Mechanisms and kinetic studies of OH-initiated atmospheric oxidation of methoxyphenols in the presence of O2 and NOx

2019 
Methoxyphenols, as the main products and tracers of biomass burning, have been demonstrated to play an important role in the formation of secondary organic aerosols. However, their chemical transformation and migration in the atmosphere haven't been well characterized. In this study, detailed gas-phase reaction mechanisms and kinetics of three representative methoxyphenols (guaiacol, creosol and syringol) with OH radicals were investigated by using the density functional theory (DFT). The initial reactions of methoxyphenols with OH radical proceed via two different patterns, including OH-addition and H-atom abstraction. Subsequent reaction schemes of the active intermediates in the presence of O2/NOx are thoughtfully modeled. Catechol, methyl glyoxylate, malealdehyde and carbonyl or carboxyl compounds were confirmed as the dominant oxidation products for guaiacol. As a supplementary, the formation pathways for the expected products nitroguaiacol as well as nitrocatechol were presented in high-NO2 conditions. Total and individual rate coefficients are calculated using MESMER program at 294 K and 1 atm. The lifetimes of guaiacol, creosol and syringol were estimated to be 4.16, 3.46 and 3.28 hours, respectively, which exhibit strong competitive to the solar photolysis of methoxyphenols.
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