Effects of Sodium Chloride on Anthracene Photolysis Kinetics in Aqueous, Organic and Mixed Aqueous-Organic Phases

Condensed phases in the atmosphere, such as aerosols, often contain significant fractions of water, organic matter (OM) and halides. Reactivity can vary greatly depending on the phase (aqueous or organic) and on the concentration of halides. Therefore, understanding how reactivity varies in these complex environments is important in order to quantify pollutant fate. We measured photolysis kinetics of the polycyclic aromatic hydrocarbon (PAH) anthracene in aqueous, organic and aqueous-organic solutions with varying concentrations of sodium chloride (NaCl). In water, anthracene photolysis rate constants exhibited a non-linear dependence on NaCl concentration. However, a linear dependence was observed in octanol. In aqueous-organic mixtures, at low salt concentrations photolysis rate constants decreased with increasing concentration of salt. At high NaCl concentrations, photolysis rate constants remained constant in mixtures that were kept stagnant (i.e. at equilibrium) but increased in stirred (turbulent) mixtures. Overall, photolysis kinetics in aqueous-organic salt mixtures were largely governed by a salting out effect. Self-association at solid salt surfaces may account for the increase in rate constants observed at high salt concentrations. Other factors such as singlet oxygen production were determined to not be significant. These results will improve predictions of PAH fate in environmental condensed phases such as aerosols.