Abstract. The chemical characterization of volcanic gas emissions gives insights into the interior of volcanoes. Monitoring of BrO/SO₂-ratios has recently been correlated with changes in the activity of a volcano. BrO and SO₂ can both be measured autonomously and simultaneously with the same instruments from a safe distance, making their ratio potentially a strong monitoring tool. However, BrO is not a primary emitted volcanic volatile and there exist still uncertainties about the formation of BrO in volcanic plumes, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. This study describes a new method for the determination of the BrO precursor, the gaseous hydrogen bromide (HBr), by quantitative collection in denuder samplers. Gas diffusion denuders use the difference in diffusion coefficients to separate gaseous from particle-phase compounds. Gaseous HBr molecules are immobilized with an organic coating at the inner walls of the denuder tubes when pumped through the denuders. Five different coatings using 1,2-epoxycyclooctane, trans-oxirane-2,3-dicarboxylic acid, 2,3-epoxy-3-phenylpropanoic acid, 9,10-epoxystearic acid, 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline (EP) were tested as denuder coatings. EP proved to be a suitable coating reagent, which at the same time, transfers the analyte into an appropriate derivate to be analyzed by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (in situ derivatization). Coating amount, breakthrough, matrix effects and the storage behavior have been characterized. No considerable cross-sensitivity with hydrogen chloride or other bromine species such as molecular bromine was observed. The comparison of HBr determination using EP-coated denuders and Raschig Tubes as alkaline traps in the laboratory showed a deviation of 2 ± 11 % for gaseous HBr between the two methods. This allows considering HBr determined by denuders as a fraction of total bromine determined by Raschig Tubes. Since other bromine species (e.g. elemental bromine, bromine oxides) are also collected and determined as bromide by Raschig Tubes, but exclusively HBr in EP-coated denuders, the method presented here allows more accurate speciation of gaseous bromine compounds and their application in volcanic plumes. The denuder sampling setup was applied with complementary denuder systems and alkaline traps in the plume of Masaya (Nicaragua) in 2016. HBr concentrations in the range between 0.44 and 2.27 ppb were measured with limits of detection and quantification below 0.1 and 0.3 ppb respectively at typical ground-based sampling conditions. The relative contribution of HBr as a fraction of total bromine decreased from 75 ± 11 % at Santiago rim (214 m distance to the volcanic emission source) to 36 ± 8 % on Nindiri rim (740 m distance). Our findings are in good agreement with previous estimations of the HBr conversion from the chemistry box model (CAABA/MECCA).

中文翻译：

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火山岩羽中的溴形态：用气体扩散剥蚀器采样法测定气态溴化氢的新方法-原位衍生LC-MS法

摘要。火山气体排放物的化学特征使人们深入了解了火山内部。最近，对BrO / SO _2-比率的监测与火山活动的变化相关。BrO和SO ₂可以同时在同一安全距离内同时使用同一仪器进行自动测量，从而使它们的比率成为强大的监视工具。但是，BrO不是主要释放出的火山挥发物，在火山羽中BrO的形成仍存在不确定性，这主要是由于缺乏某些关键化合物的准确形态分析方法所致。这项研究描述了一种通过在裸露取样器中定量收集来测定BrO前体，气态溴化氢（HBr）的新方法。气体扩散剥蚀器利用扩散系数的差异将气态与颗粒相化合物分离。气态HBr分子在泵送通过剥蚀仪时，在剥蚀仪管的内壁固定有有机涂层。使用1种五种不同的涂料反式-环氧乙烷-2,3-二羧酸，2,3-环氧-3-苯基丙酸，9,10-环氧硬脂酸，5,6-环氧-5,6-二氢-[1,10]-菲咯啉（EP ）作为剥蚀剂涂层进行了测试。事实证明，EP是一种合适的包被试剂，它同时将分析物转移到合适的衍生物中，通过高效液相色谱与电喷雾电离质谱联用（原位分析）进行分析。衍生化）。表征了包衣量，突破，基质效应和储存行为。没有观察到与氯化氢或其他溴物种（例如分子溴）的明显交叉敏感性。在实验室中使用EP涂层的剥蚀仪和Raschig管作为碱性阱进行HBr测定的比较表明，两种方法之间的气态HBr偏差为2±11％。这允许将由剥蚀剂测定的HBr视为由Raschig Tubes测定的总溴含量的一部分。由于还收集了其他种类的溴（例如元素溴，溴氧化物），并由Raschig Tubes确定为溴化物，但仅在涂有EP的剥蚀剂中为HBr，因此此处介绍的方法可以更精确地形成气态溴化合物，并将其应用于火山羽中。2016年在马萨亚（尼加拉瓜）羽流中使用了剥蚀器采样装置以及互补的剥蚀器系统和碱性阱。测量的HBr浓度在0.44到2.27 ppb的范围内，典型情况下的检出限和定量限分别低于0.1和0.3 ppb。地面采样条件。HBr占总溴含量的相对贡献从圣地亚哥边缘（距火山排放源214 m的距离）的75±11％降至Nindiri边缘（740 m的距离）的36±8％。我们的发现与化学盒模型（CAABA / MECCA）中HBr转化率的先前估计非常吻合。在典型的基于地面的采样条件下，测量到27 ppb的检出限和定量限分别低于0.1和0.3 ppb。HBr占总溴含量的相对贡献从圣地亚哥边缘（距火山排放源214 m的距离）的75±11％降至Nindiri边缘（740 m的距离）的36±8％。我们的发现与化学盒模型（CAABA / MECCA）中HBr转化率的先前估计非常吻合。在典型的基于地面的采样条件下，测量到27 ppb的检出限和定量限分别低于0.1和0.3 ppb。HBr占总溴含量的相对贡献从圣地亚哥边缘（距火山排放源214 m的距离）的75±11％降至Nindiri边缘（740 m的距离）的36±8％。我们的发现与化学盒模型（CAABA / MECCA）中HBr转化率的先前估计非常吻合。