PCBS IN UK URBAN AIR

Atmospheric PCB concentrations were routinely monitored every other we ek 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 similar to 60 km nort h of London. Eight major congeners were measured at ail of the sites w ith a further 22 included at the Manchester and Cardiff sites. Atmosph eric Sigma PCB (eight congeners) concentrations ranged from 112 to 385 0 pg m(-3) at the four sites, with the mean in London the highest. Cle ar seasonal cycling was observed in the urban atmospheres with summer concentrations being higher than winter for all congeners. The relativ e 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 mode l developed by Pankow (1) was applied to the surface area of Mancheste r to predict the vapor-phase concentration of the tetra-CB, congener 5 2. Desorption from various compartments such as vegetation, soil, and urban dust were considered. The release from building air was also est imated. The predicted gas-phase concentrations show the seasonal cycli ng observed in the ambient air concentrations. The model fit for the t hree considered compartments (veg/soil/dust) was lower than the observ ed city air concentrations. The model data reflect background rural co ncentrations more accurately, perhaps suggesting that elevated concent rations of the vapor-phase component in city air are derived from buil ding air and/or a series of point sources. Even today, many years afte r restrictions of PCB manufacture and use were introduced in the U.K., cities continue to act as sources of airborne PCBs to surrounding are as.