Impact of combined iodine and bromine release on the Arctic atmosphere (COBRA).

极地日出臭氧和汞耗尽事件是在北极和南极沿海地区发生的年度现象，对大气氧化能力、气候和健康有影响。这些事件被认为是由海冰表面释放的无机溴(Br2，BrCl2)光解形成的含溴自由基氧化臭氧和汞引起的。最近的研究表明，“霜花”--生长在新形成的海冰上的冰晶--可能是极地溴的主要来源。霜花排放的确切性质尚未得到很好的确定，而且到目前为止，还没有现场研究证实或以其他方式证实与海冰/积雪上的海盐相比，FF在溴释放中的重要作用。此外，人们对碘在极地边界层化学中的作用和来源知之甚少。含碘的气溶胶一直与极地日出时的臭氧消耗有关，但也出现在秋季--这与北极碘的唯一已知来源--冰藻在冰下春季的水华--不一致。眼镜蛇研究人员最近在南极洲观察到了碘氧化物，在北极观察到了活性有机碘化合物。到目前为止，在不同的极地地点进行的这些尚未发表的观测表明，极地大气中广泛存在着可能的非生物/光化学碘来源。最近的理论研究表明，排放到北极大气中的碘化合物比额外的溴分子具有更大的臭氧和汞消耗效应，因此我们的观察结果可能对极地卤素化学研究具有重要意义。眼镜蛇(联合释放碘和溴对北极大气的影响)本质上是一项有针对性的过程研究，由在卤素和极地化学和物理方面有良好记录的科学家组成的一个联合体结合野外、实验室和模拟技术，以：增进对碘(与溴协同)在北极气相光化学和气溶胶产生和演化中的作用的了解；调查霜花、较老的海冰/积雪、海盐气溶胶和生物源在向北极大气释放卤素方面的相对/综合作用；增进对北极与卤素有关的臭氧和汞耗竭事件的时空变异性的了解；并根据可观测的冰和气象条件制定和评估向北极大气排放卤素的参数，并利用这些参数改进北极化学和排放及其对区域/全球大气化学和气候的影响和反馈。我们将于春季和秋季在哈德逊湾北部的沿海地区开展两次地面实地活动，部署一系列痕量气体和气溶胶技术来测量无机和卤素化合物，并提供一整套支持数据，哈德逊湾北部是一个有很高霜花生长潜力的地区，也是一个溴“热点”。秋季活动将通过基于船舶的测量来扩大，以确定该地区更广泛的汞和臭氧消耗事件以及有机卤素浓度。除了沿海站点的浓度测量外，我们还将测量冰霜花形成的颗粒、臭氧和卤素的浓度和通量，以及较老的海冰/积雪和任何已发现的表面硅藻的通量。我们将在实验室中描述野外各种海冰表面的特征，并研究霜花形成的化学机制。各种形式的卤素对臭氧和汞消耗的综合影响将使用详细的过程模型进行调查，并将利用全球化学迁移模型在更广泛的范围内进行调查。

Polar sunrise ozone and mercury depletion events are yearly phenomena that occur throughout the Arctic and Antarctic coastal regions, and have implications for the atmospheric oxidative capacity, climate and health. These events are believed to be caused by oxidation of ozone and mercury by bromine-containing radicals formed from photolysis of inorganic bromine (Br2, BrCl) released from the sea-ice surface. Recent studies suggest that 'frost flowers' (FF) - ice crystals that grow on newly formed sea ice - may be the dominant source of polar bromine. The exact nature of emissions from frost flowers is not well established and so far there are no field studies to confirm or otherwise the important role of FF in bromine release, compared to sea salt on sea-ice/snow-pack. Further, little is known about the role and sources of iodine in polar boundary layer chemistry. Iodine-containing aerosol has been associated with ozone depletion at polar sunrise but also appears in autumn - this is not consistent with the only known source of Arctic iodine, the under-ice spring bloom of ice algae. COBRA investigators have recently observed iodine oxide radicals in Antarctica and reactive organic iodine compounds in the Arctic. These so far unpublished observations, in separate polar locations, suggest a widespread and likely abiotic/photochemical source of iodine to the polar atmosphere. Recent theoretical studies indicate that iodine compounds emitted to the Arctic atmosphere have a significantly greater ozone and mercury depletion effect than additional bromine molecules, so our observations may be significant for polar halogen chemistry research. COBRA (Impact of combined iodine and bromine release on the Arctic atmosphere) is essentially a targeted process study, combining field, laboratory and modelling techniques in a consortium of scientists with strong track records in halogen and polar chemistry and physics to: develop understanding of the role of iodine (in concert with bromine) in Arctic gas phase photochemistry and aerosol production and evolution; investigate the relative/combined roles of frost flowers, older sea-ice/snow pack, sea salt aerosol and biological sources in releasing halogens to the Arctic atmosphere; increase understanding of the temporal and spatial variability of halogen-related ozone and mercury depletion events in the Arctic; and develop and evaluate parameterisations for emission of halogens to the Arctic atmosphere based upon observable ice and meteorological conditions, and use these to develop improved models of Arctic chemistry and emissions and their effect and feedbacks on regional/global atmospheric chemistry and climate. We will undertake two ground-based field campaigns, deploying a range of trace gas and aerosol techniques to measure inorganic and halogen compounds and a comprehensive suite of supporting data, in spring and autumn at a coastal site in the north of Hudson Bay, an area with high potential for frost flower growth and a bromine 'hot spot'. The autumn campaign will be augmented by ship-based measurements to determine the wider extent of mercury and ozone depletion episodes and organic halogen concentrations in the region. In addition to concentration measurements at the coastal site, we will measure particle, ozone and halogen concentrations and fluxes from frost flowers formed on artificial leads created in the sea-ice, and from older sea-ice/snow pack and any identified surface diatoms. We will characterise the various sea-ice surfaces in the field and investigate chemical mechanisms of formation from frost flowers in the laboratory. The combined impact of various forms of halogens on depletion of ozone and mercury will be investigated using a detailed process model, and on a wider scale using a global chemistry-transport model.