Characterisation of gas reference materials for underpinning atmospheric measurements of stable isotopes of nitrous oxide

Ruth E Hill-Pearce,Joachim Mohn,Paul J Brewer,Kanokrat Charoenpornpukdee,Christoph Zellweger,Aimee Hillier,Eric Mussell Webber,Simon O'Doherty,David R Worton

doi:10.5194/amt-14-5447-2021

Abstract

Abstract. The precise measurement of the amount fraction of atmospheric nitrous oxide (N2O) is required to understand global emission trends. Analysis of the site-specific stable isotopic composition of N2O provides a means to differentiate emission sources. The availability of accurate reference materials of known N2O amount fractions and isotopic composition is critical for achieving these goals. We present the development of nitrous oxide gas reference materials for underpinning measurements of atmospheric composition and isotope ratio. Uncertainties target the World Metrological Organisation Global Atmosphere Watch (WMO-GAW) compatibility goal of 0.1 nmol mol−1 and extended compatibility goal of 0.3 nmol mol−1, for atmospheric N2O measurements in an amount fraction range of 325–335 nmol mol−1. We also demonstrate the stability of amount fraction and isotope ratio of these reference materials and present a characterisation study of the cavity ring-down spectrometer used for analysis of the reference materials.

Highlights

Nitrous oxide (N2O) is a greenhouse gas with a global warming potential approximately 265 times that of carbon dioxide (CO2) (Myhre et al, 2013)
We present work on the development of N2O reference materials for underpinning atmospheric composition and isotope ratio with uncertainties targeting the World Metrological Organisation Global Atmosphere Watch (WMO-GAW) compatibility goals
The combined contribution to the uncertainty due to gravimetry and purity of the components for the ambient amount fraction N2O in synthetic air reference materials produced, as detailed above, is 0.08 % (k = 2) 0.28 nmol mol−1. This uncertainty is within the World Metrological Organisation (WMO)-GAW extended compatibility goals of ±0.3 nmol mol−1

Summary

Introduction

Nitrous oxide (N2O) is a greenhouse gas with a global warming potential approximately 265 times that of carbon dioxide (CO2) (Myhre et al, 2013). Atmospheric amount fractions of N2O are increasing at a rate of ∼ 0.36 % yr−1 (WMO, 2019b). Recent measurements of N2O in the unpolluted troposphere are in an amount fraction range of 325– 335 nmol mol−1 (WMO, 2019a). Current amount fractions of 332 nmol mol−1 have been published by the WMO (WMO, 2020). The growing field of N2O research is focused on improving understanding of the global N2O budget. A comprehensive identification of the N2O sources and sinks and the contribution of each to the global N2O budget is required for N2O mitigation studies (Lewicka-Szczebak et al, 2014)

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Conclusion