surface excess concentration, \(\mathit{\Gamma}\)

https://doi.org/10.1351/goldbook.S06172
A quantity defined by \[\mathit{\Gamma}_{i} = \frac{n_{i}^{\sigma }}{A_{\text{s}}}\] where n i σ is the surface excess (or adsorption) of component i and As is the area of the dividing surface or interface.
Sources:
Green Book, 2nd ed., p. 63 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1986, 58, 967. 'Reporting data on adsorption from solution at the solid/solution interface (Recommendations 1986)' on page 970 (https://doi.org/10.1351/pac198658070967)