Preparation of primary standard mixtures for atmospheric oxygen measurements with less than 1 µmol mol⁻¹ uncertainty for oxygen molar fractions

Abstract

Abstract. Precise monitoring of changes in atmospheric O2 levels was implemented by preparing primary standard mixtures with less than 1 µmol mol−1 standard uncertainty for O2 molar fractions. In this study, these mixtures were crafted in 10 L high-pressure aluminium alloy cylinders using a gravimetric method in which unknown uncertainty factors were theoretically determined and subsequently reduced. Molar fractions of the constituents (CO2, Ar, O2, and N2) in the primary standard mixtures were mainly resolved using masses of the respective source gases (CO2, Ar, O2, and N2) that had been filled into the cylinders. To precisely determine the masses of the source gases, the difference in mass of the cylinder before and after filling the respective source gas was calculated by comparison with an almost identical reference cylinder. Although the masses of the cylinders filled with the source gas with respect to the reference cylinder tended to deviate in relation to temperature differences between the source-gas-filled cylinder and surrounding air, the degree of the deviation could be efficiently reduced by measuring the two cylinders at the exact same temperature. The standard uncertainty for the cylinder mass obtained in our weighing system was determined to be 0.82 mg. The standard uncertainties for the O2 molar fractions in the primary standard mixtures ranged from 0.7 to 0.8 µmol mol−1. Based on the primary standard mixtures, the annual average molar fractions of atmospheric O2 and Ar in 2015 at Hateruma island, Japan, were found to be 209339.1±1.1 and 9334.4±0.7 µmol mol−1, respectively. The molar fraction for atmospheric Ar was in agreement with previous reports.

Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events

“…The N 2 O-AOU for M99 was 0.088 ± 0.003 nmol µmol −1 , with an intercept of 1.6 ± 0.04 nmol and an R 2 of 0.69. This is a low value, nearly identical to results from the eastern basin of the subtropical North Atlantic, where South Atlantic Central Water is found (Cohen and Gordon, 1979;Suntharalingam and Sarmiento, 2000;Walter et al, 2006), and the eastern equatorial Atlantic (Arévalo-Martínez et al, 2017). Frame et al (2014) showed that most of the N 2 O in the Benguela Current region is produced in the water column and in the sediment by nitrifier denitrification (Frame et al, 2014).…”

“…In the case of O 2 , the atmospheric concentration was measured only sporadically with flask samples, so it was taken as a static value, viz. the mole fraction of O 2 in standard dry air, 0.2093 (Aoki et al, 2019). The in situ aqueous solubility of O 2 was calculated using the equations of García and Gordon (1992), of N 2 O using those in Weiss and Price (1980), and of CO 2 using Weiss (1974).…”

O2 : CO2 exchange ratio for net turbulent flux observed in an urban area of Tokyo, Japan, and its application to an evaluation of anthropogenic CO2 emissions

“…Although the highest CO 2 concentration of the gravimetrically prepared standard of the NIES-09 scale is similar to that of the TU-10 scale, a slope of 0.974 ppm ppm −1 is derived from a least-squares regression line fitted to the relationship between the CO 2 concentrations observed by NDIR on the TU-10 scale and those by CRDS on the NIES-09 scale with a correlation coefficient (r) of 0.978. On the other hand, we obtained a slope of 1.002 per meg per S. Ishidoya et al: O 2 : CO 2 exchange ratio for net turbulent flux meg −1 (r = 0.999) from the regression line fitted to the relationship between the O 2 concentrations of gravimetrically prepared standard gases (Aoki et al, 2019) measured by the mass spectrometer on the AIST scale and the gravimetric values of the standard gases covering a much wider range than the atmospheric variations in the O 2 concentration. Therefore, the uncertainty in OR due to the span uncertainties of O 2 and CO 2 concentrations is expected to be within 3 %.…”

New technique for high-precision, simultaneous measurements of CH<sub>4</sub>, N<sub>2</sub>O and CO<sub>2</sub> concentrations; isotopic and elemental ratios of N<sub>2</sub>, O<sub>2</sub> and Ar; and total air content in ice cores by wet extraction

“…The CH 4 , N 2 O and CO 2 concentrations are determined against Tohoku University (TU) scales, which are based on gravimetrically prepared primary standard gases (Aoki et al, 1992;Tanaka et al, 1983). Uncertainties of the TU primary standards are < ± 0.2, 0.2 and 0.03 % for CH 4 , N 2 O and CO 2 concentrations, respectively (Aoki et al, 1992 . Example of a calibration procedure for greenhouse gas concentration.…”