This work reports the study of the decomposition of three PAHs (anthracene, phenanthrene, and fluorene) in aqueous solution at different pHs (2, 7, and 11) and in the presence of methanol as a co-solvent by two different methods: conventional ozonation (O-3) and O-3/activated carbon (AC). The results showed that without AC, the decomposition of anthracene and fluorene proceeded mostly by molecular O-3 at pHs 2 and 7. The indirect ozonation mechanism expected at basic pH was inhibited by the presence of high concentrations of methanol, which acted as a radical scavenger. The ozone consumed by the radical formation under pH >7 induced a larger decomposition reaction rate (five times) for all PAHs at acidic and neutral conditions compared with the basic ones. The presence of AC modulated the decomposition rates for all PAHs at the pHs evaluated. The latter was confirmed by the similarity among the decomposition dynamics.