Nitrite-Mediated Photooxidation of Vanillin in the Atmospheric Aqueous Phase
Nitrite-Mediated Photooxidation of Vanillin in the Atmospheric Aqueous Phase
复制标题
常压水相中亚硝酸盐介导的香兰素光氧化
DOI：
10.1021/acs.est.9b03649
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发表时间：
2019
影响因子：
11.4
通讯作者：
Huang Cheng
中科院分区：
文献类型：
--
作者：
Pang Hongwei;Zhang Qi;Lu Xiaohui;Li Kangning;Chen Hong;Chen Jianmin;Yang Xin;Ma Yingge;Ma Jialiang;Huang Cheng
长期以来，亚硝酸盐(NO2-)及其共轭酸亚硝酸(HNO2)一直被认为是一种普遍存在的大气污染物，也是羟基自由基(·OH)和活性氮物种(·NO、·NO2、·N2O_3等)的重要光化学来源。在气相和水相中。尽管NO2-/HNO2在大气化学中起着重要的作用，但我们对其在大气水中有机物化学演化中的作用的认识还很不完整，还存在争议。在这项研究中，亚硝酸盐介导的光氧化香草醛(VL)是一种富含生物质燃烧排放的酚类化合物，在与大气水体相关的pH条件下进行了研究。详细讨论了溶液pH、溶解氧和·OH清除剂对VL亚硝酸盐光氧化的影响。我们的研究表明，产物的分子组成取决于溶液中NO2-/VL的摩尔比，反应的主要产物是硝基酚。我们还发现，在可见光区，氧化产物的光吸收随着pH的升高而增加，这可以归因于生成的硝基酚的去质子化。这些结果有助于更好地理解亚硝酸盐介导的甲氧基苯酚光氧化是大气水体中有毒的硝基酚和气候重要的棕色碳的来源。
Nitrite (NO2–) and its conjugate acid, nitrous acid (HNO2), have long been recognized as a ubiquitous atmospheric pollutant as well as an important photochemical source of hydroxyl radicals (·OH) and reactive nitrogen species (·NO, ·NO2, ·N2O3, etc.) in both the gas phase and aqueous phase. Although NO2–/HNO2plays an important role in atmospheric chemistry, our understanding on its role in the chemical evolution of organic components in atmospheric waters is rather incomplete and is still in dispute. In this study, the nitrite-mediated photooxidation of vanillin (VL), a phenolic compound abundant in biomass burning emissions, was investigated under pH conditions relevant for atmospheric waters. The influence of solution pH, dissolved oxygen, and ·OH scavengers on the nitrite-mediated photooxidation of VL was discussed in detail. Our study reveals that the molecular composition of the products is dependent on the molar ratio of NO2–/VL in the solution and that nitrophenols are the major reaction products. We also found that the light absorbance of the oxidative products increases with increasing pH in the visible region, which can be attributed to the deprotonation of the nitrophenols formed. These results contribute to a better understanding of methoxyphenol photooxidation mediated by nitrite as a source of toxic nitrophenols and climatically important brown carbon in atmospheric waters.