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•Degradation of atrazine was investigated in UV, UV/H2O2, UV/HSO5− and UV/S2O82− AOPs.•UV/S2O82− process was found to be more efficient as well as more economical.•The pH affected UV/S2O82− but had no significant influence on UV, UV/H2O2 and UV/HSO5−.•Second order rate constants of atrazine with SO4− and OH were found to be comparable.•Degradation mechanism was investigated by GC–MS and LC–MS/MS analysis. Degradation of atrazine was investigated under UV-254nm irradiation, alone or in combination with peroxides, i.e., hydrogen peroxide, persulfate (PS) or peroxymonosulfate (PMS). UV/PS was found to be the most efficient process in this study, which was probably due to its higher radical quantum yield under UV irradiation, considering atrazine’s comparable second order rate constant of 2.59×109M−1s−1 and 2.25×109M−1s−1 with sulfate radical and hydroxyl radical, respectively. The pH values showed no significant effect on direct photolysis of atrazine, with observed UV fluence based pseudo-first-order rate constant (kobs) of 7.59×10−4, 7.73×10−4 and 6.72×10−4cm2mJ−1 at pH 3.0, 5.7 and 11.0, respectively. Performance of UV/H2O2 and UV/PMS were more independent of initial pH values while that of UV/PS appeared to be more efficient at neutral pH condition. UV/PS was observed as a less energy consumption process. Eight new degradation by-products were identified in this study, namely, 2-chloro-4-acetamido-6-(2-hydroxy-isopropylamino)-s-triazine (CDHT), 2-hydroxy-4-(2-hydroxy-ethylamino)-6-isopropylamino-s-triazine (ONIT), 2-chloro-4-vinylamino-6-isopropylamino-s-triazine (CVIT), 2-hydroxy-4-vinylamino-6-(2-hydroxy-isopropylamino)-s-triazine (OVHT), 2-hydroxy-4-acetamido-6-isopropenylamino-s-triazine (ODPT), 2-hydroxy-4-(2-hydroxy-ethylamino)-6-vinylamino-s-triazine (ONVT), 2-hydroxy-4-(2-hydroxy-ethylamino)-6-methylamino-s-triazine (ONMT) and 2-chloro-4-vinylamino-6-amino-s-triazine (CVAT). Potential degradation pathways were further proposed. 252 393 403