Incongruent release of iodine from iodoapatite (Pb5(VO4)3I) for immobilization of129iodine, controlled by exchange of iodide and hydroxide in solution.
Atmospheric aerosols (e.g., fog droplets) are complex, multiphase mediums. Depending on location, time of day, and/or air mass source, there can be considerable variability within these droplets, relating to temperature, pH, and ionic strength. Due to the droplets' inherently small size, the reactions that occur within these droplets are determined by bulk aqueous phase and air-water interfacial conditions. In this study, the reaction of benzene and hydroxyl radicals is examined kinetically in a thin-film flow-tube reactor. By varying the aqueous volume (e.g., film thickness) along the length of the reactor, both bulk and interfacial reaction rates are measured from a single system. Temperature, pH, and ionic strength are varied to model conditions typical of fog events. Oxygen-poor conditions are measured to study oxygen's overall effect on the reaction pathway. Initial rate activation energies and the bulk aqueous phase and interfacial contributions to the overall rate constant are also obtained.
Experiments on the reactions of OH radicals in thin films of water were conducted in a photochemical reactor. The OH radical reactivity of a biogenic molecule (methyl jasmonate) was observed to be much larger in thin films of water than in the bulk aqueous phase. The pseudo-first order reaction rate was enhanced by an order of magnitude on a 38-micron film compared to the bulk liquid. However, the first order rate constant increased by 349%. This has implications in atmospheric systems like fog and mist which have large specific surface areas. The enhanced reactivity is attributable to both the partial solvation and faster diffusion at the air-water interface compared to the bulk liquid.
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