POLYCYCLIC AROMATIC-HYDROCARBONS IN UK URBAN AIR

Polycyclic aromatic hydrocarbon (PAH) data for the first two years (Ja nuary 1991-December 1992) of a national urban air monitoring scheme in the U.K. are presented. Urban sample sites were operated in the citie s of London, Manchester, and Cardiff and in the light industrial town of Stevenage. Both the particulate and vapor phases of 15 PAHs were sa mpled using high-volume air samplers at roof-top level (approximately 25 m). London, the largest urban center, had the highest annual mean S IGMAPAH concentrations of 166 ng/m3 in 1991. Phenanthrene and fluorene dominated the total PAH at each site and were present predominantly i n the vapor phase throughout the year. The heavier PAHs (MW > 250) wer e present on the collected particulate and showed a distinct seasonal variation (winter > summer). PAH profiles were similar at each site, e ven though the conurbations were different in size, indicating sources common to each site. Specific atmospheric contamination episodes, ass ociated with particular meteorological conditions, were identified thr oughout the 2-year period. NO2 concentrations were obtained for the Ma nchester site for 1991. Weak correlations (P less-than-or-equal-to 0.0 5) were found to exist between elevated NO2 concentrations and particu late-benzo[a]pyrene and SIGMAPAH concentrations. Benzo[a]pyrene concen trations measured here are compared to data reported for inner London from the 1950s, 1960s, and 1970s. Contemporary air concentrations have declined substantially over this time, perhaps by around 2 orders of magnitude.