Nguyen Tran B, Tyndall Geoffrey S, Crounse John D, Teng Alexander P, Bates Kelvin H, Schwantes Rebecca H, Coggon Matthew M, Zhang Li, Feiner Philip, Milller David O, Skog Kate M, Rivera-Rios Jean C, Dorris Matthew, Olson Kevin F, Koss Abigail, Wild Robert J, Brown Steven S, Goldstein Allen H, de Gouw Joost A, Brune William H, Keutsch Frank N, Seinfeld John H, Wennberg Paul O
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA.
Phys Chem Chem Phys. 2016 Apr 21;18(15):10241-54. doi: 10.1039/c6cp00053c. Epub 2016 Mar 29.
We use a large laboratory, modeling, and field dataset to investigate the isoprene + O3 reaction, with the goal of better understanding the fates of the C1 and C4 Criegee intermediates in the atmosphere. Although ozonolysis can produce several distinct Criegee intermediates, the C1 stabilized Criegee (CH2OO, 61 ± 9%) is the only one observed to react bimolecularly. We suggest that the C4 Criegees have a low stabilization fraction and propose pathways for their decomposition. Both prompt and non-prompt reactions are important in the production of OH (28% ± 5%) and formaldehyde (81% ± 16%). The yields of unimolecular products (OH, formaldehyde, methacrolein (42 ± 6%) and methyl vinyl ketone (18 ± 6%)) are fairly insensitive to water, i.e., changes in yields in response to water vapor (≤4% absolute) are within the error of the analysis. We propose a comprehensive reaction mechanism that can be incorporated into atmospheric models, which reproduces laboratory data over a wide range of relative humidities. The mechanism proposes that CH2OO + H2O (k(H2O)∼ 1 × 10(-15) cm(3) molec(-1) s(-1)) yields 73% hydroxymethyl hydroperoxide (HMHP), 6% formaldehyde + H2O2, and 21% formic acid + H2O; and CH2OO + (H2O)2 (k(H2O)2∼ 1 × 10(-12) cm(3) molec(-1) s(-1)) yields 40% HMHP, 6% formaldehyde + H2O2, and 54% formic acid + H2O. Competitive rate determinations (kSO2/k(H2O)n=1,2∼ 2.2 (±0.3) × 10(4)) and field observations suggest that water vapor is a sink for greater than 98% of CH2OO in a Southeastern US forest, even during pollution episodes ([SO2] ∼ 10 ppb). The importance of the CH2OO + (H2O)n reaction is demonstrated by high HMHP mixing ratios observed over the forest canopy. We find that CH2OO does not substantially affect the lifetime of SO2 or HCOOH in the Southeast US, e.g., CH2OO + SO2 reaction is a minor contribution (<6%) to sulfate formation. Extrapolating, these results imply that sulfate production by stabilized Criegees is likely unimportant in regions dominated by the reactivity of ozone with isoprene. In contrast, hydroperoxide, organic acid, and formaldehyde formation from isoprene ozonolysis in those areas may be significant.
我们使用一个大型的实验室、模型和实地数据集来研究异戊二烯与臭氧的反应，目的是更好地了解大气中C1和C4 Criegee中间体的归宿。尽管臭氧分解可以产生几种不同的Criegee中间体，但观察到的唯一能进行双分子反应的是C1稳定的Criegee（CH2OO，61±9%）。我们认为C4 Criegees的稳定化比例较低，并提出了它们的分解途径。快速反应和非快速反应在羟基自由基（OH，28%±5%）和甲醛（81%±16%）的生成中都很重要。单分子产物（OH、甲醛、甲基丙烯醛（42±6%）和甲基乙烯基酮（18±6%））的产率对水相当不敏感，即响应水蒸气变化的产率变化（绝对变化≤4%）在分析误差范围内。我们提出了一个可以纳入大气模型的综合反应机制，该机制在很宽的相对湿度范围内再现了实验室数据。该机制表明，CH2OO + H2O（k(H2O) ∼ 1 × 10(-15) cm(3) molec(-1) s(-1)）生成73%的羟甲基过氧化氢（HMHP）、6%的甲醛 + H2O2和21%的甲酸 + H2O；CH2OO + (H2O)2（k(H2O)2 ∼ 1 × 10(-12) cm(3) molec(-1) s(-1)）生成40%的HMHP、6%的甲醛 + H2O2和54%的甲酸 + H2O。竞争速率测定（kSO2/k(H2O)n=1,2 ∼ 2.2 (±0.3) × 10(4)）和实地观测表明，即使在污染事件期间（[SO2] ∼ 10 ppb），在美国东南部的森林中，水蒸气也是超过98%的CH2OO的汇。森林冠层上方观测到的高HMHP混合比证明了CH2OO + (H2O)n反应的重要性。我们发现CH2OO对美国东南部SO2或HCOOH的寿命没有实质性影响，例如，CH2OO + SO2反应对硫酸盐形成的贡献很小（<6%）。由此推断，在以臭氧与异戊二烯反应活性为主的地区，稳定的Criegees产生硫酸盐的作用可能不大。相比之下，在这些地区异戊二烯臭氧分解形成氢过氧化物、有机酸和甲醛可能很显著。
