Solubility properties of surfactants in atmospheric aerosol and cloud/fog water samples (original) (raw)
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The surface tension of aqueous solutions of some atmospheric water-soluble organic compounds
Atmospheric Environment, 2004
The surface tensions of aqueous solutions of levoglucosan, 3-hydroxybutanoic acid, 3-hydroxybenzoic acid, azelaic acid, pinonic acid, and humic acid have been measured. These compounds are suggested as model substances for the water-soluble organic compounds (WSOC) in atmospheric aerosols and droplets which may play an important role in the aerosol cycle because of their surface-active potentials. The reductions in surface tension induced by single and mixed WSOC in aqueous solution of pure water is remarkable. However, the results of this investigation cannot explain the strong reduction in surface tension in real cloud and fog water samples at concentrations of WSOC below 1 mg/mL.
Surfactants in cloud droplet activation: mixed organic-inorganic particles
Atmospheric Chemistry and Physics, 2010
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.
Reviews of Geophysics, 1983
Surface-active organic molecules are common constituents of atmospheric aerosol particles, raindrops, and snowflakes. If these compounds are present as surface films, transfer of gases into the atmospheric water systems could be impeded, evaporation could be slowed, and the aqueous chemical reactions could be influenced. To investigate these possibilities, we have reviewed the chemical literature pertaining to organic films on aqueous surfaces: their composition, structure, properties, and effects. We then review the surface-active organic compounds in atmospheric water. We report the results of new measurements of surface tension of aqueous solutions of common atmospheric organic compounds (fi-pinene, n-hexanol, eugenol, and anethole) and demonstrate that the compounds produce films with properties similar to those of the more well known surfactants. We conclude that organic films are probably common on atmospheric aerosol particles and that they may occur under certain circumstances on fog droplets, cloud droplets, and snowflakes. If present, they will increase the lifetimes of aerosol particles, fog droplets, and cloud droplets, both by inhibiting water vapor evaporation and by reducing the efficiency with which these atmospheric components are scavenged. The presence of the films will not cause a significant reduction of solar radiation within the aqueous solution. It appears likely, however, that the transport of gaseous molecules into and out of the aqueous solution will be impeded by factors of several hundred or more when organic films are present. Since incorporated gas molecules provide much of the oxidizing potential of atmospheric water droplets, the organic films will play a major role in droplet chemistry by strongly inhibiting solution oxidation.
Atmospheric Environment, 2000
A decrease in surface tension with respect to pure water was observed in wet aerosol and cloud/fog samples. The measured decrease of surface tension is positively correlated with the concentration of total soluble organic compounds in the samples. On the basis of a previously developed methodology to fractionate soluble organic compounds into three di!erent classes (neutral compounds, mono-and dicarboxylic acids and polycarboxylic acids), we investigated the surface-active behaviour of the compounds within each of these classes. Polycarboxylic acids having a molecular structure analogous to that of humic substances (humic-like substances) were found to be the most e!ective surface-active species within the droplets: three times more e!ective than mono-and dicarboxylic acids and one order of magnitude more than neutral compounds.
Salting out, non-ideality and synergism enhance surfactant efficiency in atmospheric aerosols
Scientific Reports
In Earth’s atmosphere, the surface tension of sub-micron aerosol particles is suspected to affect their efficiency in becoming cloud droplets. But this quantity cannot be measured directly and is inferred from the chemical compounds present in aerosols. Amphiphilic surfactants have been evidenced in aerosols but experimental information on the surface properties of their mixtures with other aerosol components is lacking. This work explores experimentally the surface properties of aqueous mixtures of amphiphilic surfactants (SDS, Brij35, TritonX100, TritonX114, and CTAC) with inorganic salts (NaCl, (NH4)2SO4) and soluble organic acids (oxalic and glutaric acid) using pendant droplet tensiometry. Contrary to what could be expected, inorganic salts and organic acids systematically enhanced the efficiency of the surfactants rather than reduced it, by further lowering the surface tension and, in some cases, the CMC. Furthermore, all the mixtures studied were strongly non-ideal, some even...
