OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project
OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project
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DOI：
10.5194/acp-13-9497-2013
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发表时间：
2013-09
影响因子：
6.3
通讯作者：
Peter M. Edwards;M. J. Evans;K. Furneaux;J. Hopkins;T. Ingham;C. E. Jones;James D. Lee;A. Lewis;S. Moller;D. Stone;L. Whalley;D. Heard
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文献类型：
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作者：
Peter M. Edwards;M. J. Evans;K. Furneaux;J. Hopkins;T. Ingham;C. E. Jones;James D. Lee;A. Lewis;S. Moller;D. Stone;L. Whalley;D. Heard
抽象。2008年4月，作为OP3（氧化剂和粒子光化学过程）项目的一部分，在婆罗洲的热带雨林中测量了12天的OH（羟基自由基）反应性，即羟基自由基化学寿命的倒数。观测到的最大值为83.8 ± 26.0 s-1，活动平均中午最大值为29.1 ± 8.5 s-1。使用观测到的汇的日平均浓度计算的最大OH反应性约为18 s − 1，明显低于观测值，与类似环境中的其他研究一致。OH反应性由与异戊二烯的反应主导（~30%）。在高度简化的物理和化学环境中使用主化学机理（v3.2）对异戊二烯氧化进行的数值模拟表明，稳态OH反应性是单独由异戊二烯引起的OH反应性的线性函数，具有最大乘数，以说明异戊二烯氧化产物的OH反应性，该乘数等于异戊二烯OH可攻击键的数量（10）。因此，异戊二烯的排放构成了比单独与异戊二烯的初级反应所提供的反应性排放显著更大的反应性排放，其中异戊二烯的次级氧化产物具有显著的范围以构成所观察到的缺失的OH反应性。一个物理和化学更复杂的模拟（包括物理损失，光解，和其他氧化剂）表明，计算的OH反应性降低的OH攻击键的其他氧化剂和光解，并通过物理损失（混合和沉积）的去除。计算的OH反应性通过过氧化物循环和OH浓度本身增加。在这些计算中值得注意的是，来自异戊二烯的累积OH反应性（定义为排放的异戊二烯分子及其所有氧化产物的总OH反应性）显著大于由于异戊二烯本身的反应性，并且关键地取决于中间物质的化学和物理寿命。当约束到所观察到的日平均浓度的主要挥发性有机化合物（挥发性有机化合物），O3，NOx和其他参数，该模型低估了所观察到的日平均OH反应性的30%。然而，发现（1）与异戊二烯氧化产物的寿命相比，异戊二烯和OH的寿命短，导致它们的浓度变化很大，因此计算的OH反应性变化很大;（2）在这些高异戊二烯环境中OH化学的不确定性可能导致对OH反应性的低估;（3）与OH反应的物质的物理损失在计算的OH反应性中起重要作用;以及（4）缺失的活性碳的主要来源必须以相当于异戊二烯的50%的速率排放，以解释缺失的OH汇。虽然未测量的主要排放的挥发性有机化合物的存在有助于测量的OH反应性是可能的，证据表明，这些主要物种占未测量的反应性的一个显着的部分是没有found.Thus的测量技术的发展需要关闭的OH反应性预算的二次多功能碳化合物。
Abstract. OH (hydroxyl radical) reactivity, the inverse of the chemical lifetime of the hydroxyl radical, was measured for 12 days in April 2008 within a tropical rainforest on Borneo as part of the OP3 (Oxidant and Particle Photochemical Processes) project. The maximum observed value was 83.8 ± 26.0 s−1 with the campaign averaged noontime maximum being 29.1 ± 8.5 s−1. The maximum OH reactivity calculated using the diurnally averaged concentrations of observed sinks was ~ 18 s−1, significantly less than the observations, consistent with other studies in similar environments. OH reactivity was dominated by reaction with isoprene (~ 30%). Numerical simulations of isoprene oxidation using the Master Chemical Mechanism (v3.2) in a highly simplified physical and chemical environment show that the steady state OH reactivity is a linear function of the OH reactivity due to isoprene alone, with a maximum multiplier, to account for the OH reactivity of the isoprene oxidation products, being equal to the number of isoprene OH attackable bonds (10). Thus the emission of isoprene constitutes a significantly larger emission of reactivity than is offered by the primary reaction with isoprene alone, with significant scope for the secondary oxidation products of isoprene to constitute the observed missing OH reactivity. A physically and chemically more sophisticated simulation (including physical loss, photolysis, and other oxidants) showed that the calculated OH reactivity is reduced by the removal of the OH attackable bonds by other oxidants and photolysis, and by physical loss (mixing and deposition). The calculated OH reactivity is increased by peroxide cycling, and by the OH concentration itself. Notable in these calculations is that the accumulated OH reactivity from isoprene, defined as the total OH reactivity of an emitted isoprene molecule and all of its oxidation products, is significantly larger than the reactivity due to isoprene itself and critically depends on the chemical and physical lifetimes of intermediate species. When constrained to the observed diurnally averaged concentrations of primary VOCs (volatile organic compounds), O3, NOx and other parameters, the model underestimated the observed diurnal mean OH reactivity by 30%. However, it was found that (1) the short lifetimes of isoprene and OH, compared to those of the isoprene oxidation products, lead to a large variability in their concentrations and so significant variation in the calculated OH reactivity; (2) uncertainties in the OH chemistry in these high isoprene environments can lead to an underestimate of the OH reactivity; (3) the physical loss of species that react with OH plays a significant role in the calculated OH reactivity; and (4) a missing primary source of reactive carbon would have to be emitted at a rate equivalent to 50% that of isoprene to account for the missing OH sink. Although the presence of unmeasured primary emitted VOCs contributing to the measured OH reactivity is likely, evidence that these primary species account for a significant fraction of the unmeasured reactivity is not found. Thus the development of techniques for the measurement of secondary multifunctional carbon compounds is needed to close the OH reactivity budget.