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.

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.

<p>Widely available reference materials that are traceable and consistent with international stable isotope scales are necessary in order to create a robust and sustainable global measurement infrastructure for isotope ratio of CO<sub>2</sub> and N<sub>2</sub>O.</p><p>We report on progress towards the production and certification of atmospheric amount fraction greenhouse gas reference materials with isotope ratios spanning the full atmospheric range. Reference materials are produced with a chosen delta value with uncertainties aiming to achieve the WMO GAW data quality objectives for extended compatibility of delta value of of ∂<sup>13</sup>C-CO<sub>2</sub> and ∂<sup>18</sup>O-CO<sub>2</sub> of 0.1‰ (northern hemisphere) and amount fraction of 0.2 µmolmol<sup>-1</sup> for CO<sub>2</sub> and 0.3 nmolmol<sup>-1</sup> for N<sub>2</sub>O at atmospheric amount fraction ranges.</p><p>To illustrate the work towards these challenging goals we present studies of sampling technique and isotope ratio stability with storage, pressure and cylinder passivation. The precision of blending and dilution of source gases is presented alongside studies of measurement instrument precision and drift. Contributing factors from matrix gases are also discussed. </p>

We have employed a new approach to quantify the amount fraction of nitrous oxide in a synthetic air matrix gas used to prepare high-accuracy reference materials of the same component. Until now, this was the largest contributor to the measurement uncertainty of nitrous oxide in air reference materials at atmospheric amount fractions (∼330 nmol mol–1), as identified in a recent international comparison. A novel preconcentration method has resulted in a measurement of 363 pmol mol–1 of nitrous oxide in a synthetic air matrix gas with an expanded uncertainty of 27 pmol mol–1. This represents a significant breakthrough as using these developments with an optimized dilution hierarchy (to minimize the gravimetric uncertainty) promises to result in SI traceable reference materials with expanded uncertainties as low as 0.032% relative (k = 2). This supports the World Meteorological Organization–Global Atmosphere Watch network compatibility goal for underpinning atmospheric observations.

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