Nitrous oxide (N2O), a highly climate‐relevant trace gas, is mainly derived from microbial denitrification and nitrification processes in soils. Apportioning N2O to these source processes is a challenging task, but better understanding of the processes is required to improve mitigation strategies. The N2O site‐specific 15N signatures from denitrification and nitrification have been shown to be clearly different, making this signature a potential tool for N2O source identification. We have applied for the first time quantum cascade laser absorption spectroscopy (QCLAS) for the continuous analysis of the intramolecular 15N distribution of soil‐derived N2O and compared this with state‐of‐the‐art isotope ratio mass spectrometry (IRMS).
Soil was amended with nitrate and sucrose and incubated in a laboratory setup. The N2O release was quantified by FTIR spectroscopy, while the N2O intramolecular 15N distribution was continuously analyzed by online QCLAS at 1 Hz resolution. The QCLAS results on time‐integrating flask samples were compared with those from the IRMS analysis.
The analytical precision (2σ) of QCLAS was around 0.3 ‰ for the δ15Nbulk and the 15N site preference (SP) for 1‐min average values. Comparing the two techniques on flask samples, excellent agreement (R2 = 0.99; offset of 1.2 ‰) was observed for the δ15Nbulk values while for the SP values the correlation was less good (R2 = 0.76; offset of 0.9 ‰), presumably due to the lower precision of the IRMS SP measurements.
These findings validate QCLAS as a viable alternative technique with even higher precision than state‐of‐the‐art IRMS. Thus, laser spectroscopy has the potential to contribute significantly to a better understanding of N turnover in soils, which is crucial for advancing strategies to mitigate emissions of this efficient greenhouse gas.
- laser spectroscopy
- nitrous oxide