Santos Patrícia S M, Duarte Armando C
CESAM (Centre for Environmental and Marine Studies) & Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
CESAM (Centre for Environmental and Marine Studies) & Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal.
Chemosphere. 2015 Jan;119:786-793. doi: 10.1016/j.chemosphere.2014.08.024. Epub 2014 Sep 6.
The oxidation of organic compounds from biomass burning in the troposphere is worthy of concern due to the uncertainty of chemical transformations that occur during the reactions and to the possibility of such compounds producing others more aggressive to the environment in general. In this work was studied the oxidation of relevant atmospheric organic compounds resulting from biomass burning, three small aromatic acids with similar molecular structures (benzoic, 4-hydroxybenzoic and 3,5-dihydroxybenzoic acids), in aqueous phase and in the absence of light. The oxidation process used was the Fenton-like reaction and it was evaluated by ultraviolet-visible and molecular fluorescence spectroscopies. The extent of oxidation of the acids depended on the pH of the solution, and the rate of reaction increased as the pH decreased from neutral (5) to acid (4) in atmospheric waters. Even in the absence of light, Fenton-like oxidation of the three acids originated new chromophoric compounds, which tended to be more complex than the reactants. However, after the formation of new compounds they were totally oxidized for 3,5-dihydroxybenzoic acid and only partially degraded for benzoic and 4-hydroxybenzoic acids, at least after 48 h of reaction at pH 4.5. Furthermore, the night period may be sufficient for a full degradation of the 3,5-dihydroxybenzoic acid and of their oxidation products in atmospheric waters. Thus, the results obtained in this study highlight that organic compounds from biomass burning with similar molecular structures may have different behavior regarding to their reactivity and persistence in atmospheric waters, even without light.
对流层中生物质燃烧产生的有机化合物的氧化值得关注，这是因为反应过程中发生的化学转化存在不确定性，且此类化合物有可能生成其他对环境更具侵蚀性的化合物。在这项研究中，我们研究了生物质燃烧产生的相关大气有机化合物——三种分子结构相似的小分子芳香酸（苯甲酸、4-羟基苯甲酸和3,5-二羟基苯甲酸）在水相且无光条件下的氧化情况。所采用的氧化过程是类芬顿反应，并通过紫外可见光谱和分子荧光光谱进行评估。酸的氧化程度取决于溶液的pH值，在大气水相中，随着pH值从中性（5）降至酸性（4），反应速率增加。即使在无光条件下，三种酸的类芬顿氧化也会产生新的发色化合物，这些化合物往往比反应物更复杂。然而，新化合物形成后，3,5-二羟基苯甲酸完全被氧化，而苯甲酸和4-羟基苯甲酸仅部分降解，至少在pH值为4.5的条件下反应48小时后是这样。此外，夜间时段可能足以使大气水中的3,5-二羟基苯甲酸及其氧化产物完全降解。因此，本研究获得的结果表明，分子结构相似的生物质燃烧产生的有机化合物在大气水中的反应性和持久性方面可能具有不同的行为，即使在无光条件下也是如此。
