# Effects of Microbiota on the Soiling Process of PV Modules in Arid Zones of the Atacama Desert
## 3 Results and Discussion  
### Mineralogical Characterization of Soiling  
The results obtained by XRD are presented in Figure 2, where they illustrate typical geological materials found in northern Chile [20; 21]. The mineral species identified at the UA included quartz (SiO\({}_{2}\)), calcite (CaCO\({}_{3}\)), albite (NaAlSi\({}_{3}\)O\({}_{8}\)), clinochore ((Mg,Fe)\({}_{6}\)(Si,Al)\({}_{4}\)O\({}_{10}\)(OH)\({}_{8}\)), orthoclase (KSi\({}_{3}\)AlO\({}_{8}\)), muscovite (KAl\({}_{2}\)(Si\({}_{3}\)Al)O\({}_{10}\)(OH,F)\({}_{2}\)), halite (NaCl), hematite (Fe\({}_{2}\)O\({}_{3}\)), and kaolinite (Al\({}_{2}\)Si\({}_{2}\)O\({}_{5}\)(OH)\({}_{4}\)). For the PSDA sample, the mineral species identified included quartz (SiO\({}_{2}\)), albite (NaAlSi\({}_{3}\)O\({}_{8}\)), gypsum (Ca(SO\({}_{4}\)) (H\({}_{2}\)O)\({}_{2}\)), clinochore ((Mg,Fe)\({}_{6}\)(Si,Al)\({}_{4}\)O\({}_{10}\)(OH)\({}_{8}\)), orthoclase (KSi\({}_{3}\)AlO\({}_{8}\)), and kaolinite (Al\({}_{2}\)Si\({}_{2}\)O\({}_{5}\) (OH)\({}_{4}\)). Figure 2: Powder X-ray diffraction. Dust sample deposited on PV modules installed at the PSDA (blue) and UA (red). The semi-quantitative analysis of the crystalline species concentration was performed using TOPAS software (version 3.1). The results from the UA indicate that albite (44.0%) was the most abundant compound, followed by quartz (21%), calcite (12%), muscovite (9%), clinochlore (5%), orthoclase (3%), hematite (3%), and halite (3%). Conversely, for the PSDA, the results indicate the dominance of gypsum (51%), albite (20%), kaolinite (12%), quartz (7%), orthoclase (6%), and clinochlore (4%). The results obtained show that in the case of the UA, our findings were consistent with those reported by [PERSON] et al. (2020), albeit differing due to the presence of clinochlore, muscovite, orthoclase, and hematite, which were not previously detected. These discrepancies can be attributed to the seasonality and sampling periods, which influenced the detectable amount of material by XRD. The mineral composition identified through XRD analyses aligned with the geological characteristics of the city of Antofagasta, which is situated on a dense soil layer composed of sand and medium-sized rock fragments that is abundant in mineral traces ([PERSON] et al., 2019; [PERSON] et al., 2019). These features are attributed to its proximity to the coast (Pacific Ocean) and the coastal mountain range, which contributes to the abundant presence of quartz and anorthite. Regarding the PSDA, our findings were consistent with those reported by [PERSON] et al. (2020). The mineralogical characterization of the deposited soiling at the UA and PSDA provided insights into the mineralogical environment where microorganisms thrive under the desert conditions of the Atacama Desert. The intrinsic mineral composition of the environment, along with endolithic and epilithic habitats, offer specialized ecological niches for the colonization and growth of microorganisms ([PERSON] et al., 2019; [PERSON] et al., 2019; [PERSON] et al., 2019). Analyses of typical major elements of the Earth's crust from the geology of northern Chile, such as iron (Fe) and copper (Cu), and others that are considered toxic, such as zinc (Zn), cadmium (Cd), lead (Pb), and mercury (Hg) were carried out; these elements were selected to determine their presence in the UA and PSDA areas in order to better understand the physicochemical environment in which the microbiota developed. These analyses provided information about the presence of heavy metals in the area and how they influenced the resistance and tolerance of the microbiome in this environment. The results obtained are shown in Figure 3, where it is noted that at the UA, the highest concentration corresponded to Pb, which reached an average value of 160.9 ppm, while the lowest concentration detected corresponded to Hg, with an average of 1.4 \(\times\) 10\({}^{-2}\) ppm.