Factors influencing atmospheric concentrations of polychlorinated biphenyls in Birmingham, UK

Atmospheric concentrations of PCBs were measured in Birmingham, U.K., between 7/13/97 and 7/27/98. A significant positive relationship (>95%) was detected between the cosine of the wind direction and In P for Sigma PCB and tri- and tetrachlorinated PCBs. This is consistent with input from northerly winds passing over Birmingham city center, 3 km from our site. Plots of the enthalpy of surface-air exchange (Delta H-SA) versus laboratory-measured heats of vaporization (Delta H-V) for all congeners revealed a highly significant (>99.9%) positive linear relationship. According to Simcik et al. (1), this indicates local sources to be the predominant influence. However, separate plots of Delta H-SA versus Delta H-V for (a) the tri- and tetrachlorinated PCBs and (b) the penta-, hexa-, and heptachlorinated congeners revealed a highly significant linear relationship for the latter group but Delta H-SA to be essentially constant for the former. Strict interpretation of Simcik et al.'s hypothesis (1) suggests long-range transport as the principal source of tri- and tetrachlorinated PCBs but not of the higher chlorinated congeners. This is not thought credible given the nearby influence of the city center on concentrations of the lower chlorinated congeners, and we suggest correlation between Delta H-SA and Delta H-V will only be observed when the principal source is both close to the sampling site and governed by equilibrium surface-air partitioning. We therefore believe that at our site, the principal source of tri- and tetrachlorinated PCBs is nonequilibrium short-range transport, while for penta-through heptachlorinated PCBs, equilibrium short-range transport is the predominant source. Indoor air ventilation is a short-range source governed by factors such as the building ventilation rate, rather than surface-air partitioning. We therefore hypothesize that it constitutes the principal source of tri- and tetrachlorinated PCBs at our site.