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 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.

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 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 Hygroscopic properties of Amazonian biomass burning and European background HULIS and investigation of their effects on surface tension with two models linking H-TDMA to CCNC data

2010 ◽  
Vol 10 (12) ◽  
pp. 5625-5639 ◽  
Author(s):  
E. O. Fors ◽  
J. Rissler ◽  
A. Massling ◽  
B. Svenningsson ◽  
M. O. Andreae ◽  
...  
Keyword(s):  
Surface Tension ◽  
Biomass Burning ◽  
Organic Material ◽  
Inorganic Compounds ◽  
Pure Water ◽  
Condensation Nucleus ◽  
Water Soluble ◽  
Cloud Condensation Nucleus ◽  
Rural Site ◽  
Hygroscopic Properties

Abstract. HUmic-LIke Substances (HULIS) have been identified as major contributors to the organic carbon in atmospheric aerosol. The term "HULIS" is used to describe the organic material found in aerosol particles that resembles the humic organic material in rivers and sea water and in soils. In this study, two sets of filter samples from atmospheric aerosols were collected at different sites. One set of samples was collected at the K-puszta rural site in Hungary, about 80 km SE of Budapest, and a second was collected at a site in Rondônia, Amazonia, Brazil, during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) biomass burning season experiment. HULIS were extracted from the samples and their hygroscopic properties were studied using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) at relative humidity (RH) <100%, and a cloud condensation nucleus counter (CCNC) at RH >100%. The H-TDMA measurements were carried out at a dry diameter of 100 nm and for RH ranging from 30 to 98%. At 90% RH the HULIS samples showed diameter growth factors between 1.04 and 1.07, reaching values of 1.4 at 98% RH. The cloud nucleating properties of the two sets of aerosol samples were analysed using two types of thermal static cloud condensation nucleus counters. Two different parameterization models were applied to investigate the potential effect of HULIS surface activity, both yielding similar results. For the K-puszta winter HULIS sample, the surface tension at the point of activation was estimated to be lowered by between 34% (47.7 mN/m) and 31% (50.3 mN/m) for dry sizes between 50 and 120 nm in comparison to pure water. A moderate lowering was also observed for the entire water soluble aerosol sample, including both organic and inorganic compounds, where the surface tension was decreased by between 2% (71.2 mN/m) and 13% (63.3 mN/m).

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 Hygroscopic properties of Amazonian biomass burning and European background HULIS and investigation of their effects on surface tension with two models linking H-TDMA to CCNC data

2009 ◽  
Vol 9 (6) ◽  
pp. 26925-26967 ◽  
Author(s):  
E. O. Fors ◽  
J. Rissler ◽  
A. Massling ◽  
B. Svenningsson ◽  
M. O. Andreae ◽  
...  
Keyword(s):  
Surface Tension ◽  
Biomass Burning ◽  
Organic Material ◽  
Inorganic Compounds ◽  
Pure Water ◽  
Condensation Nucleus ◽  
Water Soluble ◽  
Cloud Condensation Nucleus ◽  
Rural Site ◽  
Hygroscopic Properties

Abstract. HUmic-LIke Substances (HULIS) have been identified as major contributors to the organic carbon in atmospheric aerosol. The term HULIS is used to describe the organic material found in aerosol particles which resembles the humic organic material in river and sea water and in soils. In this study two sets of filter samples from atmospheric aerosols were collected at different sites. One sample was collected at the K-puszta rural site in Hungary, about 80 km SE of Budapest, and a second set of samples was collected at a site in Rondônia, Amazonia, Brazil, during the LBA-SMOCC biomass burning season experiment. HULIS were extracted from the samples, and their hygroscopic properties were studied using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) at relative humidity (RH) <100%, and a cloud condensation nucleus counter (CCNC) at RH >100%. The H-TDMA measurements were carried out at a dry diameter of 100 nm and for RH ranging from 30 to 98%. At 90% RH the HULIS samples showed diameter growth factors between 1.04 and 1.07, reaching values of 1.4 at 98% RH. The cloud nucleating properties of the two sets of aerosol samples were analyzed using two types of thermal static cloud condensation nucleus counters (CCNC). Two different parameterization models were used to investigate the potential effect of HULIS surface activity, both yielding similar results. For the K-puszta winter HULIS sample, the surface tension at the point of activation was estimated to be lowered by between 34% (47.7 mN/m) and 31% (50.3 mN/m) for dry sizes between 50 and 120 nm in comparison to pure water. A moderate lowering was also observed for the entire water soluble aerosol sample, including both organic and inorganic compounds, where the surface tension was decreased by between 2% (71.2 mN/m) and 13% (63.3 mN/m).

