In this work, a new CSFR method was used to examine the diffusion of CO2 and H2O in CALF-20 and H2O in MOF-303 that allowed for more rapid data collection than traditional CSFR and provided new insights into the CO2 and H2O adsorption mechanism in the presence of N2 and He. In particular, the data show that the diffusion mechanism of CO2 and H2O is sensitive to the presence of N2 in the gas stream. When CO2 is examined in He, the adsorbent provides a different adsorption mechanism compared to the experiment in N2, even though both gases are typically regarded as inert carriers. While the single-component CSFR models capture the diffusion rates of CO2 in N2, it appears that N2 participates as an adsorbate, producing a mixed-gas adsorption system. When modeled as a single-component system, the CO2 adsorption rate in He appears much faster than when assessed in N2. The data highlight the importance of co-adsorption events when studying CO2 capture and show that N2, which is typically assumed inert, can have meaningful impact on the adsorption rates of leading CO2-capture MOFs.