Surface tension depression by low-solubility organic material in aqueous aerosol mimics

Schwier, A. N.; Mitroo, Dhruv; McNeill, V. Faye

doi:10.1016/j.atmosenv.2012.02.032

Cited by 27 publications

(22 citation statements)

References 69 publications

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“…In the macroscopic measurements, variation in A is induced through physical compression of the surfactant in a Langmuir-Blodgett trough. The A 0 values for the wet droplets compare well to those in macroscopic systems (Voss et al, 2007;Mao et al, 2013;Seoane et al, 2000). However, the film-model-derived π values seem to be higher than the macroscopic system, both in the compression and collapsed region.…”

Section: Surface and Bulk Partitioningsupporting

confidence: 60%

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Establishing the impact of model surfactants on cloud condensation nuclei activity of sea spray aerosol mimics

et al. 2018

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Surface-active compounds present in aerosols can increase their cloud condensation nuclei (CCN) activation efficiency by reducing the surface tension (σ ) in the growing droplets. However, the importance of this effect is poorly constrained by measurements. Here we present estimates of droplet surface tension near the point of activation derived from direct measurement of droplet diameters using a continuous flow streamwise thermal gradient chamber (CFSTGC). The experiments used sea spray aerosol (SSA) mimics composed of NaCl coated by varying amounts of (i) oleic acid, palmitic acid or myristic acid, (ii) mixtures of palmitic acid and oleic acid, and (iii) oxidized oleic acid. Significant reductions in σ relative to that for pure water were observed for these mimics at relative humidity (RH) near activation ( ∼ 99.9 %) when the coating was sufficiently thick. The calculated surface pressure (π = σ H 2 O − σ observed ) values for a given organic compound or mixture collapse onto one curve when plotted as a function of molecular area for different NaCl seed sizes and measured RH. The observed critical molecular area (A 0 ) for oleic acid determined from droplet growth was similar to that from experiments conducted using macroscopic solutions in a Langmuir trough. However, the observations presented here suggest that oleic acid in microscopic droplets may exhibit larger π values during monolayer compression. For myristic acid, the observed A 0 compared well to macroscopic experiments on a fresh subphase, for which dissolution has an important impact. A significant kinetic limitation to water uptake was observed for NaCl particles coated with pure palmitic acid, likely as a result of palmitic acid (with coating thicknesses ranging from 67 to 132 nm) being able to form a solid film. However, for binary palmitic-acid-oleic-acid mixtures there was no evidence of a kinetic limitation to water uptake. Oxidation of oleic acid had a minor impact on the magnitude of the surface tension reductions observed, potentially leading to a slight reduction in the effect compared to pure oleic acid. A CCN counter was also used to assess the impact on critical supersaturations of the substantial σ reductions observed at very high RH. For the fatty-acid-coated NaCl particles, when the organic fraction (ε org ) was > 0.90 small depressions in critical supersaturation were observed. However, when ε org < 0.90 the impact on critical supersaturation was negligible. Thus, for the fatty acids considered here, the substantial σ reductions observed at high RH values just below activation have limited impact on the ultimate critical supersaturation. A surface film model is used to establish the properties that surface-active organic molecules must have if they are to ultimately have a substantial impact on the activation efficiency of SSA. To influence activation, the average properties of surface-active marine-derived organic molecules must differ substantially from the long-chain fatty acids examined, having either smaller molecular volumes o...

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Section: Surface and Bulk Partitioningsupporting

confidence: 60%

“…Error bars on individual points and the film model fit (dashed black lines) are based on the precision in RH. Macroscopic solution measurements (red lines) adapted fromVoss et al (2007),Mao et al (2013), andSeoane et al (2000) are included for reference.…”

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confidence: 99%

Establishing the impact of model surfactants on cloud condensation nuclei activity of sea spray aerosol mimics

et al. 2018

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“…Longchain fatty acids are an important class of organic compounds found in submicron SSA particles (Cochran et al, 2017;Cochran et al, 2016). Since this class of organic species is surface active (Schwier et al, 2012) they have the potential to enhance observed CCN activation efficiency by 20 depressing surface tension, but the overall effect of fatty acid addition on CCN activation efficiency of salt particles has been shown to be minimal (Nguyen et al, 2017). In this work we will clarify why such highly surface active species have little impact CCN activation efficiency.…”

Section: Introductionmentioning

confidence: 95%

Establishing the Impact of Model Surfactants on Cloud Condensation Nuclei Activity of Sea Spray Aerosols

