Fenton-like oxidation of small aromatic acids from biomass burning in water and in the absence of light: Implications for atmospheric chemistry

• Published in: Chemosphere (Oxford) 2015-01, Vol.119, p.786-793
• Main Authors: Santos, Patrícia S.M., Duarte, Armando C.
• Format: Article
• Language: English
• Subjects: Aromatic acids; Atmospheric water; Atmospherics; Benzoic Acid - chemistry; Biomass; Biomass burning; Degradation; Fenton-like reaction; Fluorescence; Hydrogen Peroxide - chemistry; Hydroxybenzoates - chemistry; Iron - chemistry; Light absence; Molecular structure; Organic compounds; Oxidation; Oxidation-Reduction; Parabens - chemistry; Resorcinols - chemistry; Transformations; Water Pollutants, Chemical - chemistry
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2014.08.024

•The pH decrease from neutral to acid in atmospheric waters increase the oxidation rate.•In a 1st stage the oxidation led to the formation of new chromophoric compounds.•In a 2nd stage the oxidation degrade totally the 3,5-dihydroxybenzoic acid up to 24h.•Benzoic and 4-hydroxybenzoic acids are only partially degraded up to 48h of reaction.•Compounds with similar structure may have different behavior in atmospheric waters. 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 48h 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.