Kohler Theory Research Articles

Resolution Of The Main Character's Inner Conflict In The Novel Sunset & Rosie By Tere Liye (Wolfgang Kohler's Theory)

Resolution Of The Main Character's Inner Conflict In The Novel Sunset & Rosie By Tere Liye (Wolfgang Kohler's Theory)

Hybrid water adsorption and solubility partitioning for aerosol hygroscopicity and droplet growth

Abstract. In this work, we studied the cloud condensation nuclei (CCN) activity and subsaturated droplet growth of phthalic acid (PTA), isophthalic acid, (IPTA) and terephthalic acid (TPTA), significant benzene polycarboxylic acids and structural isomers found in the atmosphere. Köhler theory (KT) can be effectively applied for hygroscopicity analysis of PTA due to its higher aqueous solubility compared to IPTA and TPTA. As with other hygroscopicity studies of partially water-soluble and effectively water-insoluble species, the supersaturated and subsaturated hygroscopicity derived from KT principles do not agree. To address the disparities in the sub- and supersaturated droplet growth, we developed a new analytical framework called the Hybrid Activity Model (HAM). HAM incorporates the aqueous solubility of a solute within an adsorption-based activation framework. Frenkel–Halsey–Hill (FHH) adsorption theory (FHH-AT) was combined with the aqueous solubility of the compound to develop HAM. Analysis from HAM was validated using laboratory measurements of pure PTA, IPTA, TPTA and PTA–IPTA internal mixtures. Furthermore, the results generated using HAM were tested against traditional KT and FHH-AT to compare their water uptake predictive capabilities. A single hygroscopicity parameter was also developed based on the HAM framework. Results show that the HAM-based hygroscopicity parameter can successfully simulate the water uptake behavior of the pure and internally mixed samples. Results indicate that the HAM framework may be applied to atmospheric aerosols of varying chemical structures and aqueous solubility.

Drying of virus-containing particles: modelling effects of droplet origin and composition

Background and purposeVirus-containing aerosol droplets emitted by breathing, speech or coughing dry rapidly to equilibrium with ambient relative humidity (RH), increasing in solute concentration with effects on virus survival and decreasing in diameter with effects on sedimentation and respiratory uptake. The aim of this paper is to model the effect of ionic and macromolecular solutes on droplet drying and solute concentration.MethodsDeliquescence-efflorescence concepts and Kohler theory were used to simulate the evolution of solute concentrations and water activity in respiratory droplets, starting from efflorescence data on mixed NaCl/KCl aerosols and osmotic pressure data on respiratory macromolecules.ResultsIn NaCl/KCl solutions total salt concentrations were shown to reach 10-13 M at the efflorescence RH of 40-55%, depending on the K:Na ratio. Dependence on K:Na ratio implies that the evaporation curves differ between aerosols derived from saliva and from airway surfaces. The direct effect of liquid droplet size through the Kelvin term was shown to be smaller and restricted to the evolution of breath emissions. Modelling the effect of proteins and glycoproteins showed that salts determine drying equilibria down to the efflorescence RH, and macromolecules at lower RH.ConclusionDifferences in solute composition between airway surfaces and saliva are predicted to lead to different drying behaviour of droplets emitted by breathing, speech and coughing. These differences may influence the inactivation of viruses.

A Lagrangian Cloud Model for the Study of Marine Fog

A large-eddy simulation model is coupled with a Lagrangian cloud model to study marine fog. In this model, aerosols and droplets are treated from a Lagrangian frame of reference, in contrast to the traditional bulk and bin microphysical models. Droplet growth via condensation is governed by Kohler theory and environmental conditions local to the droplet. Coupling to the vapour and temperature fields of the flow ensures mass, momentum, and energy conservation between the air and droplet phases. Based on the recent C-FOG field campaign, a simulation is performed which highlights the benefits and potential of this type of model. By initializing the simulation with the measured aerosol size distribution and making assumptions about the chemical composition of the multiple peaks, the simulations provide a clear explanation for the observed bimodal droplet distribution during C-FOG: high supersaturation levels cause condensational growth of nearly all coarse-mode aerosols (presumed to be composed of marine salt), as well as a large number of accumulation model aerosols (presumed to be of continental origin with a lower hygroscopicity). The largest peak in the resulting droplet distribution is created from coarse-mode aerosols with high hygroscopicity, while the secondary peak is only possible due to the limited impact of the largest peak on saturation levels inside the fog. Thus, for the simulated levels of supersaturation, it is the limited number of coarse-mode aerosols which is responsible for the emergence of a larger second peak.

