## 3 Results and Discussion
### Microstructural Characterization  
To observe the soiling process at a microscopic level, SEM tests were conducted. Figure 3a shows soiling deposition at the lower part of the PV glass. The deposited material is formed by particles of different sizes and a mixture that has a diverse morphology. The particles tend to generate agglomerates between them and this covers the glass surface. This phenomenon is more clearly shown in Figure 3b,c, which corresponds to a random section of the lower PV glass quadrant and shows the presence of prismatic particles surrounded by other particles with a random geometry. Both random high-resolution images show how prismatic particles capture the deposited material, encapsulating the deposited material that adheres to the PV glass surface. Figure 3d shows this effect better and corresponds to the PV glass cross-section. Prismatic particles cause an effect on agglomerate formation and this fosters soiling crust formation. To further understand the interaction process between the deposited material and crust formation, tests were conducted via EDX elemental mapping. Figure 4 shows a random section of the exposed glass and focuses on the presence of prismatic material owing to its ability to generate agglomerates. The selected area shows great amounts of O (\(\sim\)56.3%), Si (\(\sim\)19.5%), Al (\(\sim\)10.1%) Ca (\(\sim\)6.7%), and a few Mg (\(\sim\)1.3%), K (\(\sim\)0.8%), S (\(\sim\)3.5), and Na (\(\sim\)4.5%). Figure 4e,f show that prismatic particles are formed by sulphur and  
Figure 2: Site geology influence on PV module material deposition: (a) Random picture of PSDA soil; (b) Pit 5; and (c) material deposited on the fine layer module at PSDA. calcium, which are attributable to gypsum (CaSO\({}_{4}\cdot\)H\({}_{2}\)O). Thus, the results confirm that prismatic particles produce material agglomeration, thus capturing silicon grains (sand), as shown in Figure 4d. Prismatic particles do not only influence the adhesion of more abundant particles, but there is also an interaction with all the deposited materials. The adhesion of this material was also documented by [PERSON] et al. [25], who reported that the soluble material responsible for cementation does not only serve as an adherent to the glass surface, but also as a focus of attraction for other minerals. As to PSDA, gypsum is the only hygroscopic material that can interact with the humidity on the site. This material is related to the results obtained from the pits, which indicate the presence of soluble material, which are not abundant, but there is enough for soiling crust formation. The close interconnection between the prismatic particles, glass, and the rest of the material confirms the influence of the cementation process due to condensation and evaporation cycles that occur on the site. This phenomenon was documented by [PERSON] et al., who reported that the meteorological conditions on the site, along with the physicochemical characteristics of the material, generated the cementation process [18]. Evaluating and comparing different periods of time is important to confirm that cementation is a phenomenon that occurs on site, and is not unique to a certain year. This allows us to establish long-term action plans for places characterized by the presence of crustal soil. Figure 3: Scanning electron microscopy: (**a**) Sample of soiling deposited on the lower part of the PV glass; (**b,c**) random prismatic particle analysis; and (**d**) PV glass cross-section. The topography of the deposited material was performed by AFM-Raman. The results are shown in Figure 5a. The analysis confirms the presence of agglomeration produced by the deposited material, which is the deposition thickness that grows on the lower part of the PV glass. Relative humidity and condensation interact with the deposited material, thereby producing mud with soluble and insoluble material which, due to gravity, flows to the lower part of the glass [11; 26; 27].