## 3 Results and Discussion
As already found in a previous work [7], it is often difficult when dealing with real samples to resolve the O1s region into the component peaks if many oxygenated groups \begin{table}
\begin{tabular}{c c c c c} \hline
**XPS Regions** & **Peaks** & **Corrected BEs** & **Normalized Areas \(\pm\) 10\%** & **Assignments** \\ \hline C(1s) & 1 & 283.6 & 93.0 & _carbide_, _polycyclic carbons_ \\ \cline{2-5} _Internal Standard (IS)_ & 2 & 285.0 & 520.7 & _C-C aliphatic/aromatic_ \\ \cline{2-5} \cline{2-5} _Standard (IS)_ & 3 & 286.4 & 232.4 & _C-O_- \\ \cline{2-5} \cline{2-5} \cline{2-5} \(4\) & 288.0 & 243.1 & _C=O_ \\ \cline{2-5} \cline{2-5} \(5\) & 289.6 & 1369.2 & _(Ca)-CO3_ \\ \cline{2-5} \cline{2-5} _6,7_ & 298.6/301.5 & 77.5/87.0 & _slake up satellites_ \\ \hline Ca(2p) & 1(2p3/2) & 344.9 & 69.5 & _CaO_ \\ \cline{2-5} \cline{2-5} _2(2p3/2)_ & 347.1 & 967.6 & _Ca_(CO3) \\ \cline{2-5} \cline{2-5} _3(2p1/2)_ & 348.3 & 34.8 & _CaO_ \\ \cline{2-5} \cline{2-5} _4(2p1/2)_ & 350.7 & 471.3 & _CaCO3_ \\ \cline{2-5} \cline{2-5} \(5\) & 355.2/358.8 & 48.4/39.5 & _slake up satellites_ \\ \hline Fe(2p3/2) & 1 & 712.4 & 64.2 & _Fe2O3_ \\ \cline{2-5} _Al(2s)_ & 1 & 119.0 & 195.3 & _Al2O3_ \\ \hline Si(2p) & 1 & 100.4 & 50.94 & _SiC_ \\ \cline{2-5} \cline{2-5} \(2\) & 102.4 & 455.9 & _SiOx_ \\ \hline O(1s) & 1 & 529.6 & 600.0 & _Fe2O3, CaO_ \\ \cline{2-5} \cline{2-5} \(2\) & 531.9. & 7552.5 & _SiO2, CaCO3_ \\ \cline{2-5} \(3\) & 534.1 & 378.8 & _H2O/hydroxyls_ \\ \hline \end{tabular}
\end{table} 
Table 1: Peaks resolved by curve-fitting the detailed regions of Figure 4 (0R sample), identified and quantified as explained in the Figure 4 caption. The chemical groups associated in the pie chart of Figure 4 are the following. contribute to it and their chemical states are too close in terms of binding energy, BE, for the given instrumental resolution, using achromatic X-ray sources. In this case, the three curve-fitted oxygen peaks, although belonging to differentiated classes of oxygenated compounds, characterizing the reference calcarenite 0R [7; 15], actually are not of the right intensity to individually correspond to the oxygenated compounds defined in the assignments and identified in the corresponding detailed regions, listed in Table 1. Therefore, also in this work, the only way to successfully perform the oxygen'mass balance' is to refer all the oxygenated compounds to the total O1s area, taking into account their stoichiometry. Initial XPS processing of calcarenite degradation. The curve-fitting procedure adopted for the reference sample (0R) was repeated for all the acquired XPS spectra, following the sampling interval of 3, 6, 9, 12, 21 and 52 months from the north, east, south and west walls of the externally exposed calcarenite cube, as shown in the Section 2. As found by the XPS characterization of sample 0R, the composition of calcarenite surfaces was already of a certain complexity in the starting/unexposed reference and, from the visual comparison of the two wide spectra in Figure 3, it is expected to evolve over time. Indeed, the coexistence of single stoichiometric compounds identified by curve-fitting the detailed regions of Figure 4 is certainly a simplification of the interconnected chemical bonds representing the composition of'real' surfaces. However, the grouping classification, mainly consisting of mixed compounds, listed in the legend of Table 1 and reported in the pie chart, proves very useful to verify the counterions balance so as to estimate the neutrality of the surface composition. In this way, a good assessment of their compositional variation over time can also be performed, which is necessary to extrapolate the trend of calcarenite degradation from comparative XPS characterizations. The first processing of the XPS temporal monitoring is shown in Supplementary Figure S1a-d, represented by equidistant analyses, three months-spaced sampling, of the cube walls, cardinally oriented, in the first nine months of outside exposure.