Influence of organic compounds on the cloud droplet activation: A model investigation considering the volatility, water solubility, and surface activity of organic matter

2002 ◽  
Vol 107 (D22) ◽  
Author(s):  
Tatu Anttila
Keyword(s):  
Organic Matter ◽  
Organic Compounds ◽  
Surface Activity ◽  
Water Solubility ◽  
Cloud Droplet ◽  
Model Investigation ◽  
Droplet Activation

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 Tight coupling of particle size, number and composition in atmospheric cloud droplet activation

2012 ◽  
Vol 12 (7) ◽  
pp. 3253-3260 ◽  
Author(s):  
D. O. Topping ◽  
G. McFiggans
Keyword(s):  
Water Vapour ◽  
Organic Compounds ◽  
Radiative Forcing ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Compositional Dependence ◽  
Ambient Conditions ◽  
Tight Coupling ◽  
Aerosol Composition ◽  
Droplet Activation

Abstract. The substantial uncertainty in the indirect effect of aerosol particles on radiative forcing in large part arises from the influences of atmospheric aerosol particles on (i) the brightness of clouds, exerting significant shortwave cooling with no appreciable compensation in the long wave, and on (ii) their ability to precipitate, with implications for cloud cover and lifetime. Predicting the ambient conditions at which aerosol particles may become cloud droplets is largely reliant on an equilibrium relationship derived by Köhler (1936). However, the theoretical basis of the relationship restricts its application to particles solely comprising involatile compounds and water, whereas a substantial fraction of particles in the real atmosphere will contain potentially thousands of semi-volatile organic compounds in addition to containing semi-volatile inorganic components such as ammonium nitrate. We show that equilibration of atmospherically reasonable concentrations of organic compounds with a growing particle as the ambient humidity increases has potentially larger implications on cloud droplet formation than any other equilibrium compositional dependence, owing to inextricable linkage between the aerosol composition, a particles size and concentration under ambient conditions. Whilst previous attempts to account for co-condensation of gases other than water vapour have been restricted to one inorganic condensate, our method demonstrates that accounting for the co-condensation of any number of organic compounds substantially decreases the saturation ratio of water vapour required for droplet activation. This effect is far greater than any other compositional dependence; more so even than the unphysical effect of surface tension reduction in aqueous organic mixtures, ignoring differences in bulk and surface surfactant concentrations.

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 Uncertainty in aerosol hygroscopicity resulting from semi-volatile organic compounds

2017 ◽  
Author(s):  
Olivia Goulden ◽  
Matthew Crooks ◽  
Paul Connolly
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Uncertainty Range ◽  
Volatile Organic ◽  
Cloud Droplet Number Concentration ◽  
Novel Method ◽  
Droplet Activation ◽  
Aerosol Properties

Abstract. We present a novel method of exploring the effect of uncertainties in aerosol properties on cloud droplet number using existing cloud droplet activation parameterisations. Aerosol properties of a single involatile particle mode are randomly sampled within an uncertainty range and resulting maximum supersaturations and critical diameters calculated using the cloud droplet activation scheme. Hygroscopicity parameters are subsequently derived and the values of the mean and uncertainty are found to be comparable to experimental observations. A recently proposed cloud droplet activation scheme that includes the effects of co-condensation of semi-volatile organic compounds onto a single lognormal mode of involatile particles is also considered. In addition to the uncertainties associated with the involatile particles, concentrations, volatility distributions and chemical composition of the semi-volatile organic compounds are randomly sampled and hygroscopicity parameters are derived using the cloud droplet activation scheme. The inclusion of semi-volatile organic compounds is found to have a significant effect on the hygroscopicity and contributes a large uncertainty. For non-volatile particles that are effective cloud condensation nuclei, the co-condensation of semi-volatile organic compounds reduces their actual hygroscopicity by approximately 25 %. A new concept of an effective hygroscopicity parameter is introduced that can computationally efficiently simulate the effect of semi-volatile organic compounds on cloud droplet number concentration without direct modelling of the organic compounds. These effective hygroscopicities can be as much as a factor of two higher than those of the non-volatile particles onto which the volatile organic compounds condense.

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 Tight coupling of particle size and composition in atmospheric cloud droplet activation

2011 ◽  
Vol 11 (9) ◽  
pp. 25155-25171 ◽  
Author(s):  
D. Topping ◽  
G. McFiggans
Keyword(s):  
Water Vapour ◽  
Organic Compounds ◽  
Radiative Forcing ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Compositional Dependence ◽  
Ambient Conditions ◽  
Tight Coupling ◽  
Aerosol Composition ◽  
Droplet Activation

