Local order and valence state of Fe in urban suspended particulate matter

X-ray absorption spectroscopy investigations were carried out on urban suspended particulate matter (PM2.5) with the aim of studying the local order and valence state of iron, a metal abundant in this type of material, particularly in urban environments. XANES results, based on the comparison with model compounds fayalite (Fe2þ) and ferrihydrite (Fe3þ), show that iron is prevalent as Fe3þ, whereas EXAFS data attribute the prevalent Fe3þ to a nanocrystalline phase of ferrihydrite. The dominance of Fe3þ (less soluble than Fe2þ) is further confirmed by the fact that previous leaching experiments did not show Fe presence in the solution.