State Key Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University , Beijing 100871, People's Republic of China.
Environ Sci Technol. 2014 Sep 16;48(18):10614-23. doi: 10.1021/es5023416. Epub 2014 Aug 21.
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.
含氧挥发性有机化合物（OVOCs）的非均相氧化既是 OVOCs 的重要汇，也是次生有机物质的来源。然而，气相氧化剂在这些反应中的作用还知之甚少。在这项工作中，我们首次在存在气态 H2O2 的情况下，研究了异相条件下甲基丙烯醛（MACR）在各种矿物尘埃颗粒上的反应。结果表明，气态 H2O2 的存在显著促进了 MACR 在高岭土、α-Al2O3、α-Fe2O3 和 TiO2 上的吸收和氧化，但在 CaCO3 上则不然。MACR 的氧化产生有机酸作为其主要的低分子量产物，其产率在 H2O2 的存在下提高了 2-6 倍。此外，只有在 H2O2 存在的情况下，才会形成过氧甲酸、过氧乙酸等有机过氧化物，而甲基过氧化物的形成表明 MACR 在表面上的氧化涉及与 OH 自由基的反应。使用水杨酸的探针反应验证了 H2O2 在高岭土、α-Al2O3、α-Fe2O3 和 TiO2 上分解产生 OH 自由基，这解释了在这些颗粒上观察到的增强的 MACR 氧化。在 H2O2 存在的情况下，MACR 在高岭土、α-Fe2O3 和 TiO2 上的吸收系数在 10(-5)-10(-4)之间。我们的研究结果为大气中有机物种的形成和化学演化提供了新的认识。
