Selectivity Across the Interface: A Test of Surface Activity in the Composition of Organic-Enriched Aerosols from Bubble Bursting

Abstract

Although theories have been developed that describe surface activity of organic molecules at the air-water interface, few studies have tested how surface activity impacts the selective transfer of molecules from solution phase into the aerosol phase during bubble bursting. The selective transfer of a series of organic compounds that differ in their solubility and surface activity from solution into the aerosol phase is quantified experimentally for the first time. Aerosol was produced from solutions containing salts and a series of linear carboxlyates (LCs) and dicarboxylates (LDCs) using a bubble bursting process. Surface activity of these molecules dominated the transport across the interface, with enrichment factors of the more surface-active C4-C8 LCs (55 ± 8) being greater than those of C4-C8 LDCs (5 ± 1). Trends in the estimated surface concentrations of LCs at the liquid-air interface agreed well with their relative concentrations in the aerosol phase. In addition, enrichment of LCs was followed by enrichment of calcium with respect to other inorganic cations and depletion of chloride and sulfate.

Calcium enrichment in sea spray aerosol particles

“…A similar depletion of K + in fresh sea spray aerosol (relative to Mg 2+ ) was observed by both Keene et al [2007] and Cochran et al [2016]. Presenting the data in this way clearly reveals the enrichment of Ca 2+ as particle size decreases below 1 μm in both the North Atlantic seawater and the artificial seawater.…”

“…Leck and Svensson [2015 suggested that the significant enrichment of Ca 2+ in a number of ambient aerosol samples collected over the central Arctic Ocean during summer using a low pressure impactor originated from bubbles bursting in open leads. In another laboratory study, Cochran et al [2016] observed enrichment of Ca 2+ in nascent sea spray aerosol generated from artificial seawater spiked with linear carboxylates. The authors attributed this enrichment to Ca 2+ complexed to organic matter in the form of polymer gels (see Verdugo [2012] for a review on polymer gels).…”

Primary marine aerosol physical flux and chemical composition during a nutrient enrichment experiment in mesocosms in the Mediterranean Sea

“…The enrichment of Ca in the aerosol phase compared to the seawater composition is of the order of 500 %. A significant enrichment of calcium in the PM 1 primary marine aerosol compared to the composition of the seawater has also been reported in earlier studies (Keene et al, 2007;Cochran et al, 2016;Salter et al, 2016), with an increased enrichment with decreasing aerosol size. The study by Salter et al (2016) suggests that some calcium ions are clustering close to the sea surface (probably in the form of carbonate ions), and that if calcium is complexing to organic matter at the seawater surface, it is with minor amounts of organic compounds.…”

Revising the hygroscopicity of inorganic sea salt particles

“…). If the surface composition is driving the water uptake at these small sizes, only minute amounts of surface-tension-reducing substances are needed to result in a notable effect29. Salter et al 24.…”