Improvement of aerosol activation/ice nucleation in a source-oriented WRF-Chem model to study a winter Storm in California

Abstract The source-oriented Weather Research and Forecasting chemistry (SOWC) model is modified to improve mixed-phase cloud parameterization by including aerosol aging processes (external mixture) in cloud activation/nucleation. The improved SOWC model is applied to investigate how aerosol mixing state influences cloud and ice formation and atmospheric optical properties during a winter storm. SOWC tracks 6-dimensional chemical variables (X, Z, Y, Size Bins, Source Types, Species) through an explicit simulation of atmospheric chemistry and physics. A new module is implemented into the enhanced SOWC model to simulate microphysics processes with all source-oriented hydrometeors (cloud, ice, rain, snow and graupel) by using the modified Morrison two-moment microphysics scheme. In this study, all aerosol source types can activate to form cloud droplets based on the Kohler theory, but the dust source type is the only source of ice nuclei (IN). The Goddard shortwave and longwave radiation schemes are modified to use a new geometric optics method to estimate cloud optical properties by considering the chemistry components and the physical shape of each hydrometeor. The improved SOWC model is used to study a winter storm event that occurred on 6 March 2011, along the western coast of the United States. Compared to ground-based observations, SOWC with the modified Morrison microphysics scheme and modified Goddard radiation schemes predicts reasonable rainfall but the onset of precipitation is delayed by 6 h. Contact freezing is the main mechanism for ice nuclei formation over the ocean because of the number of collisions and large radius gaps between cloud droplets and ice nuclei. However, immersion freezing becomes the dominant nucleation process when the storm approached over land due to increased CCN concentrations and smaller radius gaps between cloud droplets and ice nuclei, especially for the internally mixed simulation, as well as the orographic lifting effect. Increasing CCN and IN in the internal mixing experiment results in 1.7% less rainfall and snowfall over the western coast of the United States.

Capillary Condensation with a Grain of Salt

Capillary condensation (CC), namely, the formation from the vapor of a stable phase of drops below the saturation pressure, is a prevalent phenomenon. It may occur inside porous structures or between surfaces of particles. CC between surfaces, a liquid "bridge", is of particular practical interest because of its resulting adhesive force. To date, studies have focused on pure water condensation. However, nonvolatile materials, such as salts and surfactants, are prevalent in many environments. In the current study, the effect of these contaminants on CC is investigated from a thermodynamic point of view. This is done by computing the Gibbs energy of such systems and developing the modified Kelvin equation, based on the Kohler theory. The results demonstrate that nonvolatile solutes may have a number of major effects, including an increase in the critical radius and the stabilization of the newly formed phase.

CCN characteristics over a tropical coastal station during south-west monsoon: observations and closure studies

Number concentration measurements of cloud condensation nuclei (CCN) at five supersaturation values between 0.2 and 1.0% were made from a coastal site (Thiruvananthapuram) of peninsular India using a single column CCN counter during the summer monsoon period (June–September) of 2013 and 2014. The CCN concentration over this site showed diurnal variations of high values during nighttime and low values during daytime in association with the change in mesoscale circulation patterns. The inter-annual variations of CCN (CCN0.4% = 2,232 ± 672 cm−3 during August 2013 and CCN0.4% = 941 ± 325 cm−3 during August 2014) are mostly associated with the varying intensity of monsoon rainfall. The variation of CCN number concentration with supersaturation is found to be steeper during nighttime (indicating a less CCN active aerosol system) than during daytime (CCN active system). The CCN activation ratio estimated using simultaneous measurements of CCN and aerosol number (CN) concentration clearly depict the role of land-sea breeze circulations with higher values during daytime than the nighttime. The CCN number concentration predicted for different supersaturations, from measured aerosol number size distribution using Kohler theory, indicate the importance of the change in aerosol composition associated with different airmasses in a coastal environment.

