A Kinetic Study of the Atmospheric Aqueous-Phase Reactions of OH Radicals with Methoxyphenolic Compounds
Lin He,Thomas Schaefer and Hartmut Herrmann
Leibniz Institute for Tropospheric Research, Atmospheric Chemistry Department (ACD), Permoserstraße 15, 04318 Leipzig, Germany
Methoxyphenols, which are emitted from biomass burning, are important species in atmospheric multiphase chemistry. In the present study, the temperature-dependent OH radical reactions with six methoxyphenol compounds in the aqueous phase have been investigated by laser flash photolysis for the first time. The competition kinetics method using SCN- has been used to determine the rate constants. The following rate constants at T = 298K (in unit of L mol-1 s-1) have been obtained: 2-methoxyphenol, k = (1.0 ± 0.1) × 1010, 3-methoxyphenol, k = (1.4 ± 0.1) × 1010, 2,6-dimethoxyphenol, k = (1.7 ± 0.1) × 1010, 3-methoxycatechol, k = (1.9 ± 0.1) × 1010,
2-methoxy-4-methylphenol, k = (1.7 ± 0.1) × 1010, 4-(2-methoxyethyl)phenol, k = (1.7 ± 0.1) × 1010. With the obtained rate constant and their T-dependencies, the Arrhenius parameters of these reactions have been derived. Meanwhile, the rate constant for fully diffusion controlled reaction of each case have been calculated based on the well-known Smoluchowski equation and, furthermore by DFT calculations. Moreover, the Hammett plots of phenolic compounds have been established with our measurement result, which could be used for predicting the unknown rate constants of other phenolic compounds. All of the findings are expected to enhance the predictive capabilities of models such as the chemical aqueous-phase radical mechanism (CAPRAM).