XAFS spectroscopic characterization of elements in combustion ash and fineparticulate matter

X-ray absorption fine structure (XAFS) spectroscopy is a powerful non-destr uctive, direct technique for determining the speciation of environmentally important elements in products derived from combustion of fossil fuels. Suc h information is potentially important (i) for assessing the threat to huma n health posed by specific forms and oxidation states of such elements in c ombustion products (ash) or in combustion-derived airborne particulate matt er (PM), and (ii) for possible source identification and apportionment in P M investigations. The specific examples discussed include the speciation of various elements classified as hazardous air pollutants (HAPs) in ash prod ucts from combustion of coal (As and Cr), residual oil (Ni and Cr), and bio mass (Cd and Zn) and in airborne PM collected on a PM10 filter (S, Cl, Cr a nd As). Chromium and arsenic, which could exist in these materials in diffe rent oxidation states, were typically found predominantly in less toxic oxi dation states, Cr(III) and As(V). All metal species (Cr, Ni, Cd, Zn, As) we re shown to be present in the combustion ashes in predominantly oxidic envi ronments (i.e., oxides, sulfates, arsenates, etc.). Most of the sulfur in t he PM10 filter sample was present as sulfate, but minor organosulfur forms (thiophene) were also identified. For comparison with the data obtained for elements on the PM10 filter, XAFS data are also presented for the correspo nding elements in two National Institute of Standards and Technology (NIST) particulate matter Standard Reference Materials (SRMs): Urban PM (SRM 1648 ), and Diesel PM (SRM 1650). (C) 2000 Elsevier Science B.V. All rights rese rved.