Temperature dependence of atmospheric PCB concentrations.

An analysis of data from the U.S. Integrated Atmospheric Deposition Network (IADN) sites near the Great Lakes and a review of the literature shows that the temperature dependence of atmospheric PCB concentrations cannot be used to distinguish sites dominated by long-distance transport from those with local sources. We observe that calculations based on data sets with only approximately 25 measurements over a period of 1 year are unreliable indicators of the long-term temperature dependence at a given location, that temperature independence occurs at temperatures below freezing, and that low PCB concentrations can bias analyses toward a weaker temperature dependence. After accounting for these factors, a similar temperature dependence is observed at all IADN sites, and this temperature dependence increases for PCBs with increasing chlorination. Although previously described models do fit the data, the resulting calculated constants are not meaningful. Instead, a simple new model in which temperatures < 273 K are set equal to 273 K, and the Clausius-Clapeyron equation is used, can account for observed temperature dependence phenomena.