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 (Fe2+) and ferrihydrite (Fe3+), show that iron is prevalent as Fe3+, whereas EXAFS data attribute the prevalent Fe3+ to a nanocrystalline phase of ferrihydrite. The dominance of Fe3+ (less soluble than Fe2+) is further confirmed by the fact that previous leaching experiments did not show Fe presence in the solution.