Using a Photoacoustic Cell for Spectroscopy of Toxic Air Pollutants including CO2, SO2 and NO Gases

Abstract

Due to the rise in global temperature and climate change, the detection of CO2, SO2 and NO pollutants is important in smart cities. In this paper, an H-shaped photoacoustic cell is utilized for the detection of low-concentration gases. The geometry of the cell is miniaturized and designed with specific parameters in order to increase its efficiency and performance. The designed cell eliminates problems such as bulkiness and cost, which prevent the use of sensors in detecting greenhouse gases. The simplicity of the design expands the application rate of the cell in practice. In order to consider the viscosity and thermal effects, the cell is formulized by fully linearized Navier–Stokes equations, and various parameters, such as acoustic pressure, frequency response, sound speed (sound velocity) and quality factor, are investigated for the mentioned gases. The performance of the system is frequency-based, and the target gases can be detected by using a microelectromechanical resonator as a pressure sensor. Quality factor analysis expresses that CO2, SO2 and NO gases have quality factors of 27.84, 33.62 and 33.32, respectively. The performance of the cell in the resonance state can be expressed by the linear correlation between the results. The background noise generated in the photoacoustic research has been removed by miniaturization due to the obtained resonance, and the proposed cell provides a proper signal-to-noise ratio. The results of the proposed system represent the increase in the quality factor, which reduces the losses and thus increases the sensitivity of the system in the study of greenhouse gases.