Recent improvements of long-path DOAS measurements: impact on accuracy and stability of short-term and automated long-term observations
Recent improvements of long-path DOAS measurements: impact on accuracy and stability of short-term and automated long-term observations
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长路径 DOAS 测量的最新改进：对短期和自动化长期观测的准确性和稳定性的影响
DOI：
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发表时间：
2019
影响因子：
3.8
通讯作者：
U. Platt
中科院分区：
文献类型：
--
作者：
Jan;Philipp G. Eger;D. Pöhler;Stefan Schmitt;U. Friess;U. Platt
抽象的。在过去的几十年里，差分光学吸收光谱（DOAS）已被用作同时测量各种大气痕量气体丰度的常用技术。利用微量气体分子独特的差异吸收截面，可以通过测量沿定义的光路的光密度并应用比尔-朗伯定律来得出混合比。主动长光程 (LP-DOAS) 仪器可以沿着几百米至 20 公里的光路检测痕量气体，混合比的灵敏度低至 ppbv 和 pptv 水平，具体取决于痕量气体种类。为了实现高测量精度和低检测限，减少导致分析残余光谱中出现系统结构的仪器伪影至关重要。 LP-DOAS 测量系统的大多数组件（即光源）可以在系统组件之间或在光谱仪和检测器级别传输测量信号时引入光谱残留结构。本文重点介绍通过首次应用新型光源以及随后为提高测量精度而对光学设置进行的更改所带来的最新改进。大多数最先进的 LP-DOAS 仪器都基于光纤，并使用氙弧灯或发光二极管 (LED) 作为光源。在这里，我们介绍了激光驱动光源（LDLS）的应用，与传统光源相比，它显着提高了测量质量。此外，LDLS 的寿命比典型的氙弧灯高大约一个数量级。 LDLS 的小且非常稳定的等离子体放电点允许应用改进的光纤配置。这能够实现更好的光耦合、更高的光吞吐量、更高的传输均匀性以及更好地抑制来自干扰波长区域的光。此外，通过改进的机械处理增强了光纤的模式混合特性。综合效应导致光谱残余结构在 5-10×10-5 均方根（rms；以光密度为单位）范围内。与之前的设置相比，这意味着典型痕量气体种类的检测限降低了 3-4 倍。这种新装置的高时间稳定性和降低的操作复杂性允许低维护、自动化 LP-DOAS 系统的运行，正如在南极洲两年多的连续观测所证明的那样。
Abstract. Over the last few decades, differential optical absorption spectroscopy (DOAS) has been used as a common technique to simultaneously measure abundances of a variety of atmospheric trace gases. Exploiting the unique differential absorption cross section of trace-gas molecules, mixing ratios can be derived by measuring the optical density along a defined light path and by applying the Beer–Lambert law. Active long-path (LP-DOAS) instruments can detect trace gases along a light path of a few hundred metres up to 20 km, with sensitivities for mixing ratios down to ppbv and pptv levels, depending on the trace-gas species. To achieve high measurement accuracy and low detection limits, it is crucial to reduce instrumental artefacts that lead to systematic structures in the residual spectra of the analysis. Spectral residual structures can be introduced by most components of a LP-DOAS measurement system, namely by the light source, in the transmission of the measurement signal between the system components or at the level of spectrometer and detector. This article focuses on recent improvements by the first application of a new type of light source and consequent changes to the optical setup to improve measurement accuracy. Most state-of-the-art LP-DOAS instruments are based on fibre optics and use xenon arc lamps or light-emitting diodes (LEDs) as light sources. Here we present the application of a laser-driven light source (LDLS), which significantly improves the measurement quality compared to conventional light sources. In addition, the lifetime of LDLS is about an order of magnitude higher than of typical Xe arc lamps. The small and very stable plasma discharge spot of the LDLS allows the application of a modified fibre configuration. This enables a better light coupling with higher light throughput, higher transmission homogeneity, and a better suppression of light from disturbing wavelength regions. Furthermore, the mode-mixing properties of the optical fibre are enhanced by an improved mechanical treatment. The combined effects lead to spectral residual structures in the range of 5-10×10-5 root mean square (rms; in units of optical density). This represents a reduction of detection limits of typical trace-gas species by a factor of 3–4 compared to previous setups. High temporal stability and reduced operational complexity of this new setup allow the operation of low-maintenance, automated LP-DOAS systems, as demonstrated here by more than 2 years of continuous observations in Antarctica.
死海边界层中 BrO 的垂直分布
影响因子：
4.3
作者：
S. Schmitt;U. Friess;D. Pöhler;J. Zingler;U. Corsmeier;U. Platt
通讯作者：
U. Platt