Research on analysis methods for overlapping interference of gas spectral lines in laser photoacoustic spectroscopy

Laser photoacoustic spectroscopy is employed to measure dissolved gases in transformer oil, which include C 2 H 2 , C 2 H 4 , C 2 H 6 , CH 4 , CO 2 and CO. The wavelength of 1532.83 nm was selected as the absorption line for C 2 H 2 . However, near this wavelength, the absorption line of CO 2 also appears, causing a spectral overlap phenomenon with C 2 H 2 . An experimental photoacoustic spectroscopy measurement system was established using lasers operating at 1532.83 nm and 1579.6 nm. Driven by a sinusoidal signal, the laser scanned the rising and falling sections of the C 2 H 2 Voigt extended line profile at 1532.83 nm. The area under the waveform of the generated photoacoustic signal was calculated via integration. It was found that the influence of CO 2 on the measured C 2 H 2 concentration exhibited a specific discrepancy, which was consistent with the ratio of the line profile areas corresponding to the rising and falling sections of the C 2 H 2 Voigt profile near 1532.83 nm where CO 2 absorbs. By using the 1579.6 nm laser to measure the CO 2 concentration independently, the portion of the photoacoustic signal area at 1532.83 nm attributable to CO 2 —calculated based on the Voigt profile—could be subtracted. This method effectively compensates for the interference in determining the C 2 H 2 concentration. Experimental results demonstrate that for various concentration ratios of CO 2 and C 2 H 2 , the calculated concentrations of both gases after applying this area subtraction method are in good agreement with the expected results. This approach provides a viable solution for addressing interference issues in subsequent multi-gas measurement processes.