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X-ray absorption fine structure (XAFS) spectroscopy has been used to investigate the valence states and molecular structures of sulfur (S), chromium (Cr), arsenic (As), and zinc (Zn) in fine particulate matter (PM) separated from coal fly ash produced in a laboratory combustion system. A cyclone separator was used to separate the PM into fractions <2.5 μm in mean diameter (PM_2.5) and >2.5 μm in diameter (PM_2.5+). Sulfate was the dominant form of S present. However, thiophene was present in many samples, and sulfite was significant in two of the PM_2.5+ samples. For Cr and As, the valence states were of primary concern. Analysis of the X-ray absorption near-edge structure (XANES) regions of the spectra revealed that the toxic Cr⁶⁺ valence state accounted for approximately 10 to 30% of the Cr in PM derived from the fly ash of several coals from the western United States. However, only Cr³⁺ was observed in a …