Total radical yields from tropospheric ethene ozonolysis
Total radical yields from tropospheric ethene ozonolysis
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DOI：
10.1039/c0cp02342f
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发表时间：
2011-01-01
影响因子：
3.3
通讯作者：
Bloss, William J.
中科院分区：
文献类型：
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作者：
Alam, Mohammed S.;Camredon, Marie;Bloss, William J.
臭氧与烯烃的气相反应可能是地球大气中自由基（OH，HO（2）和RO（2））的重要来源。在这项研究中，总的自由基生产和乙烯臭氧分解的降解产物已被测量，在对流层相关的条件下，在一系列详细的模拟室实验。实验在欧洲光反应器EUPHORE中进行（瓦伦西亚，西班牙），利用各种仪器，包括化学电离反应飞行时间质谱仪（CIR-TOF-MS）测量挥发性有机化合物/氧化挥发性有机化合物（VOCs/OVOCs），用于测量HO（2）自由基产物的激光诱导荧光（LIF）系统和测量HO（2）+的过氧自由基化学放大（PERCA）仪器Sigma RO（2）.为了抑制副反应的发生，研究了在有和没有OH自由基清除剂的情况下乙烯+臭氧反应体系。在干燥和潮湿条件下测量自由基浓度，并通过详细的化学室箱模型进行解释，并结合主化学机制（MCMv3.1）乙烯降解方案，更新了乙烯-臭氧反应机理的更明确的表述。乙烯+臭氧反应的速率系数被测量为（1.45 +/-0.25）× 10（-18）cm（3）molecules（-1）s（-1），并且从过量CO清除剂实验确定稳定的Criegee中间体产率为0.54 +/-0.12。使用环己烷清除剂方法，通过监测OH引发的环己烷氧化产物和HO（2）的形成，确定OH自由基产率为0.17 +/-0.09。结果突出了在推导自由基产率时了解[HO（2）]（特别是在烯烃限制条件和高[O（3）]下）和清除剂化学的重要性。通过LIF/模型拟合确定平均HO（2）产率为0.27 +/-0.07。所观察到的产量解释在假设的乙烯臭氧分解机制内的每个通道的分支比。
The gas-phase reactions of ozone with alkenes can be significant sources of free radicals (OH, HO(2) and RO(2)) in the Earth's atmosphere. In this study the total radical production and degradation products from ethene ozonolysis have been measured, under conditions relevant to the troposphere, during a series of detailed simulation chamber experiments. Experiments were carried out in the European photoreactor EUPHORE (Valencia, Spain), utilising various instrumentation including a chemical-ionisation-reaction time-of-flight mass-spectrometer (CIR-TOF-MS) measuring volatile organic compounds/oxygenated volatile organic compounds (VOCs/OVOCs), a laser induced fluorescence (LIF) system for measuring HO(2) radical products and a peroxy radical chemical amplification (PERCA) instrument measuring HO(2) + Sigma RO(2). The ethene + ozone reaction system was investigated with and without an OH radical scavenger, in order to suppress side reactions. Radical concentrations were measured under dry and humid conditions and interpreted through detailed chemical chamber box modelling, incorporating the Master Chemical Mechanism (MCMv3.1) degradation scheme for ethene, which was updated to include a more explicit representation of the ethene-ozone reaction mechanism.The rate coefficient for the ethene + ozone reaction was measured to be (1.45 +/- 0.25) x 10(-18) cm(3) molecules(-1) s(-1) at 298 K, and a stabilised Criegee intermediate yield of 0.54 +/- 0.12 was determined from excess CO scavenger experiments. An OH radical yield of 0.17 +/- 0.09 was determined using a cyclohexane scavenger approach, by monitoring the formation of the OH-initiated cyclohexane oxidation products and HO(2). The results highlight the importance of knowing the [HO(2)] (particularly under alkene limited conditions and high [O(3)]) and scavenger chemistry when deriving radical yields. An averaged HO(2) yield of 0.27 +/- 0.07 was determined by LIF/model fitting. The observed yields are interpreted in terms of branching ratios for each channel within the postulated ethene ozonolysis mechanism.