Adsorption of benzene, naphthalene, anthracene, and phenanthrene at the aqueous surface is investigated by means of molecular dynamics simulations. Potentials of mean force, i.e., free energy profiles obtained when moving the studied molecules across an aqueous slab were evaluated. In all cases, deep surface free energy minima, corresponding to orders of magnitude of surface enhancement of the aromatic molecule, were located. This enhancement, which increases with the size of the solute, points to the importance of the aqueous surface for the chemistry of polycyclic aromatic hydrocarbons (PAHs). Supporting evidence in the atmospheric environment related to the heterogeneous chemistry of PAHs on water droplets and planar surfaces is summarized. There is good agreement between the hydration free energies computed from MD calculations and the experimentally determined values. Data pertaining to the importance of the air-water interface in the adsorption and transport of PAHs on micron sized water droplets are described. The relevant data on adsorption and reaction (ozonation and photochemical) at the air-water interface of planar surfaces and droplets are also summarized.

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The effect of compressed CO2 on the critical micelle concentration (cmc) and aggregation number of sodium bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles in isooctane solution was studied by UV/Vis and fluorescence spectroscopy methods in the temperature range of 303.2-318.2 K and at different pressures or mole fractions of CO2 (X(CO2)). The capacity of the reverse micelles to solubilize water was also determined by direct observation. The standard Gibbs free energy (DeltaGo(m)), standard enthalpy (DeltaHo(m)), and standard entropy (DeltaSo(m)) for the formation of the reverse micelles were calculated by using the cmc data determined. It was discovered that the cmc versus X(CO2) curve and the DeltaGo(m) versus X(CO2) curve for a fixed temperature have a minimum, and the aggregation number and water-solubilization capacity of the reverse micelles reach a maximum at the X(CO2) value corresponding to that minimum. These results indicate that CO2 at a suitable concentration favors the formation of and can stabilize AOT reverse micelles. A detailed thermodynamic study showed that the driving force for the formation of the reverse micelles is entropy.

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Combination of reverse micellar solutions and supercritical or compressed carbon dioxide (CO 2) is a new and interesting topic. This work conducted the first study on the effect of compressed CO 2 on the micro-properties ͑e.g., micropolarity, ionic strength, pH) of the sodium bis͑2-ethylhexyl͒ sulfosuccinate reverse micelles in isooctane by phase behavior measurement, Fourier transform infrared and UV-vis spectroscopic techniques. The results show that CO 2 can dissolve in both the organic-continuous phase and the water cores of the reverse micelles. The properties of the reverse micelles can be tuned continuously by changing the pressure of CO 2 because the solubility of CO 2 in the solution and in the water cores depends on the pressure. CO 2 in the water cores can be ionized to produce HCO 3 Ϫ1 and H ϩ. The micropolarity and ionic strength of the water cores increase with the pressure of CO 2. Accordingly, the pH is reduced as the pressure and water-to-surfactant molar ratio (w 0) are increased.