We present experimental evidence of modification of O 2 /N 2 , Ar/N 2 , 29 N 2 / 28 N 2 , 34 O 2 / 32 O 2 ratios and CO 2 mole fraction in dry air standards resulting from gas handling. Correlated variations among high precision measurements of multiple molecular pair ratios show diffusive fractionation to be the main modifying process. This mechanism can account for much of the previously unexplained CO 2 instability commonly observed in air standards used by the atmospheric CO 2 measurement community. I…
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