Are you aware of the term used for the phenomena where O2 displaces CO2 in lungs?
Haldane effect
Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin which increases the removal of CO2. We call this Haldane effect.
The Haldane effect facilitates the release of O2 at the tissues and the uptake of O2 at the lungs. This effect results from the fact that deoxygenated hemoglobin has a higher affinity for CO2 than does oxyhemoglobin.