Why CO2 levels don't rise as fast as 02 levels fall...

[phuturephysician]

Why do CO2 levels not rise as fast as 02 levels fall in arterial blood??

Does it have to do with differences in partial pressure gradients for the two gases? Or what about the weak and reversible bond between O2 and hemoglobin? Or the Bohr effect, where in the presence of higher concentrations of CO2 or H+ , the affinity of O2 for hemoglobin is decreased, as would be the case in unloading of O2 in systemic circulation?

Please help me clarify. Thanks