scholarly journals Surfactants in cloud droplet activation: mixed organic-inorganic particles

2009 ◽  
Vol 9 (6) ◽  
pp. 24669-24715 ◽  
Author(s):  
N. L. Prisle ◽  
T. Raatikainen ◽  
A. Laaksonen ◽  
M. Bilde
Keyword(s):  
Surface Tension ◽  
Pure Water ◽  
Sodium Dodecyl ◽  
Cloud Droplet ◽  
Droplet Growth ◽  
Inorganic Particles ◽  
Surfactant Properties ◽  
Surface Partitioning ◽  
Kohler Theory ◽  
Droplet Activation

Abstract. Organic compounds with surfactant properties are commonly found in atmospheric aerosol particles. Surface activity can significantly influence the cloud droplet forming ability of these particles. We have studied the cloud droplet formation by two-component particles comprising one of the organic surfactants sodium octanoate, sodium decanoate, sodium dodecanoate, and sodium dodecyl sulfate, mixed with sodium chloride. Critical supersaturations were measured with a static diffusion cloud condensation nucleus counter (Wyoming CCNC-100B). Results were modeled from Köhler theory applying three different representations of surfactant properties: (1) using concentration-dependent surface tension reduction during droplet growth and explicitly accounting for surfactant surface partitioning in both solute suppression (Raoult effect) and curvature enhancement (Kelvin effect) contributions to the droplet equilibrium water vapor supersaturation, (2) disregarding surfactant partitioning and using a concentration-dependent surface tension for the droplets corresponding to a macroscopic (bulk) aqueous solution of the same overall composition, and (3) disregarding surfactant properties and assuming the constant surface tension of pure water throughout droplet activation. We confirm previous results for single-component organic surfactant particles, that experimental critical supersaturations are greatly underpredicted, if reduced surface tension is applied in Köhler theory while ignoring the effects of surface partitioning in droplets. We further show that assuming the constant surface tension of pure water can also lead to significant underpredictions of experimental critical supersaturations. The full account for surfactant partitioning in activating droplets generally predicts experimental critical supersaturations well. In addition, for mixed particles comprising less than 50% by mass of surfactant, ignoring surfactant properties and simply using the constant surface tension of pure water also provides a good first-order approximation of the observed activation.

scholarly journals Surfactants in cloud droplet activation: mixed organic-inorganic particles

2010 ◽  
Vol 10 (12) ◽  
pp. 5663-5683 ◽  
Author(s):  
N. L. Prisle ◽  
T. Raatikainen ◽  
A. Laaksonen ◽  
M. Bilde
Keyword(s):  
Surface Tension ◽  
Good Description ◽  
Pure Water ◽  
Sodium Dodecyl ◽  
Cloud Droplet ◽  
Cloud Condensation Nucleus ◽  
Inorganic Particles ◽  
Surfactant Properties ◽  
Surface Partitioning ◽  
Droplet Activation

Abstract. Organic compounds with surfactant properties are commonly found in atmospheric aerosol particles. Surface activity can significantly influence the cloud droplet forming ability of these particles. We have studied the cloud droplet formation by two-component particles comprising one of the organic surfactants sodium octanoate, sodium decanoate, sodium dodecanoate, and sodium dodecyl sulfate, mixed with sodium chloride. Critical supersaturations were measured with a static diffusion cloud condensation nucleus counter (Wyoming CCNC-100B). Results were modeled from Köhler theory applying three different representations of surfactant properties in terms of surfactant surface partitioning and reduced droplet surface tension. We here confirm previous results for single-component organic surfactant particles, that experimental critical supersaturations are greatly underpredicted, if reduced surface tension is used while ignoring the effects of surface partitioning in droplets. Furthermore, disregarding surfactant properties by ignoring surface partitioning and assuming the constant surface tension of pure water can also lead to significant underpredictions of experimental critical supersaturations. For the mixed particles comprising less than 50% by mass of surfactant, this approach however still provides a good description of the observed droplet activation. A comprehensive account for surfactant properties, including both surface tension reduction and effects of surface partitioning in activating droplets, generally predicts experimental critical supersaturations well.

scholarly journals Joint effect of organic acids and inorganic salts on cloud droplet activation

