. . . "Many advanced oxidation technologies have been developed to remove ammonia in wastewater. All these technologies have one common characteristic, that is, the removal processes involve OH radical (\u2022OH). In this research work, H2O2 was selected as \u2022OH precursor. The removal of ammonia under 253.7 nm irradiation from low-pressure mercury lamp in the presence of H2O2 was studied to investigate the ammonia removal efficiency by \u2022OH. Results show that the \u2022OH, generated by H2O2 photolysis, could oxidize NH3 to NO2\u2212 and further to NO3\u2212. Removal efficiencies of ammonia were low and were affected by initial pH value and ammonia concentration. Laser flash photolysis technique with transient absorption spectra of nanosecond was used to investigate the oxidation pathway and kinetics of ammonia oxidation by \u2022OH. Results illustrate that \u2022OH could oxidize NH3 to form \u2022NH2 with a second-order rate constant of (1.0 \u00B1 0.1) \u00D7 108 M\u22121 s\u22121 (20 \u00B0C). \u2022NH2, the main product of \u2022OH with NH3, would further react with H2O2 to yield \u2022NHOH. Since \u2022NHOH could not stay stable in solution, it would rapidly convert to NH2O2\u2212 and consequently NO2\u2212 and NO3\u2212. The rate constants for these elementary reactions were also given. The low removal efficiency of ammonia by \u2022OH was mainly due to the slow reaction rate constant." . . . . . . . . . . "By using laser flash photolysis and steady state photolysis, the removal pathway and kinetics for ammonia oxidation by \u2022OH are obtained." . . . "Removal of Ammonia by OH Radical in Aqueous Phase" . . . . .