I suppose, given that a lot of the research into CO2 levels is based on ice cores, that you could pursue that angle. If they can tell the CO2 level then surely they must define it as parts per million or something along those lines. I don't know where to look, but would suspect that key words such as Arctic, Antarctic, CO, research might google something for you.
I still think that you are unlikely to be successful, I'm pretty certain that I read somewhere that the amount of O was pretty much constant.
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