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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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摘要

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, NO_x 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.
机译：作为OP3（氧化剂和粒子光化学过程）项目的一部分，2008年4月在婆罗洲的热带雨林中测量了OH（羟基自由基）反应性，该反应时间是羟基自由基化学寿命的倒数。观测值的最大值为83.8±26.0 s-1，活动的平均午间最大值为29.1±8.5 s-1。使用观察到的汇的日平均浓度计算得出的最大OH反应性为〜18 s-1，明显低于观察值，这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。在高度简化的物理和化学环境中使用主化学机理（v3.2）进行异戊二烯氧化的数值模拟表明，稳态OH反应性是仅由于异戊二烯引起的OH反应性的线性函数，具有最大乘数对于异戊二烯氧化产物的OH反应性，其值等于异戊二烯OH可攻击键的数量（10）。因此，异戊二烯的排放构成的反应性的排放显着大于单独与异戊二烯的初级反应所提供的反应性的排放，并且异戊二烯的次级氧化产物具有显着的范围以构成观察到的缺失的OH反应性。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去除OH可攻击键以及物理损失（混合和沉积），可以降低所计算的OH反应性。通过过氧化物循环和通过OH本身的浓度来增加计算的OH反应性。在这些计算中值得注意的是，异戊二烯的累积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）明显大于异戊二烯本身的反应性，并且在很大程度上取决于化学和物理寿命中间物种。当受制于主要VOC（挥发性有机化合物），O3，NO_x和其他参数的每日平均观测浓度时，该模型将观测到的每日平均OH反应性低估了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反应性有显着变化; （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的OH反应性中起重要作用; （4）缺少的主要活性碳源必须以异戊二烯的50％的速率排放，以解决缺少的OH吸收剂的问题。尽管可能存在未测量的主要排放的挥发性有机化合物，这些挥发性有机物有助于测量到的OH反应性，但没有发现这些主要种类占未测量的反应性的很大部分的证据。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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