Gas Concentration Measurement Technology Based On The Study Of Peak Values Of Spectral Line Profiles

Environmental pollutions have given rise to world-wide concerns currently. Among the various environmental pollutions, air pollution is extremely harmful. Thus, how to analyze the ingredients of the mixed gases quantitatively and accurately plays an important role in the control of environmental pollutions. Recent years have seen the rapid development of gas detection techniques with the laser technology and the theory of molecular absorption spectrum based on the Lambert-Beer Law. In these gas detection techniques, the peak value of the spectral line profile of a gas is an important parameter and sensitive to pressure and temperature of the surroundings.In this paper, the influences of temperature and pressure on the peak values of spectral lines were analyzed. A method of calculating the peak values of spectra lines with the consideration of the effects of temperature and pressure was proposed as well. Furthermore, experiments that detect and measure the concentration of an acetylene gas by using an infrared laser, a high-resolution photo-detector and a gas cavity have been implemented. A practical measurement technique for the accurate detection of a gas was also obtained.After optimizing the calculation of the peak value of the Voigt profile and considering both the influences of temperature and pressure on the peak values of spectral lines, we found that the Lorentz profile has broader applicable ranges of pressure and temperature. We further found that the Gauss profile is only applicable under some extreme conditions. For a certain range of temperature and pressure, when only the fluctuation of temperature or pressure is considered in the calculation of the peak values of the spectral line profiles such as Gauss, Lorentz, and Voigt, the corresponding relative errors are greater than0.1. Thus, both the influences of temperature and pressure on the peak values of the spectral line profiles should be taken into consideration. Practically, we obtained similar conclusions when using the proposed method to measure the concentrations of some gases such as CH4, CO2, CO, and NO. However, due to the variations of wavelength of the laser beam, the coefficient of the pressure-broadening, the relative molecular mass, and the temperature, the results do not exactly match with the simulation ones.In the experiments, a PHOENIXTM Tunable Laser Source which consists of an infrared laser and a high-resolution photo-detector was used to measure the concentration of an acetylene gas sample. By constructing an experimental configuration based on this equipment, we have proposed a framework to measure the concentration of a gas in the laboratory.In the future, this system can be used to measure the concentrations of multiple gases simultaneously with the theoretical and technical improvements. We expect that the research results will be of great value for gas detection and environmental pollution control.