A Picard 1, R S Davis 1, M Gläser 2 and K Fujii 3
1
Bureau International des Poids et Mesures, Pavillon de Breteuil, F-92310 Sèvres Cedex, France
2
Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany
3
National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST), Central 3, 1-1, Umezono 1-chome, Tsukuba, Ibaraki 305-8563, Japan
A Picard et al 2008 Metrologia 45 149
Measurements of air density determined gravimetrically and by using the CIPM-81/91 formula, an equation of state, have a relative deviation of 6.4 × 10−5.
This difference is consistent with a new determination of the mole fraction of argon xAr carried out in 2002 by the Korea Research Institute of Standards and Science (KRISS) and with recently published results from the LNE. The CIPM equation is based on the molar mass of dry air, which is dependent on the contents of the atmospheric gases, including the concentration of argon. We accept the new argon value as definitive and amend the CIPM-81/91 formula accordingly. The KRISS results also provide a test of certain assumptions concerning the mole fractions of oxygen and carbon dioxide in air. An updated value of the molar gas constant R is available and has been incorporated in the CIPM-2007 equation. In making these changes, we have also calculated the uncertainty of the CIPM-2007 equation itself in conformance with the Guide to the Expression of Uncertainty in Measurement, which was not the case for previous versions of this equation. The 96th CIPM meeting has accepted these changes.
Issue 2 (April 2008)
Received 8 January 2008
Published 18 February 2008
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