scholarly journals Surfactants and cloud droplet activation: A systematic extension of Köhler theory based on analysis of droplet stability

2021 ◽  
Vol 154 (2) ◽  
pp. 024707
Author(s):  
Robert McGraw ◽  
Jian Wang
Keyword(s):  
Cloud Droplet ◽  
Droplet Stability ◽  
Kohler Theory ◽  
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

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 Importance of aerosol composition and mixing state for cloud droplet activation in the high Arctic

2014 ◽  
Vol 14 (15) ◽  
pp. 21223-21283 ◽  
Author(s):  
C. Leck ◽  
E. Svensson
Keyword(s):  
Water Vapor ◽  
Cloud Droplet ◽  
Polymer Gels ◽  
High Arctic ◽  
Water Soluble ◽  
Local Source ◽  
Aerosol Composition ◽  
Pack Ice ◽  
Kohler Theory ◽  
Droplet Activation

Abstract. Concentrations of cloud condensation nuclei (CCN) were measured throughout an expedition by icebreaker around the central Arctic Ocean, including a 3 week ice drift operation at 87° N, from 3 August to 9 September 2008. In agreement with previous observations in the area and season median daily CCN concentrations at 0.2% water vapor supersaturation were typically in the range of 15 to 30 cm−3, but concentrations varied by two to three orders of magnitude over the expedition and were occasionally below 1 cm−3. The CCN concentrations were highest near the ice edge and fell by a factor of three in the first 48 h of transport from the open sea into the pack ice region. For longer transport times they increased again indicating a local source over the pack ice, suggested to be polymer gels, via drops injected into the air by bubbles bursting on open leads. By assuming Köhler theory and simulating the cloud nucleation process using a Lagrangian adiabatic air parcel model that solves the kinetic formulation for condensation of water on size resolved aerosol particles we inferred the properties of the unexplained non-water soluble aerosol fraction that is necessary for reproducing the observed concentrations of CCN. We propose that the portion of the internally/externally mixed water insoluble particles was larger in the corresponding smaller aerosol sizes ranges. These particles were physically and chemically behaving as polymer gels: the interaction of the hydrophilic and hydrophobic entities on the structures of polymer gels during cloud droplet activation would at first only show a partial wetting character and only weak hygroscopic growth. Given time, a high CCN activation efficiency is achieved, which is promoted by the hydrophilicity or surface-active properties of the gels. Thus the result in this study argues for that the behavior of the high Arctic aerosol in CCN-counters operating at water vapor supersaturations > 0.4% (high relative humidities) may not be properly explained by conventional Köhler theory.

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 Importance of aerosol composition and mixing state for cloud droplet activation over the Arctic pack ice in summer

2015 ◽  
Vol 15 (5) ◽  
pp. 2545-2568 ◽  
Author(s):  
C. Leck ◽  
E. Svensson
Keyword(s):  
Water Vapour ◽  
Cloud Droplet ◽  
Polymer Gels ◽  
Water Soluble ◽  
The Arctic ◽  
Local Source ◽  
Aerosol Composition ◽  
Pack Ice ◽  
Kohler Theory ◽  
Droplet Activation

Abstract. Concentrations of cloud condensation nuclei (CCN) were measured throughout an expedition by icebreaker around the central Arctic Ocean, including a 3 week ice drift operation at 87° N, from 3 August to 9 September 2008. In agreement with previous observations in the area and season, median daily CCN concentrations at 0.2% water vapour supersaturation (SS) were typically in the range of 15 to 30 cm−3, but concentrations varied by 2 to 3 orders of magnitude over the expedition and were occasionally below 1 cm−3. The CCN concentrations were highest near the ice edge and fell by a factor of 3 in the first 48 h of transport from the open sea into the pack ice region. For longer transport times they increased again, indicating a local source over the pack ice, suggested to be polymer gels, via drops injected into the air by bubbles bursting on open leads. We inferred the properties of the unexplained non-water soluble aerosol fraction that was necessary for reproducing the observed concentrations of CCN. This was made possible by assuming Köhler theory and simulating the cloud nucleation process using a Lagrangian adiabatic air parcel model that solves the kinetic formulation for condensation of water on size resolved aerosol particles. We propose that the portion of the internally/externally mixed water insoluble particles was larger in the corresponding smaller aerosol size ranges. These particles were physically and chemically behaving as polymer gels: the interaction of the hydrophilic and hydrophobic entities on the structures of polymer gels during cloud droplet activation would at first only show a partial wetting character and only weak hygroscopic growth. Given time, a high CCN activation efficiency is achieved, which is promoted by the hydrophilicity or surface-active properties of the gels. Thus the result in this study argues that the behaviour of the high Arctic aerosol in CCN-counters operating at water vapour SSs > 0.4% (high relative humidities) may not be properly explained by conventional Köhler theory.

