In an ozone-containing water a suspension of a few milligrams per liter of activated carbon (AQ or carbon black (CB) initiates a radical-type chain reaction that then proceeds in the aqueous phase and accelerates the transformation of O3into secondary radicals, such as hydroxyl radicals (°OH). This results in an Advanced Oxidation Process (AOP) that is similar to an O3-based AOP involving application of H2O2or UV-irradiation. We have studied these phenomena by observing the effect of suspensions of AC and CB on the rate of transformation of O3in lakewater and in well-characterized solutions. In addition, the stoichiometric yield factor of the AC-catalyzed conversion of O3, into °OH has been shown to be comparable to that which is achieved by a slower process in the absence of AC. This comparison has been based on the measured depletion of an O3-resistant organic °OH probe that was added as a trace reference compound and that competed with a kinetic excess of solutes that controlled the lifetime of °OH. The AC-catalyzed transformation of O3into °OH for creating an O3-based AOP may be of practical interest to water utilities as an alternative to extended reaction times, to hydrogen peroxide addition, or to UV-catalyzed transformation of O3. We propose the name “Carbozone Process” for this new type of AOP.