Abstract. The substantial uncertainty in the indirect effect on radiative forcing in large part arises from the influences of atmospheric aerosol particles on (i) the brightness of clouds, exerting significant shortwave cooling with no appreciable compensation in the longwave, and on (ii) their ability to precipitate, with implications for cloud cover and lifetime. Predicting the ambient conditions at which aerosol particles may become cloud droplets is largely reliant on an equilibrium relationship derived in 1936. However, the theoretical basis of the relationship restricts its application to particles solely comprising involatile compounds and water, whereas a substantial fraction of particles in the real atmosphere will contain potentially thousands of semi-volatile organic compounds in addition to containing semi-volatile inorganic components such as ammonium nitrate. We show that equilibration of atmospherically reasonable concentrations of organic compounds with a growing particle as the ambient humidity increases has larger implications on cloud droplet formation than any other equilibrium compositional dependence, owing to inextricable linkage between the aerosol composition and a particles size under ambient conditions. Whilst previous attempts to account for co-condensation of gases other than water vapour have been restricted to one inorganic condensate, our method demonstrates that accounting for the co-condensation of any number of organic compounds substantially decreases the saturation ratio of water vapour required for droplet activation. This effect is far greater than any other compositional dependence; moreso even than the unphysical effect of surface tension reduction in aqueous organic mixtures, ignoring differences in bulk and surface surfactant concentrations.

scholarly journals Uncertainty in aerosol hygroscopicity resulting from semi-volatile organic compounds

2018 ◽  
Vol 18 (1) ◽  
pp. 275-287
Author(s):  
Olivia Goulden ◽  
Matthew Crooks ◽  
Paul Connolly
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Uncertainty Range ◽  
Volatile Organic ◽  
Cloud Droplet Number Concentration ◽  
Novel Method ◽  
Droplet Activation ◽  
Aerosol Properties

Abstract. We present a novel method of exploring the effect of uncertainties in aerosol properties on cloud droplet number using existing cloud droplet activation parameterisations. Aerosol properties of a single involatile particle mode are randomly sampled within an uncertainty range and resulting maximum supersaturations and critical diameters calculated using the cloud droplet activation scheme. Hygroscopicity parameters are subsequently derived and the values of the mean and uncertainty are found to be comparable to experimental observations. A recently proposed cloud droplet activation scheme that includes the effects of co-condensation of semi-volatile organic compounds (SVOCs) onto a single lognormal mode of involatile particles is also considered. In addition to the uncertainties associated with the involatile particles, concentrations, volatility distributions and chemical composition of the SVOCs are randomly sampled and hygroscopicity parameters are derived using the cloud droplet activation scheme. The inclusion of SVOCs is found to have a significant effect on the hygroscopicity and contributes a large uncertainty. For non-volatile particles that are effective cloud condensation nuclei, the co-condensation of SVOCs reduces their actual hygroscopicity by approximately 25 %. A new concept of an effective hygroscopicity parameter is introduced that can computationally efficiently simulate the effect of SVOCs on cloud droplet number concentration without direct modelling of the organic compounds. These effective hygroscopicities can be as much as a factor of 2 higher than those of the non-volatile particles onto which the volatile organic compounds condense.

scholarly journals Cloud condensation nuclei activity of six pollenkitts and the influence of their surface activity

2019 ◽  
Vol 19 (7) ◽  
pp. 4741-4761 ◽  
Author(s):  
Nønne L. Prisle ◽  
Jack J. Lin ◽  
Sara Purdue ◽  
Haisheng Lin ◽  
J. Carson Meredith ◽  
...  
Keyword(s):  
Surface Tension ◽  
Surface Activity ◽  
Water Uptake ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Surface Partitioning ◽  
Aqueous Surface ◽  
Droplet Activation

Abstract. The role of surfactants in governing water interactions of atmospheric aerosols has been a recurring topic in cloud microphysics for more than two decades. Studies of detailed surface thermodynamics are limited by the availability of aerosol samples for experimental analysis and incomplete validation of various proposed Köhler model frameworks for complex mixtures representative of atmospheric aerosol. Pollenkitt is a viscous material that coats grains of pollen and plays important roles in pollen dispersion and plant reproduction. Previous work suggests that it may also be an important contributor to pollen water uptake and cloud condensation nuclei (CCN) activity. The chemical composition of pollenkitt varies between species but has been found to comprise complex organic mixtures including oxygenated, lipid, and aliphatic functionalities. This mix of functionalities suggests that pollenkitt may display aqueous surface activity, which could significantly impact pollen interactions with atmospheric water. Here, we study the surface activity of pollenkitt from six different species and its influence on pollenkitt hygroscopicity. We measure cloud droplet activation and concentration-dependent surface tension of pollenkitt and its mixtures with ammonium sulfate salt. Experiments are compared to predictions from several thermodynamic models, taking aqueous surface tension reduction and surfactant surface partitioning into account in various ways. We find a clear reduction of surface tension by pollenkitt in aqueous solution and evidence for impact of both surface tension and surface partitioning mechanisms on cloud droplet activation potential and hygroscopicity of pollenkitt particles. In addition, we find indications of complex nonideal solution effects in a systematic and consistent dependency of pollenkitt hygroscopicity on particle size. The impact of pollenkitt surface activity on cloud microphysics is different from what is observed in previous work for simple atmospheric surfactants and more resembles recent observations for complex primary and secondary organic aerosol, adding new insight to our understanding of the multifaceted role of surfactants in governing aerosol–water interactions. We illustrate how the explicit characterization of pollenkitt contributions provides the basis for modeling water uptake and cloud formation of pollen and their fragments over a wide range of atmospheric conditions.

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