Accurate measurement of trace H2S concentration based oncavity ring-down absorption spectroscopy underCO2/CO disturbance br

Since H2S is a corrosive and toxic gas pollutant, the accurate measurement of its concentration issignificant. However, in the practical industrial processes, it is difficult to implement because of the disturbancecaused by other emissions such as CO2 and CO. Therefore, in this work, the concentration of H2S, CO2 and COare measured simultaneously based on cavity ring-down spectroscopy (CRDS) as a viable alternative to measurethe concentration of H2S accurately when CO2 and CO exist. First, the wavelength of mixed gas within a rangeof 6336-6339 cm-1 is selected as the target region where the spectral line intensity of H2S is stronger than 10times that of CO2 or CO and the water absorption is extremely weak. Second, the influence of the samplinglength (Tm) on the accuracy of the ring-down time is analyzed by evaluating average (accuracy), standarddeviation (precision) and consumption time (speed). Third, the experiments are carried out at differentpressures in order to obtain the optimal pressure condition. Fourth, the concentration of trace H2S is measuredwhen the disturbances caused by CO2 or CO are added, and the error of the measured concentration isanalyzed. Finally, the detection limit of CRDS-based system is calculated to be 6.9 ppb by analyzing the SNRof four groups of low concentration H2S spectra, while the lower limit of detection of CRDS-based system iscalculated to be 2 ppb by analyzing the Allan variance of long-term data. The measured concentration and itsdesired value show a good linearity at different dilution ratios. Both the high linearity and the low detectionlimit of H2S indicate the effectiveness of the CRDS-based measurement system to measure H2S when CO2 andCO exist. The successful application of the CRDS-based system to the measurement of H2S shows its promisingprospect in gas concentration measurement for practical industrial processes.