The ozone decomposition reaction is analyzed in a homogeneous reactor through in-situ measurement of the ozone depletion. The experiments were carried out at pHs between 1 to 11 in H2PO4-/HPO42 buffers at constant ionic strength (0.1 M) and between 5 and 35 ºC. A kinetic model for ozone decomposition is proposed considering the existence of two chemical subsystems, one accounting for direct ozone decomposition leading to hydrogen peroxide and the second one accounting for the reaction between the hydrogen peroxide with the ozone to give different radical species. The model explains the apparent reaction order respect of the ozone for the entire pH interval. The decomposition kinetics at pH 4.5, 6.1, and 9.0 is analyzed at different ionic strength and the results suggest that the phosphate ions do not act as a hydroxyl radical scavenger in the ozone decomposition mechanism.J. 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