Effect of surfactant film on solubility of hydrophobic organic compounds in fog droplets

A HOCs-enrichment reactor was developed to investigate the elevated solubility of n-octane, a surrogate of the hydrophobic organic compounds (HOCs), in the artificial fog droplets containing sodium dodecyl sulfate (SDS), a surrogate of the natural surfactants. The enrichment of n-octane is strongly related to the SDS concentration. In comparison with the solubility of n-octane based on the Henryʹs law for the ideal aqueous solution, the enrichment factors of n-octane in the fog droplets are between 27.2 and 1.87, depending on the SDS concentration (2.85 × 10−3 to 5.15 × 10−5 M). In addition, when SDS concentration is below the specific concentration, 1.03 × 10−4 M, the larger fog droplets show higher enrichment effect than the smaller fog droplets do. Moreover, we present an enrichment model to describe the micro-states of the n-octane molecules partitioning in the SDS organic film at the air/fog interface and the SDS monomers inside the fogwater. The experimental results can easily be expounded and discussed by use of this model.