Direct photolysis with UV radiation (254 nm) and oxidation with ozone combined with UV radiation of three polynuclear aromatic hydrocarbons, fluorene, phenanthrene, and acenaphthene, has been studied. Quantum yields of the direct photolysis of the PAHs determined were 7.5 x 10(-3), 6.9 x 10(-3), and 52 x 10(-3) mol(photon)(-1) for fluorene, phenanthrene, and acenaphthene, respectively. Contributions of direct ozonation, direct photolysis, and radical oxidation have also been estimated for the oxidation with ozone combined with UV radiation. Fluorene is oxidized by direct photolysis and radical reactions, phenanthrene through direct mechanisms, ozonation, and photolysis, and acenaphthene mainly by direct ozonation.