scholarly journals Cloud droplet activation of secondary organic aerosol is mainly controlled by molecular weight, not water solubility

2018 ◽  
Author(s):  
Jian Wang ◽  
John E. Shilling ◽  
Jiumeng Liu ◽  
Alla Zelenyuk ◽  
David M. Bell ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Water Solubility ◽  
Global Climate ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Average Molecular Weight ◽  
Cloud Droplet ◽  
Oxidation Level ◽  
Organic Species ◽  
Droplet Activation

Abstract. Aerosol particles strongly influence global climate by modifying the properties of clouds. An accurate assessment of the aerosol impact on climate requires knowledge of the concentration of cloud condensation nuclei (CCN), a subset of aerosol particles that can activate and form cloud droplets in the atmosphere. Atmospheric particles typically consist of a myriad of organic species, which frequently dominate the particle composition. As a result, CCN concentration is often a strong function of the hygroscopicity of organics in the particles. Earlier studies showed organic hygroscopicity increases nearly linearly with oxidation level. Such increase of hygroscopicity is conventionally attributed to higher water solubility for more oxidized organics. By systematically varying the water content of activating droplets, we show that for the majority of secondary organic aerosols (SOA), essentially all organics are dissolved at the point of droplet activation. Therefore, the organic hygroscopicity is not limited by solubility, but is dictated mainly by the molecular weight of organic species. Instead of increased water solubility as previously thought, the increase of the organic hygroscopicity with oxidation level is largely because (1) SOA formed from smaller precursor molecules tend to be more oxidized and have lower average molecular weight and (2) during oxidation, fragmentation reactions reduce average organic molecule weight, leading to increased hygroscopicity. A simple model of organic hygroscopicity based on molecular weight, oxidation level, and volatility is developed, and it successfully reproduces the variation of SOA hygroscopicity with oxidation level observed in the laboratory and field studies.

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 An investigation into the performance of four cloud droplet activation parameterisations

2014 ◽  
Vol 7 (4) ◽  
pp. 1535-1542 ◽  
Author(s):  
E. Simpson ◽  
P. Connolly ◽  
G. McFiggans
Keyword(s):  
Aerosol Particle ◽  
Large Scale ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Particle Growth ◽  
Systematic Evaluation ◽  
Climate Modelling ◽  
Median Diameter ◽  
Droplet Activation ◽  
Simulation Time

Abstract. Cloud droplet number concentration prediction is central to large-scale weather and climate modelling. The benchmark cloud parcel model calculation of aerosol particle growth and activation, by diffusion of vapour to aerosol particles in a rising parcel of air experiencing adiabatic expansion, is too computationally expensive for use in large-scale global models. Therefore the process of activation of aerosol particles into cloud droplets is parameterised with an aim to strike the optimum balance between numerical expense and accuracy. We present a detailed systematic evaluation of three cloud droplet activation parameterisations that are widely used in large-scale models and one recent update. In all cases, it is found that there is a tendency to overestimate the fraction of activated aerosol particles when the aerosol particle "median diameter" is large (between 250 and 2000 nm) in a single lognormal mode simulation. This is due to an infinite "effective simulation time" of the parameterisations compared to a prescribed simulation time in the parcel model. This problem arises in the parameterisations because it is assumed that a parcel of air rises to the altitude where maximum supersaturation occurs, regardless of whether this altitude is above the cloud top. Such behaviour is problematic because, in some cases, large aerosol can completely suppress the activation of drops. In some cases when the "median diameter" is small (between 5 and 250 nm) in a single lognormal mode the fraction of activated drops is underestimated by the parameterisations. Secondly, it is found that in dual-mode cases there is a systematic tendency towards underestimation of the fraction of activated drops, which is due to the methods used by the parameterisations to approximate the sink of water vapour.

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