Experimental Determination of Air Density Using a 1 kg Mass Comparator in Vacuum

Abstract

The density of ambient air has been determined by a straightforward experimental method. The apparent masses of two artefacts having about the same mass and surface, but different well-known volumes, have been compared by using a 1 kg balance in vacuum and in air. The differences of apparent masses and volumes yield the air density with a relative uncertainty (1σ) of 5 × 10-5. From measurements made using a third artefact, surface sorption effects caused by the change between vacuum and air conditions gave a coefficient of about 0,2 μg cm-2.

Mass determination of silicon spheres used for the Avogadro project

“…If the air density is determined according to the air density equation, internationally recommended by the Comité International des Poids et Mesures (CIPM), the relative standard uncertainty of the air density u(ρ)/ρ is in the order of magnitude of 1⋅10 -4 [4,5] which leads to an uncertainty contribution of about 50 µg. This contribution can be significantly reduced if two buoyancy artefacts with a similar mass and surface, but different volumes, are used for a gravimetric determination of the air density [7,9]. With these buoyancy artefacts the relative standard uncertainty for the air density determination can be reduced to less than 5⋅10 -5 , which leads to a standard uncertainty of the buoyancy correction of less than 25 µg.…”

Bilateral comparison of buoyancy artefacts between PTB and KRISS

“…The adsorbed mass per surface area μ is estimated to be (0.21 ± 0.1) µg cm -2 for the PTB artefacts [1] and (0.35 ± 0.1) µg cm -2 for the KRISS artefacts [2]. The vacuum mass difference has to be corrected for the sorption influence on the small difference of surface area between BAs of KRISS and PTB.…”

“…It is about 10 µg. To reduce this uncertainty, the determination of air density by using buoyancy artefacts is studied by many national metrology institutes (NMI) [1][2][3]. The CIPM formula to determine air density is a function of the temperature T, pressure p, dew-point temperature t d and the CO 2 content of the air x CO2 .…”

Uncertainty evaluation of mass values determined by electronic balances in analytical chemistry: a new method to correct for air buoyancy

“…It is assumed that the air climate parameters of the room are held within the limits of spatiotemporal specification for the room. The mass of the unknown sample can be calculated without determining the air density [14,15,16] which is generally calculated by approximation formulas using independently measured values for air temperature, air pressure and relative air humidity. A constant and fixed composition of the air is assumed.…”