Hydrogen Peroxide Enhances the Oxidation of Oxygenated Volatile Organic Compounds on Mineral Dust Particles: A Case Study of Methacrolein
2014
Zhao, Yue | Huang, Dao | Huang, Liubin | Chen, Chongming
Heterogeneous oxidation of oxygenated volatile organic compounds (OVOCs) serves as an important sink of OVOCs as well as a source of secondary organic material. However, the roles of gas phase oxidants in these reactions are poorly understood. In this work, we present the first laboratory study of the heterogeneous reactions of methacrolein (MACR) on various mineral dust particles in the presence of gaseous H₂O₂. It is found that the presence of gaseous H₂O₂ significantly promotes both the uptake and oxidation of MACR on kaolinite, α-Al₂O₃, α-Fe₂O₃, and TiO₂, but not on CaCO₃. The oxidation of MACR produces organic acids as its major low-molecular-weight product, whose yields are enhanced by a factor of 2–6 in the presence of H₂O₂. In addition, organic peroxides such as methyl hydroperoxide, peroxyformic acid, and peroxyacetic acid are only formed in the presence of H₂O₂, and the formation of methyl hydroperoxide indicates that MACR oxidation on the surface involves reaction with OH radicals. A probe reaction using salicylic acid verifies the production of OH radicals from H₂O₂ decomposition on kaolinite, α-Al₂O₃, α-Fe₂O₃, and TiO₂, which rationalizes the enhanced MACR oxidation observed on these particles. The uptake coefficients of MACR on kaolinite, α-Fe₂O₃, and TiO₂ in the presence of H₂O₂ are on the order of 10–⁵–10–⁴. Our results provide new insights into the formation and chemical evolution of organic species in the atmosphere.
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