A spectroscopic instrument based on a mid-infrared external cavity quantum cascade laser (EC-QCL) was developed for high-accuracy measurements of dinitrogen pentoxide (N₂O₅) at the ppbv-level. A specific concentration retrieval algorithm was developed to remove, from the broadband absorption spectrum of N₂O₅, both etalon fringes resulting from the EC-QCL intrinsic structure and spectral interference lines of H₂O vapour absorption, which led to a significant improvement in measurement accuracy and detection sensitivity (by a factor of 10), compared to using a traditional algorithm for gas concentration retrieval. The developed EC-QCL-based N₂O₅ sensing platform was evaluated by real-time tracking N₂O₅ concentration in its most important nocturnal tropospheric chemical reaction of NO₃ + NO₂ ↔ N₂O₅ in an atmospheric simulation chamber. Based on an optical absorption path-length of L_eff = 70 m, a minimum detection limit of 15 ppbv was achieved with a 25 s integration time and it was down to 3 ppbv in 400 s. The equilibrium rate constant K_eq involved in the above chemical reaction was determined with direct concentration measurements using the developed EC-QCL sensing platform, which was in good agreement with the theoretical value deduced from a referenced empirical formula under well controlled experimental conditions. The present work demonstrates the potential and the unique advantage of the use of a modern external cavity quantum cascade laser for applications in direct quantitative measurement of broadband absorption of key molecular species involved in chemical kinetic and climate-change related tropospheric chemistry.

中文翻译：

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量子级联激光器在大气模拟室内 高精度，高灵敏度光谱法测量五氧化二氮（N ₂ O ₅）

开发了一种基于中红外外腔量子级联激光器（EC-QCL）的光谱仪，用于在ppbv级高精度测量五氧化二氮（N ₂ O ₅）。开发了一种特定的浓度检索算法，以从N ₂ O ₅的宽带吸收光谱中去除EC-QCL固有结构产生的标准具条纹和H ₂ O蒸气吸收的光谱干扰线，从而显着改善了H ₂ O吸收率。与使用传统算法进行气体浓度检索相比，测量精度和检测灵敏度（降低了10倍）。研发的基于EC-QCL的N ₂ O ₅感测平台通过实时评价跟踪Ñ ₂ ø ₅在其最重要的夜间对流层化学NO的反应浓度₃ + NO ₂ ↔Ñ ₂ ø ₅在大气模拟室。基于L _eff = 70 m的光吸收路径长度，在25 s的积分时间内实现了15 ppbv的最小检测极限，并在400 s内降至3 ppbv。平衡速率常数K _eq使用开发的EC-QCL传感平台，通过直接浓度测量确定了涉及上述化学反应的分子，这与在受控实验条件下从参考经验公式推导出的理论值非常吻合。本工作证明了使用现代外腔量子级联激光器在直接定量测量涉及化学动力学和与气候变化有关的对流层化学的关键分子种类的宽带吸收的应用中的潜力和独特优势。