Todd Fatheree wrote:
,,,
(http://www.climateark.org/articles/1999/atoxfall.htm) from 1999 measured
the atmospheric oxygen change over a 20-year period to be (are you sitting
down) 0.03%. One wonders the amount of error contained in that calculation
and if it has any application outside of the Cape Grim Baseline Air
Pollution Station in Tasmania. ...

One supposes that if the online article was based on published papers
the error you wonder about will be estimated therein.

I think the longest running record of direct measurement of atmospheric

CO2 is from teh Mauna Loa observatory. Here is one paper addressing
it:

Thoning, K.W., P.P. Tans and W.D. Komhyr. 1989. Atmospheric carbon
dioxide at Mauna Loa Observatory, 2, Analysis of the NOAA/GMCC data,
1974 - 1985, J. Geophys. Res., 94, 8549-8565.

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FF