled Marine Aerosol Chemistry,” Geophysical Research Letters 43(15), 8306-13. DOI: 10.1002/2016GL069070.