2010 ◽  
Vol 10 (7) ◽  
pp. 17981-18023
Author(s):  
M. Frosch ◽  
N. L. Prisle ◽  
M. Bilde ◽  
Z. Varga ◽  
G. Kiss
Keyword(s):  
Surface Tension ◽  
Sodium Chloride ◽  
Organic Acids ◽  
Organic Acid ◽  
Water Activity ◽  
Inorganic Salt ◽  
Cloud Droplet ◽  
Surface Partitioning ◽  
Kohler Theory ◽  
Droplet Activation

Abstract. We have investigated CCN properties of internally mixed particles composed of one organic acid (oxalic acid, succinic acid, adipic acid, citric acid, cis-pinonic acid, or nordic reference fulvic acid) and one inorganic salt (sodium chloride or ammonium sulphate). Surface tension and water activity of aqueous model solutions with concentrations relevant for CCN activation were measured using a tensiometer and osmometry, respectively. The measurements were used to calculate Köhler curves, which were compared to measured critical supersaturations of particles with the same chemical compositions, determined with a cloud condensation nucleus counter. Surfactant surface partitioning was not accounted for. For the mixtures containing cis-pinonic acid or fulvic acid, a depression of surface tension was observed, but for the remaining mixtures the effect on surface tension was negligle at concentrations relevant for cloud droplet activation, and water activity was the more significant term in the Köhler equation. The surface tension depression of aqueous solutions containing both organic acid and inorganic salt was approximately the same as or smaller than that of aqueous solutions containing the same mass of the corresponding pure organic acids. Water activity was found to be highly dependent on the type and amount of inorganic salt. Sodium chloride was able to decrease water activity more than ammonium sulphate and both inorganic compounds had a higher effect on water activity than the studied organic acids, and increasing the mass ratio of the inorganic compound led to a decrease in water activity. Water activity measurements were compared to results from the E-AIM model and values estimated from both constant and variable van't Hoff factors to evaluate the performance of these approaches. The correspondence between measuments and estimates was overall good, except for highly concentrated solutions. Critical supersaturations calculated with Köhler theory based on measured water activity and surface tension, but not accounting for surface partitioning, compared well with measurements, except for the solutions containing sodium chloride or one of the more surface active organic compounds. In such cases, significantly lower values were obtained from Köhler theory than the measured critical supersaturations, suggesting that surfactant partitioning and/or an effect of sodium chloride on solubility of the organic component is important.

scholarly journals Modeling CCN activity of chemically unresolved model HULIS, including surface tension, non-ideality, and surface partitioning

2018 ◽  
Author(s):  
Nonne L. Prisle ◽  
Bjarke Molgaard
Keyword(s):  
Surface Tension ◽  
Water Activity ◽  
Cloud Droplet ◽  
Tension Reduction ◽  
Surface Tension Reduction ◽  
Surface Partitioning ◽  
Critical Supersaturation ◽  
Surface Active ◽  
Droplet Activation ◽  
Ccn Activity

Abstract. Cloud condensation nuclei (CCN) activity of aerosol particles comprising surface active Nordic Aquatic Fulvic Acid (NAFA) and NaCl was modeled with four different approaches to account for NAFA bulk-to-surface partitioning and the combined influence of NAFA and NaCl on surface tension and water activity of activating droplets. Calculations were made for particles with dry diameters of 30–230 nm and compositions covering the full range of relative NAFA and NaCl mixing ratios. Continuous ternary parametrizations of aqueous surface tension and water activity with respect to independently varying NAFA and NaCl mass concentrations were developed from previous measurements on macroscopic bulk solutions and implemented to a Köhler model framework. This enabled comprehensive thermodynamic predictions of cloud droplet activation, including equilibrium surface partitioning, for particles comprising chemically unresolved organic NAFA mixtures. NAFA here serves as a model for surface active atmospheric humic-like substances (HULIS) and for chemically complex organic aerosol in general. Surfactant effects are gauged via predictions of a suite of properties for activating droplets, including critical supersaturation and droplet size, bulk phase composition, surface tension, Kelvin effect, and water activity. Assuming macroscopic solution properties for activating droplets leads to gross overestimations of reported experimental CCN activation, mainly by overestimating surface tension reduction from NAFA solute in droplets. Failing to account for bulk-to-surface partitioning of NAFA introduces severe biases in evaluated droplet bulk and surface composition and critical size, which here specifically affect cloud activation thermodynamics, but more generally could also impact heterogeneous chemistry on droplet surfaces. Model frameworks based on either including surface partitioning and/or neglecting surface tension reduction give similar results for both critical supersaturation and droplet properties and reproduce reported experimental CCN activity well. These perhaps counterintuitive results reflect how the bulk phase is nearly depleted in surface active organic from surface partitioning in submicron droplets with large surface area for a given bulk volume. As a result, NAFA has very little impact on surface tension and water activity at the point of droplet activation. In other words, the predicted surfactant strength of NAFA is significantly lower in sub-micron activating droplets than in macroscopic aqueous solutions of the same overall composition. These results show similar effects of chemically complex surfactants as have previously been seen only for simple surfactants with well-defined molecular properties and add to the growing appreciation of the complex role of surface activity in cloud droplet activation.