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

2004 ◽  
Vol 4 (6) ◽  
pp. 7463-7485 ◽  
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 40–130 nm. 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 Aerosol hygroscopicity at high (99 to 100%) relative humidities

2009 ◽  
Vol 9 (4) ◽  
pp. 15595-15640 ◽  
Author(s):  
C. R. Ruehl ◽  
P. Y. Chuang ◽  
A. Nenes
Keyword(s):  
Surface Tension ◽  
Inorganic Compounds ◽  
Droplet Diameter ◽  
Pure Water ◽  
Sodium Dodecyl ◽  
Bulk Solution ◽  
Active Compounds ◽  
Surface Active ◽  
Surface Active Compounds ◽  
Aerosol Hygroscopicity

Abstract. The hygroscopicity of an aerosol largely determines its influence on climate and, for smaller particles, atmospheric lifetime. While much aerosol hygroscopicity data is available at lower relative humidities (RH) and under cloud formation conditions (RH>100%), relatively little data is available at high RH (99.2 to 99.9%). We measured the size of droplets at high RH that had formed on particles composed of one of seven compounds with dry diameters between 0.1 and 0.5 μm, and calculated the hygroscopicity of these compounds. We use a parameterization of the Kelvin term, in addition to a standard parameterization (κ) of the Raoult term, to express the hygroscopicity of surface-active compounds. For inorganic compounds, hygroscopicity could reliably be predicted using water activity data and assuming a surface tension of pure water. In contrast, most organics exhibited a slight to mild increase in hygroscopicity with droplet diameter. This trend was strongest for sodium dodecyl sulfate (SDS), the most surface-active compound studied. The results suggest that partitioning of surface-active compounds away from the bulk solution, which reduces hygroscopicity, dominates any increases in hygroscopicity due to reduced surface tension. This is opposite to what is typically assumed for soluble surfactants. Furthermore, we saw no evidence that micellization limits SDS activity in micron-sized solution droplets, as observed in macroscopic solutions. These results suggest that while the high-RH hygroscopicity of inorganic compounds can be reliably predicted using readily available data, surface-activity parameters obtained from macroscopic solutions with organic solutes may be inappropriate for calculations of the hygroscopicity of micron-sized droplets.

scholarly journals Modeling the surface tension of complex, reactive organic–inorganic mixtures

2013 ◽  
Vol 13 (21) ◽  
pp. 10721-10732 ◽  
Author(s):  
A. N. Schwier ◽  
G. A. Viglione ◽  
Z. Li ◽  
V. Faye McNeill
Keyword(s):  
Surface Tension ◽  
Organic Compounds ◽  
Atmospheric Aerosols ◽  
Goodness Of Fit ◽  
Cloud Droplet ◽  
Aqueous Mixtures ◽  
Surface Tension Data ◽  
Inorganic Systems ◽  
Experimental Surface ◽  
Using Data

Abstract. Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as heterogeneous reactivity, ice nucleation, and cloud droplet formation. We present new experimental data for the surface tension of complex, reactive organic–inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2–6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two semi-empirical surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well described by a weighted Szyszkowski–Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling of aerosol systems because the Henning model (using data obtained from organic–inorganic systems) and Tuckermann approach provide similar modeling results and goodness-of-fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

Sign in / Sign up

Export Citation Format

Share Document