Correlation between Surface Tension and the Bulk Dynamics in Salty Atmospheric Aquatic Droplets

The properties of the liquid–gas interface in the presence of surface-active organic matter, and the bulk response to changes of the resulting surface tension are key factors in assessing cloud microphysics or condensation/evaporation dynamics for atmospheric particles. A fundamental question rises on how we can induce changes in the bulk of an aquatic droplet by varying its surface-activity. The challenging aspect of answering such a question rises from the fact that water exerts complexity in its interactions giving rise to many anomalous properties. Here, we employ molecular dynamics simulations on salty aquatic droplets, associated with new particle formation in the atmosphere. We present a correlation between surface tension and a bulk property like the static dielectric constant, which is closely related to the water activity in Kohler theory of droplet formation and growth. We thus correlate surface to bulk properties. The particles we probe consist of water, salt (ammonium bisulfate), and surface-...

Integrating Cloud Condensation Nuclei Predictions with Fast Time Resolved Aerosol Instrumentation to Determine the Hygroscopic Properties of Emissions Over Transient Drive Cycles

The physical and chemical properties of aerosols emitted from vehicles can vary in composition under different driving conditions. Thus, characterizing ephemeral changes in aerosol cloud condensation nuclei (CCN) activity and apparent hygroscopicity for vehicle-testing procedures conducted over transient drive cycles can be challenging. To evaluate CCN activity of these emitted aerosols, a closure method integrating traditional CCN measurements with fast time resolved aerosol instrumentation typically used to measure engine exhaust was utilized. Calibration of the method predicted activation diameters, Dd, within 10% and 15% of Dd derived from Kohler theory for two stable sources, aerosolized ammonium sulfate and α-pinene secondary organic aerosol, respectively. It was then applied to a transient source to estimate the effect of six different ethanol and iso-butanol gasoline blends on the hygroscopic properties of emissions downstream a gasoline direct injection light duty passenger vehicle over transient...

Supersaturation and diffusional droplet growth in liquid clouds: Polydisperse spectra

AbstractEvolution of droplet size distribution (DSD) due to the water vapor diffusion in a vertically moving adiabatic parcels is investigated. Analytical expressions for height dependences of the main DSD parameters and DSD moments are obtained. The asymptotic behavior of the DSD parameters at large heights above cloud base is determined. It is shown that during diffusion growth, the width and the relative dispersion of the DSD decrease with height as z− 1/3 and z− 2/3, respectively. The paper presents examples of DSD evolution in cases DSD forms on aerosols with a three‐mode lognormal distribution. The aerosol distribution parameters used in the study correspond to four aerosol types: “Marine,” “Clean continental,” “Background,” and extremely polluted “Urban.” The vertical profiles of DSD parameters are compared with the asymptotic profiles. It is shown that in case of polydisperse DSD evolution, the vertical profile of supersaturation within several hundred meters above the cloud base can be approximated by a supersaturation profile corresponding to the “equivalent” monodisperse DSD. The initial radius of this equivalent DSD is equal to the mean radius of polydisperse DSD (haze size distribution) at cloud base, which is estimated using the Kohler theory. This result of the relation between the polydisperse and monodisperse solutions is universal. A new equation for estimation of supersaturation maximum for polydisperse case is obtained. The obtained analytical expressions and numerical results are useful for understanding the mechanisms of DSD formation in clouds and for parameterization of warm microphysical processes in cloud models.

