Publication Date:
2015-05-19
Description:
Laser spectroscopy is an emerging technology for measuring nitrous oxide (N 2 O) 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 N 2 O analyzer) to an air/water gas equilibration device to collect continuous in situ dissolved N 2 O molar concentration and bulk nitrogen isotopic (δ 15 N-N 2 O) data. The δ 15 N-N 2 O values measured by the CRDS unit were found to be significantly affected by changes in the mixing ratios of O 2 , CO, CH 4 , and CO 2 . There was also an effect of N 2 O mixing ratio on δ 15 N-N 2 O. A series of equations was developed to correct for the matrix effect of O 2 and the spectral interference by CH 4 . Chemical traps effectively prevented interferences by CO and CO 2 . The maximum corrections required for N 2 O 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 CH 4 correction only became important at mixing ratios greater than 500 ppmv (〉0.5‰). Measurements of N 2 O molar concentration and δ 15 N-N 2 O from the CRDS isotopic N 2 O 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 N 2 O isotopologues in aquatic habitats, allowing for further constraints to be placed on the pathways of N 2 O cycling in aquatic system.
Electronic ISSN:
1541-5856
Topics:
Biology
,
Geosciences
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