Interactions of bromine, chlorine, and iodine photochemistry during ozone depletions in Barrow, Alaska
Interactions of bromine, chlorine, and iodine photochemistry during ozone depletions in Barrow, Alaska
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DOI：
10.5194/acp-15-9651-2015
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发表时间：
2015-01-01
影响因子：
6.3
通讯作者：
Weinheimer, A.
中科院分区：
文献类型：
--
作者：
Thompson, C. R.;Shepson, P. B.;Weinheimer, A.
众所周知，北极春季对流层臭氧的消耗是由雪、冰或气溶胶表面释放的卤素原子前体产生的活性卤素光化学引起的。溴在驱动臭氧消耗事件（ODEs）中的作用已被普遍接受，但对氯自由基在臭氧消耗化学中的作用知之甚少。虽然高北极地区碘的潜在影响尚不确定，但有迹象表明，通过观察到可过滤碘化物的增强，对流层IO的可能检测，以及最近观察到积雪光化学产生I-2，有活性碘化学的迹象。尽管进行了数十年的研究，但与溴催化臭氧耗竭有关的化学机制以及由于卤素化学而发生在极地边界层中的复杂相互作用仍然存在很大的不确定性。为了研究这一点，我们开发了一个零维光化学模型，该模型受到2009年阿拉斯加巴罗OA-SIS野外活动测量结果的约束。为了研究不同条件下卤素自由基的相互作用，我们在3月下旬模拟了一个为期7天的周期，其中包括持续3天的完全臭氧消耗事件和随后的臭氧恢复。此外，还研究了碘对基础模型的影响。虽然溴原子是臭氧消耗的主要原因，但发现氯和碘提高了臭氧消耗率，而且发现碘在消耗臭氧方面比溴更有效。氯和溴之间的相互作用是复杂的，因为氯的存在可以增加Br原子的回收和产生，同时在一定条件下也会增加反应性溴汇。氯化学也被发现对HO2和RO2都有显著的影响，有机化合物是Cl原子的主要反应伙伴。这项工作的结果突出表明，需要进一步研究Br-2和Cl-2的产生机制，以及碘在北极高海拔地区的潜在影响。
The springtime depletion of tropospheric ozone in the Arctic is known to be caused by active halogen photochemistry resulting from halogen atom precursors emitted from snow, ice, or aerosol surfaces. The role of bromine in driving ozone depletion events (ODEs) has been generally accepted, but much less is known about the role of chlorine radicals in ozone depletion chemistry. While the potential impact of iodine in the High Arctic is more uncertain, there have been indications of active iodine chemistry through observed enhancements in filterable iodide, probable detection of tropospheric IO, and recently, observation of snowpack photochemical production of I-2. Despite decades of research, significant uncertainty remains regarding the chemical mechanisms associated with the bromine-catalyzed depletion of ozone, as well as the complex interactions that occur in the polar boundary layer due to halogen chemistry. To investigate this, we developed a zero-dimensional photochemical model, constrained with measurements from the 2009 OA-SIS field campaign in Barrow, Alaska. We simulated a 7-day period during late March that included a full ozone depletion event lasting 3 days and subsequent ozone recovery to study the interactions of halogen radicals under these different conditions. In addition, the effects of iodine added to our Base Model were investigated. While bromine atoms were primarily responsible for ODEs, chlorine and iodine were found to enhance the depletion rates and iodine was found to be more efficient per atom at depleting ozone than Br. The interaction between chlorine and bromine is complex, as the presence of chlorine can increase the recycling and production of Br atoms, while also increasing reactive bromine sinks under certain conditions. Chlorine chemistry was also found to have significant impacts on both HO2 and RO2, with organic compounds serving as the primary reaction partner for Cl atoms. The results of this work highlight the need for future studies on the production mechanisms of Br-2 and Cl-2, as well as on the potential impact of iodine in the High Arctic.