Photochemical production of molecular bromine in Arctic surface snowpacks
Photochemical production of molecular bromine in Arctic surface snowpacks
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DOI：
10.1038/ngeo1779
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发表时间：
2013-05-01
影响因子：
18.3
通讯作者：
Stirm, Brian H.
中科院分区：
文献类型：
--
作者：
Pratt, Kerri A.;Custard, Kyle D.;Stirm, Brian H.
在春季极地日出之后，对流层低层的臭氧浓度间歇性地下降到接近零的水平（1）。这些臭氧消耗事件是由大气中活性溴水平的增加引发的（2-5）。在这些条件下，北极对流层的氧化能力被改变，导致许多运输的痕量气体污染物，包括汞（6）。然而，导致大气中活性溴含量增加的来源和机制仍然不确定，限制了北极大气化学与快速变化的海冰景观的模拟（7、8）。在这里，我们研究了分子溴生产的各种样品中的盐雪和海冰，在存在和不存在的阳光和臭氧，在户外雪室在阿拉斯加的潜力。分子溴仅在暴露于阳光下的表面雪（采集于苔原和第一年海冰之上）中检测到。这表明溴化物的氧化是通过光化学机制促进的，这对于以增强的溴化物与氯化物比率为特征的更酸性的样品是最有效的。分子溴浓度显着增加时，雪暴露于臭氧，符合间隙空气放大机制。基于飞机的观测证实，在雪表面附近，溴氧化物的含量增加了。我们认为，表面雪中分子溴的光化学产生是活性溴的主要来源，这导致北极春季对流层臭氧的阶段性消耗。
Following the springtime polar sunrise, ozone concentrations in the lower troposphere episodically decline to near-zero levels(1). These ozone depletion events are initiated by an increase in reactive bromine levels in the atmosphere(2-5). Under these conditions, the oxidative capacity of the Arctic troposphere is altered, leading to the removal of numerous transported trace gas pollutants, including mercury(6). However, the sources and mechanisms leading to increased atmospheric reactive bromine levels have remained uncertain, limiting simulations of Arctic atmospheric chemistry with the rapidly transforming sea-ice landscape(7,8). Here, we examine the potential for molecular bromine production in various samples of saline snow and sea ice, in the presence and absence of sunlight and ozone, in an outdoor snow chamber in Alaska. Molecular bromine was detected only on exposure of surface snow ( collected above tundra and first-year sea ice) to sunlight. This suggests that the oxidation of bromide is facilitated by a photochemical mechanism, which was most efficient for more acidic samples characterized by enhanced bromide to chloride ratios. Molecular bromine concentrations increased significantly when the snow was exposed to ozone, consistent with an interstitial air amplification mechanism. Aircraft-based observations confirm that bromine oxide levels were enhanced near the snow surface. We suggest that the photochemical production of molecular bromine in surface snow serves as a major source of reactive bromine, which leads to the episodic depletion of tropospheric ozone in the Arctic springtime.