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PCBs in U.K. Urban Air.

Atmospheric PCB concentrations were routinely monitored every other week over a 2-year period (1991-1992) in four U.K. urban centers. These sites included the major cities of London, Manchester, and Cardiff and the light industrial town of Stevenage, located ∼60 km north of London. Eight major congeners were measured at all of the sites with a further 22 included at the Manchester and Cardiff sites. Atmospheric ΣPCB (eight congeners) concentrations ranged from 112 to 3850 pg m -3 at the four sites, with the mean in London the highest. Clear seasonal cycling was observed in the urban atmospheres with summer concentrations being higher than winter for all congeners. The relative amplitude change in this cycling pattern was greatest for the higher chlorinated congeners ; summer :winter ratios were 2.0, 1.7, 3.2, and 5.0 for congeners 28, 52, 153, and 180, respectively. A simple box model developed by Pankow (1) was applied to the surface area of Manchester to predict the vapor-phase concentration of the tetra-CB, congener 52. Desorption from various compartments such as vegetation, soil, and urban dust were considered. The release from building air was also estimated. The predicted gas-phase concentrations show the seasonal cycling observed in the ambient air concentrations. The model fit for the three considered compartments (veg/soil/dust) was lower than the observed city air concentrations. The model data reflect background rural concentrations more accurately, perhaps suggesting that elevated concentrations of the vapor-phase component in city air are derived from building air and/or a series of point sources. Even today, many years after restrictions of PCB manufacture and use were introduced in the U.K., cities continue to act as sources of airborne PCBs to surrounding areas.