Baseline contamination assessment for a new resource recovery facility in Germany Part IV: Atmospheric concentrations of polychlorinated biphenyls and hexachlorobenzene

Abstract

The atmospheric levels of hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs) were measured continuously over almost 1 year at 8 sites near the southern German city of Augsburg. The PCB profiles were similar at all locations, but the levels were about two times higher at sampling points on the edge of the city than at a more remote location. Whereas the PCB profile in the total air varied with time, the profile in the gas phase was very constant over the whole year at all stations. A pronounced annual cycle in the gaseous levels of the PCBs was observed, with levels in summer that were up to 5 times higher than levels in winter. The data were fully consistent with the hypothesis that the concentrations of PCBs in the atmosphere are determined by volatilization of PCB residues stored in soils and other sorbents on the earth's surface. The same behaviour as for the PCBs was also observed for HCB. Equations for the gaseous concentrations of these compounds as a function of temperature were derived and found to explain 90% of the variability in the monitoring data. However, the enthalpies of phase change estimated from the data were about two times less than the enthalpies of vaporization of the compounds. Although there are a number of possible explanations for this observation, more research into the exchange of semivolatile organic contaminants between the atmosphere and the earth's surface is needed to establish why the enthalpies of phase change are so much lower than expected.