Saccharide Transfer to Sea Spray Aerosol Enhanced by Surface Activity, Calcium, and Protein Interactions

Abstract

Sea spray aerosol (SSA) represents the largest source of natural primary aerosol with climate relevance in cloud formation. The aerosol-cloud activation process is influenced by saccharides, which comprise a large SSA organic mass fraction. Saccharides are enriched relative to sodium in SSA by several orders of magnitude but the mechanisms of that enrichment remain poorly understood. Here, saccharide enrichment in laboratory-generated SSA was quantified via bubble bursting experiments using marine-relevant model systems. The resulting particles exhibited core−shell morphology previously observed in SSA, as identified by single particle atomic force microscopy (AFM). Measured enrichment factors (EFs) from filters indicated significant enrichment in aerosol <250 nm in diameter (EF = 1.68 ± 0.19) for the anionic polysaccharide (alginate) and no enrichment (EF = 1) for neutral short-chain saccharides (glucose, sucrose, raffinose, and cyclodextrin). Concurrent surface tension depression was observed for the surface microlayer (SML) with alginate (−Δ12.2 mN m −1 relative to seawater matrix) but not for the short-chain saccharides. Together, results indicate that surface activity of these systems result in saccharide enrichment. Moreover, model system complexity was increased through calcium addition which significantly increased alginate enrichment in aerosol <250 nm in diameter (EF = 2.44 ± 0.26). Separately, protein addition caused the greatest alginate enrichment increase in 500−1000 nm diameter aerosol (EF = 5.77 ± 0.61). These results indicate saccharide surface activity and cooperative interactions with protein and calcium that enhance saccharide enrichment. However, the model systems have not reproduced EFs of natural SSAs and the role of complex ocean biology still needs to be evaluated.

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

“…Enhanced saccharide enrichment in laboratory-generated SSA in the presence of divalent cations and other surface-active organic material strongly suggests a co-adsorption mechanism mediated by divalent cationic bridging. 12,31 A divalent cation mediated co-adsorption mechanism was also postulated by Schill et al to explain enrichment of the monosaccharide glucuronic acid in laboratory-generated SSA. 12 Glucuronic acid likely co-adsorbs to an insoluble palmitic acid (hexadecanoic acid, CH3(CH2)14COOH) monolayer via seawater divalent cationic bridging interactions.…”

“…Hasenecz et al has shown that the polysaccharide alginate is enriched in laboratory-generated marine aerosol, and alginate enrichment can be enhanced upon adding protein and additional CaCl2 salt to the model seawater solution. 31 Alginate is a type of exopolymeric substance derived from marine brown algae and bacteria; 32,33 it is composed of (1→4)-linked α-ʟ-guluronic (G) and β-ᴅ-mannuronic (M) monomers that form a block copolymer with random sequences of M-, G-, and MG-blocks. [34][35][36][37][38][39] Alginate polymers undergo ionic crosslinking to form hydrophilic gels via metal ion coordination primarily to the G residue carboxylic acid moieties.…”

Aerosol Marine Primary Carbohydrates and Atmospheric Transformation in the Western Antarctic Peninsula

“…20,56 In tank and microcosm experiments, CCHO enrichments in aerosol particles increased after the addition of typical seawater matrix compounds, such as calcium, proteins, and heterotrophic bacteria, while short-chained DFCHO were not enriched. 57,58 However, once entered the atmosphere, OM undergoes complex changes; first, abiotically due to chemical reactions, e.g., with OH and NO 3 radicals, and also biologically by microbial degradation. 59,60 Latest studies revealed that airborne bacteria can survive in the atmosphere even in the harsh polar environments and are, similar to bacteria in seawater, metabolically active in the aqueous phase of clouds, as well as on the surface or in the bulk of aerosol particles.…”

Probing the Water Uptake and Phase State of Individual Sucrose Nanoparticles Using Atomic Force Microscopy

“…Second, atmospheric aerosols can exhibit size-dependent properties. For example, Hasenecz et al observed an increase in the organic mass fraction with a decreasing particle size, reaching ∼70% for sub-180 nm SSAs . Furthermore, the morphologies of SSAs have been found to vary significantly with the particle size. − Finally, atmospheric aerosols from the same source and similar size range can exhibit significant particle-to-particle variability .…”