scholarly journals Cloud droplet activation and surface tension of mixtures of slightly soluble organics and inorganic salt

2005 ◽  
Vol 5 (2) ◽  
pp. 575-582 ◽  
Author(s):  
S. Henning ◽  
T. Rosenørn ◽  
B. D'Anna ◽  
A. A. Gola ◽  
B. Svenningsson ◽  
...  
Keyword(s):  
Surface Tension ◽  
Sodium Chloride ◽  
Inorganic Salt ◽  
Cloud Droplet ◽  
Dicarboxylic Acids ◽  
Solid Particles ◽  
Particle Phase ◽  
Critical Supersaturation ◽  
Kohler Theory ◽  
Droplet Activation

Abstract. Critical supersaturations for internally mixed particles of adipic acid, succinic acid and sodium chloride were determined experimentally for dry particles sizes in the range 40-130nm. Surface tensions of aqueous solutions of the dicarboxylic acids and sodium chloride corresponding to concentrations at activation were measured and parameterized as a function of carbon content. The activation of solid particles as well as solution droplets were studied and particle phase was found to be important for the critical supersaturation. Experimental data were modelled using Köhler theory modified to account for limited solubility and surface tension lowering.

scholarly journals Joint effect of organic acids and inorganic salts on cloud droplet activation

2011 ◽  
Vol 11 (8) ◽  
pp. 3895-3911 ◽  
Author(s):  
M. Frosch ◽  
N. L. Prisle ◽  
M. Bilde ◽  
Z. Varga ◽  
G. Kiss
Keyword(s):  
Surface Tension ◽  
Sodium Chloride ◽  
Organic Acids ◽  
Aqueous Solutions ◽  
Fulvic Acid ◽  
Water Activity ◽  
Inorganic Salt ◽  
Cloud Droplet ◽  
Surface Partitioning ◽  
Kohler Theory

Abstract. We have investigated CCN properties of internally mixed particles composed of one organic acid (oxalic acid dihydrate, succinic acid, adipic acid, citric acid, cis-pinonic acid, or Nordic reference fulvic acid) and one inorganic salt (sodium chloride or ammonium sulphate). Surface tension and water activity of aqueous model solutions with concentrations relevant for CCN activation were measured using a tensiometer and osmometry, respectively. The measurements were used to calculate Köhler curves and critical supersaturations, which were compared to measured critical supersaturations of particles with the same chemical compositions, determined with a cloud condensation nucleus counter. Surfactant surface partitioning was not accounted for. For the aqueous solutions containing cis-pinonic acid and fulvic acid, a depression of surface tension was observed, but for the remaining solutions the effect on surface tension was negligible at concentrations relevant for cloud droplet activation. The surface tension depression of aqueous solutions containing both organic acid and inorganic salt was approximately the same as or smaller than that of aqueous solutions containing the same mass of the corresponding pure organic acids. Water activity was found to be highly dependent on the type and amount of inorganic salt. Sodium chloride was able to decrease water activity more than ammonium sulphate and both inorganic salts are predicted to have a smaller Raoult term than the studied organic acids. Increasing the mass ratio of the inorganic salt led to a decrease in water activity. Water activity measurements were compared to results from the E-AIM model and values estimated from both constant and variable van't Hoff factors. The correspondence between measurements and estimates was overall good, except for highly concentrated solutions. Critical supersaturations calculated with Köhler theory based on measured water activity and surface tension, but not accounting for surface partitioning, compared well with measurements, except for the solutions containing sodium chloride and oxalic acid or one of the more surface active organic compounds. In such cases, significantly lower values were obtained from Köhler theory than the measured critical supersaturations with deviations above 50% for a 60 nm particle containing 50% (dry mass) of Nordic reference fulvic acid, suggesting that surfactant partitioning and/or an effect of sodium chloride on solubility of the organic component is important.

