HYDROPHOBIC ORGANIC-CHEMICALS IN URBAN FOG

The concentrations and aqueous/particle distributions of three classes of hydrophobic organic chemicals, n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) were measured during the autumn of 1986's fog events in the urban area of Zurich, Switzerland. Concentrations of the chemicals in fog were in the range of 10-110 ng ml-1 for n-alkanes (C19-C35), 6-60 ng ml-1 for PAHs (21 compounds) and 7-22 ng ml-1 for PCBs (31 congeners). In many samples, the concentration of individual n-alkanes and PAHs exceeded their water solubility, probably due to their association with dissolved and/or colloidal organic matter. All of the PAHs, except for phenanthrene, were measured as part of the particulate phase. Both the n-alkanes and PCBs showed a trend of increasing particle association with increasing hydrophobicity, but the trends were distinctly different. The presence of PCBs, PAHs, and n-alkanes at these concentrations suggest that fog is an excellent scavenger of hydrophobic organic chemicals. For a forested area near Zurich, Switzerland, it was estimated that the deposition of n-alkanes and PAHs by fog may be about equal to deposition via rain, but that fog may be 100 times more important than rain for the deposition of PCBs.