Forestieri¹,

Staudt²,

Kuborn³

et al. 2018

Preprint

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Surface active compounds present in aerosols can increase their cloud condensation nuclei (CCN) activation efficiency by reducing the surface tension (σ) in the growing droplets.However, the importance of this effect is poorly constrained by measurements. Here we present estimates of droplet surface tension near the point of activation derived from direct measurement 15 of droplet diameters using a continuous flow stream-wise thermal gradient chamber (CFSTGC).The experiments used sea spray aerosol mimics composed of NaCl coated by varying amounts of (i) oleic acid, palmitic acid or myristic acid, (ii) mixtures of palmitic acid and oleic acid, and (iii) oxidized oleic acid. Significant reductions in σ relative to that for pure water were observed for these mimics at relative humidity (RH) near activation (~99.9%) when the coating was 20 sufficiently thick. The calculated surface pressure (π = σH2O -σobserved) values for a given organic compound or mixture collapse onto one curve when plotted as a function of molecular area for different NaCl seed sizes and measured RH. The observed critical molecular area (A0) for oleic acid determined from droplet growth was similar to that from bulk experiments conducted in a Langmuir trough. However, the observations presented here suggest that oleic acid in 25 microscopic droplets may exhibit larger π values during monolayer compression. For myristic acid, the observed A0 compared well to bulk experiments on a fresh subphase, for which dissolution has an important impact. A significant kinetic limitation to water uptake was observed for NaCl particles coated with pure palmitic acid, likely as a result of palmitic acid Atmos. Chem. Phys. Discuss., https://doi.

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“…While aqueous solutions of LEV and KS exhibit surface tensions approximately equal to the surface tension of water (Tuckermann and Cammenga, 2004;Tuckermann, 2007), to our knowledge no previous surface tension measurements of MNC aqueous solutions have been made. Our assumption applying the surface tension of water at all OH exposures could result in an overestimation of κ since the presence of surface-active organics can decrease σ s/a Schwier et al, 2012;Noziére et al, 2014;Harmon et al, 2013). We do not have surface tension data of the different mixtures applied in this study.…”

Section: Hygroscopicity and Ccn Activity Determinationmentioning

confidence: 99%

Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity

et al. 2015

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Abstract. Multiphase OH and O 3 oxidation reactions with atmospheric organic aerosol (OA) can influence particle physicochemical properties including composition, morphology, and lifetime. Chemical aging of initially insoluble or low-soluble single-component OA by OH and O 3 can increase their water solubility and hygroscopicity, making them more active as cloud condensation nuclei (CCN) and susceptible to wet deposition. However, an outstanding problem is whether the effects of chemical aging on their CCN activity are preserved when mixed with other organic or inorganic compounds exhibiting greater water solubility. In this work, the CCN activity of laboratory-generated biomass burning aerosol (BBA) surrogate particles exposed to OH and O 3 is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type, mixing state, and OH and O 3 exposure applying a CCN counter (CCNc) coupled to an aerosol flow reactor (AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative BBA compounds that exhibit different hygroscopicity, water solubility, chemical functionalities, and reactivity with OH radicals, and thus exemplify the complexity of mixed inorganic/organic aerosol in the atmosphere. The CCN activities of all of the particles were unaffected by O 3 exposure. Following exposure to OH, κ of MNC was enhanced by an order of magnitude, from 0.009 to ∼ 0.1, indicating that chemically aged MNC particles are better CCN and more prone to wet deposition than pure MNC particles. No significant enhancement in κ was observed for pure LEV particles following OH exposure. κ of the internally mixed particles was not affected by OH oxidation. Furthermore, the CCN activity of OH-exposed MNCcoated KS particles is similar to the OH unexposed atomized 1 : 1 by mass MNC : KS binary-component particles. Our results strongly suggest that when OA is dominated by watersoluble organic carbon (WSOC) or inorganic ions, chemical aging has no significant impact on OA hygroscopicity. The organic compounds exhibiting low solubility behave as if they are infinitely soluble when mixed with a sufficient number of water-soluble compounds. At and beyond this point, the particles' CCN activity is governed entirely by the watersoluble fraction and is not influenced by the oxidized organic fraction. Our results have important implications for heterogeneous oxidation and its impact on cloud formation given that atmospheric aerosol is a complex mixture of organic and inorganic compounds exhibiting a wide range of solubilities.

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Surface tension depression by low-solubility organic material in aqueous aerosol mimics

Cited by 27 publications

References 69 publications

Establishing the impact of model surfactants on cloud condensation nuclei activity of sea spray aerosol mimics

Establishing the impact of model surfactants on cloud condensation nuclei activity of sea spray aerosol mimics

Establishing the Impact of Model Surfactants on Cloud Condensation Nuclei Activity of Sea Spray Aerosols

Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity

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