Extended Experimental Studies of Reactive Halogen Chemistry in the Polar Troposphere (HALOPOLE III)

卤素自由基在极地边界层的化学中起着重要的作用。每年春季，覆盖数百万平方公里的大片地区受到活性溴浓度大幅增加的影响，这些溴是从北极和南极的盐水表面排放的。这种现象被称为溴爆炸。 此外，卫星和地面的光谱测量都表明，在南极上空存在大量的碘氧化物自由基，但在北极上空没有。这种不对称的原因尚不清楚，但在南极边界层中存在几个ppt的活性碘应该对大气的化学平衡产生重大影响，预计也会在南方春季扩大活性溴对臭氧的破坏。第三次Halopole框架内的活动将侧重于我们在第一次Halopole和第二次Halopole期间的活动中出现的与极地地区活性卤素物质的来源、汇和转化过程有关的关键问题。基于对迄今为止收集的长期和实地数据的协同分析以及在南极洲的新测量，主要重点将是：（1）调查Halopole II期间主动和被动DOAS测量的IO观测的显著差异。(2)全面分析在Neumayer站（南极洲）、Arrival Heights（南极洲）和Alert（加拿大）收集的长期MAX-DOAS数据，包括气象学影响、气团来源、垂直分布以及雪、海冰和霜花对活性溴释放的贡献。(3)在详细分析BROMEX 2012活动期间在巴罗/阿拉斯加收集的机载MAX-DOAS测量结果的基础上，对BrO增强的小尺度空间和时间变化进行调查。(4)分析最近在Polarstern船上南极洲边缘冰区进行的测量，包括BrO和IO的水平和垂直分布，以及卤素化学对臭氧和汞循环的影响。(5)根据在南极洲哈雷湾进行的测量活动，进一步深入研究卤素自由基，特别是氯和碘对极地边界层化学平衡的影响。(6)使用将在本项目内开发的新型长路径DOAS仪器，对南极洲Neumayer站的卤素自由基和相关化合物进行更详细的长期测量。除了现有的MAX-DOAS测量外，它还将允许全年测量整个昼夜周期，不仅可以调查溴和碘，还可以调查氯的化学性质。

Halogen radicals play an important role in the chemistry of the polar boundary layer. Each year during springtime, huge areas, covering several millions of square kilometres, are influenced by strongly enhanced concentrations of reactive bromine, which is emitted from saline surfaces in the Arctic and Antarctic. This phenomenon is referred to as bromine explosion. In addition, both satellite-borne and ground-based spectroscopic measurements show the presence of significant amounts of iodine oxide radicals over the Antarctic, but not over the Arctic. The reason for this asymmetry is yet unknown, but the presence of several ppt of reactive iodine in the Antarctic boundary layer should have a significant impact on the chemical balance of the atmosphere, and is also expected to amplify the ozone destruction by reactive bromine during austral spring. The activities in the framework of HALOPOLE III will focus on the key questions that emerged from our activities during HALOPOLE I and II related to the sources, sinks and transformation processes of reactive halogen species in Polar Regions. Based both on the synergistic analysis of the long-term and field data collected so far and on novel measurements in Antarctica, the main foci will be on:(1) The investigation of a striking discrepancy in the IO observations from active and passive DOAS measurements during HALOPOLE II.(2) A thorough analysis of the long-term MAX-DOAS data collected at Neumayer Station (Antarctica), Arrival Heights (Antarctica) and Alert (Canada) with respect to the influence of meteorology, origin of the air masses, vertical distribution, and the contribution of snow, sea ice and frost flowers to the release of reactive bromine.(3) The investigation of the small-scale spatial and temporal variability of BrO enhancements on the basis of a detailed analysis of the airborne MAX-DOAS measurements collected during the BROMEX 2012 campaign in Barrow/Alaska.(4) The analysis of the recently performed measurements in the marginal ice zone of Antarctica onboard Polarstern with respect to the horizontal and vertical distribution of BrO and IO, as well as the impact of halogen chemistry on ozone and the mercury cycle.(5) Further in-depth studies of the impact of halogen radicals, in particular chlorine and iodine, on the chemical balance of the polar boundary layer on the basis of a measurement campaign at Halley Bay, Antarctica.(6) More detailed long-term measurements of halogen radicals and related compounds at Neumayer Station, Antarctica, using a novel long-path DOAS instrument that will be developed within this project. In addition to the existing MAX-DOAS measurements, it will allow for year-round measurements of the full diurnal cycle and for the investigation not only of bromine- and iodine, but also of chlorine chemistry.