The artile doi: 10.1021/jacs.3c00515, and the attached image is Figure S42 (a) in supporting information.

This image shows the breakthrough curve of a MOF, NTU-85-WNT, which is applied for the adsorption of C3H6. I have some questions regarding the calculation of Qmax. Logically, the green area in the graph represents the adsorbed C3H6, which is correlated with Qmax. In my view, the integration below the figure (i.e. Ci(0)-Ci(t)) corresponds directly to this green area. Therefore, this integration alone should be used to calculate Qmax. However, the authors opted for a subtraction method instead. It appears that they consider this integration to be the area under the curve rather than the green area. Could someone help me figure out whether my understanding is incorrect or if there are other aspects I've overlooked?