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Evaluation of photoacoustic infrared spectroscopy for simultaneous measurement of N2O and CO2 gas concentrations and fluxes at the soil surface

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Abstract

Simultaneous measurement of N2O and CO2 flux at the soil surface with photoacoustic infrared spectroscopy (PAS) is gaining popularity due to portability, low maintenance, and ease-of-operation. However, the ability of PAS to measure N2O with accuracy and precision similar to gas chromatography (GC) is uncertain due to overlap in N2O, CO2, and H2O absorbance spectra combined with the large range in analyte concentrations. We tested the ability of six PAS units to simultaneously measure N2O and CO2 gas concentrations and fluxes with accuracy and precision similar to two GC units. We also evaluated H2O vapor and CO2 interferences with N2O measurement. The accuracy and precision of standard gas concentration measurements with PAS and GC were similar. High water vapor (~26 600 ppm) and CO2 concentrations (~4500 ppm) did not interfere with N2O measurement across the concentration range typically observed in static flux chambers at the soil surface (~0.5–3.0 ppm N2O). On average, N2O fluxes measured with the six PAS were 4.7% higher than one GC and 9.9% lower than the second GC.

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