Cloud condensation nuclei activity and droplet activation kinetics of wet processed regional dust samples and minerals

Abstract. This study reports laboratory measurements of particle size distributions, cloud condensation nuclei (CCN) activity, and droplet activation kinetics of wet generated aerosols from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. The dependence of critical supersaturation, sc, on particle dry diameter, Ddry, is used to characterize particle-water interactions and assess the ability of Frenkel-Halsey-Hill adsorption activation theory (FHH-AT) and Köhler theory (KT) to describe the CCN activity of the considered samples. Wet generated regional dust samples produce unimodal size distributions with particle sizes as small as 40 nm, CCN activation consistent with KT, and exhibit hygroscopicity similar to inorganic salts. Wet generated clays and minerals produce a bimodal size distribution; the CCN activity of the smaller mode is consistent with KT, while the larger mode is less hydrophilic, follows activation by FHH-AT, and displays almost identical CCN activity to dry generated dust. Ion Chromatography (IC) analysis performed on regional dust samples indicates a soluble fraction that cannot explain the CCN activity of dry or wet generated dust. A mass balance and hygroscopicity closure suggests that the small amount of ions (from low solubility compounds like calcite) present in the dry dust dissolve in the aqueous suspension during the wet generation process and give rise to the observed small hygroscopic mode. Overall these results identify an artifact that may question the atmospheric relevance of dust CCN activity studies using the wet generation method. Based on the method of threshold droplet growth analysis, wet generated mineral aerosols display similar activation kinetics compared to ammonium sulfate calibration aerosol. Finally, a unified CCN activity framework that accounts for concurrent effects of solute and adsorption is developed to describe the CCN activity of aged or hygroscopic dusts.

Ozone oxidation of oleic acid surface films decreases aerosol cloud condensation nuclei activity

[1] Heterogeneous oxidation of aerosols composed of pure oleic acid (C18H34O2, an unsaturated fatty acid commonly found in continental and marine aerosol) by gas-phase O3 is known to increase aerosol hygroscopicity and activity as cloud condensation nuclei (CCN). Whether this trend is preserved when the oleic acid is internally mixed with other electrolytes is unknown and addressed in this study. We quantify the CCN activity of sodium salt aerosols (NaCl and Na2SO4) internally mixed with sodium oleate (SO) and oleic acid (OA). We find that particles containing roughly one monolayer of SO/OA show similar CCN activity to pure salt particles, whereas a tenfold increase in organic concentration slightly depresses CCN activity. O3 oxidation of these multicomponent aerosols has little effect on the critical diameter for CCN activation for unacidified particles at all conditions studied, and the activation kinetics of the CCN are similar in each case to those of pure salts. SO-containing particles which are acidified to atmospherically relevant pH before analysis in order to form oleic acid, however, show depressed CCN activity upon oxidation. This effect is more pronounced at higher organic concentrations. The behavior after oxidation is consistent with the disappearance of the organic surface film, supported by Kohler Theory Analysis (KTA). The κ-Kohler calculations show a small decrease in hygroscopicity after oxidation. The important implication of this finding is that oxidative aging may not always enhance the hygroscopicity of internally mixed inorganic-organic aerosols.

Importance of adsorption for CCN activity and hygroscopic properties of mineral dust aerosol

This study uses published data on dust‐water interactions to examine the importance of including water adsorption effects when describing the hygroscopic and cloud condensation nuclei (CCN) behavior of mineral dust aerosol. Adsorption activation theory (AT) better represents fresh dust‐water interactions than Köhler theory (KT), as i) a consistent set of adsorption parameters can describe the hygroscopic behavior of dust (under both sub and supersaturated conditions), and ii) the dependence of critical supersaturation, sc, with particle dry diameter, Ddry, is closer to observations. The long adsorption timescale could also contribute to the large differences observed between dry and wet generated dust hygroscopicity. If KT and AT are consistently applied to the same dust size distribution, KT predicts up to tenfold higher CCN and 40% higher droplet number concentration than AT. This profoundly different behavior between the theories suggests that both may be required for a comprehensive description of atmospheric dust CCN activity.

