Atmospheric deposition of metals associated with air particulate matter: Fractionation of particulate-bound metals using continuous-flow sequential extraction

Abstract

The fractionation and elemental association of some heavy metals in air particulate matter from two different sources, a smelter and heavy vehicle traffic, were investigated using a continuous-flow sequential extraction procedure. Air particulate matter (a combination of wet and dry deposition) was collected monthly for one year and was analyzed by a four-step continuous-flow sequential extraction procedure employing a modified Tessier scheme. Examination of crustal enrichment factors (EFcrust) suggested that the Cd, Zn and Pb in the air particulate matter were predominantly of anthropogenic origin. Total Pb deposition in the dry season was found to be higher than that in the wet season, and may be attributed to soil dust. However, the fractional distribution of metals between forms did not differ between seasons. The results showed that the reducible phase (Fe/Mn oxides) was the largest fraction of Pb in air particulate matter from both the smelter and heavy traffic sites. The overlain metal extraction profiles demonstrated a close elemental association between Al and Pb in the acid-soluble phase of air particulate matter. In the reducible fraction, Pb was found to dissolve earlier than Fe indicating that Pb could occur adsorbed onto Fe oxide surfaces in the air particulate matter.