Department of Civil, Environmental and Architectural Engineering , University of Colorado , Boulder , Colorado 80309 , United States.
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133 , CH-8600 Dübendorf , Switzerland.
Environ Sci Technol. 2019 May 21;53(10):5622-5632. doi: 10.1021/acs.est.8b06410. Epub 2019 May 9.
This study focused on the effects of ozonation on the photochemical and photophysical properties of dissolved organic matter (DOM). Upon ozonation, a decrease in DOM absorbance was observed in parallel with an increase in singlet oxygen (O) and fluorescence quantum yields (Φ and Φ). The increase in Φ was attributed to the formation of quinone-like moieties during ozonation of the phenolic moieties of DOM, while the increase in Φ can be explained by a significant decrease in the internal conversion rate of the first excited singlet state of the DOM (DOM*). It is a consequence of an increase in the average energy of the first electronic transition (S → S) that was assessed using the wavelength of maximum fluorescence emission (λ). Furthermore, ozonation did not affect the ratio of the apparent steady-state concentrations of excited triplet DOM (DOM*) and O, indicating that ozonation does not affect the efficiency of O production from DOM*. The consequences of these changes for the phototransformation rates of micropollutants in surface waters were examined using photochemical model calculations. The decrease in DOM absorbance caused by ozonation leads to an enhancement of direct photolysis rates due to the increased transparency of the water. Rates of indirect photooxidation induced by O and DOM* slightly decrease after ozonation.
本研究聚焦于臭氧氧化对溶解有机质（DOM）光化学和光物理性质的影响。臭氧氧化过程中，DOM 的吸光度呈下降趋势，而单线态氧（1O）和荧光量子产率（Φ和Φ）呈上升趋势。Φ的增加归因于臭氧氧化 DOM 中酚类部分形成醌类结构，而Φ的增加可以用 DOM （DOM*）的第一激发单线态的内转换速率显著降低来解释。这是由于第一电子跃迁（S→S）的平均能量增加所致，可通过最大荧光发射波长（λ）来评估。此外，臭氧氧化对激发三重态 DOM（DOM*）和 1O 的表观稳态浓度比没有影响，表明臭氧氧化不影响 DOM产生 1O 的效率。使用光化学模型计算研究了这些变化对地表水中微污染物光转化速率的影响。臭氧氧化导致 DOM 吸光度下降，从而由于水的透明度增加而增强直接光解速率。臭氧氧化后，由 1O 和 DOM诱导的间接光氧化速率略有下降。
