Applying cavity ring-down spectroscopy for the measurement of dissolved nitrous oxide concentrations and bulk nitrogen isotopic composition in aquatic systems: Correcting for interferences and field application

作者：Erler D V^*; Duncan T M; Murray R; Maher D T; Santos I R; Gatland J R; Mangion P; Eyre B D

来源：Limnology and Oceanography: Methods , 2015, 13(8): 391-401.

DOI：10.1002/lom3.10032

Laser spectroscopy is an emerging technology for measuring nitrous oxide (N2O) dynamics in the environment, but most studies have focused on atmospheric applications. We have coupled a commercially available cavity ring-down spectroscope (CRDS) (Picarro G5101-I isotopic N2O analyzer) to an air/water gas equilibration device to collect continuous in situ dissolved N2O molar concentration and bulk nitrogen isotopic (delta N-15-N2O) data. The delta N-15-N2O values measured by the CRDS unit were found to be significantly affected by changes in the mixing ratios of O-2, CO, CH4, and CO2. There was also an effect of N2O mixing ratio on delta N-15-N2O. A series of equations was developed to correct for the matrix effect of O-2 and the spectral interference by CH4. Chemical traps effectively prevented interferences by CO and CO2. The maximum corrections required for N2O mixing ratio and O-2 matrix effects, were 1% (at a mixing ratio of 1.2 ppmv), and 11% (at 0% O-2 content), respectively. The CH4 correction only became important at mixing ratios greater than 500 ppmv (>0.5%). Measurements of N2O molar concentration and delta N-15-N2O from the CRDS isotopic N2O analyzer were similar to those measured with isotope ratio mass spectrometry. We demonstrated the utility of the laser-based system with field deployments in three estuarine tidal creeks in subtropical Australia. Future work in this field should focus on the application of the laser-based system to the measurement of N2O isotopologues in aquatic habitats, allowing for further constraints to be placed on the pathways of N2O cycling in aquatic system.

• 出版日期2015-8