Cooperative Interactions of Marine Macromolecules at the Air-Water Interface
EMSL Project ID
48281
Abstract
Sea spray aerosol (SSA) particles formed from bubbles bursting at the ocean surface contain a large fraction of organic matter. The presence of this organic matter is driven by the adsorption of surface-active materials onto bubble films.We have recently developed a parameterization that predicts the enrichment of surfactants in ocean bubble films and subsequent transfer into the atmospheric aerosol. This model uses the classical Langmuir isotherm to calculate the adsorption behavior of model compounds. One of the central assumptions underpinning the Langmuir isotherm is a lack of interaction between molecules at the surface. However, evidence suggests that cooperative adsorption of surfactants, soluble non-surfactants and ions may substantially modify the amount and nature of material that adsorbs to ocean bubbles and thereby enters the atmospheric aerosol.
We will test this hypothesis by performing a series of experiments at EMSL's High Resolution Broadband Vibrational Sum Frequency Generation (HR-BB-VSFG) facility. These experiments will investigate interactions in stearic acid-chitosan and cholesterol-stearic acid mixtures at a planar air-water interface. Additionally, we will investigate the sensitivity of these interactions to changes in pH, including differences between the acidic pH frequently used in studies of organic surfactants at the air-water interface, and the slightly alkaline pH typical of ocean conditions.
VSFG is uniquely suited to this problem because it selectively probes molecules at interfaces, providing information on molecular orientation. EMSL's unique facility provides unsurpassed spectral resolution, which is required to differentiate complex organic molecules at the surface that have similar elemental composition.
Supplementing the SFG experiments, we will use a miniature Wilhelmy Plate/Langmuir Trough assembly, recently constructed at Montana State University, to measure the equilibrium adsorption characteristics of the surfactants and surface energetics of heterogeneous monolayer films, and to control the interface's surface pressure during SFG experiments. Furthermore, a liquid chromatograph at EMSL will be used to analyze changes in bulk solution content as a function of monolayer film formation. Relationships between thermodynamic properties (measured with the Langmuir Trough) and molecular structure (measured with HR-BB-VSFG) will provide unprecedented insight into interactions between relevant marine species co-adsorbed to the aqueous vapor interface.
Complementing the laboratory investigation, numerical simulations of molecular dynamics in NWChem will be used to interpret and supplement the laboratory investigation. These simulations will be used to aid understanding of the mechanisms of cooperative adsorption, and to explore the sensitivity of molecular interactions to temperatures from 0 degrees C to 40 degrees C, the temperature range of most of the ocean surface.
Finally, results from these experiments will be incorporated into ongoing development of a parameterization of SSA composition for use in regional and global atmospheric models developed within PNNL's Atmospheric Sciences and Global Change Division, and ocean models developed within Los Alamos National Laboratory's Climate, Ocean and Sea Ice Modeling (COSIM) group. These models form a critical component of the nationwide Earth System Modeling effort of the Department of Energy (DOE-ESM). The laboratory results obtained in this project will enable an improved representation of variations in atmospheric SSA composition with geographic location and season, with impacts for cloud radiative forcing and thereby for simulations of global climate.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2014-10-01
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Burrows SM, EA Gobrogge, L Fu, KA Link, S Elliott, H Wang, and RA Walker. 2016. "OCEANFILMS-2: Representing Coadsorption of Saccharides in Marine Flms and Potential Impacts on Modeled Marine Aerosol Chemistry." Geophysical Research Letters 43(15):8306-8313. doi:10. 1002/2016GL069070
Link, KA. Cooperative adsorption in model sea spray aerosols with vibrational sum frequency generation. Pacific Conference on Spectroscopy and Dynamics, San Diego, CA, January 26, 2018.
Link, KA. Cooperative adsorption in model sea spray aerosols with vibrational sum frequency generation. Tohoku Universitys Chemistry Summer School, Sendai, Japan, August 22, 2017.
OCEANFILMS: Modelling organic enrichment in submicron sea spray aerosol from ocean surface films. Invited keynote presentation at the workshop ``The Ocean Surface Microlayer and Biogeochemical Feedbacks in the Earth System, Kiel, Germany, July 2015.
Susannah Burrows, OCEANFILMS: A process model for the organic enrichment of sea spray particles. American Chemical Society Annual Meeting, symposium on the Physical Chemistry of Complex Environmental Interfaces, San Diego, California, March 2016.