scholarly journals The role of surfactants in Köhler theory reconsidered

2004 ◽  
Vol 4 (8) ◽  
pp. 2107-2117 ◽  
Author(s):  
R. Sorjamaa ◽  
B. Svenningsson ◽  
T. Raatikainen ◽  
S. Henning ◽  
M. Bilde ◽  
...  
Keyword(s):  
Surface Tension ◽  
Organic Compounds ◽  
Inorganic Compounds ◽  
Sodium Dodecyl ◽  
Cloud Droplet ◽  
Droplet Surface ◽  
Cloud Condensation Nucleus ◽  
Hygroscopic Properties ◽  
Critical Supersaturation ◽  
Droplet Activation

Abstract. Atmospheric aerosol particles typically consist of inorganic salts and organic material. The inorganic compounds as well as their hygroscopic properties are well defined, but the effect of organic compounds on cloud droplet activation is still poorly characterized. The focus of the present study is the organic compounds that are surface active i.e. tend to concentrate on droplet surface and decrease the surface tension. Gibbsian surface thermodynamics was used to find out how partitioning between droplet surface and the bulk of the droplet affects the surface tension and the surfactant bulk concentration in droplets large enough to act as cloud condensation nuclei. Sodium dodecyl sulfate (SDS) was used together with sodium chloride to investigate the effect of surfactant partitioning on the Raoult effect (solute effect). While accounting for the surface to bulk partitioning is known to lead to lowered bulk surfactant concentration and thereby to increased surface tension compared to a case in which the partitioning is neglected, the present results show that the partitioning also alters the Raoult effect, and that the change is large enough to further increase the critical supersaturation and hence decrease cloud droplet activation. The fraction of surfactant partitioned to droplet surface increases with decreasing droplet size, which suggests that surfactants might enhance the activation of larger particles relatively more thus leading to less dense clouds. Cis-pinonic acid-ammonium sulfate aqueous solutions were studied in order to study the partitioning with compounds found in the atmosphere and to find out the combined effects of dissolution and partitioning behavior. The results show that the partitioning consideration presented in this paper alters the shape of the Köhler curve when compared to calculations in which the partitioning is neglected either completely or in the Raoult effect. In addition, critical supersaturation was measured for SDS particles with dry radii of 25-60nm using a static parallel plate Cloud Condensation Nucleus Counter. The experimentally determined critical supersaturations agree very well with theoretical calculations taking the surface to bulk partitioning fully into account and are much higher than those calculated neglecting the partitioning.

scholarly journals Ternary solution of sodium chloride, succinic acid and water; surface tension and its influence on cloud droplet activation

2008 ◽  
Vol 8 (16) ◽  
pp. 4595-4604 ◽  
Author(s):  
J. Vanhanen ◽  
A.-P. Hyvärinen ◽  
T. Anttila ◽  
T. Raatikainen ◽  
Y. Viisanen ◽  
...  
Keyword(s):  
Surface Tension ◽  
Sodium Chloride ◽  
Succinic Acid ◽  
Pure Water ◽  
Cloud Droplet ◽  
Ternary Solution ◽  
Marine Aerosol ◽  
Surface Tensions ◽  
Cloud Models ◽  
Droplet Activation

