HISTORICAL TRENDS OF AIRBORNE TRACE-METALS IN DETROIT FROM 1971 TO 1992

Ambient concentrations of particulate Fe, Zn, Pb, Ni, Cr, Cd and Hg we re measured at nine sites located in the metropolitan area of Detroit from 1971 to 1992. The ambient concentrations of all the trace metals were found to be generally higher at industrial and commercial sites. The concentrations show significant variations between residential and commercial areas and between residential and industrial areas; howeve r, no significant variation was found between the industrial and comme rcial settings. The spatial variation of trace metal levels within the urban area was influenced by the frequency distribution of the wind d irection as well as type and location of emission sources. The ambient concentrations of the trace metals during the decade of 1971-1981 dec lined by 37-88%. In the 1980s many of the trace metals reversed this t rend with the exception of Fe and Pb which continued to decline at ann ual rates of 2% and 9.8%, respectively. The sharp decrease in Pb conce ntrations during the 1980s, reflected the significant reduction of Pb content in gasoline from 0.28 g/liter in the 1982 to 0.026 g/liter in the 1989. The ambient concentrations of Zn, Ni, Cr, Cd and Hg showed a n upward trend during the 1980s with an annual rate in the range of 0. 6% to 10.6%. The long-term trends of selected U.S. market parameters, analyzed as potential long-term indicators of emission sources activit yies, were consistent with the changes of ambient concentrations, the correlation coefficient being in the range of 0.58 to 0.84 for most of the trace metals.