Division of Chemistry and Chemical Engineering, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States.
J Phys Chem A. 2014 Feb 20;118(7):1237-46. doi: 10.1021/jp4107958. Epub 2014 Feb 6.
Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-β- and trans-β-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-β- and trans-β, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10(-11), (1.52 ± 0.07) × 10(-11), and (0.98 ± 0.05) × 10(-11) cm(3) molecule(-1) s(-1) for the δ1, cis-β, and trans-β isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions.
异戊二烯环氧化二醇（IEPOX）在低 NO 条件下由 OH 引发的异戊二烯氧化作用下以高收率生成。这些化合物对二次有机气溶胶的形成有重要贡献。然而，它们的气相化学性质在很大程度上仍未得到探索。在这项研究中，我们研究了 OH 引发的异戊二烯氧化作用生成 IEPOX 异构体的情况。我们发现顺式-β-和反式-β-IEPOX 是主要生成的异构体，并且它们是由低 NO 氧化异戊二烯以大约 1:2 的比例生成的。我们合成了三种 IEPOX 异构体，包括顺式-β-和反式-β-异构体，并在高 NO 和低 NO 条件下在环境室中用 OH 将它们氧化。我们发现 IEPOX 在 299 K 时与 OH 反应的速率系数分别为（0.84 ± 0.07）× 10(-11)、（1.52 ± 0.07）× 10(-11)和（0.98 ± 0.05）× 10(-11)cm(3)分子(-1) s(-1)，分别对应于 δ1、顺式-β-和反式-β-异构体。最后，我们测量了 IEPOX + OH 氧化的第一代产物的产率，并提出了一种新的 IEPOX 氧化机制来解释观察到的产物。IEPOX 氧化生成的大量乙二醛和甲基乙二醛可能有助于解释在高异戊二烯排放的低 NO 环境中观察到的这些化合物的高浓度水平。
