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首页> 外文期刊>Atmospheric chemistry and physics >OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project
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OH reactivity in a South East Asian tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

机译：氧化剂和颗粒光化学过程（OP3）项目期间东南亚热带雨林中的OH反应性

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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 Borneoas 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 diurnallyaveraged concentrations of observed sinks was ~ 18 s?1,significantly less than the observations, consistent with other studies insimilar environments. OH reactivity was dominated by reaction with isoprene(~ 30%). Numerical simulations of isoprene oxidation using theMaster Chemical Mechanism (v3.2) in a highly simplified physical and chemicalenvironment show that the steady state OH reactivity is a linear function ofthe OH reactivity due to isoprene alone, with a maximum multiplier, toaccount for the OH reactivity of the isoprene oxidation products, being equalto the number of isoprene OH attackable bonds (10). Thus the emission ofisoprene constitutes a significantly larger emission of reactivity than isoffered by the primary reaction with isoprene alone, with significant scopefor the secondary oxidation products of isoprene to constitute the observedmissing OH reactivity. A physically and chemically more sophisticatedsimulation (including physical loss, photolysis, and other oxidants) showedthat the calculated OH reactivity is reduced by the removal of the OHattackable bonds by other oxidants and photolysis, and by physical loss(mixing and deposition). The calculated OH reactivity is increased byperoxide cycling, and by the OH concentration itself. Notable in thesecalculations is that the accumulated OH reactivity from isoprene, defined asthe total OH reactivity of an emitted isoprene molecule and all of itsoxidation products, is significantly larger than the reactivity due toisoprene itself and critically depends on the chemical and physical lifetimesof intermediate species. When constrained to the observed diurnally averagedconcentrations of primary VOCs (volatile organic compounds), O3, NOx and otherparameters, the model underestimated the observed diurnal mean OH reactivityby 30%. However, it was found that (1) the short lifetimes of isopreneand OH, compared to those of the isoprene oxidation products, lead to a largevariability in their concentrations and so significant variation in thecalculated OH reactivity; (2) uncertainties in the OH chemistry in these highisoprene environments can lead to an underestimate of the OH reactivity;(3) the physical loss of species that react with OH plays a significant rolein the calculated OH reactivity; and (4) a missing primary source of reactivecarbon would have to be emitted at a rate equivalent to 50% that ofisoprene to account for the missing OH sink. Although the presence ofunmeasured primary emitted VOCs contributing to the measured OH reactivity islikely, evidence that these primary species account for a significantfraction of the unmeasured reactivity is not found. Thus the development oftechniques for the measurement of secondary multifunctional carbon compoundsis needed to close the OH reactivity budget.
机译：在2008年4月，在OP3（氧化剂和颗粒光化学过程）项目的婆罗洲部分热带雨林中，测量了OH（羟基自由基）反应性，即羟基自由基化学寿命的倒数，为期12天。最高观察值为83.8±26.0 s ？1 ，活动的平均午间最大值为29.1±8.5 s ？1 。使用观察到的汇的每日平均浓度计算出的最大OH反应性约为〜18 s ？1 ，明显低于观察值，与类似环境中的其他研究一致。 OH反应性主要是通过与异戊二烯（〜30％）反应。使用Master化学机理（v3.2）在高度简化的物理和化学环境中进行异戊二烯氧化的数值模拟表明，稳态OH反应性是OH反应性的线性函数，这归因于单独的异戊二烯，最大乘数反映了OH反应性异戊二烯氧化产物的数量，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的反应活性的排放显着大于单独与异戊二烯进行的初级反应所提供的活性的排放，并且对于异戊二烯的次级氧化产物构成观察到的缺少OH反应性的显着范围。物理和化学上更复杂的模拟（包括物理损失，光解和其他氧化剂）表明，通过其他氧化剂和光解作用除去OH可攻击键，以及物理损失（混合和沉积），降低了所计算的OH反应性。通过过氧化物循环和通过OH浓度本身，可以提高计算出的OH反应性。在这些计算中值得注意的是，异戊二烯累积的OH反应性（定义为释放的异戊二烯分子及其所有氧化产物的总OH反应性）显着大于异戊二烯本身的反应性，并且在很大程度上取决于中间物种的化学和物理寿命。当受制于主要VOC（挥发性有机化合物），O 3 ，NO x 和其他参数的每日平均浓度时，该模型低估了每日平均OH反应性30％。然而，发现：（1）与异戊二烯氧化产物相比，异戊二烯和OH的寿命短，导致它们的浓度变化很大，因此计算出的OH反应性显着变化; （2）在这些高异戊二烯环境中OH化学的不确定性可能导致OH反应性的低估;（3）与OH反应的物质的物理损失在计算得出的OH反应性中起重要作用; （4）缺少的主要活性炭源排放量必须等于异戊二烯的50％，以解决缺少的OH吸收剂的问题。尽管很可能存在未测出的一级排放出的挥发性有机化合物，这些挥发性有机物有助于测出的OH反应性，但没有发现这些主要物质占未测出的反应性的重要部分的证据。因此，需要开发用于测量次要多功能碳化合物的技术，以结束OH反应性预算。

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