LAUSR

Abstract The atmospheric oxidation mechanism of 1-chloropyrene (1-ClPy) initiated by OH radical was studied using density functional theory calculations. The molecular structures of all stationary points included in the studied reactions were optimized at the MPWB1K/6-311+G(3df,2p) level. By considering the Wigner tunneling correction, traditional transition state theory was employed to estimate the rate constants for key elementary reaction steps. The computed results show that the addition reactions between 1-ClPy and OH radicals would produce seven main intermediate adducts (INTm, m = 3, 4, 5, 6, 8, 9, and 10). The contributions of OH addition occurring at C1, C2, and C7 positions on atmospheric oxidation degradation of 1-ClPy were calculated to be negligible. The subsequent secondary reactions of INT3, INT6, and INT8 under atmospheric conditions were different from those for INT4, INT5, INT9, and INT10; however, the main atmospheric oxidation products were all pyrenols. Intramolecular H-shifts from OH to OO for peroxy radical intermediates (1-ClPy-OH-O2), which can afford ring-cleaved final products, were highly endothermic reactions that were unlikely to occur. The same was true for isomerization of 1-ClPy-OH-O2 to pentacyclic intermediates ultimately forming ring-cleaved products. In the presence of NO2 or NO, the respective ensuing reactions of INTm or 1-ClPy-OH-O2 are all very slow because of the very high Gibbs free energies of activation for the involved rate-determining steps.