Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) – applicability and corrections
Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) – applicability and corrections
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DOI：
10.5194/amt-2-713-2009
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发表时间：
2008-12
影响因子：
3.8
通讯作者：
U. Platt;J. Meinen;D. Pöhler;T. Leisner
中科院分区：
文献类型：
--
作者：
U. Platt;J. Meinen;D. Pöhler;T. Leisner
摘要。空腔辅助长程吸收光谱法测量大气痕量气体是一项新兴技术。一种有趣的方法是将CEAS与宽带光源相结合，即宽带CEAS （BB-CEAS）。BB-CEAS适合应用DOAS技术分析衍生吸收光谱。虽然DOAS方法在测量的灵敏度和特异性方面具有巨大的优势，但一个重要的含义是痕量气体吸收减少了光路，因为气体吸收引起的腔损失降低了腔的质量(Q)。事实上，在波长处，BB-CEAS腔体的质量主要由微量气体吸收决定（特别是在非常高的镜面反射率下），平均光程将与微量气体浓度几乎成反比变化，并且波段强度将仅弱依赖于腔体中微量气体浓度c（微分光密度与微量气体浓度的对数成正比）。只有在所有波长的镜面反射率决定Q的极限情况下，CE-DOAS仪器看到的波段强度才与浓度c成正比。我们详细研究了这些关系，并提出了校正上述两个极端之间情况的方法，这当然是实践中重要的。
Abstract. Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broadband light sources, the broadband CEAS (BB-CEAS). BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light path by the trace gas absorption, since cavity losses due to absorption by gases reduce the quality (Q) of the cavity. In fact, at wavelength, where the quality of the BB-CEAS cavity is dominated by the trace gas absorption (especially at very high mirror reflectivity), the average light path will vary nearly inversely with the trace gas concentration and the strength of the band will become only weakly dependent on the trace gas concentration c in the cavity, (the differential optical density being proportional to the logarithm of the trace gas concentration). Only in the limiting case where the mirror reflectivity determines Q at all wavelength, the strength of the band as seen by the CE-DOAS instrument becomes directly proportional to the concentration c. We investigate these relationships in detail and present methods to correct for the cases between the two above extremes, which are of course the important ones in practice.