To further understand the difference in mechanism observed for CO2 diffusing in CALF-20 with and without N2 present, more CO2 data was collected, both with and without N2, as shown in Figure . Figure shows that at low CO2 concentrations, the mixed gas behavior is not as strong, but at around 2% CO2 in the N2 case, the mixed-gas behavior begins to emerge. The effect is even more pronounced at 4%. These observations are important because traditionally, N2 adsorption under ambient conditions and its impact on the adsorption of other species is largely neglected; however, in the case of CALF-20, N2 is shown to have a measurable effect on the diffusion mechanism of CO2. Data collection becomes challenging for the particular mass spectrometer detector used in these experiments near CO2 concentrations around 10% or higher. The input square wave with no adsorbent must be detectable as a clean square wave by the detector, and as the concentration increases, this is no longer the case for the detector used for these experiments. Thus, at higher concentrations of CO2, sine waves are necessary. For this reason, this work does not report data that is higher than 10% CO2. This is, however, not necessarily a limitation of the FT-CSFR technique but rather an inability of the detector to measure a clean square wave at these higher concentrations. With a dedicated CO2 probe, it is possible that this method may be extended to higher CO2 concentrations, provided that a clean square wave with a high sampling rate can be obtained with the probe.