Influence of CO₂ adsorption on cylinders and fractionation of CO₂ and air during the preparation of a standard mixture

Abstract. We evaluated carbon dioxide (CO2) adsorption on the internal surface of cylinder and fractionation CO2 air during preparation standard mixtures with atmospheric level through multistep dilution. The molar fractions in deviated from gravimetric values by -0.207±0.060 µmol mol−1 average, which is larger than compatibility goal (0.1 mol−1) recommended World Meteorological Organization. deviation was consistent those calculated using two factors: one estimated mother–daughter transfer experiment CO2–air were transferred a mother to an evacuated daughter cylinder, another computed applying Rayleigh model change source gas as its pressure depleted 11.5 1.1 MPa. experiments showed that caused (CO2–air mixture higher fraction prepared mixture). less significant when speed decreased 3 L min−1, indicating thermal diffusion mainly fractionation. experimentally emitting cylinder. When reduced 11.0 0.1 MPa, exiting increased 0.16±0.04 mol−1. By Langmuir adsorption–desorption measured data, amount adsorbed surfaces 10 aluminum preparing be 0.027±0.004 at