This work has, for the first time, investigated the optical and chemical properties and oxidative potential of aqueous-phase photooxidation products of eugenol (a biomass-burning-emitted compound) and elucidated the interplay among these properties. Large mass yields exceeding 100 % were found, and the aqueous processing is a source of BrC (likely relevant with humic-like substances). We also show that aqueous processing can produce species that are more toxic than that of its precursor.