Effect of Solute Core Curvature on Solubility Luz Teresa Padró April 26, 2004.
Introduction • Aerosols are composed of: • Inorganic and organic matter • Implications of organics in cloud condensation nuclei (CCN) activity • Composition, structure and surface affect activation diameters at different supersaturations
Raymond and Pandis  • Studied cloud activation of single component aerosol particles at 0.3% and 1% supersaturation • 15 compounds • Hygroscopic secondary organics • Hydrophobic primary organics • Compared results with classical Köhler theory and one that takes into account solubility
Results • Theoretical and experimental values do not agree • Attributing this to the particles solubility in water • More solute is being dissolved than that calculated by solubility studies • Is the organic completely soluble?
Modification of Results • Assumed everything dissolved • No core present • Theoretical and experimental values have better agreement • Low solubility compounds activation may be determined by the curvature or Kelvin effect alone
Köhler Theory where: pw(Dp) - water vapor pressure over the droplet diameter Dp po - water vapor pressure over a flat surface at the same temperature Mw - molecular weight of water σw - surface tension of water R - ideal gas constant T – temperature ρw - density of water ns - moles of solute
Critical Parameters Dpc and Sc • Critical Droplet Diameter, Dpc • Critical Saturation, Sc
Sc : Accounting for Solute where: ν - van’t Hoff factor ds - dry particle diameter ρs - density of the solute Ms - molecular weight of the solute
Compounds Studied • Adipic acid • Glutamic acid • Glutaric acid • Norpinic acid • Pinic acid • Pinonic acid
Method • Theory calculations: • ns required by theory • Dpc required for ns • mass of water in Dpc • nsolubility in mass of water • Ratio of ns/nsolubility for each compound
Theory to Solubility Table 1. Theory to solubility ratio for (a) 0.3% supersaturation and (b) 1% supersaturation. where: A – adipic acid GR – glutaric acid GM – glutamic acid N – norpinic acid PI – pinic acid PO – pinonic acid
Method II • Experimental Calculations: • nexperimental • Core diameters • Kelvin effect • greater than 1? • curvature enhanced-solubility
Theory to Experimental Table 2. Theory to experimental ratio for (a) 0.3% supersaturation and (b) 1% supersaturation.
Core diameter Mass Balance where: dw – core diameter ds – dry particle diameter ms – mass of solute Table 3. Dry core diameter for (a) 0.3% supersaturation and (b) 1% supersaturation.
Kelvin effect Table 4. Kelvin effect of compounds that have a core for (a) 0.3% supersaturation and (b) 1% supersaturation.
Summary of Results • Solubility shows no activation: • at both supersaturations • glutamic acid and pinonic acid • at 1% supersaturation • adipic acid, glutaric acid, norpinic acid and pinic acid
Summary of Results II • Experiments shows no activation: • At both supersaturations • glutamic acid • At 0.3% supersaturation • norpinic acid • Kelvin effect > 1 • Shows possibility of curvature-enhanced solubility • Will be studied using a dissolution kinetics model