Abstract. Surface tension of ternary solution of sodium chloride, succinic acid and water was measured as a function of both composition and temperature by using the capillary rise technique. Both sodium chloride and succinic acid are found in atmospheric aerosols, the former being main constituent of marine aerosol. Succinic acid was found to decrease the surface tension of water already at very low concentrations. Sodium chloride increased the surface tension linearly as a function of the concentration. Surface tensions of both binary solutions agreed well with the previous measurements. Succinic acid was found to lower the surface tension even if sodium chloride is present, indicating that succinic acid, as a surface active compound, tends to concentrate to the surface. An equation based on thermodynamical relations was fitted to the data and extrapolated to the whole concentration range by using estimated surface tensions for pure compounds. As a result, we obtained an estimate of surface tensions beyond solubility limits in addition to a fit to the experimental data. The parameterization can safely be used at temperatures from 10 to 30°C. These kinds of parameterizations are important for example in atmospheric nucleation models. To investigate the influence of surface tension on cloud droplet activation, the surface tension parameterization was included in an adiabatic air parcel model. Usually in cloud models the surface tension of pure water is used. Simulations were done for characteristic marine aerosol size distributions consisting of the considered ternary mixture. We found that by using the surface tension of pure water, the amount of activated particles is underestimated up to 8% if particles contain succinic acid and overestimated it up to 8% if particles contain only sodium chloride. The surface tension effect was found to increase with increasing updraft velocity.

scholarly journals A predictive thermodynamic framework of cloud droplet activation for chemically unresolved aerosol mixtures, including surface tension, non-ideality, and bulk–surface partitioning

2021 ◽  
Vol 21 (21) ◽  
pp. 16387-16411
Author(s):  
Nønne L. Prisle
Keyword(s):  
Surface Tension ◽  
Surface Activity ◽  
Chemical Species ◽  
Cloud Droplet ◽  
Droplet Surface ◽  
Droplet Growth ◽  
Surface Tension Reduction ◽  
Surface Partitioning ◽  
Bulk Surface ◽  
Surface Active

Abstract. This work presents a thermodynamically consistent framework that enables self-contained, predictive Köhler calculations of droplet growth and activation with considerations of surface adsorption, surface tension reduction, and non-ideal water activity for chemically complex and unresolved surface-active aerosol mixtures. The common presence of surface-active species in atmospheric aerosols is now well-established. However, the impacts of different effects driven by surface activity, in particular bulk–surface partitioning and resulting bulk depletion and/or surface tension reduction, on aerosol hygroscopic growth and cloud droplet activation remain to be generally established. Because specific characterization of key properties, including water activity and surface tension, remains exceedingly challenging for finite-sized activating droplets, a self-contained and thermodynamically consistent model framework is needed to resolve the individual effects of surface activity during droplet growth and activation. Previous frameworks have achieved this for simple aerosol mixtures, comprising at most a few well-defined chemical species. However, atmospheric aerosol mixtures and more realistic laboratory systems are typically chemically more complex and not well-defined (unresolved). Therefore, frameworks which require specific knowledge of the concentrations of all chemical species in the mixture and their composition-dependent interactions cannot be applied. For mixtures which are unresolved or where specific interactions between components are unknown, analytical models based on retrofitting can be applied, or the mixture can be represented by a proxy compound or mixture with well-known properties. However, the surface activity effects evaluated by such models cannot be independently verified. The presented model couples Köhler theory with the Gibbs adsorption and Szyszkowski-type surface tension equations. Contrary to previous thermodynamic frameworks, it is formulated on a mass basis to obtain a quantitative description of composition-dependent properties for chemically unresolved mixtures. Application of the model is illustrated by calculating cloud condensation nuclei (CCN) activity of aerosol particles comprising Nordic aquatic fulvic acid (NAFA), a chemically unresolved and strongly surface-active model atmospheric humic-like substance (HULIS), and NaCl, with dry diameters of 30–230 nm and compositions spanning the full range of relative NAFA and NaCl mixing ratios. For comparison with the model presented, several other predictive Köhler frameworks, with simplified treatments of surface-active NAFA, are also applied. Effects of NAFA surface activity are gauged via a suite of properties evaluated for growing and activating droplets. The presented framework predicts a similar influence of surface activity of the chemically complex NAFA on CCN activation as was previously shown for single, strong surfactants. Comparison to experimental CCN data shows that NAFA bulk–surface partitioning is well-represented by Gibbs adsorption thermodynamics. Contrary to several recent studies, no evidence of significantly reduced droplet surface tension at the point of activation was found. Calculations with the presented thermodynamic model show that throughout droplet growth and activation, the finite amounts of NAFA in microscopic and submicron droplets are strongly depleted from the bulk, due to bulk–surface partitioning, because surface areas for a given bulk volume are very large. As a result, both the effective hygroscopicity and ability of NAFA to reduce droplet surface tension are significantly lower in finite-sized activating droplets than in macroscopic aqueous solutions of the same overall composition. The presented framework enables the influence of surface activity on CCN activation for other chemically complex and unresolved aerosol mixtures, including actual atmospheric samples, to be systematically explored. Thermodynamic input parameters can be independently constrained from measurements, instead of being either approximated by a proxy or determined by retrofitting, potentially confounding several mechanisms influenced by surface activity.

