New Mechanistic Insights into Atmospheric Oxidation of Aniline Initiated by OH Radicals

• Published in: Environmental science & technology Vol. 55; no. 12; pp. 7858 - 7868
• Main Authors: Mai, Tam V.-T, Nguyen, Thi T.-D, Nguyen, Hieu T, Nguyen, Trang T, Huynh, Lam K
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 15.06.2021
• Subjects: Aniline; Anthropogenic Impacts on the Atmosphere; Free radicals; Low temperature; Oxidation; Photolysis; Pressure dependence; Stochasticity; Temperature dependence; thermodynamics; aniline; OH-initiated oxidation; atmospheric degradation; ab initio kinetics
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.1c01865

This study theoretically reports the comprehensive kinetic mechanism of the aniline + OH reaction in the range of 200–2000 K and 0.76–7600 Torr. The temperature- and pressure-dependent behaviors, including time-resolved species profiles and rate coefficients, were studied within the stochastic RRKM-based master equation framework with the reaction energy profile, together with molecular properties of the species involved, characterized at the M06-2X/aug-cc-pVTZ level. Hindered internal rotation and Eckart tunneling treatments were included. The H-abstraction from the −NH2 moiety (to form C6H5NH (P1)) is found to prevail over the OH-addition on the C atom at the ortho site of aniline (to form 6-hydroxy-1-methylcyclohexa-2,4-dien-1-yl (I2)) with the atmospheric rate expressions (in cm3/molecule/s) as k abstraction(P1) = 3.41 × 101 × T –4.56 × exp (−255.2 K/T) for 200–2000 K and k addition(I2) = 3.68 × 109 × T –7.39 × exp (−1163.9 K/T) for 200–800 K. The U-shaped temperature-dependent characteristics and weakly positive pressure dependence at low temperatures (e.g., T ≤ 800 K and P = 760 Torr) of k total(T) are also observed. The disagreement in k total(T) between the previous calculations and experimental studies is also resolved, and atmospheric aniline is found to be primarily removed by OH radicals (τOH ∼ 1.1 h) in the daytime. Also, via TD-DFT simulations, it is recommended to include P1 and I2 in any atmospheric photolysis-related model.