Another duplicate set of ozone decomposition experiments was carried out in semi-batch mode in order to follow the formation of hydrogen peroxide as a product of the aqueous ozone decomposition. In these experiments, a continuous stream of anoxygen-ozone mixture (30 L h−1 flow rate, 50 mg L−1ozone concentration) was continuously supplied to the reactor, which was previously charged with 500 mL of 10 mM phosphate-buffered organic-free water (Milli-Q Millipore system). The solar simulator lamp was kept on throughout the experiment except in blank experiments for which the lamp was always off. At different times,aqueous samples were taken from the reactor to be analyzed for dissolved ozone and hydrogen peroxide concentrations.