| Abstrakt: |
Environmental media affect the atmospheric oxidation processes of phenolic compounds (PhCs) released from biomass burning in the troposphere. Phenol (Ph), 4-hydroxybenzaldehyde (4-HBA), and vanillin (VL) are chosen as model compounds to investigate their reaction mechanism and kinetics at the air-water (A-W) interface, on TiO2 clusters, in the gas phase, and in bulk water using a combination of molecular dynamics simulation and quantum chemical calculations. Of them, Ph was the most reactive one. The occurrence percentages of Ph, 4-HBA, and VL staying at the A-W interface are ~72 %, ~68 %, and ~73 %, respectively. As the size of (TiO2)n clusters increases, the adsorption capacity decreases until n > 4, and beyond this, the capacity remains stable. A-W interface and TiO2 clusters facilitate Ph and VL reactions initiated by the O3 and HO•, respectively. However, oxidation reactions of 4-HBA are little affected by environmental media because of its electron-withdrawing group. The O3- and HO•-initiated reaction rate constant (k) values follow the order of PhA-W > VLTiO2 > VLA-W > 4-HBAA-W > 4-HBATiO2 > PhTiO2 and VLTiO2 > PhA-W > VLA-W > 4-HBATiO2 > PhTiO2 > 4-HBAA-W, respectively. Some byproducts are more harmful than their parent compounds, so should be given special attention. This work provides key evidence for the rapid oxidation observed in the O3/HO• + PhCs experiments at the A-W interface. More importantly, differences in oxidation of PhCs by different environmental media due to the impact of substituent groups were also identified. [ABSTRACT FROM AUTHOR] |
