Quasi-simultaneous detection of ammonia and nitrous oxide by photoacoustic phase-resolved method : a proof-of-concept

Abstract

This work presents a method for the quasi-simultaneous detection of trace gas molecules using photoacoustic spectroscopy with phase-resolved method. By utilizing two lasers to excite ammonia (NH3) and nitrous oxide (N2O) in a mixture and employing phase-sensitive detection, the individual contributions of these gases were separated. The separation was achieved by adjusting the phase modulation of the N2O exciting laser until a 90-degree phase difference was established between its signal and that of NH3. The results demonstrate the absence of spectral overlap between the two compounds, enabling independent and quasi-simultaneous detection. Calibration curves highlighted the behavior and cross-interference between NH3 and N2O. For NH3, linear profiles with regression coefficients R = 0.998 and R = 0.999 were observed, when N2 or N2 + N2O were used as diluent gases, respectively. The corresponding sensitivities were (3.0 ± 0.1) μV·ppmv–1and (3.10 ± 0.08) μV·ppmv–1. The lower detection limits (LDLs) were 51 ppbv and 67 ppbv, respectively. For N2O, calibration data were similarly robust with LDLs of 262 ppbv and 255 ppbv when diluted with N2 and N2 + NH3, respectively. Minimal cross-interference effects were found, confirming the selectivity and reliability of this method for quantifying NH3 and N2O in gas mixtures. The technique offers advantages over other methods and is applicable to studying emissions related to agriculture with nitrogen fertilizers.