Speciation of elements in NIST particulate matter SRMs 1648 and 1650

X-ray absorption fine structure (XAFS) spectra for S, Cl, V, Cr, Mn, Cu, Zn , As, Br, Cd and Pb and Mossbauer spectra for Fe have been obtained for two National Institute of Standards and Technology (NIST) particulate matter ( PM) standard reference materials (SRMs): urban PM (SRM 1648) and diesel PM (SRM 1650). The spectral data, complemented by information on elemental con centrations from proton-induced X-ray-emission (PIXE) spectroscopy, were us ed to interpret the speciation of these elements in these complex materials . It appears that all the metallic elements investigated occur in oxidized forms, principally as sulfates in the diesel PM SRM and as sulfates, oxides , and possibly other forms (e.g. clays?) in the urban PM. A minor fraction of the sulfur and major fractions of the halogens, Cl and Pr, occur as orga nosulfide (thiophene) and organohalide occurrences, respectively, that must be associated with the abundant carbonaceous matter that constitutes the m ajor component of the two PM SRMs. Most of the sulfur, however, occurs as s ulfate in the urban PM and as bisulfate in the diesel PM. In addition, elem ental oxidation states have been determined directly by the spectroscopic t echniques. Such information is often the key parameter in determining the t oxicity and solubility of specific elements in PM, both of which are import ant in understanding the threat that such elements may pose to human health . For the two HAP elements, Cr and As, for which the toxicity depends great ly on oxidation state, the XAFS data showed that both elements are present in both SRMs predominantly in the less toxic oxidation states, Cr(III) and As(V). The potential of the XAFS spectra for use as source apportionment si gnatures is illustrated by reference to chromium, which exists in these two PM SRMs in very different forms. (C) 2000 Elsevier Science B.V. All rights reserved.