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首页> 外文期刊>Atmospheric environment >Measuring a 10,000-fold enhancement of singlet molecular oxygen (~1O_2) concentration on illuminated ice relative to the corresponding liquid solution
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Measuring a 10,000-fold enhancement of singlet molecular oxygen (~1O_2) concentration on illuminated ice relative to the corresponding liquid solution

机译：相对于相应的液体溶液，测量冰​​上的单线态分子氧（〜1O_2）浓度增加10,000倍

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Much attention has focused on the highly reactive hydroxyl radical in the oxidation of trace organic compounds on snow and ice (and subsequent release of volatile organics to the atmospheric boundary layer) but other oxidants are likely also important in this processing. Here we examine the ice chemistry of singlet molecular oxygen (~1O*_2), which can be significant in atmospheric water drops but has not been examined in ice or snow. To examine ~1O*_2 on ice we illuminate laboratory ices containing Rose Bengal (RB) as the source of ~1O*_2 furfuryl alcohol (FFA) as the probe, and Na_2SO_4 to control the total solute concentration. We find that the ~1O*_2-mediated loss of FFA (and, thus, the ~1O*_2 concentration) is up to 11,000 times greater on ice than in the equivalent liquid sample at the same photon flux. We attribute this large increase in the ~1O*_2 steady-state concentration to the freeze-concentration of solutes into liquid-like regions (LLRs) in/on ice: compared to the initial solution, in the LLRs of ice the sources for ~1O*_2 are highly concentrated, while the concentration of the dominant sink for ~1O*_2 (i.e., water) remains largely unchanged. Similar to results expected in liquid solution, rates of FFA loss in ice depend on both the initial sensitizer concentration and temperature, providing evidence that these reactions occur in LLRs. However, we find that the enhancement in ~1O*_2 concentrations on ice does not follow predictions from freezing-point depression, likely because experiments were conducted below the eutectic temperature for sodium sulfate, where all of the salt should have precipitated. We also explore a method for separating ~1O*_2 and ·OH contributions to FFA oxidation in laboratory ices and show its application to two natural snow samples. We find that ~1O*_2 concentrations in these snows are approximately 100 times higher than observed in polluted, mid-latitude fog waters, showing that the enhancement of ~1O*_2 on ice is environmentally relevant and that ~1O*_2 could be a significant sink for electron-rich organic compounds in snow.
机译：在雪和冰上的痕量有机化合物的氧化（以及随后的挥发性有机物向大气边界层的释放）的氧化中，高度关注的是羟基自由基，但是其他氧化剂在该过程中也可能很重要。在这里，我们研究了单线态分子氧（〜1O * _2）的冰化学，这在大气中的水滴中可能很重要，但在冰或雪中尚未进行过检查。为了检查冰上的〜1O * _2，我们对实验室冰进行照明，其中包含玫瑰孟加拉（RB）作为〜1O * _2糠醇（FFA）的来源，并用Na_2SO_4来控制总溶质浓度。我们发现，在相同光子通量下，冰上〜1O * _2介导的FFA的损失（因此〜1O * _2浓度）比等效液体样品高多达11,000倍。我们将〜1O * _2稳态浓度的大幅增加归因于溶质在冰中或冰上的冻结浓度冻结成液体状区域（LLR）：与初始溶液相比，在冰的LLR中，〜 1O * _2高度集中，而〜1O * _2（即水）的主要汇的浓度基本保持不变。与液体溶液中预期的结果相似，冰中FFA的损失速率取决于初始敏化剂浓度和温度，从而提供了这些反应在LLR中发生的证据。但是，我们发现冰上〜1O * _2浓度的增加并未遵循冰点降低的预测，这很可能是因为在低于共晶温度的硫酸钠进行了实验的情况下，所有盐都应该沉淀了。我们还探索了一种分离实验室冰块中〜1O * _2和·OH对FFA氧化贡献的方法，并展示了其在两个天然雪样中的应用。我们发现这些雪中的〜1O * _2浓度比在受污染的中纬度雾水中观察到的浓度高约100倍，这表明冰上〜1O * _2的增强与环境有关，并且〜1O * _2可能是一种雪中​​富含电子的有机化合物的重要汇。

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