Research On The Quantitative Analysis Method Of Methane Under Stratosphere Environmental Conditions

As one of most important greenhouse gases,CH4 is distributed not only in the terrestrial atmosphere near earth surface but also in stratosphere.The absorption spectral feature of CH4 will be affected by those harsh environmental conditions(i.e.low temperature,low gas pressure).Tunable Diode Laser Absorption Spectroscopy(TDLAS)is a powerful and rapid spectral tool with high sensitivity and selectivity which is a potential payload for CH4 detection in stratosphere.In this study,a simulated stratosphere environment system coupling with TDLAS was built based on a vacuum chamber for the CH4 study under low temperature and low pressure conditions.Based on the simulated system,the transmission spectrum and second harmonic signal of CH4 were recorded and analyzed under simulated stratosphere gas conditions(gas pressure:1000Pa-400Pa;gas temperature:23? to-80?)by TDLAS.Based on the peak intensity of second harmonic signal,a prediction model of concentration of CH4 was built,and the limit of detection(LOD),the linear regression coefficient was analyzed.The effect of low pressure and low temperature on the spectral feature of CH4 was also well investigated.And the technical scheme of in-situ CH4 detection in stratosphere was also proposed.Our results show that the prediction model of CH4 fits well for stratospheric CH4 detection.Low pressure(1000Pa-400Pa)almost has no effect on the spectral profile of second harmonic signal of TDLAS.The HWHM(half width at half-maximum)of second harmonic signal in low temperature(-80?)is shipper,and the spectral resolution of TDLAS was increased under low gas temperature.This indicates that TDLAS is a potential tool for detection of CH4 in stratosphere.