Observations on PAH, PCB, and PCDD/F Trends in U.K. Urban Air, 1991−1995

Ambient air concentrations at London and Manchester are reported for PCBs, PAHs, and PCDD/Fs from 1991 to 1995. This data set suggests that urban PAH concentrations are trending downward in the U.K. ∑PCB concentrations (∑ = congeners 28, 52, 101, 118, 138, 153, and 180) were usually ∼0.2−2 ng m -3 over the study period, with concentrations of the seven PCB congeners (∑PCB) in London generally 2−3 times higher than in Manchester. PCB concentrations have remained quite stable year-on-year over the study period. PCDD/F trends at the two sites were similar, with a decline through 1991−1994, followed by an upturn in 1995. Summer:winter seasonality of PCDD/Fs at both sites has been highly erratic year-on-year and compound-by-compound, far more so than for PAHs and PCBs. This is perhaps best interpreted as a sign that various sources (presumably combustion-derived) have contributed different mixtures of PCDD/Fs of different source strengths at different times to the air at these urban sites. Possible causes are discussed.