BARIUM AND OTHER TRACE-METALS AS INDICATORS OF VEHICLE EMISSIONS

In the Siena urban environment, unwashed Q when leaves had a significa ntly higher Al, Ba, Cr, Fe, Mn, Na, Ni, Pb, Ti, and V content than sam ples from a neighbouring Mediterranean maquis. Significant relationshi ps between element pairs indicated both the presence of metals emitted by motor vehicles and lithophilic elements, presumably from soil part icles, resuspended by wind or turbulence generated by traffic. In orde r to minimize the effects of soil dust contamination and to seek clues to the metal sources, the estimated substrate contribution was subtra cted from the raw concentrations of elements in Q. ilex leaves. Normal ization for local soil composition confirmed that automotive emissions are the principal source of pollution in Siena. On the basis of a ver y significant relationship between normalized concentrations of Pb and Ba and the presence of the latter element in diesel and unleaded gaso line, Ba was recognized as a valuable tracer for vehicle emissions, in the place of Pb.