scholarly journals Technical Note: The Role of Evolving Surface Tension in the Formation of Cloud Droplets

2018 ◽  
Author(s):  
James F. Davies ◽  
Andreas Zuend ◽  
Kevin R. Wilson
Keyword(s):  
Surface Tension ◽  
Pure Water ◽  
Cloud Droplet ◽  
Technical Note ◽  
Activation Mechanism ◽  
Activation Process ◽  
Cloud Droplets ◽  
Evolving Surface ◽  
Droplet Activation

Abstract. The role of surface tension (σ) in cloud droplet activation has long been ambiguous. Recent studies have reported observations attributed to the effects of an evolving surface tension in the activation process. However, adoption of a surface-mediated activation mechanism has been slow and many studies continue to neglect the composition-dependence of aerosol/droplet surface tension, using instead a value equal to the surface tension of pure water (σw). In this technical note, we clearly describe the fundamental role of surface tension in the activation of multicomponent aerosol particles into cloud droplets. It is demonstrated that the effects of surface tension in the activation process depend primarily on the evolution of surface tension with droplet size, typically varying in the range 0.5σw ≲ σ ≤ σw due to the partitioning of organic species with a high surface affinity. We go on to report some recent laboratory observations that exhibit behavior that may be associated with surface tension effects, and propose a measurement coordinate that will allow surface tension effects to be better identified using standard atmospheric measurement techniques. However, interpreting observations using theory based on surface film and liquid-liquid phase separation models remains a challenge. Our findings highlight the need for experimental measurements that better reveal the role of composition-dependent surface tensions, critical for advancing predictive theories and parameterizations of cloud droplet activation.

scholarly journals The role of surfactants in Köhler theory reconsidered

2004 ◽  
Vol 4 (3) ◽  
pp. 2781-2804 ◽  
Author(s):  
R. Sorjamaa ◽  
T. Raatikainen ◽  
A. Laaksonen
Keyword(s):  
Surface Tension ◽  
Organic Compounds ◽  
Inorganic Compounds ◽  
Cloud Condensation Nuclei ◽  
Sodium Dodecyl ◽  
Cloud Droplet ◽  
Droplet Surface ◽  
Surface Thermodynamics ◽  
Hygroscopic Properties ◽  
Droplet Activation

Abstract. Atmospheric aerosol particles typically consist of inorganic salts and organic material. The inorganic compounds as well as their hygroscopic properties are well defined, but the effect of organic compounds on cloud droplet activation is still poorly characterized. The focus of the present study is in the organic compounds that are surface active i.e. they concentrate on droplet surface and decrease droplet surface tension. Gibbsian surface thermodynamics were used to find out how partitioning in binary and ternary aqueous solutions affects the droplet surface tension and the droplet bulk concentration in droplets large enough to act as cloud condensation nuclei. Sodium dodecyl sulfate was used as a model compound together with sodium chloride to find out the effect the correct evaluation of surfactant partitioning has on the solute effect (Raoult effect). While the partitioning is known to lead to higher surface tension compared to a case in which partitioning is neglected, the present results show that the partitioning also alters the solute effect, and that the change is large enough to further increase the critical supersaturation and hence decrease the droplet activation. The fraction of surfactant partitioned to droplet surface increases with decreasing droplet size, which suggests that surfactants might enhance the activation of larger particles relatively more thus leading to less dense clouds. Cis-pinonic acid-ammonium sulfate aqueous solution was studied in order to relate the partitioning to more realistic atmospheric situation and to find out the combined effects of dissolution and partitioning behaviour. The results show that correct partitioning consideration alters the shape of the Köhler curve when compared to a situation in which the partitioning is neglected either completely or in the Raoult effect.

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