Calcium Bridging Drives Polysaccharide Co-Adsorption to a Proxy Sea Surface Microlayer

Saccharides comprise a significant mass fraction of organic carbon in sea spray aerosol (SSA), but the mechanisms through which saccharides are transferred from seawater to the ocean surface and eventually into SSA are unclear. It is hypothesized that saccharides cooperatively adsorb to other insoluble organic matter at the air/sea interface, known as the sea surface microlayer (SSML). Using a combination of surface-sensitive infrared reflection-absorption spectroscopy and all-atom molecular dynamics simulations, we demonstrate that the marine-relevant, anionic polysaccharide alginate co-adsorbs to an insoluble palmitic acid monolayer via divalent cationic bridging interactions. Ca2+ induces the greatest extent of alginate co-adsorption to the monolayer, evidenced by the ~30% increase in surface coverage, whereas Mg2+ only facilitates one-third the extent of co-adsorption at seawater-relevant cation concentrations due to its strong hydration propensity. Na+ cations alone do not facilitate alginate co-adsorption, and palmitic acid protonation hinders the formation of divalent cationic bridges between the palmitate and alginate carboxylate moieties. Alginate co-adsorption is largely confined to the interfacial region beneath the monolayer headgroups, so surface pressure, and thus monolayer surface coverage, only changes the amount of alginate co-adsorption by less than 5%. Our results provide physical and molecular characterization of a potentially significant polysaccharide enrichment mechanism within the SSML.

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Calcium bridging drives polysaccharide co-adsorption to a proxy sea surface microlayer

Physical Chemistry Chemical Physics ◽

10.1039/d1cp01407b ◽

2021 ◽

Author(s):

Kimberly Anne Carter-Fenk ◽

Abigal Dommer ◽

Michelle E. Fiamingo ◽

Jeongin Kim ◽

Rommie Amaro ◽

...

Keyword(s):

Organic Carbon ◽

Mass Fraction ◽

Co Adsorption ◽

Ocean Surface ◽

Sea Surface ◽

Sea Spray ◽

Surface Microlayer ◽

Sea Surface Microlayer ◽

Sea Spray Aerosol ◽

Significant Mass

Saccharides comprise a significant mass fraction of organic carbon in sea spray aerosol (SSA), but the mechanisms through which saccharides are transferred from seawater to the ocean surface and eventually...

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

Atmosphere ◽

10.3390/atmos9120476 ◽

2018 ◽

Vol 9 (12) ◽

pp. 476 ◽

Cited By ~ 6

Author(s):

Steven Schill ◽

Susannah Burrows ◽

Elias Hasenecz ◽

Elizabeth Stone ◽

Timothy Bertram

Keyword(s):

Divalent Cation ◽

Organic Material ◽

Large Fraction ◽

Co Adsorption ◽

Sea Spray ◽

Surface Microlayer ◽

Volume Fractions ◽

Sea Surface Microlayer ◽

Sea Spray Aerosol ◽

The Impact

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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Heterogeneous ice nucleation ability of aerosol particles generated from Arctic sea surface microlayer and surface seawater samples at cirrus temperatures

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-13903-2021 ◽

2021 ◽

Vol 21 (18) ◽

pp. 13903-13930

Author(s):

Robert Wagner ◽

Luisa Ickes ◽

Allan K. Bertram ◽

Nora Els ◽

Elena Gorokhova ◽

...

Keyword(s):

Aerosol Particles ◽

Ice Nucleation ◽

Sea Surface ◽

Ice Formation ◽

Sea Spray ◽

Surface Microlayer ◽

Sea Surface Microlayer ◽

Sea Spray Aerosol ◽

Seawater Samples ◽

Heterogeneous Ice Nucleation

Abstract. Sea spray aerosol particles are a recognised type of ice-nucleating particles under mixed-phase cloud conditions. Entities that are responsible for the heterogeneous ice nucleation ability include intact or fragmented cells of marine microorganisms as well as organic matter released by cell exudation. Only a small fraction of sea spray aerosol is transported to the upper troposphere, but there are indications from mass-spectrometric analyses of the residuals of sublimated cirrus particles that sea salt could also contribute to heterogeneous ice nucleation under cirrus conditions. Experimental studies on the heterogeneous ice nucleation ability of sea spray aerosol particles and their proxies at temperatures below 235 K are still scarce. In our article, we summarise previous measurements and present a new set of ice nucleation experiments at cirrus temperatures with particles generated from sea surface microlayer and surface seawater samples collected in three different regions of the Arctic and from a laboratory-grown diatom culture (Skeletonema marinoi). The particles were suspended in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber and ice formation was induced by expansion cooling. We confirmed that under cirrus conditions, apart from the ice-nucleating entities mentioned above, also crystalline inorganic salt constituents can contribute to heterogeneous ice formation. This takes place at temperatures below 220 K, where we observed in all experiments a strong immersion freezing mode due to the only partially deliquesced inorganic salts. The inferred ice nucleation active surface site densities for this nucleation mode reached a maximum of about 5×1010 m−2 at an ice saturation ratio of 1.3. Much smaller densities in the range of 108–109 m−2 were observed at temperatures between 220 and 235 K, where the inorganic salts fully deliquesced and only the organic matter and/or algal cells and cell debris could contribute to heterogeneous ice formation. These values are 2 orders of magnitude smaller than those previously reported for particles generated from microlayer suspensions collected in temperate and subtropical zones. While this difference might simply underline the strong variability of the number of ice-nucleating entities in the sea surface microlayer across different geographical regions, we also discuss how instrumental parameters like the aerosolisation method and the ice nucleation measurement technique might affect the comparability of the results amongst different studies.

