KEYWORDS: Photoacoustic spectroscopy, Signal detection, Thermal effects, Adsorption, Nitrogen dioxide, Photolysis, Signal to noise ratio, Light sources, Temperature metrology, Temperature control
Nitrogen dioxide (NO2) is a toxic gas to organisms, and one of the main factors in forming acid rain. Recently, some scholars have developed NO2 photoacoustic detection setups, but there are few reports about the effects of thermal decomposition and adsorption on photoacoustic detection of NO2. This work carried out detailed research on NO2 photoacoustic detection. Based on the photolysis effect of NO2, the thermal decomposition effect of NO2 excited by high-power laser was found and verified. Additionally, to reduce the influence of the adsorption effect of the photoacoustic cell wall on the detection results, a temperature control model of the photoacoustic cell was constructed, and the optimal detection temperature of 30 ℃ was ensured through experiments. The cross experimental verification was conducted with acetylene (C2H2) that was not decomposed by high temperature, which further explained the influence of NO2 thermal decomposition and adsorption effect on the detection accuracy. Based on the research results, a photoacoustic detection setup was built with a 450 nm laser and a differential H-type photoacoustic cell as the core. The experimental results showed that when the photoacoustic cell temperature was 30 ℃, the minimum detection limit of 206 ppt was achieved within 5 s average detection time. In conclusion, this work provides a reference for developing of high-precision NO2 photoacoustic detection setup.
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