Thermodynamicversusnon-equilibrium stability of palmitic acid monolayers in calcium-enriched sea spray aerosol proxy systems

Rudd, Bethany A. Wellen; Vidalis, Andrew S.; Allen, Heather C.

doi:10.1039/c8cp01188e

Cited by 25 publications

(27 citation statements)

References 79 publications

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“…Additionally, fatty acid molecules such as OA have been found to form complex three-dimensional aggregates at the air–water interface under certain conditions, disrupting the two-dimensional monolayer structure . The high surface pressure and ionic strength used in this study may play a role in inhibiting the formation of these aggregates, thus stabilizing the monolayer throughout measurement …”

Section: Resultsmentioning

confidence: 86%

“…The inclusion of a secondary surfactant in a fatty acid monolayer has been shown to alter film packing structure, thermodynamic behavior, and monolayer stability . Despite the considerable impact monolayer composition can have on film structure and stability, single-component monolayer studies dominate the field. ,,,− ,,− To the author’s knowledge, no previous studies have investigated how monolayer composition impacts trace metal surface enrichment.…”

Section: Resultsmentioning

confidence: 99%

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Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces

Auvil

Vasquez

Allen

2021

ACS Earth Space Chem.

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Organic coatings on sea spray aerosol are largely comprised of fatty acids in addition to a vast array of other organic molecules including fatty alcohols. The seawater from which sea spray aerosol originates contains metal ions that interact with the organic coating at the air–seawater interface, resulting in transport of these metals into the atmosphere. Metal binding within single-substance monolayers on aqueous solutions has been previously studied. However, such binding events within mixed monolayers, especially those of ocean-relevant ratios, are not well-explored. Here, we examine four monolayer ratios of octadecanoic acid (stearic acid) to octadecanol (stearyl alcohol) on aqueous solutions with varying ZnCl2 concentrations and a seawater-relevant NaCl concentration of 0.465 M. Surface pressure–area (Π-A) isotherms and infrared reflection–absorption spectroscopy (IRRAS) are used to quantify the Zn2+–carboxylate surface binding affinities for each monolayer composition. We find that Zn2+–carboxylate binding is enhanced by ∼300 times at the surface when compared to the bulk solution. Addition of 10% octadecanol reduces the apparent surface binding affinity by over 50% from 3.6 × 103 to 1.4 × 103 M–1; this is significantly more than predicted from the slight reduction in viable 1:1 binding sites. Furthermore, 1:2 Zn2+–carboxylate binding is shown to only be viable for the 100 and 95% fatty acid film, whereas 1:1 binding is observed for all film ratios investigated.

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Section: Resultsmentioning

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces

Auvil

Vasquez

Allen

2021

ACS Earth Space Chem.

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“…Palmitic acid (pK a = 8.6-8.8 [63]) and glucuronic acid (pK a = 2.93 [64]) were chosen as proxies for the insoluble surfactant and soluble saccharide, respectively. It is important to note that the presence of salt ions in solution has been shown to interact with the carboxylic acid head group of fatty acids [65,66] which decreases the effective pK a . For this reason, both compounds used in this study were expected to form anions in solution at pH 8, and we hypothesized that divalent metal cations play a critical role, Atmosphere 2018, 9,476 4 of 17 by acting as an ionic bridge between insoluble and soluble organic molecules that is necessary for the transfer of soluble saccharides to the SSA.…”

Section: Methodsmentioning

confidence: 99%

The Impact of Divalent Cations on the Enrichment of Soluble Saccharides in Primary Sea Spray Aerosol

