Method of measuring atmospheric CO₂ based on Fabry-Perot interferometer

Abstract

CO₂ is one of the main greenhouse gases. Its emission and accumulation lead to the strengthening of the greenhouse effect, which in turn causes global climate change. Therefore, it is of great significance to obtain the change of CO₂ concentration in the atmospheric environment for the study of climate change. In order to meet the requirements of low cost, fast, on-line and accurate measurement of CO₂ in atmospheric environment, a CO₂ gas concentration measurement system based on Fabry-Perot interferometer is built in this work. The thermal radiation source based on micro-electro-mechanical system (MEMS) technology is used as a light source of the Fabry-Perot interferometer system, and the transmission optical path is designed to replace the common refractive optical path. By electrostatically controlling the distance between the two lenses and changing the interference spectrum, the interference peak adjustment of the center wavelength of the 10 nm step is realized, and the absorption spectrum is obtained by scanning. Based on the principle of differential optical absorption spectroscopy, the concentration of CO₂ gas is obtained, and the real-time on-line monitoring of CO₂ concentration is realized. Using the sample gas calibration system and the commercial photoacoustic spectroscopy multi-gas analyzer to verify the system, the results show that the detection limit of the system is 1.09×10^–6, the detection accuracy is ±1.13×10^–6, and the measurement error is less than 1%. Real-time online monitoring of atmospheric CO₂ has been conducted in Huaibei, a coal city. A comparative observational experiment is performed between this system and a commercial photoacoustic spectroscopy multi-gas analyzer. The two systems show consistent trends in measuring CO₂ variations, with a correlation coefficient of <i>R</i>=0.92. It shows that the Fabry-Perot interferometer system can meet the requirement of rapid, convenient and high precision measurement of CO₂ concentration in the environment.