Reactive bromine chemistry in Mount Etna's volcanic plume: the influence of total Br, high-temperature processing, aerosol loading and plume–air mixing
Reactive bromine chemistry in Mount Etna's volcanic plume: the influence of total Br, high-temperature processing, aerosol loading and plume–air mixing
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埃特纳火山火山羽流中的反应性溴化学：总溴、高温处理、气溶胶负载和羽流与空气混合的影响
DOI：
10.5194/acp-14-11201-2014
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发表时间：
2014
影响因子：
6.3
通讯作者：
L. Jourdain
中科院分区：
文献类型：
--
作者：
T. Roberts;R. S. Martin;L. Jourdain
摘要。火山排放物通过快速的羽流化学反应将排放的HBr转化为更具反应性的形式，如BrO，向对流层提供了活性卤素的来源。这一过程的性质很少被量化，但对于了解火山对对流层的影响以及从火山气体测量（即BrO / SO2比率）推断火山活动很有意义。最近来自埃特纳的观测报告称，随着下风距离的增加，BrO / SO2比值开始增加，随后趋于平稳或下降。我们提出了白天PlumeChem模式模拟，再现并解释了埃特纳火山BrO / SO2的趋势，包括最初的上升和随后的平台。模型模拟还研究了火山气溶胶负荷、溴排放和羽流-空气混合率对顺风羽流化学的影响。喷出的火山HBr通过自催化溴化学循环转化为活性溴，模型高温初始化加速了反应周期的开始。这些快速的化学循环还通过Br、Br2、BrO、BrONO2、BrCl、HOBr的相互转化影响了活性溴的形成。我们预测烟柱中Br物种形成的新演变。BrO, Br2， Br和HBr是下风附近的主要羽流种类，而BrO和HOBr则出现在进一步的下风处（BrONO2和BrCl也占一小部分）。预计BrNO2只是一个相对较小的羽流成分。随着臭氧被带入羽流，其与Br的反应促进了BrO的净形成，BrO / SO2开始上升。气溶胶对近下风（6公里）下风羽流的BrO / SO2影响不大。假设低/中和高埃特纳溴排放情景的模拟表明，溴排放对进一步顺风的BrO / SO2有较大的影响，而在顺风附近的影响较小，并显示HBr分别完全或部分转化为活性溴，产生的BrO含量高达总溴的50%或20%（在几10秒或几分钟的时间尺度上）。羽流-空气混合对下风BrO / SO2的影响呈非线性变化。较大的火山喷发通量导致下风附近的BrO / SO2比值降低，但也延迟了BrO / SO2随后的下降，从而在下风处产生更高的BrO / SO2比值。我们强调了羽流化学模型在解释火山喷发期间/之前观测到的BrO / SO2变化以及量化火山羽流对大气化学的影响方面的重要作用。模拟羽流影响包括臭氧、HOx和NOx消耗，后者转化为HNO3。虽然在模拟的3小时内臭氧的累积损失是持续的，但臭氧的部分恢复发生在下风的距离上。
Abstract. Volcanic emissions present a source of reactive halogens to the troposphere, through rapid plume chemistry that converts the emitted HBr to more reactive forms such as BrO. The nature of this process is poorly quantified, yet is of interest in order to understand volcanic impacts on the troposphere, and infer volcanic activity from volcanic gas measurements (i.e. BrO / SO2 ratios). Recent observations from Etna report an initial increase and subsequent plateau or decline in BrO / SO2 ratios with distance downwind. We present daytime PlumeChem model simulations that reproduce and explain the reported trend in BrO / SO2 at Etna including the initial rise and subsequent plateau. Suites of model simulations also investigate the influences of volcanic aerosol loading, bromine emission, and plume–air mixing rate on the downwind plume chemistry. Emitted volcanic HBr is converted into reactive bromine by autocatalytic bromine chemistry cycles whose onset is accelerated by the model high-temperature initialisation. These rapid chemistry cycles also impact the reactive bromine speciation through inter-conversion of Br, Br2, BrO, BrONO2, BrCl, HOBr. We predict a new evolution of Br speciation in the plume. BrO, Br2, Br and HBr are the main plume species near downwind whilst BrO and HOBr are present further downwind (where BrONO2 and BrCl also make up a minor fraction). BrNO2 is predicted to be only a relatively minor plume component. The initial rise in BrO / SO2 occurs as ozone is entrained into the plume whose reaction with Br promotes net formation of BrO. Aerosol has a modest impact on BrO / SO2 near-downwind ( 6 km) downwind plume. Simulations assuming low/medium and high Etna bromine emissions scenarios show that the bromine emission has a greater influence on BrO / SO2 further downwind and a modest impact near downwind, and show either complete or partial conversion of HBr into reactive bromine, respectively, yielding BrO contents that reach up to ~50 or ~20% of total bromine (over a timescale of a few 10 s of minutes). Plume–air mixing non-linearly impacts the downwind BrO / SO2, as shown by simulations with varying plume dispersion, wind speed and volcanic emission flux. Greater volcanic emission flux leads to lower BrO / SO2 ratios near downwind, but also delays the subsequent decline in BrO / SO2, and thus yields higher BrO / SO2 ratios further downwind. We highlight the important role of plume chemistry models for the interpretation of observed changes in BrO / SO2 during/prior to volcanic eruptions, as well as for quantifying volcanic plume impacts on atmospheric chemistry. Simulated plume impacts include ozone, HOx and NOx depletion, the latter converted into HNO3. Partial recovery of ozone occurs with distance downwind, although cumulative ozone loss is ongoing over the 3 h simulations.
影响因子：
3.9
作者：
R. S. Martin;T. Roberts;T. Mather;D. Pyle
通讯作者：
R. S. Martin;T. Roberts;T. Mather;D. Pyle
埃特纳火山喷发中 CO2、SO2、HCl 和 HNO3 的演变
影响因子：
5.2
作者：
C. Voigt;P. Jeßberger;T. Jurkat;S. Kaufmann;R. Baumann;H. Schlager;N. Bobrowski;G. Guffirda;G. Salerno
通讯作者：
G. Salerno
NOVAC 网络中扫描 DOAS 测量结果的 BrO/SO 2 摩尔比
影响因子：
3.4
作者：
P. Lübcke;N. Bobrowski;S. Arellano;Bo Galle;G. Garzón;Leif Vogel;U. Platt
通讯作者：
U. Platt