Progress towards atmospheric isotope ratio carbon dioxide and nitrous oxide reference materials that meet the WMO-GAW data quality objectives for compatibility

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 CO₂ and N₂O.

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 ∂¹³C-CO₂ and ∂¹⁸O-CO₂ of 0.1‰ (northern hemisphere) and amount fraction of 0.2 µmolmol^-1 for CO₂ and 0.3 nmolmol^-1 for N₂O at atmospheric amount fraction ranges.

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.