Cloud droplet activation of secondary organic aerosol

Measurements of hygroscopicity and cloud condensation nuclei (CCN) activity were conducted on secondary organic aerosol (SOA) formed in a smog chamber. SOA precursors included α‐pinene, β‐pinene, Δ3‐carene, and toluene, representative of both naturally and anthropogenically emitted organic species. Measured CCN activation was comparable for all of the species studied and occurred at humidity conditions which are readily attained in the atmosphere. Further, there was little variation in hygroscopic growth between compounds. However, measured droplet activation conditions were inconsistent with hygroscopicity measured below water saturation and Köhler theory expressions based on Raoult’s law for several parameterizations for water activity. In the atmosphere, SOA may compose a large fraction of atmospheric particulate matter and will often exist internally mixed with inorganic species. Using the current results, we compare SOA to insoluble organic species to calculate CCN activation from mixed organic‐sulfate particles for a range of atmospheric conditions. We find that droplet activation behavior of mixed particles containing SOA is the same as that of mixed particles for which the organic component is nonhygroscopic, except for cases in which there are low particle concentrations, low updraft velocities, and the aerosol composition is dominated by organics.

CCN predictions: Is theory sufficient for assessments of the indirect effect?

This study quantitatively assesses the sensitivity of cloud droplet number (CDNC) to errors in cloud condensation nuclei (CCN) predictions that arise from application of Köhler theory. The CDNC uncertainty is assessed by forcing a droplet activation parameterization with a comprehensive dataset of CCN activity and aerosol size and chemical composition obtained during the ICARTT field campaign in August 2004. Our analysis suggests that, for a diverse range of updraft velocity, droplet growth kinetics and airmass origin, the error in predicted CDNC is (at most) half of the CCN prediction error. This means that the typical 20–50% error in ambient CCN closure studies would result in a 10–25% error in CDNC. For the first time, a quantitative link between aerosol and CDNC prediction errors is available, and can be the basis of a robust uncertainty analysis of the first aerosol indirect effect.

CCN Activation of Pure and Coated Carbon Black Particles

The CCN (cloud condensation nucleus) activation of pure and coated carbon black particles was investigated using the University of Vienna cloud condensation nuclei counter (Giebl, H.; Berner, A.; Reischl, G.; Puxbaum, H.; Kasper-Giebl, A.; Hitzenberger, R. J. Aerosol Sci. 2002, 33, 1623-1634). The particles were produced by nebulizing an aqueous suspension of carbon black in a Collison atomizer. The activation of pure carbon black particles was found to require higher supersaturations than predicted by calculations representing the particles as insoluble, wettable spheres with mobility equivalent diameter. To test whether this effect is an artifact due to heating of the light-absorbing carbon black particles in the laser beam, experiments at different laser powers were conducted. No systematic dependence of the activation of pure carbon black particles on laser power was observed. The observations could be modeled using spherical particles and an effective contact angle of 4-6 degrees of water at their surface. The addition of a small amount of NaCl to the carbon black particles (by adding 5% by mass NaCl to the carbon black suspension) greatly enhanced their CCN efficiency. The measured CCN efficiencies were consistent with Kohler theory for particles consisting of insoluble and hygroscopic material. However, coating the carbon black particles with hexadecanol (a typical film-forming compound with one hydrophobic and one hydrophilic end) efficiently suppressed the CCN activation of the carbon black particles.

Cloud condensation nucleus activity of internally mixed ammonium sulfate/organic acid aerosol particles

The ability of mixed ammonium sulfate/organic acid particles to act as cloud condensation nuclei (CCN) has been studied in the laboratory using a continuous flow, thermal-gradient diffusion chamber operated at supersaturations between 0.3% and 0.6%. The organic acids studied were malonic acid, azelaic acid, hexanoic acid, cis-pinonic acid, oleic acid and stearic acid, and the particles were largely prepared by condensation of the organic vapor onto a dry ammonium sulfate core. For malonic acid and hexanoic acid, the mixed particles activated as predicted by a simple Kohler theory model where both species are assumed to be fully soluble and the droplet has the surface tension of water. Three low-solubility species, cis-pinonic acid, azelaic acid and oleic acid, are well modeled where the acid was assumed to be either partially or fully insoluble. Interestingly, although thin coats of stearic acid behaved in a manner similar to that displayed by oleic and cis-pinonic acid, we observed that thick coats led to a complete deactivation of the ammonium sulfate, presumably because the water vapor could not diffuse through the solid stearic acid. We observed no CCN behavior that could be clearly attributed to a lowering of the surface tension of the growing droplet by the presence of the organic constituents, some of which are highly surface active.

