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Theoretical study on the mechanisms, kinetics and ecotoxicity assessment of OH-initiated reactions of guaiacol in atmosphere and wastewater

An, Zexiu, Sun, Jianfei, Han, Dandan, Mei, Qiong, Wei, Bo, Wang, Xueyu, He, Maoxia
The Science of the total environment 2019 v.685 pp. 729-740
aerosols, aqueous solutions, ecotoxicology, energy, formates, gases, guaiacol, half life, nitrogen dioxide, quinones, solvents, toxicity, wastewater
The OH-initiated transformation mechanisms, kinetics and ecotoxicity assessment of guaiacol (2-methoxyphenol) in the presence of O2/NOx were investigated both in atmosphere and wastewater. The solvent effect lowers the energy barriers of initial OH-addition reactions more than H-abstraction reactions, leading to much higher addition branching ratio (Γadd) of 0.92 in aqueous solution than that of 0.42 in gas-phase. At 298 K, the overall rate constants of the title reactions in atmosphere and wastewater are 5.56 × 10−12 and 1.41 × 10−11 cm3 molecule−1 s−1 with corresponding half-lives of 34.6 h and 0.82 s, respectively. In atmosphere, all the proposed favorable products including nitroguaiacols, methoxybenzoquinone, 2-hydroxyphenyl formate, 2-methoxybenzene-1, 3-diol and dialdehyde could contribute to secondary organic aerosols (SOAs). In wastewater, NO2 addition reactions lead to higher toxicity of products (nitroguaiacols and 2-methoxybenzene-1, 4-diol) than that of parental guaiacol. However, O2/NO addition pathways may generate less harmful products except for methoxybenzoquinone (P3) which is with higher toxicity than guaiacol. Therefore, more attention should be focused on the products formed from OH-initiated reactions of guaiacol both in atmosphere and wastewater.