Highly Sensitive Sphere-Tube Coupled Photoacoustic Cell Suitable for Detection of a Variety of Trace Gases: NO2 as an Example

Abstract

The concentration of trace gases in the atmospheric environment is extremely low, but it has a great impact on the living environment of organisms. Photoacoustic spectroscopy has attracted extensive attention in the field of trace gas detection because of its high sensitivity, good selectivity, and fast response. As the core of a photoacoustic detection setup, the photoacoustic cell has a significant impact on detection performance. To improve detection sensitivity, a sphere-tube coupled photoacoustic cell (STPAC) was developed, which was mainly composed of a diffuse-reflective sphere and an acoustic resonance tube. Modulated light was reflected multiple times in the sphere to increase optical path, and photoacoustic (PA) signals were further amplified by the tube. Based on STPAC, a PA gas detection setup was built with a laser diode (LD) at 450 nm as the light source. The experimental results showed that the minimum detection limit (noise equivalent concentration, NEC) of NO2 was ~0.7 parts per billion (ppb). Compared with the T-type PA cell (TPAC) in which the modulated light passed through the sphere, the signal-to-noise ratio of STPAC was increased by an order of magnitude at the same concentration of the NO2 sample.

Optimization design of sphere‐tube‐coupled photoacoustic cell and application of nitrogen dioxide detection

“…It has good diffuse reflectance (about ≥95%) in UV‐NIR band (250–2500 nm). Therefore, for gases with absorption peaks in this band, such as O 3 , SO 2 , NO 2 , C 2 H 2 , CO 2 , 21 and HF (Figure 5B,C 23,24 ), a long optical path could be realized by multiple reflections. In photoacoustic spectroscopy, the improvement of the optical path could be equivalent to the increase in light source power or gas absorption intensity.…”

“…20 Li et al used a 450 nm laser diode as the radiation source, and the laser was reflected multiple times in an absorption cell made of a diffuse reflection sphere, which improved the response capacity of NO 2 to 0.52546 mV/ppm. 21 In this study, based on our previous research, 21 the geometric parameters of the sphere-tube-coupled photoacoustic cell were further analyzed and optimized through finite element simulation with the aim of improving the gas detection performance. While the robustness against noise was ensured, the volume of the cell was reduced.…”

“…In this study, based on our previous research, 21 the geometric parameters of the sphere‐tube‐coupled photoacoustic cell were further analyzed and optimized through finite element simulation with the aim of improving the gas detection performance. While the robustness against noise was ensured, the volume of the cell was reduced.…”

“…The following year, Jin et al used the mirror to increase the number of light beam reflections to enhance the photoacoustic effect, so that the response capacity was improved to 0.2562 µV/ppb 20 . Li et al used a 450 nm laser diode as the radiation source, and the laser was reflected multiple times in an absorption cell made of a diffuse reflection sphere, which improved the response capacity of NO 2 to 0.52546 mV/ppm 21 …”

Effects of thermal decomposition and adsorption on photoacoustic detection of nitrogen dioxide

“…Nitrogen dioxide is a toxic gas to organisms, and one of the main factors in forming acid rain, which is mainly discharged into the atmosphere through the burning process of substances [1,2] . As a gas detection technology, photoacoustic spectroscopy has the advantages of high sensitivity, fast response, and good selectivity [3][4][5][6][7] , and is widely used in the fields of atmospheric monitoring, medical diagnosis, combustion analysis, and electric power detection [8][9][10][11][12] . Recently, some scholars have developed NO2 photoacoustic detection setups [13][14][15][16][17] .…”