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

<p>The precise measurement of the amount fraction of atmospheric nitrous oxide (N<span class="inline-formula">₂</span>O) is required to understand global emission trends. Analysis of the site-specific stable isotopic composition of N<span class="inline-formula">₂</span>O provides a means to differentiate emission sources. The availability of accurate reference materials of known N<span class="inline-formula">₂</span>O 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<span class="inline-formula">⁻¹</span> and extended compatibility goal of 0.3 nmol mol<span class="inline-formula">⁻¹</span>, for atmospheric N<span class="inline-formula">₂</span>O measurements in an amount fraction range of 325–335 nmol mol<span class="inline-formula">⁻¹</span>. 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>