[Lonesome in Massachussets]

Certainly can't think of any reason for that to be true. He may be maintaining that CO₂ may have more of certain isotopes, e.g., C14 vs. C12 or O18 vs. O16, depending on it's genesis.

If true, exactly what the consequences would be is beyond me. The troposphere is so turbulent that very little settling takes place, so the horizontal distribution would hardly be affected. The interaction with infrared radiation would be slightly shifted, because it depends on the mass of molecules, as well as the electronic bonds.

I truly fail to see the relevance.

I guess I'd have to see his comments in context.

[P-40]

He may be maintaining that CO2 may have more of certain isotopes

I assume that is what he is getting at.