Tu Tan

Trace gas detection based on off-beam quartz enhanced photoacoustic spectroscopy: Optimization and performance evaluation

A gas sensor based on off-beam quartz enhanced photoacoustic spectroscopy was developed and optimized. Specifically, the length and diameter of the microresonator tube were optimized, and the outer tube shape is modified for enhancing the trace gas detection sensitivity. The impact of the distance between the quartz tuning fork and an acoustic microresonator on the sensor performance was experimentally investigated. The sensor performance was evaluated by determining the detection sensitivity to H(2)O vapor in ambient air at normal atmospheric pressure. A normalized noise equivalent absorption coefficient (1σ) of 6.2×10(-9) cm(-1) W/Hz(1/2) was achieved.

Application of a broadband blue laser diode to trace NO2 detection using off-beam quartz-enhanced photoacoustic spectroscopy.

We applied for the first time, to our knowledge, broadband off-beam quartz-enhanced photoacoustic spectroscopy (BB-OB-QEPAS) to trace NO2 detection using a broadband blue laser diode centered at 450 nm. A detection limit of 18 ppbv (parts in 10(9) by volume) for NO2 in N2 at atmospheric pressure was achieved with an average laser power of 7 mW at a 1 s integration time, which corresponds to a 1 σ normalized noise equivalent absorption coefficient of 4.1×10(-9)  cm(-1) W=Hz(1=2). An Allan variance analysis was performed to investigate the long-term stability of the BB-OB-QEPAS-based NO2 sensor.

Recent advances of laser absorption spectroscopy based technologies for sensing of atmosphere

Summary form only given. Laser absorption spectroscopy is a powerful and versatile chemical analysis tool for the identification and quantification of molecular constituents, which offers the advantages that include fast response, high sensitivity, realtime, in situ and non contact measurements of species without any sample preparation. Therefore, it was widely used in siening of atmosphere or environment monitoring. In this presentation, recent advances of laser absorption spectroscopy based technologies developed in our laboratory for sensing of atmospheric gases or aerosols, including highly sensitive laser absorptioin spectroscopy with novel compact dense-pattern multipass cell [1], photoacoustic spectroscopy, quartz enhanced photoacoustic spectroscopy [2, 3] and laser heterodyne radiometer, will be reported.

Quantitative analysis of ammonium salts in coking industrial liquid waste treatment process based on Raman spectroscopy

Quantitative analysis of ammonium salts in the process of coking industrial liquid waste treatment is successfully performed based on a compact Raman spectrometer combined with partial least square (PLS) method. Two main components (NH4SCN and (NH4)2S2O3) of the industrial mixture are investigated. During the data preprocessing, wavelet denoising and an internal standard normalization method are employed to improve the predicting ability of PLS models. Moreover, the PLS models with different characteristic bands for each component are studied to choose a best resolution. The internal and external calibration results of the validated model show a mass percentage error below 1% for both components. Finally, the repeatabilities and reproducibilities of Raman and reference titration measurements are also discussed.