Detection of Nitrogen Dioxide Based on Multi-pass Absorption and Quartz-enhanced Photoacoustic Spectroscopy
I-Yun Chen1*, Yu-Xuan Wu2,1, 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,
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