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The role of jet and film drops in controlling the mixing state of submicron sea spray aerosol particles

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1702420114 ◽

2017 ◽

Vol 114 (27) ◽

pp. 6978-6983 ◽

Cited By ~ 56

Author(s):

Xiaofei Wang ◽

Grant B. Deane ◽

Kathryn A. Moore ◽

Olivia S. Ryder ◽

M. Dale Stokes ◽

...

Keyword(s):

Chemical Composition ◽

Volume Fraction ◽

Water Soluble ◽

Sea Surface ◽

Sea Spray ◽

Surface Microlayer ◽

Mixing State ◽

Organic Species ◽

Sea Surface Microlayer ◽

Sea Spray Aerosol

The oceans represent a significant global source of atmospheric aerosols. Sea spray aerosol (SSA) particles comprise sea salts and organic species in varying proportions. In addition to size, the overall composition of SSA particles determines how effectively they can form cloud droplets and ice crystals. Thus, understanding the factors controlling SSA composition is critical to predicting aerosol impacts on clouds and climate. It is often assumed that submicrometer SSAs are mainly formed by film drops produced from bursting bubble-cap films, which become enriched with hydrophobic organic species contained within the sea surface microlayer. In contrast, jet drops formed from the base of bursting bubbles are postulated to mainly produce larger supermicrometer particles from bulk seawater, which comprises largely salts and water-soluble organic species. However, here we demonstrate that jet drops produce up to 43% of total submicrometer SSA number concentrations, and that the fraction of SSA produced by jet drops can be modulated by marine biological activity. We show that the chemical composition, organic volume fraction, and ice nucleating ability of submicrometer particles from jet drops differ from those formed from film drops. Thus, the chemical composition of a substantial fraction of submicrometer particles will not be controlled by the composition of the sea surface microlayer, a major assumption in previous studies. This finding has significant ramifications for understanding the factors controlling the mixing state of submicrometer SSA particles and must be taken into consideration when predicting SSA impacts on clouds and climate.

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Heterogeneous ice nucleation ability of aerosol particles generated from Arctic sea surface microlayer and surface seawater samples at cirrus temperatures

10.5194/acp-2021-252 ◽

2021 ◽

Author(s):

Robert Wagner ◽

Luisa Ickes ◽

Allan K. Bertram ◽

Nora Els ◽

Elena Gorokhova ◽

...

Keyword(s):

Aerosol Particles ◽

Ice Nucleation ◽

Sea Surface ◽

Ice Formation ◽

Sea Spray ◽

Surface Microlayer ◽

Sea Surface Microlayer ◽

Sea Spray Aerosol ◽

Seawater Samples ◽

Heterogeneous Ice Nucleation

Abstract. Sea spray aerosol particles are a recognised type of ice-nucleating particles under mixed-phase cloud conditions. Entities that are responsible for the heterogeneous ice nucleation ability include intact or fragmented cells of marine microorganisms as well as organic matter released by cell exudation. Only a small fraction of sea salt aerosol is transported to the upper troposphere, but there are indications from mass-spectrometric analyses of the residuals of sublimated cirrus particles that sea salt could also contribute to heterogeneous ice nucleation under cirrus conditions. Experimental studies on the heterogeneous ice nucleation ability of sea spray aerosol particles and their proxies at temperatures below 235 K are still scarce. In our article, we summarise previous measurements and present a new set of ice nucleation experiments at cirrus temperatures with particles generated from sea surface microlayer and surface seawater samples collected in three different regions of the Arctic and from a laboratory-grown diatom culture (Skeletonema marinoi). The particles were suspended in a large cloud chamber and ice formation was induced by expansion cooling. We confirmed that under cirrus conditions, apart from the ice-nucleating entities mentioned above, also crystalline inorganic salt constituents can contribute to heterogeneous ice formation. This takes place at temperatures below 220 K, where we observed in all experiments a strong immersion freezing mode due to the only partially deliquesced inorganic salts. The inferred ice nucleation active surface site densities for this nucleation mode reached a maximum of about 5·1010 m−2 at an ice saturation ratio of 1.3. Much smaller densities in the range of 108–109 m−2 were observed at temperatures between 220 and 235 K, where the inorganic salts fully deliquesced and only the organic matter and/or algal cells and cell debris could contribute to heterogeneous ice formation. These values are two orders of magnitude smaller than those previously reported for particles generated from microlayer suspensions collected in temperate and subtropical zones. While this difference might simply underline the strong variability of the amount of ice-nucleating entities in the sea surface microlayer across different geographical regions, we also discuss how far instrumental parameters like the aerosolisation method and the ice-nucleation measurement technique might affect the comparability of the results amongst different studies.

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