A New Double-Moment Microphysics Parameterization for Application in Cloud and Climate Models. Part I: Description

Abstract A new double-moment bulk microphysics scheme predicting the number concentrations and mixing ratios of four hydrometeor species (droplets, cloud ice, rain, snow) is described. New physically based parameterizations are developed for simulating homogeneous and heterogeneous ice nucleation, droplet activation, and the spectral index (width) of the droplet size spectra. Two versions of the scheme are described: one for application in high-resolution cloud models and the other for simulating grid-scale cloudiness in larger-scale models. The versions differ in their treatment of the supersaturation field and droplet nucleation. For the high-resolution approach, droplet nucleation is calculated from Kohler theory applied to a distribution of aerosol that activates at a given supersaturation. The resolved supersaturation field and condensation/deposition rates are predicted using a semianalytic approximation to the three-phase (vapor, ice, liquid) supersaturation equation. For the large-scale version of the scheme, it is assumed that the supersaturation field is not resolved and thus droplet activation is parameterized as a function of the vertical velocity and diabatic cooling rate. The vertical velocity includes a subgrid component that is parameterized in terms of the eddy diffusivity and mixing length. Droplet condensation is calculated using a quasi-steady, saturation adjustment approach. Evaporation/deposition onto the other water species is given by nonsteady vapor diffusion allowing excess vapor density relative to ice saturation.

Link between aerosol hygroscopic growth and droplet activation observed for hill-capped clouds at connected flow conditions during FEBUKO

Abstract Within the ground-based cloud passage experiment FEBUKO, which was carried out at the mountain ridge Thuringer Wald (Germany) during October 2001 and 2002, the dry number size distribution and hygroscopic growth of aerosol particles upwind cloud and the dry number size distributions of interstitial particles and cloud droplet residuals inside cloud were measured at connected flow conditions. The connected flow between the upwind and in-cloud summit site was meteorologically predicted and experimentally confirmed for three selected cloud events. For these events, it could be verified that entrainment and droplet deposition had only a minor influence on the evolution of the particle size distribution between the two sites. Hence, the size resolved soluble volume fraction of the cloud input aerosol particles determined from the hygroscopic growth measurements could be related to the particle activation inferred from the particle size distributions observed inside cloud. The shape and steepness of the scavenging fraction as a function of particle diameter was found to correlate with the increase of soluble volume fraction with size, which had implications for the droplet activation diameter of the cloud condensation nuclei (CCN) that ranged between 110 and 180 nm. The minimum soluble volume fraction e min that was required to serve as CCN was determined for three different dry diameters from the relation of the particle volume fraction and scavenging fraction. From the comparison with e min predictions from classical Kohler theory it is inferred that aerosol particles remained in the interstitial phase although they should have been activated. A discussion of different processes which have the general ability to explain this finding favoured the hypothesis of organic surface films retarding the uptake of water molecules.

CCN activation of slightly soluble organics: the importance of small amounts of inorganic salt and particle phase

Using a static thermal-gradient diffusion cloud condensation nucleus chamber we study the effect of small amounts of inorganic salts on the cloud droplet activation of two slightly soluble organic aerosol components (adipic and succinic acid) and experimentally confirm the two maxima predicted by Kohler theory modified to take limited solubility into account. Equally importantly we suggest (and confirm experimentally) that solid and liquid (supersaturated) particles of slightly soluble organic compounds follow two different Kohler curves and that knowledge about the particle phase and thereby the humidity history is important for interpretation of experimental data and modelling of the aerosol indirect climate effect.