Cloud droplet activation of organic–salt mixtures predicted from two model treatments of the droplet surface

Lin, J. J.; Malila, Jussi; Prisle, Nønne L.

doi:10.1039/c8em00345a

Cited by 27 publications

(72 citation statements)

References 75 publications

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“…First, the monolayer partitioning model is fully predictive, has no free parameters, and is only constrained by measurements not related to the droplet experiments, in contrast to the 2D van der Waals model. Second, the Gibbs model tends to overestimate partitioning, as discussed in greater detail in previous modeling studies (17,43,44), and has compared poorly against experimental and field studies in some cases (12,20), providing unphysically large estimations of surface layer thicknesses (20). Here, we compare the experimental data for the glutaric acid-Triton X-100 droplets to a Gibbs model (22) and, similar to these previous studies (12,17,20,43,44), we observe that the extent of surface partitioning is overpredicted relative to the measurements (i.e., the Gibbs model overestimates N surface and underestimates N bulk ), thereby predicting much higher surface tensions than experimentally measured (SI Appendix, Fig.…”

Section: Resultsmentioning

confidence: 94%

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The surface tension of surfactant-containing, finite volume droplets

Bzdek

Reid

Malila

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Surface tension influences the fraction of atmospheric particles that become cloud droplets. Although surfactants are an important component of aerosol mass, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. By studying picoliter droplet coalescence, we demonstrate that surfactants can significantly reduce the surface tension of finite-sized droplets below the value for water, consistent with recent field measurements. Significantly, this surface tension reduction is droplet size-dependent and does not correspond exactly to the macroscopic solution value. A fully independent monolayer partitioning model confirms the observed finite-size-dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation, potentially substantially increasing cloud droplet number concentration and modifying radiative cooling relative to current estimates assuming a water surface tension. The results highlight the need for improved constraints on the identities, properties, and concentrations of atmospheric aerosol surfactants in multiple environments and are broadly applicable to any discipline where finite volume effects are operative, such as studies of the competition between reaction rates within the bulk and at the surface of confined volumes and explorations of the influence of surfactants on dried particle morphology from spray driers.

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Section: Resultsmentioning

confidence: 94%

“…With increasing initial surfactant concentration, an increasing fraction of droplet growth occurs with a surface tension <72 mN•m −1 . The effects on critical radius (R c ), critical supersaturation (SS c ), and surface tension at activation (γ c ), as predicted by the Köhler equation(2,44), are shown inFig. 5C and…”

mentioning

confidence: 99%

The surface tension of surfactant-containing, finite volume droplets

Bzdek

Reid

Malila

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

110

119

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“…In the monolayer model, 18,20 the composition of the bulk and surface are related via the semi-empirical equation…”

Section: Modelingmentioning

confidence: 99%

“…Including bulk/surface partitioning of surface-active aerosol components to the cloud condensation nuclei (CCN) activation framework has two effects due to the nite size of submicron solution droplets: (1) it signicantly changes the droplet bulk concentration, which is used to evaluate the surface tension from macroscopic isotherms, and (2) in the cases of mixtures involving both surface-active and non-surface-active solutes, partitioning changes the relative solute composition in both surface and bulk phases from the nominal. 15,[18][19][20] The presence of surfactants can therefore have opposing effects on aerosol activation into cloud droplets in the framework of Köhler theory. While the depression of droplet surface tension by surface-active solute is expected to increase CCN activity via the Kelvin effect, the depletion of solute from the bulk will also decrease CCN activity via the Raoult effect.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the surface tension decrease may be much smaller than indicated by the total concentration of surface-active material in the droplet. 15,[18][19][20] Therefore, continuous parameterizations of solution properties, such as surface tension, that encompass independent variations in all solution components are necessary to comprehensively account for these effects as droplets grow and both composition and surface to volume ratio changes.…”

Section: Introductionmentioning

confidence: 99%

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Effects of surface tension time-evolution for CCN activation of a complex organic surfactant

Lin

Kristensen

Calderón

et al. 2020

Environ. Sci.: Processes Impacts

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Model for estimating activity coefficients in binary and ternary ionic surfactant solutions

2020

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We introduce the CMC based Ionic Surfactant Activity model (CISA) to calculate activity coefficients in ternary aqueous solutions of an ionic surfactant and an inorganic salt. The surfactant can be either anionic or cationic and in the present development, the surfactant and inorganic salts share a common counterion. CISA incorporates micellization into the Pitzer–Debye–Hückel (PDH) framework for activities of mixed electrolyte solutions. To reduce computing requirements, a parametrization of the critical micelle concentration (CMC) is used to estimate the degree of micellization instead of explicit equilibrium calculations. For both binary and ternary systems, CISA only requires binary experimentally-based parameters to describe water–ion interactions and temperature–composition dependency of the CMC. The CISA model is intended in particular for atmospheric applications, where higher-order solution interaction parameters are typically not constrained by experiments and the description must be reliable across a wide range of compositions. We evaluate the model against experimental activity data for binary aqueous solutions of ionic surfactants sodium octanoate and sodium decanoate, as common components of atmospheric aerosols, and sodium dodecylsulfate, the most commonly used model compound for atmospheric surfactants. Capabilities of the CISA model to describe ternary systems are tested for the water–sodium decanoate–sodium chloride system, a common surrogate for marine background cloud condensation nuclei and to our knowledge the only atmospherically relevant system for which ternary activity data is available. For these systems, CISA is able to provide continuous predictions of activity coefficients both below and above CMC and in all cases gives an improved description of the water activity above the CMC, compared to the alternative model of Burchfield and Wolley [J. Phys. Chem., 88(10), 2149–2155 (1984)]. The water activity is a key parameter governing the formation and equilibrium growth of cloud droplets. The CISA model can be extended from the current form to include the effect of other inorganic salts with the existing database of binary PDH parameters and using appropriate mixing rules to account for ion specificity in the micellization process.

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Cloud droplet activation of organic–salt mixtures predicted from two model treatments of the droplet surface

Abstract: A new monolayer model predicts the bulk-surface partitioning, surface composition, and thickness of droplets comprising chemically unresolved, atmospherically relevant organic aerosols.

Cited by 27 publications

References 75 publications

The surface tension of surfactant-containing, finite volume droplets

The surface tension of surfactant-containing, finite volume droplets

Effects of surface tension time-evolution for CCN activation of a complex organic surfactant

Model for estimating activity coefficients in binary and ternary ionic surfactant solutions

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