Articles | Volume 9, issue 5
Research article
11 May 2016
Research article |  | 11 May 2016

Development of automated preparation system for isotopocule analysis of N2O in various air samples

Sakae Toyoda and Naohiro Yoshida

Abstract. Nitrous oxide (N2O), an increasingly abundant greenhouse gas in the atmosphere, is the most important stratospheric ozone-depleting gas of this century. Natural abundance ratios of isotopocules of N2O, NNO molecules substituted with stable isotopes of nitrogen and oxygen, are a promising index of various sources or production pathways of N2O and of its sink or decomposition pathways. Several automated methods have been reported to improve the analytical precision for the isotopocule ratio of atmospheric N2O and to reduce the labor necessary for complicated sample preparation procedures related to mass spectrometric analysis. However, no method accommodates flask samples with limited volume or pressure. Here we present an automated preconcentration system which offers flexibility with respect to the available gas volume, pressure, and N2O concentration. The shortest processing time for a single analysis of typical atmospheric sample is 40 min. Precision values of isotopocule ratio analysis are < 0.1 ‰ for δ15Nbulk (average abundances of 14N15N16O and 15N14N16O relative to 14N14N16O), < 0.2 ‰ for δ18O (relative abundance of 14N14N18O), and < 0.5 ‰ for site preference (SP; difference between relative abundance of 14N15N16O and 15N14N16O). This precision is comparable to that of other automated systems, but better than that of our previously reported manual measurement system.

Short summary
Tiny variation in natural abundance ratios of stable isotopes of nitrogen and oxygen in nitrous oxide (N2O) can be used as a fingerprint of this trace gas that causes greenhouse effect and stratospheric ozone depletion. Toward the understanding of the global budget of N2O and its temporal change, we developed an automated sample preparation system that can be used to measure the stable isotope ratios in N2O in various air samples collected into flasks with high precision and less labor.