Study of atmospheric PCB concentrations over the eastern Mediterranean Sea

[1] Air samples were collected between April 1999 and March 2001 at a background marine site in the eastern Mediterranean Sea and analyzed for polychlorinated biphenyls (PCBs). The average concentrations of total PCB congeners (SigmaPCBs) in the gas and particulate phases of the atmosphere were 68.1 +/- 28.8 and 2.3 +/- 1.8 pg/m(3), respectively. The lack of seasonal variation for the atmospheric concentration of individual congeners and SigmaPCBs and the shallow slopes obtained from the Clausius-Clapeyron (CC) plots for several PCB congeners indicated that long-range transport is the main factor controlling the atmospheric levels of PCBs in this area. Most of the episodes with elevated concentrations of SigmaPCBs concurred with air transport from western and central Europe. This observation was mostly attributed to the predominance of N-NW winds in eastern Mediterranean. The wind speed apparently did not affect the atmospheric concentration of PCBs. Significant changes observed on the homologue group profile of PCBs were mostly related to the origin of air parcels sampled and during summer were most probably related to the reaction of the lighter congeners with OH radicals. Partitioning of PCBs between gas and particulate phases was well correlated with the subcooled liquid vapor pressure (P-L(o)) for 11 of the 37 samples. The slopes of log K-p versus log P-L(o) ranged between -0.233 and -0.445 and are among the shallowest measured worldwide. This fact may indicate absorption of PCBs in particles covered by a polar film.