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Rapid formation of isoprene photo-oxidation products observed in Amazonia

机译：在亚马逊地区观察到异戊二烯光氧化产物的快速形成

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Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photooxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian Aerosol Characterization Experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photooxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. Recently reported fast secondary production could explain 50% of the observed discrepancy with the remaining part possibly produced via a novel primary production channel, which has been proposed theoretically. The observations of OVOCs are also used to test a recently proposed HO_x recycling mechanism via degradation of isoprene peroxy radicals. If generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in uncertainties of modelled OH reactivity, potentially explaining a fraction of the missing OH sink over forests which has previously been largely attributed to a missing source of primary biogenic VOCs.
机译：异戊二烯代表热带大气中大气化学中最重要的单一反应性烃。它在全球和区域大气化学以及可能的气候反馈中发挥着核心作用。伯碳氢化合物（例如异戊二烯）的光氧化会导致形成氧化的VOC（OVOC）。这些中间体的释放会影响大气的氧化能力（通过与OH反应），并且可能导致二次气溶胶形成，这是一个鲜为人知的过程。对于区域空气质量和全球气候的模型模拟，需要准确，定量地了解VOC氧化过程。根据在亚马逊气溶胶表征实验（AMAZE-08）期间进行的现场测量，我们表明，标准化学方案大大降低了低层大气中异戊二烯光氧化法生产某些OVOC（例如羟丙酮）的可能性。最近报道的快速二次生产可以解释观察到的差异的50％，其余部分可能是通过新颖的一次生产渠道生产的，这在理论上已经提出。 OVOC的观察结果还用于通过异戊二烯过氧自由基的降解来测试最近提出的HO_x循环机制。如果将其概括，我们的观察结果表明，迅速的光化学形成OVOC和VOC氧化方案中的其他不确定性可能会导致模拟的OH反应性的不确定性，这可能解释了森林中缺少的OH汇的一部分，这在很大程度上归因于缺少主要的来源生物VOC。

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