A fully automatic system for underway N₂O measurements based on cavity ring-down spectroscopy

ABSTRACT

N₂O is one of the most important greenhouse and ozone-depleting gases and has been the source of considerable concern in recent years. The oceans account for ~ 1/4 of the global N₂O emission budget; however, the oceanic N₂O source/sink characteristics are not well understood. To enhance the study of oceanic N₂O source/sink characteristics, our laboratory developed a fully automatic underway system for surface water N₂O concentration and atmospheric N₂O mole fraction measurements consisting of a cavity ring-down spectroscopy (CRDS) instrument and an upstream device. The developed device can be programmed to switch the CRDS measurements from the equilibrator headspace to the atmospheric sample and the reference gas sample. The surface water N₂O concentration is calculated from the equilibrium headspace N₂O mole fraction in the equilibrator. The response time of this equilibrator is ~ 3.4 min, and the estimated precision of this method for surface water N₂O measurements is better than 0.5% (relative standard deviation, RSD), which is one order of magnitude better than that of traditional gas chromatographic methods and can be further optimised. Data are acquired every 20 s, and the calibration frequency requirement of this system is approximately 7–10 days. This labor-saving underway system is a powerful tool for high-precision and high-resolution measurements of atmospheric and oceanic N₂O and can significantly improve the study of the characteristics of oceanic N₂O sources/sinks and their response to climate change.

KEYWORDS:

• Nitrous oxide
• cavity ring-down spectroscopy
• underway
• automatic

Acknowledgments

This work was supported by the National Natural Science Foundation of China (grants 41230529, 41676186, and 41506225), the Chinese Projects for Investigations and Assessments of the Arctic and Antarctic (grants CHINARE2012-2017 for 01-4-02, 02-1, 03-04-02), and the Chinese International Cooperation Projects (IC201114, IC201201, IC201308, and 2016YFE0103300).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [41230529,41506225,41676186];CHINARE [2012-2017- 02-1,2012-2017-01-4-02,2012-2017-03-04-02];and the Chinese International Cooperation Projects [IC201308,2016YFE0103300,IC201114,IC201201];