A broadband absorption spectrometer using light emitting diodes for ultrasensitive, in situ trace gas detection
A broadband absorption spectrometer using light emitting diodes for ultrasensitive, in situ trace gas detection
复制标题
DOI：
10.1063/1.3046282
复制
发表时间：
2008-12-01
影响因子：
1.6
通讯作者：
Jones, Roderic L.
中科院分区：
文献类型：
--
作者：
Langridge, Justin M.;Ball, Stephen M.;Jones, Roderic L.
研制了一种用于高灵敏度、高选择性痕量气体在线测量的宽带吸收光谱仪。该仪器采用两种不同的工作模式：(I)宽带腔增强吸收光谱(BBCEAS)用于根据样品混合物的特征吸收特征来量化气体浓度；(Ii)使用阶跃扫描相移腔振荡谱(PSCRDS)定期测量腔镜的反射率。后一种PSCRDS方法提供了一种独立的替代方法，通过测量已知组成的校准样品的BBCEAS吸收光谱来确定镜面反射率。此外，该仪器的两种操作模式使用来自相同发光二极管的光，在相同的光学对准中穿过腔体，从而最大限度地减少了镜面反射率测定和浓度测量之间的系统误差。该仪器量化吸收体浓度的能力在NO2(与激光宽带腔环形光谱仪)和H2O(与商用湿度计)的仪器比对练习中进行了测试。还提出了一种计算有效吸收截面的方法，用于拟合BBCEAS光谱中的微分结构，因为强的、窄的吸收线是欠分辨的，因此在BBCEAS测量的分辨率下表现出非Beer-Lambert定律行为。对水蒸气在650 nm附近的4v+增量吸收带的BBCEAS光谱进行了测试。本仪器最直接的分析应用是量化环境大气中活性痕量气体的浓度。使用Allan方差分析，详细讨论了仪器对NO3的检测限作为积分时间的函数。在实验室条件下的实验表明，对于10个S的采集时间，1西格玛检测下限为0.25pptv，随着400个S的信号平均达到0.09pptv，该检测下限进一步提高。最后，给出了该仪器在野外工作条件下测量海洋边界层中的NO3+N2O5浓度总和的例子，在这种情况下，在海洋边界层场战役中获得了反应性卤素。
A broadband absorption spectrometer has been developed for highly sensitive and target-selective in situ trace gas measurements. The instrument employs two distinct modes of operation: (i) broadband cavity enhanced absorption spectroscopy (BBCEAS) is used to quantify the concentration of gases in sample mixtures from their characteristic absorption features, and (ii) periodic measurements of the cavity mirrors' reflectivity are made using step-scan phase shift cavity ringdown spectroscopy (PSCRDS). The latter PSCRDS method provides a stand-alone alternative to the more usual method of determining mirror reflectivities by measuring BBCEAS absorption spectra for calibration samples of known composition. Moreover, the instrument's two modes of operation use light from the same light emitting diode transmitted through the cavity in the same optical alignment, hence minimizing the potential for systematic errors between mirror reflectivity determinations and concentration measurements. The ability of the instrument to quantify absorber concentrations is tested in instrument intercomparison exercises for NO2 (versus a laser broadband cavity ringdown spectrometer) and for H2O (versus a commercial hygrometer). A method is also proposed for calculating effective absorption cross sections for fitting the differential structure in BBCEAS spectra due to strong, narrow absorption lines that are under-resolved and hence exhibit non-Beer-Lambert law behavior at the resolution of the BBCEAS measurements. This approach is tested on BBCEAS spectra of water vapor's 4v+delta absorption bands around 650 nm. The most immediate analytical application of the present instrument is in quantifying the concentration of reactive trace gases in the ambient atmosphere. The instrument's detection limits for NO3 as a function of integration time are considered in detail using an Allan variance analysis. Experiments under laboratory conditions produce a 1 sigma detection limit of 0.25 pptv for a 10 s acquisition time, which improves with further signal averaging to 0.09 pptv in 400 s. Finally, an example of the instrument's performance under field work conditions is presented, in this case of measurements of the sum of NO3+N2O5 concentrations in the marine boundary layer acquired during the Reactive Halogens in the Marine Boundary Layer field campaign.