Real-time, field deployable measurements of the stable isotopes of nitrous oxide using Cavity Ring-Down Spectroscopy (CRDS) in the Mid-IR
Abstract
Nitrous oxide is a significant contributor to global warming and stratospheric ozone depletion. Importantly, the isotopomer ratios of N2O, i.e., the abundances of 14N15N16O and 15N14N16O relative to 14N14N16O, are particularly promising for elucidation of N2O biogeochemistry1. However, studies of these molecules have been limited by the unavailability of real-time, in-situ measurements. Picarro, Inc. has developed a novel field deployable, laser based instrument, able to measure the abundance of 14N15N16O and 15N14N16O relative to 14N14N16O in ambient concentrations of nitrous oxide (N2O). The analyzer is easy to use and makes continuous measurements in real time. Unlike with mass spectrometry, the 14N15N16O and 15N14N16O configurations can be clearly distinguished using high precision, time-based CRDS technology. This unique capability is possible because the spectral features of the 14N15N16O and 15N14N16O isotopomers are defined by the molecular mass AND the molecular configuration. In isotopic ratio mass spectrometry (IRMS), the charge to mass ratio must be different in order to discriminate different molecules. Therefore distinguishing isotopomers using IRMS requires additional analyses of N2O mass fragments generated by the ion source. This new instrument is unique from other isotopic N2O analyzers because it incorporates Picarro's low-drift design, does not require cryogens, and has an optical path length of over 2 km for high precision performance. The major sources from terrestrial ecosystems are the microbial processes of nitrification and denitrification occurring in soils. Although isotopic signatures of inorganic N species tend to vary because of the high turnover of N in terrestrial ecosystems, variations in their 15N isotopic and isotopomeric ratios can provide important information about ecosystem functions without disturbing the environment through the addition of inhibitors and tracer-labeled compounds2. For example, nitrogen isotopic site preference (the difference between the isotope ratios of the central and terminal nitrogen atoms) can be useful to distinguish between N2O produced via hydroxylamine oxidation versus nitrite reduction. In this work we will present the results of field testing of this newly developed instrument showing its performance, including precision and drift in real world applications. 1 K. Koba,*, K. Osaka, Y. Tobari, S. Toyoda, N. Ohte, M. Katsuyama, N. Suzuki, M. Itoh, H. Yamagishi, M. Kawasaki, S.J. Kim, N. Yoshida, T. Nakajima (2009) Biogeochemistry of nitrous oxide in groundwater in a forested ecosystem elucidated by nitrous oxide. Geochimica et Cosmochimica Acta 73 (2009) 3115-3133. 2 Ostrom N. E., Hedin L. O., von Fischer J. C. and Robertson G. P.(2002) Nitrogen transformations and NO3- removal at a soil-stream interface: a stable isotope approach. Ecol. Appl. 12(4), 1027-1043.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B31E0370J
- Keywords:
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- 0315 ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions;
- 0469 BIOGEOSCIENCES / Nitrogen cycling;
- 0486 BIOGEOSCIENCES / Soils/pedology;
- 4870 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Stable isotopes