Kinetics and mechanisms of aqueous ozone reactions with bromide, sulfite, hydrogen sulfite, iodide, and nitrite ions

Reactions of ozone with Br-, SO32-, HSO3-, I-, and NO2-, studied by stopped-flow and pulsed-accelerated-flow techniques, are first order in the concentration Of O-3(aq) and first order in the concentration of each anion. The rate constants increase by a factor of 5 x 10(6) as the nucleophilicities of the anions increase from Br- to SO32-. Ozone adducts with the nucleophiles are proposed as steady-state intermediates prior to oxygen atom transfer with release Of O-2. Ab initio calculations show possible structures for the intermediates. The reaction between Br- and O-3 is accelerated by HI but exhibits a kinetic saturation effect as the acidity increases. The kinetics indicate formation of BrOOO- as a steady-state intermediate with an acid-assisted step to give BrOH and O-2, Temperature dependencies of the reactions of Br- and HSO3- With O-3 in acidic solutions are determined from I to 25 degreesC. These kinetics are important in studies of annual ozone depletion in the Arctic troposphere at polar sunrise.