The Influence of Meteorology and Air Masses on Daily Atmospheric PCB and PAH Concentrations at a UK Location

Daily (24 h) air samples were collected on 161 occasions during March−October and December 1994 at a semirural, maritime-influenced site in northwest England and analyzed for PCBs and PAHs. ∑PCB and some low molecular weight PAH concentrations followed similar trends, but the magnitude of the daily concentration changes varied between these two sets of compounds. ∑PCB concentrations only ranged by a factor of 7, between 54 and 375 pg m-3, with ∑PAH varying over a factor of 20 (1.4−40 ng m-3). This is interpreted as evidence that PCBs are becoming well mixed regionally, while PAH concentrations are influenced by ongoing primary sources. A positive relationship between air temperature and concentration was found for some PCB congeners, certain PCB homologue groups, the lighter molecular weight PAHs and ∑PCBs; the heavier molecular weight particulate associated PAHs exhibited a negative relationship with temperature, suggesting combustion sources of these compounds which increase as ambient temperature decreases. A range of standard meteorological parameters was also analyzed, but no consistent correlations were found between any of the parameters and the daily concentrations of PCBs or PAHs. Clausius Clapeyron plots for the PCB data produced slopes that were similar to those at urban U.K. sites suggesting that concentrations at this site are influenced by volatilization of PCBs from the earth's surface. However, the correlations were weak, suggesting that advection also plays a role in controlling the concentrations of PCBs at the site. Generally, air masses that originated to the north of the U.K. contained lower concentrations than those originating to the south; masses which had recently passed over land also tended to have concentrations higher than those that had passed over water. Several factors combine together to influence the daily air concentrations at the site, including temperature, passage over marine and land masses source areas, and (presumably) the frequency and intensity of deposition events.