Determination of the argon concentration in ambient dry air for the calculation of air density

Abstract

The mole fraction of argon in ambient dry air has been measured using gas phase chromatography calibrated with gravimetric gas standards prepared at the Laboratoire National de Métrologie et d'Essais. Different air samples, operators and gas standards were used to obtain a value of 0.9330 × 10−2 mol mol−1 ± 0.0032 × 10−2 mol mol−1. This value is significantly different from the conventional value (0.917 × 10−2 mol mol−1) used in the 81/91 formula of the Comité International des Poids et Mesures (CIPM) (Davies 1992 Metrologia 29 67–70) for the determination of air density during comparisons of mass standards.This value confirms the result obtained by the Korea Research Institute of Standards and Science, which found a concentration of 0.9332 × 10−2 mol mol−1 ± 0.0006 × 10−2 mol mol−1 by mass spectrometry in 2004.This new value explains the difference between the CIPM formula method and the artefact method used for the determination of air density.