Ring-opening yields and auto-oxidation rates of the resulting peroxy radicals from OH-oxidation of α-pinene and β-pinene
Ring-opening yields and auto-oxidation rates of the resulting peroxy radicals from OH-oxidation of α-pinene and β-pinene
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DOI：
10.1039/d2ea00133k
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发表时间：
2023-01-05
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影响因子：
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通讯作者：
Thornton, Joel A.
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文献类型：
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作者：
Lee, Ben H.;Iyer, Siddharth;Thornton, Joel A.
单萜（C10 H16）的大气氧化有助于环境颗粒数量和质量浓度，部分原因是所产生的过氧自由基经历自动氧化成低挥发性高含氧分子（HOM）。第一代羟基过氧自由基（C10 H17 O3）的结构异构体中只有一种是由环丁基环的开口形成的，被认为是大多数由OH引发的α和β-蒎烯氧化产生的HOM的原因。我们通过使用同位素标记的前体，如D-3-α-蒎烯，和过氧自由基和闭壳产物的直接测量的独特组合，仅类似于0.7秒的反应时间后，限制这种异构体的产率和自动氧化速率。通过竞争速率研究和量子化学计算，我们发现这些开环过氧自由基的产率为0.47（0.2，0.6）对于α-蒎烯和0.66 β-蒎烯为（0.4，0.8），自氧化率为2.9（1.1，4.7）s（-1）和0.8（0.4，1.6）s（-1），其中括号中的值表示基于实验和机械不确定性的上限和下限。这些速率和产率与由独立方法确定的HOM产率大体一致，并且在其中OH驱动的单萜HOM形成对于宽范围的条件在大气中是重要的范围内。
Atmospheric oxidation of monoterpenes (C10H16) contributes to ambient particle number and mass concentrations due, in part, to the resulting peroxy radicals undergoing auto-oxidation to low-volatility highly oxygenated molecules (HOMs). Only one of the structural isomers of the first-generation hydroxy peroxy radical (C10H17O3), that formed with an opening of the cyclobutyl ring, is thought to be responsible for the majority of HOMs derived from OH-initiated oxidation of alpha and beta-pinene. We constrain the yield and auto-oxidation rate of this isomer by using a unique combination of isotopically labeled precursors, such as D-3-alpha-pinene, and direct measurements of peroxy radicals and closed-shell products after a reaction time of only similar to 0.7 s. Using competitive rate studies and quantum chemical calculations, we find that the yields of these ring-opened peroxy radicals are 0.47 (0.2, 0.6) for alpha-pinene and 0.66 (0.4, 0.8) for beta-pinene, and the rates of auto-oxidation are 2.9 (1.1, 4.7) s(-1) and 0.8 (0.4, 1.6) s(-1), respectively, where values in the parentheses represent upper and lower bounds based on experimental and mechanistic uncertainties. These rates and yields are in general agreement with HOM yields determined from independent methods and in a range where OH driven monoterpene HOM formation will be atmospherically important for a wide set of conditions.