FAGE measurements of OH, HO2 and IO during COBRA

COBRA(碘和溴联合释放对北极大气的影响)联盟项目已经通过国际极年赠款获得资助，其主要目标是通过减少重要化学物种的不确定性以及化学和物理机制，提高对北极臭氧和汞消耗事件的认识，包括在气相和冰雪表面的不确定性。臭氧是一种重要的温室气体，而汞是一种有毒、持久性和生物累积性污染物。因此，重要的是要了解可持续的、发生在春季(极地日出)的耗竭事件，因为它们对大气氧化能力、气候和健康有影响。眼镜蛇协会的主要活动之一是2008年春季在哈德逊湾东南海岸的Kuujjuarapik开展实地活动，该地点有臭氧和汞消耗事件的既定记录(一个溴“热点”)。现有联盟成员将测量BrO、Br2、BrCL、IO、I2、卤化碳、其他VOCs、CO、O3、气溶胶碘，以及各种冻结表面的卤素、颗粒和臭氧的通量测量。该项目涉及6个英国机构和3个在卤素、极地化学和物理方面有良好记录的海外合作伙伴，将以一维和三维化学模型为基础，后者使用遥感海冰形成。在这笔小额赠款中，我们建议参与Kuujjuarapik现场活动，并使用利兹开发的小型、紧凑的飞机FAGE仪器，通过激光诱导荧光光谱原位测量OH、HO2和IO自由基的浓度。这些测量将显著提高COBRA的能力，因为OH提供了氧化能力的测量，而HO2和OH密切参与了涉及溴和碘的臭氧消耗循环。人们对碘在极地边界层化学中的作用和来源知之甚少，但在最近在南极洲哈雷举行的夏布利战役中，观察到IO自由基浓度升高，这表明极地大气中可能存在广泛的非生物/光化学来源的碘。在夏布利期间，我们还测量了OH和HO2自由基，显著的结论是这两个物种的收支主要是与卤素物种的耦合。眼镜蛇是检验这一假设的理想机会，该假设认为这些耦合在北极发挥着重要作用。对OH、HO2和IO的测量将提供理想的目标，以便与基于我们目前对Hox和卤素的非均相和气相化学机制以及相关海洋-雪-冰-大气相互作用的详细模型计算进行比较。一个重要目标是改进北极化学和排放模型及其对区域/全球大气化学和气候的影响和反馈。在这种极地环境中进行测量是一个巨大的挑战，我们将利用眼镜蛇联盟的现有框架，该联盟将组织所有的竞选后勤。我们的低成本参与代表了NERC在眼镜蛇IPY项目中已经进行的投资的重大杠杆作用。

The COBRA (Impact of combined iodine and bromine release on the Arctic atmosphere) consortium project is already funded via an International Polar Year (IPY) grant, with the main objectives of improving the understanding of Arctic ozone and mercury depletion events through reducing the uncertainties in important chemical species and chemical and physical mechanisms, both in the gas phase and on surfaces of snow and sea-ice. Ozone is a significant greenhouse gas whilst mercury is a toxic, persistent and bioaccumulative pollutant. Hence it is important to understand the depletion events, which can be sustained and occur in spring (polar sunrise), as they have implications for the atmospheric oxidising capacity, climate and health. One of the major activities within COBRA is a field campaign at Kuujjuarapik on the south-eastern shore of Hudson Bay in spring 2008, a site with an established record of ozone and mercury depletion episodes (a bromine 'hotspot'). Measurements by existing consortium members will be made of BrO, Br2, BrCl, IO, I2, halocarbons, other VOCs, CO, O3, aerosol iodine, as well as flux measurements of halogens, particles and ozone from a variety of frozen surfaces. The project, which involves 6 UK institutions and 3 overseas partners with strong track records in halogen and polar chemistry and physics, will be underpinned by 1D and 3D chemical modelling, the latter using remotely-sensed sea-ice formation. In this small grant we propose to participate in the Kuujjuarapik field campaign and make in situ measurements of the concentrations of OH, HO2 and IO radicals by laser-induced fluorescence spectroscopy using the small, compact aircraft FAGE instrument developed at Leeds. These measurements will enhance significantly the capability of COBRA, as OH provides a measure of the oxidising capacity and HO2 and OH are intimately involved in ozone depleting cycles involving bromine and iodine. Little is known about the role and sources of iodine in polar boundary layer chemistry but during the recent CHABLIS campaign at Halley, Antarctica, elevated concentrations of IO radicals were observed suggesting a widespread and likely abiotic/photochemical source of iodine to the polar atmosphere. During CHABLIS we also made measurements of OH and HO2 radicals, and the striking conclusion was that the budgets of both species were dominated by coupling with halogen species. COBRA represents an ideal opportunity to test the hypothesis that these couplings play a major role in the Arctic. Measurements of OH, HO2 and IO would provide ideal targets for comparison with detailed model calculations based on our current understanding of heterogeneous and gas-phase chemical mechanisms of HOx and halogens, and relevant ocean-snow-ice-atmosphere interactions. An important goal is to improve models of Arctic chemistry and emissions and their effect and feedbacks on regional/global atmospheric chemistry and climate. Making measurements in this polar environment presents significant challenges and we will take advantage of the existing framework of the COBRA consortium, which will organise all campaign logistics. Our involvement at low-cost represents significant gearing of the investment already made by NERC in the COBRA IPY project.