| Abstract
| - XAFS spectroscopy has been employed to evaluate theeffect of fuel compositions and combustion conditions onthe amount, form, and distribution of sulfur and nickelin size-fractionated ROFA PM. Analysis of S K-edge XANESestablish that sulfate is abundant in all PM. However,depending upon the combustion conditions, lesser amountsof thiophenic sulfur, metal sulfide, and elemental sulfurmay also be observed. Least-squares fitting of Ni K-edgeXANES reveals that most of the nickel in PM is present asbioavailable NiSO4.nH2O. The insoluble Ni mainly existsas a minor species, as nickel ferrite in PM2.5 (PM < 2.5 μm)and nickel sulfide, NixSy in PM2.5+ (PM > 2.5 μm). TheNi K-edge XANES results are in agreement with the EXAFSdata. Such detailed speciation of Ni and S in PM isneeded for determining their mobility, bioavailability, andreactivity, and hence, their role in PM toxicity. This informationis also important for understanding the mechanism ofPM formation, developing effective remediation measures,and providing criteria for identification of potentialemission sources. Transition metals complexing withsulfur is ubiquitous in nature. Therefore, this informationon metal sulfur complex can be critical to a large body ofenvironmental literature.
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