Study On Monitoring Technology Of Atmospheric Carbon Dioxide Concentration Based On TDLAS

As technology and industrial level is higher and higher in recent years, the globaltemperature have been increasing gradually that generated a series of environmentproblems, including the melting of polar glacier, land desertification and so on.Consequently, global warming has become one of the major environment problemshuman concerned. Furthermore, carbon dioxide caused by daily life and industrialproduction generates greenhouse effect, which is an important reason of globalwarming. Accordingly, it is very necessary to monitor the carbon dioxide of atmosphere.Tunable Diode Laser Absorption Spectroscopy (TDLAS), with features of highsensitivity, fast response and high resolution, has been widely applied in theatmospheric trace gas monitoring field.According to the principles of spectroscopy, each material has its owncharacteristic absorption spectrum. Combining with the light source selection, thispaper select the absorption spectrum near1572nm. Direct absorption spectroscopy,modulation spectroscopy and harmonic detection are commonly used in the TDLAStechnology to detect gas concentration. In order to reduce the interference of noise, thissystem that combines wavelength modulation applied in semiconductor laser withsecond harmonic detection, can measure carbon dioxide concentration with highaccuracy. It is introduced that the basic principle of measuring gas concentration basedon TDLAS, and the theory of wavelength modulation and second harmonic detectionare derived.Through the analysis of the theory of TDLAS technology measuring gasconcentration, the design scheme is proposed. Owing to the effect of corner reflector,the laser will be back to lens after it is launched to atmosphere, then to be received andprocessed. This system consists of transmitting system, signal modulation anddemodulation system, receiving system and information acquisition and processing system, then the key device selection is introduced in detail. After completing thebuilding of system, the semiconductor is tested to determine its working temperatureand current. After the determination of different concentration of the carbon dioxide inthe multiple-reflection cell, then measures the carbon dioxide of atmosphere for a longtime, and processes second harmonic of the above two with the linear least-squaresfitting. Finally this system gets the concentration of carbon dioxide of atmosphere, andthe result is satisfactory.This paper has basically completed the field optical path measurements ofconcentration atmospheric carbon dioxide, which deserves to consult as to themonitoring technology of atmospheric carbon dioxide. However, because of the limitof experimental time and condition, the research content needs to be deepened, and toconsider the influence of temperature and pressure, and system needs to be improved.The system can be set up two optical path in the atmosphere to avoid influence oftemperature and pressure, and increased analysis of systematic error to improve thedetection sensitivity of system. Furthermore, increasing the comparison of maturemeasuring instrument, to test the accuracy of system.