ATMOSPHERIC CONCENTRATIONS OF TRACE-ELEMENTS IN URBAN AREAS OF THE UNITED-KINGDOM

Measurements of atmospheric concentrations of particulate trace elements Ag, Al, As, Br, Cd, Ce, Cl, Cr, Fe, Hg, Na, Ni, Pb, Sc, Se, Sm, V and Zn have been made since the early 1970s at seven urban sites across the U.K. Urban concentrations of atmospheric trace elements were found to be typically between 3 and 10 times higher than those at two rural sites and were broadly comparable with other urban data from Europe and North America, with the exception of one urban site in Walsall which was located near to a smelter. Elements were shown to vary spatially within urban areas. Both crustal and combustion related elements showed significant differences but the exposure to vehicle emissions, in terms of Pb and Br, was the dominant factor in differences between sites in the same urban area. The elements which showed significant seasonal variability were generally from anthropogenic and marine sources, i.e. Br, Pb, Zn, V, Cl and Na, and the wintertime maxima in concentrations can be explained in terms of increased fuel usage, frequency of inversions and higher wind speeds bringing marine aerosols. Mean urban concentrations of all non-marine elements generally declined over the measurement period, but in particular for the elements Br, Pb, As, Cd, V and Ag. The elements which showed smaller reductions had predominantly crustal or marine sources, i.e. Al, Fe, Cr, Ce, Cl and Na. Concentrations of Pb showed clear reductions in the year immediately after the reduction of lead in petrol in 1986 but small subsequent increases were observed in following years. None of the elements exceeded the occupational exposure limit divided by 40, a commonly used unofficial guideline and the long-term concentrations were all at least an order of magnitude lower than these guideline values. Long-term mean concentrations of Cd approached or exceeded World Health Organisation guidelines at all sites but in recent years have been lower and the urban guideline has only been exceeded at Walsall. Lead was found to exceed the annual guideline set by the European Community on a quaterly basis only at a site in the vicinity of a smelter. In recent years, much improvement in air quality has been made with regard to Pb concentrations are generally below the lower limit of the more stringent World Health Organisation guidelines at all urban sites, with the exception of Walsall, and an order of magnitude lower at the two rural sites.