Detection of Nitrogen Dioxide Based on Multi-pass Absorption and Quartz-enhanced Photoacoustic Spectroscopy

I-Yun Chen^1*, Yu-Xuan Wu^2,1, Pei-Ling Luo¹

¹Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
²Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan

* Presenter:I-Yun Chen, email:yiyunchen21@gmail.com

Nitrogen dioxide (NO₂) is widely known as a key pollutant in the atmosphere. In order to achieve real-time monitoring of NO₂ concentration with sufficient sensitivity, we built up a Herriott-type multi-pass absorption cell and a quartz-enhanced photoacoustic spectroscopy (QEPAS) module to detect NO₂. A 520-nm laser was coupled into the Herriott cell with an effective optical path length of 18.36 m for real-time concentration calibration of NO₂. Furthermore, a high-power 450-nm laser with amplitude modulation was sent into the QEPAS cell and the laser-induced acoustic signal was demodulated by a lock-in amplifier and recorded with a data acquisition board. In this work, the NO₂ absorption signals can be detected simultaneously by using two different methods. The capability and the normalized noise equivalent absorption (NNEA) coefficients of different methods are also presented and compared.

Keywords: Photoacoustic spectroscopy, Quartz-enhanced photoacoustic spectroscopy, Multi-pass absorption spectroscopy, NO₂, Trace gas detection