11/8/2023 0 Comments Ultra fractal 6 license![]() The theory combines the FHH adsorption isotherm 7, 8, 9 with the Kelvin equation. ![]() The so called Frenkel–Halsey–Hill (FHH)-adsorption–activation theory 2 has been applied by several authors in recent years to calculate critical supersaturations of different types of water-insoluble particles 3, 4, 5, 6. In this paper, our aim is to provide an improved description of the liquid drop activation by incorporating the effect of mineral dust porosity into the CCN activation theory. It is quite obvious that elucidation of ice deposition nucleation onto mineral dusts is difficult if even the liquid drop activation by the dust particles is not well understood. Current theories are unable to predict the critical supersaturations required for deposition nucleation to take place 1. In the so called deposition nucleation, ice is formed by direct condensation of water vapour on the aerosol without an intermediate liquid phase. However, at low temperatures many insoluble particle types such as mineral dusts are efficient nuclei for ice clouds. Water soluble aerosols are in general more efficient CCN than insoluble aerosols and exhibit lower critical supersaturations. The threshold (or critical) supersaturation at which the activation of CCN to cloud droplets takes place depends on the CCN material. ![]() We suggest that a closure can be obtained between experimental critical supersaturation for cloud drop activation and that calculated based on water adsorption data, if the latter is corrected using the surface fractal dimension of the insoluble cloud nucleus.Ĭloud droplets are formed when supersaturated water vapour starts condensing on aerosol particles, or cloud condensation nuclei (CCN). ![]() Besides proving the usefulness of the new method for general surface characterization of materials, our results show that the surface fractal dimension is an important determinant in cloud drop formation on water insoluble particles. We show that our method agrees well with previous methods based on measurement of nitrogen adsorption. Here we propose a new method for determining D, based on measuring both the water vapour adsorption isotherm of a given substance and its ability to act as a cloud condensation nucleus when introduced to humidified air in aerosol form. The surface fractal dimension D is a measure that indicates the amount that a surface fills a space and can thereby be used to characterize the surface porosity. Surface porosity affects the ability of a substance to adsorb gases. ![]()
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