Revised formula for the density of moist air (CIPM-2007)

Abstract

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 x Ar 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.

Violent expiratory events: on coughing and sneezing

“…Characteristics of a typical cough. Parameters include the temperature of the fluid exhaled T f , its relative humidity RH f and the resulting density ⇢ f computed using the evaporation model of Picard et al (2008). The ambient air density ⇢ a = 1.172 kg m 3 for typical winter conditions (temperature 23 C, relative humidity 19.1 %).…”

Numerical analysis of the accuracy of bivariate quantile distributions utilizing copulas compared to the GUM supplement 2 for oil pressure balance uncertainties

“…as discussed by Picard et al [7] where M a = 28.96546 Â 10 À3 kg mol À1 is the molar mass of dry air, M v = 18.01528 Â 10 À3 kg mol À1 is the molar mass of water, Z is the air compressibility, R = 8.314472 J mol À1 K À1 is the CODATA-2006 recommended value for the universal gas constant, and x v is the mole fraction of water vapour for the corresponding pressure, temperature and relative humidity conditions for the surrounding ambient air. The previous formulae may now be combined and rearranged as a nonlinear function f ⭑ ðp; q ⭑ 1 ; .…”

Determination of pressure balance distortion coefficient and zero-pressure effective area uncertainties

“…where p a , t a and h a represents the atmospheric pressure, temperature and relative humidity respectively following the notation of Picard et al [12] where the relative humidity is represented by a number such that 0 ≤ h a ≤ 1. In the above model S is the actual instantaneous area at temperature t and by setting α = α p + α c where α p and α c are the linear thermal expansion coefficents of the piston and cylinder respectively one may account for the thermal expansion/contraction of the piston-cylinder when there is a temperature difference (t− t ref…”

“…If the pressure balance is operated in absolute mode then the atmospheric pressure p a above the piston will typically consist of a working gas such as nitrogen in which case the density ρ a can be calculated from the equation of state, whilst if the pressure balance is operated in gauge mode then ρ a can be calculated in terms of p a , t a and h a as per the CIPM-2007 formula for the density of moist air [12].…”

“…where ε is a term to acount for the underlying uncertainty in the CIPM-2007 equation for the air density factoring in consideration of the mole fraction of argon and other terms and which is ε = (22 × 10 −6 )ρ a according to the literature [12].…”