Selectivity and stability of organic films at the air–aqueous interface
Journal of Colloid and Interface Science, 2004
It has recently been determined that organic compounds represent a significant percentage of the composition of certain atmospheric aerosols. Amphiphilic organics, such as fatty acids and alcohols, partition to the interface of aqueous aerosols. In this way, the air-aqueous interface of an aerosol has the ability to act as both a concentrator and a selector of organic surfactants. Isotherms of nonanoic acid, stearic acid, 1-octadecanol, and a binary of mixture of nonanoic and stearic acids were used to infer the packing ability and molecular orientation of the surfactants at the interface. The selectivity of the air-aqueous interface was studied by monitoring the composition of binary organic films as a function of film exposure time. The films were formed, aged, and collected with the use of a Langmuir trough. The composition of the aged film was determined via GC-MS. Surfactants with differing carbon number and chemical functionalities were studied. These included stearic acid, lauric acid, 1-octadecanol, and octadecane. The stability and packing ability of stearic and lauric acid films were examined as a function of subphase pH. The relevance of these findings as they relate to the composition and structure of organic aerosols as well as recent surface-sensitive aerosol field measurements is discussed.
Enrichment of surface-active compounds in coalescing cloud drops
Geophysical Research Letters, 2008
Surfactants often found in tropospheric aerosols, can affect the onset and development of clouds. Due to high dilution during droplet growth, the effects of surfactants on cloud microphysical processes have been mostly neglected. However, while cloud growth by coalescence conserves the combined volume of all cloud droplets, it reduces the combined surface area. This could lead to enrichment of water-insoluble surfactants (WIS) and to reduced surface tension of droplets forming in warm processes. Measurements of individual raindrops reveal the presence of water insoluble surfactants. Our field and laboratory studies as well as simple theoretical arguments suggest that by causing varying and size-dependent surface tension, WIS can affect cloud microphysics.
Extraction and Characterization of Surfactants from Atmospheric Aerosols
Journal of Visualized Experiments, 2017
Surface-active compounds, or surfactants, present in atmospheric aerosols are expected to play important roles in the formation of liquid water clouds in the Earth's atmosphere, a central process in meteorology, hydrology, and for the climate system. But because specific extraction and characterization of these compounds have been lacking for decades, very little is known on their identity, properties, mode of action and origins, thus preventing the full understanding of cloud formation and its potential links with the Earth's ecosystems. In this paper we present recently developed methods for 1) the targeted extraction of all the surfactants from atmospheric aerosol samples and for the determination of 2) their absolute concentrations in the aerosol phase and 3) their static surface tension curves in water, including their Critical Micelle Concentration (CMC). These methods have been validated with 9 references surfactants, including anionic, cationic and non-ionic ones. Examples of results are presented for surfactants found in fine aerosol particles (diameter <1 μm) collected at a coastal site in Croatia and suggestions for future improvements and other characterizations than those presented are discussed. Video Link The video component of this article can be found at https://www.jove.com/video/55622/ Further improvements and other types of characterizations, that could be used in complement to those presented, will be discussed. Recent applications of these methods have already shown how such analyses can improve the understanding of the role of surfactants in cloud formation, by evidencing this role itself, 3 determining the surfactant concentrations in atmospheric aerosols 3,4,5,6 and mode of action in cloud droplet formation, 3,6 evidencing their biogenic origin, 3,4,7 and explaining their lack of observation by classical instruments.
Effect of Surfactant on Cloud Formation
2022
Atmospheric aerosols can consist of inorganic and organic substances, including surfactants at a significant concentration. Importantly, the latter can reduce the surface tension at the liquid-vapor surfaces, where they preferentially adsorb due to their amphiphilic structure. As a result, processes such as droplet coalescence, development of precipitation and ultimately cloud lifetime, may depend on the presence of surfactants in the aerosols. Here, we present a numerical model for cloud droplet formation, which is based on the Lagrangian particle-based microphysics-scheme super-droplet method and takes into account the presence of surfactant in the droplets. Our results show that surfactant facilitates cloud formation by increasing the number and size of activated droplets, which concentrate at the bottom of the cloud, while the largest droplets are concentrated at the top of the cloud. This indicates a circulation of droplets that involves activation and growth processes from the bottom of the cloud towards the top. Moreover, our conclusions are independent of the particular approach used for modeling the diffusion of Eulerian variables due to the subgrid-scale turbulence. We anticipate that our results will enrich our understanding of the role of surfactants in the behavior of atmospheric aerosols and, importantly, will pave the way for further developments in the numerical modeling of systems with surfactants at macroscopic scales.