Intercomparison of O<sub>2</sub> ∕ N<sub>2</sub> ratio scales among AIST, NIES, TU, and SIO based on a round-robin exercise using gravimetric standard mixtures

Abstract. A study was conducted to compare the δ(O2/N2) scales used by four laboratories engaged in atmospheric measurements. These are Research Institute for Environmental Management Technology, Advanced Industrial Science and Technology (EMRI/AIST); National Studies (NIES); Tohoku University (TU); Scripps Institution of Oceanography (SIO). Therefore, five high-precision standard mixtures O2 molar fraction gravimetrically prepared Metrology Japan, AIST (NMIJ/AIST) with a uncertainty less than 5 per meg (0.001 ‰) were as round-robin mixtures. EMRI/AIST, NIES, TU, SIO reported analyzed values on their own scales, compared determined NMIJ/AIST (the scale). The temporal drift during intercomparison experiment from May 2017 March 2020 corrected based before after laboratory measurements EMRI/AIST. offsets zero span. relative span against scale -0.11%±0.10%, -0.10%±0.13%, 3.39 %±0.13 %, 0.93 %±0.10 respectively. largest offset corresponded 0.30 Pg yr−1 decrease increase global estimates land biospheric oceanic CO2 uptakes trends δ(O2/N2). deviations measured 65.8±2.2, 425.7±3.1, 404.5±3.0, 596.4±2.4 SIO, difference between observed at Hateruma Island (HAT; 24.05∘ N, 123.81∘ E), EMRI/AIST NIES reduced -329.3±6.9 -6.6±6.8 converting scale.