Production and Release of Molecular Bromine and Chlorine from the Arctic Coastal Snowpack
Production and Release of Molecular Bromine and Chlorine from the Arctic Coastal Snowpack
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DOI：
10.1021/acsearthspacechem.7b00014
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发表时间：
2017-05-01
影响因子：
3.4
通讯作者：
Pratt, K. A.
中科院分区：
文献类型：
--
作者：
Custard, K. D.;Raso, A. R. W.;Pratt, K. A.
大气中的溴和氯原子对大气化学物质加工的途径有重要影响。分子卤素的光解以及随后与臭氧、汞和碳氢化合物的反应是春季极地日出之后在北极边界层中常见的现象。虽然最近确定Br-2是从阳光照射的地表积雪中释放出来的，但Cl-2和BrCl产生的来源和机制仍然未知。由于缺乏对这些物种的来源和排放率的了解，目前模拟北极大气成分的努力受到限制。在这里，我们首次同时直接测量了积雪间隙空气中的Br-2、Cl-2和BrCl，以及首次测量了Br-2和Cl-2从积雪排放到大气中的速率。利用化学电离质谱法，2014年2月，在AK Utqiagvik附近的冻土带表面积雪中，经过人工和自然照射，观察到Br-2、Cl-2和BrCl的产生，符合光解产生机制。从积雪到上覆大气的最大Cl-2和Br-2通量被量化，并在正午辐射峰值期间达到最大值。当空气温度低于形成NaCl的共晶点时，积雪中Br-2和BrCl的产量增加，而Cl-2的产量减少。2H(2)O，表明与在该共晶点以上的空气温度下生产相比，氯化物的可用性有限。这些新的观测结果提高了社区模拟北极边界层组成和污染物命运的能力。
Atmospheric bromine and chlorine atoms have a significant influence on the pathways of atmospheric chemical species processing. The photolysis of molecular halogens and subsequent reactions with ozone, mercury, and hydrocarbons are common occurrences in the Arctic boundary layer during spring, following polar sunrise. While it was recently determined that Br-2 is released from the sunlit surface snowpack, the source(s) and mechanisms of Cl-2 and BrCl production have remained unknown. Current efforts to model Arctic atmospheric composition are limited by the lack of knowledge of the sources and emission rates of these species. Here, we present the first simultaneous direct measurements of Br-2, Cl-2, and BrCl in snowpack interstitial air, as well as the first measured emission rates of Br-2 and Cl-2 out of the snowpack into the atmosphere. Using chemical ionization mass spectrometry, Br-2, Cl-2, and BrCl were observed to be produced within the tundra surface snowpack near Utqiagvik, AK, during Feb 2014, following both artificial and natural irradiation, consistent with a photolytic production mechanism. Maximum Cl-2 and Br-2 fluxes from the snowpack to the overlying atmosphere were quantified and reached maxima at mid-day during peak radiation. In-snowpack Br-2 and BrCl production was enhanced, with Cl-2 production reduced, at air temperatures below the eutectic point for the formation of NaCl. 2H(2)O, suggesting limited chloride availability, as compared to production at air temperatures above this eutectic point. These new observations improves the ability of the community to simulate Arctic boundary layer composition and pollutant fate.