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 [2002] 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?

0.3% Supersaturation

1% Supersaturation

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

Complete Solubility Assumption

Köhler Theory where: p w (D p ) - water vapor pressure over the droplet diameter Dp p o - water vapor pressure over a flat surface at the same temperature M w - molecular weight of water σ w - surface tension of water R - ideal gas constant T – temperature ρ w - density of water n s - moles of solute

Köhler Curves

Critical Parameters D pc and S c Critical Droplet Diameter, D pc Critical Saturation, S c

S c : Accounting for Solute where: ν - van’t Hoff factor d s - dry particle diameter ρ s - density of the solute M s - molecular weight of the solute

Compounds Studied Adipic acid Glutamic acid Glutaric acid Norpinic acid Pinic acid Pinonic acid

Method Theory calculations: n s required by theory D pc required for n s mass of water in D pc n solubility in mass of water Ratio of n s /n solubility for each compound

Theory to Solubility n s /n A n s /n GR n s /n GM n s /n N n s /n PI n s /n PO a b where: A – adipic acid GR – glutaric acid GM – glutamic acid N – norpinic acid PI – pinic acid PO – pinonic acid Table 1. Theory to solubility ratio for (a) 0.3% supersaturation and (b) 1% supersaturation.

Method II Experimental Calculations: n experimental Core diameters Kelvin effect greater than 1? curvature enhanced-solubility

Theory to Experimental n s /n A n s /n GR n s /n GM n s /n N n s /n PI n s /n PO a b Table 2. Theory to experimental ratio for (a) 0.3% supersaturation and (b) 1% supersaturation.

Core diameter d wA (cm)d wGR (cm)d wGM (cm)d wN (cm)d wPI (cm)d wPO (cm) a 1.57E E E E E E-03 b 1.06E E E E E E-05 Table 3. Dry core diameter for (a) 0.3% supersaturation and (b) 1% supersaturation. Mass Balance where: d w – core diameter d s – dry particle diameter m s – mass of solute

Kelvin effect C curved surface /C flat surface A C curved surface /C flat surface GM C curved surface /C flat surface N C curved surface /C flat surface PI C curved surface /C flat surface PO a b 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

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