et al. 2018

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Field measurements have shown that sub-micrometer sea spray aerosol (SSA) is significantly enriched in organic material, of which a large fraction has been attributed to soluble saccharides. Existing mechanistic models of SSA production struggle to replicate the observed enhancement of soluble organic material. Here, we assess the role for divalent cation mediated co-adsorption of charged surfactants and saccharides in the enrichment of soluble organic material in SSA. Using measurements of particle supersaturated hygroscopicity, we calculate organic volume fractions for molecular mimics of SSA generated from a Marine Aerosol Reference Tank. Large enhancements in SSA organic volume fractions (Xorg > 0.2) were observed for 50 nm dry diameter (dp) particles in experiments where cooperative ionic interactions were favorable (e.g., palmitic acid, Mg2+, and glucuronic acid) at seawater total organic carbon concentrations (<1.15 mM C) and ocean pH. Significantly smaller SSA organic volume fractions (Xorg < 1.5 × 10−3) were derived from direct measurements of soluble saccharide concentrations in collected SSA with dry diameters <250 nm, suggesting that organic enrichment is strongly size dependent. The results presented here indicate that divalent cation mediated co-adsorption of soluble organics to insoluble surfactants at the ocean surface may contribute to the enrichment of soluble saccharides in SSA. The extent to which this mechanism explains the observed enhancement of saccharides in nascent SSA depends strongly on the concentration, speciation, and charge of surfactants and saccharides in the sea surface microlayer.

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“…47,75 Compared to a well-studied saturated long-chain fatty acid such as palmitic acid, we observe smaller peak intensity in the alkyl region and an ~10 cm -1 blue shift for the CH2-antisymmetric stretching mode. 25,76,77 The peak shift indicates there are more gauche conformers (more conformational disorder) of the alkyl chains in the algae spectrum compared to the organized fatty acid spectrum (SI, Figure S4). Moreover, we collect the IRRAS spectra with spolarized light, which probes vibrations lateral to the surface, further supporting the presence of surface disorder caused by the gauche conformations.…”

Section: Organic Partitioning To the Aqueous Surface Using Infrared Rmentioning

confidence: 99%

The Ocean’s Elevator: Evolution of the Air-Seawater Interface During a Small-Scale Algal Bloom

Rogers¹,

Neal²,

Saha³

et al. 2020

Preprint

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We explore in situ the surface properties of marine algal blooms of diatom monocultures by utilizing surface techniques of Brewster angle microscopy (BAM) imaging, vibrational sum frequency generation spectroscopy (SFG), and infrared reflection absorption spectroscopy (IRRAS). Over the course of the bloom, the marine algae produce surface-active biogenic molecules that temporally partition to the topmost interfacial layers and are selectively probed through surface imaging and spectroscopic measurements. BAM images show morphological structural changes and heterogeneity in the interfacial films with increasing density of surface-active biogenic molecules. Film thickness calculations quantified the average surface thickness over time. The image results reveal an ~5 nm thick surface region in the late stages of the bloom which correlates to typical sea surface nanolayer thicknesses. Our surface-specific SFG spectroscopy results show significant diminishing in the intensity of the dangling OH bond of surface water molecules consistent with organic molecules partitioning and replacing water at the air-seawater interface as the algal bloom progresses. Interestingly, we observe a new broad peak appear between 3500 cm-1 to 3600 cm-1 in the late stages of the bloom that is attributed to weak hydrogen bonding interactions of water to the surface-active biogenic matter. IRRAS confirms the presence of organic molecules at the surface as we observe increasing intensity of vibrational alkyl modes and the appearance of a proteinaceous amide band. Our work shows the often overlooked but vast potential of tracking changes in the interfacial regime of small-scale laboratory marine algal blooms. By coupling surface imaging and vibrational spectroscopies to complex, time-evolving, marine-relevant systems, we provide additional insight into unraveling the temporal complexity of sea spray aerosol compositions.

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Thermodynamicversusnon-equilibrium stability of palmitic acid monolayers in calcium-enriched sea spray aerosol proxy systems

Cited by 25 publications

References 79 publications

Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces

Zinc–Carboxylate Binding in Mixed Octadecanoic Acid and Octadecanol Monolayers on Proxy Seawater Solution Surfaces

The Impact of Divalent Cations on the Enrichment of Soluble Saccharides in Primary Sea Spray Aerosol

The Ocean’s Elevator: Evolution of the Air-Seawater Interface During a Small-Scale Algal Bloom

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