Kohler theory

GCMOM with RH ZSR equation simulated MDRH Hysteresis is treated composition-resolved CCN/IDN based on Kohler theory activation, Nucl. scavenging (rainout), autoconversion for size-resolved cloud droplets or precip. rate dependent of aerosol size and composition hydrometeor coag. (washout), calculated precip. rate dependent of aerosol size and composition dependent sedimentation for all aerosols and hydrometeors... 

MIRAGE2 Bulk equilibrium with RH based on Kohler theory. Hysteresis is treated Mechanistic, parameterized activation based on Kohler theory bulk CCN only Modal activation. Brownian diffusion, autoconversion, precip. rate independent of aerosols Calculated modal scaveng. coeff using a parameterization of the collective efficiency of aerosol particles by rain drops with size dependence Two-moment sedimentation for aerosols, nosedimentation for cloud droplets/ices... 

Kohler theory was originally developed for inorganic salt solutes and, as in Section 17.2.5, can be readily adapted to an insoluble substance as well. Recently Kohler theory has been extended to soluble trace gases, slightly soluble substances, and solutes that... 

The CCN behavior of ambient particles can be measured by drawing an air sample into an instrument in which the particles are subjected to a known supersaturation, a so-called CCN counter (Nenes et al. 2001). If the size distribution and chemical composition of the ambient particles are simultaneously measured, then the measured CCN behavior can be compared to that predicted by Kohler theory on the basis of their size and composition. Such a comparison can be termed a CCN closure, that is, an assessment of the extent to which measured CCN activation can be predicted theoretically [see, for example, VanReken et al. (2003), Ghan et al. (2006), and Rissman et al. (2006)]. The next level of evaluation is an aerosol-cloud drop closure, in which a cloud parcel model, which predicts cloud drop concentration using observed ambient aerosol concentration, size distribution, cloud updraft velocity, and thermodynamic state, is evaluated against direct airborne measurements of cloud droplet number concentration as a function of altitude above cloud base. The predicted activation behavior can also be evaluated by independent measurements by a CCN instrument on board the aircraft. Such an aerosol-cloud drop closure was carried out by Conant et al. (2004) for warm cumulus clouds in Florida. 

A.1 Modified Form of Kohler Theory for a Soluble Trace Gas... 

A.2 Modified Form of the Kohler Theory for a Slightly Soluble Substance... 

Kohler theory describes cloud droplet activation and growth from soluble particles as an equilibrium process [171], The Kohler equation takes into account two competing effects the Raoult or solute, effect which tends to decrease the equilibrium vapor pressure of water over the growing droplet, and the Kelvin, or curvature effect, which serves to increase the equilibrium vapor pressure. The Kohler curve O ig. 3) for a growing droplet describes the equilibrium saturation ratio of water as a function of droplet size and several parameters inherent to the aerosol particle [171, 172] ... 

Padro et al. developed a method called Kohler theory analysis (KTA) which uses Kohler theory coupled with measurements of surface tension, chemical composition, and CCN activity to infer molar volume and solubility [178]. This is a powerful tool for the characterization of the cloud droplet formation potential of ambient particles containing water-soluble organic compounds (WSOC). 

In agreement with previous smdies, Pradeep Kumar et al. showed that particles composed of highly soluble smaller acids like oxalic, malmiic, and glutaric acids activate as predicted by Kohler theory, whereas particles containing long-chain fatty acids such as stearic and oleic acids, which are essentially insoluble in water, do not activate for particle diameters up to 140 nm and supersaturations of 0.6 and... 

Fig. 5 Experimental results of Broekhuizen et al. [225] and Raymond and Pandis [169] compared to those predicted by Kohler theory. For Broekhuizen et al. [225] each point represents an experiment conducted at a fixed supersaturation between 0.33% and 0.89%. The solid symbols represent experimental results compared to the full Kohler theory for the crystalline organic and the open symbols represent those compared to traditional Kohler theory assuming full solubility. The different species studied by Raymond and Pandis [169] are listed on the graph. In this case, the open symbols represent a supersaturation of 0.3% and the solid symbols represent a supersaturation of 1.0%. In this case, for the theoretical diameters, Kohler theory assuming complete solubility is used for species which are wetted by water and assiuning limited solubility themy fm those species which make a finite, nonzero contact angle with water...

Li and coworkers modeled the surface-bulk pardtitming of SDS in mixed SDS/NaCl particles using Kohler theory and chemical properties of the surfactant, allowing the solute concentration and surface tension of the aerosol to vary as the organic partitiOTied between the gas-aerosol interface and the particle bulk [257]. This partitioning was found to affect both the Raoult and Kelvin terms, leading to a net increase in Sc-... 

It is assumed in Kohler theory that cloud droplet activation is a process whereby the particle instantly reaches thermodynamic equilibrium with the local supersaturation condition [266]. However, kinetic limitations on droplet growth can render this... 

CCN closure studies, where observations of ambient aerosol CCN activity are compared to the CCN concentration predicted via Kohler theory based on the particle size distribution and composition, often show discrepancies that can be attributed to kinetic limitations to droplet growth. Besides affecting cloud properties, kinetic limitations to droplet growth in the atmosphere may also impact the lifetime of aerosol particles. Changes in particle lifetime may influence the aerosol composition due to photochemical aging or heterogeneous processing of the aerosol. 

Asa-Awuku A, Nenes A (2007) Effect of solute dissolution kinetics on cloud droplet formation extended Kohler theory. J Geophys Res Atmos 112 D22201. doi 10.1029/ 2005JD006934... 

Li X, Hede T, Tu Y, Leek C, Agren H (2011) Glycine in aerosol water droplets a critical assessment of Kohler theory by predicting surface tension from molecular dynamics simulations. Atmos Chem Phys 11 519-527... 

Sorjamaa R, Svermrngsson B, Raatikainen T, Henning S, Bilde M, Laaksonen A (2004) The role of surfactants in Kohler theory reconsidered. Atmos Chem Phys 4 2107—2117... 

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