Oxidation of Isoprene by Neutral Iron Oxide Nanoclusters in the Gas Phase

Understanding the heterogeneous oxidation of isoprene is crucial to discover the missing sink of the atmospheric isoprene. Iron oxide nanoparticles dominate the most abundant type of anthropogenic Fe-bearing particles in the atmosphere. In this study, by using a homemade time-of-flight mass spectrometer coupled with a laser ablation cluster source and a vacuum ultraviolet laser system, the neutral iron oxide clusters (FexOy) with the size up to 1 nm have been successfully generated and detected. The reactions of FexOy with isoprene (C5H8) to form CH2O, C4H6O, and C5H6O have been identified, and the mechanisms of Fe4O6 + C5H8 have been interpreted by using the quantum chemistry calculations. Based on the experimentally observed size-dependent reactivity, the total contribution of atmospheric iron oxide nanoparticles to isoprene heterogeneous oxidation has been estimated to be comparable with the contribution of OH radicals that are the dominant species for isoprene oxidation in the current atmospheric chemistry models. The heterogeneous oxidation of isoprene by iron oxide clusters is thus very important in atmospheric chemistry.