Experimental evidence for efficient hydroxyl radical regeneration in isoprene oxidation
Experimental evidence for efficient hydroxyl radical regeneration in isoprene oxidation
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DOI：
10.1038/ngeo1964
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发表时间：
2013-12-01
影响因子：
18.3
通讯作者：
Wahner, A.
中科院分区：
文献类型：
--
作者：
Fuchs, H.;Hofzumahaus, A.;Wahner, A.
地球大气中的大多数污染物都是通过高活性的羟基自由基氧化去除的。现场测量显示，在生物源性挥发性有机化合物异戊二烯负荷高的地区，羟基自由基的浓度比预期的要高得多（1-8）。已经提出了不同的异戊二烯降解机制来解释观察到的高水平羟基自由基（5,9-11）。这些机制中的一种或多种是否在自然环境中实际起作用，以及对气候和空气质量的潜在影响仍不确定（12-14）。在这里，我们提出了一套完整的测量羟基和过氧自由基收集的异戊二烯氧化实验在一个大气模拟室进行，在受控的大气条件下。我们检测到的羟基自由基浓度明显高于基于模型计算的预期，这为在异戊二烯存在的情况下，由于自由基的额外回收，羟基自由基的增强提供了直接证据。具体来说，我们的发现与量子化学计算假设的异戊二烯衍生过氧自由基的单分子反应一致（9-11）。我们的实验表明，在异戊二烯丰富的区域，如森林中，超过一半的羟基自由基被这些与异戊二烯的单分子反应回收。虽然这种循环不足以解释在野外观察到的高浓度羟基自由基，但我们得出结论，它对富异戊二烯地区大气的氧化能力有重要贡献。
Most pollutants in the Earth's atmosphere are removed by oxidation with highly reactive hydroxyl radicals. Field measurements have revealed much higher concentrations of hydroxyl radicals than expected in regions with high loads of the biogenic volatile organic compound isoprene(1-8). Different isoprene degradation mechanisms have been proposed to explain the high levels of hydroxyl radicals observed(5,9-11). Whether one or more of these mechanisms actually operates in the natural environment, and the potential impact on climate and air quality, has remained uncertain(12-14). Here, we present a complete set of measurements of hydroxyl and peroxy radicals collected during isoprene-oxidation experiments carried out in an atmospheric simulation chamber, under controlled atmospheric conditions. We detected significantly higher concentrations of hydroxyl radicals than expected based on model calculations, providing direct evidence for a strong hydroxyl radical enhancement due to the additional recycling of radicals in the presence of isoprene. Specifically, our findings are consistent with the unimolecular reactions of isoprene-derived peroxy radicals postulated by quantum chemical calculations(9-11). Our experiments suggest that more than half of the hydroxyl radicals consumed in isoprene-rich regions, such as forests, are recycled by these unimolecular reactions with isoprene. Although such recycling is not sufficient to explain the high concentrations of hydroxyl radicals observed in the field, we conclude that it contributes significantly to the oxidizing capacity of the atmosphere in isoprene-rich regions.