# Effects of Microbiota on the Soiling Process of PV Modules in Arid Zones of the Atacama Desert
## 3 Results and Discussion
### Soiling Mechanism  
One of the challenges faced by studies on soiling is that the mechanisms of this phenomenon are often considered without distinguishing between its organic and inorganic components. An example of this is the approach proposed by [PERSON] et al. [4], which describes in detail the soiling mechanism in desert environments but overlooks the potential contribution of microbiota. This proposed mechanism establishes fundamental steps for soiling, such as deposition, adhesion, cementation, rebound, and particle resuspension, by considering the physicochemical characteristics of soiling and local atmospheric conditions. Based on this study, [PERSON] et al. [49] proposed a soiling mechanism for the Atacama Desert centered on its salinity, where the solubility of the deposited material plays a crucial role in the adhesion of particles. Based on the results obtained from this research, it is possible to enhance the understanding of soiling mechanisms by incorporating the biological contributions (microbiota) at various stages of the soiling process. To understand the soiling process, it is necessary to know the atmospheric parameters of the study locations. Parameters such as the wind speed, which acts as an airborne agent for particulate matter, combine with the relative humidity and temperature to cause the adhesion of soiling particles to the surface of the PV module [50; 51]. The atmospheric parameters evaluated at the UA and PSDA are shown in Figure 7, namely, the wind speed (WS), relative humidity (RH), and ambient temperature (T\({}_{\text{amb}}\)). The results show that at the UA, the WS typically ranged between 1.5 and 2 m/s. Additionally, it was observed that wind gusts could reach up to 5 m/s, although these were infrequent. However, these gusts have the strength to transport particulate matter. For RH, it was observed that all four seasons exhibited a similar pattern, with a majority frequency between 50% and 80%. These values aligned with the geographical location of the UA, as it is strongly influenced by the Pacific Ocean. Lastly, the T\({}_{\text{amb}}\) exhibited similar patterns in winter, autumn, and spring, where it oscillated between 10 \({}^{\circ}\)C and 23 \({}^{\circ}\)C. However, in summer, an increase in T\({}_{\text{amb}}\) was observed, where the values ranged between 15 \({}^{\circ}\)C and 25 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Dominant Bacterial Genera**} & \multicolumn{4}{c}{**Location**} \\ \cline{2-5}  & **Antofagasta (UA)** & \begin{tabular}{c} **Valencia,** \\ **Spain**[9; 40] \\ \end{tabular} & \
\begin{tabular}{c} **Berkeley, CA, USA**[10] \\ \end{tabular} &
\begin{tabular}{c} **Sorocaba-Itatiba,** \\ **Brazil**[8] \\ \end{tabular} \\ \hline _Alternaria_ & & & & x \\ _Arttrobacter_ & x & & & x \\ _Craurococcus-Caldovatus_ & & & x \\ _Deinococcus_ & x & x & x \\ _Friedmanntiella_ & & & x \\ _Hymenobacter_ & x & x & x \\ _Kineococcus_ & & & x \\ _Massilia_ & x & & x \\ _Mmethylobacterium-Methylorubrum_ & & & x \\ _Modesbacter_ & & x & x \\ _Noviherbspirillum_ & x & & \\ _Novosphingobium_ & & x & \\ _Pontibacter_ & x & & \\ _Rubellimetricobium_ & & x & \\ _Sphingomonas_ & & x & x \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of predominant taxonomic diversity characterized by massive sequencing at the genus level of bacteria in soiling samples deposited on PV modules in different geographic areas. For the PSDA, the atmospheric conditions were different from those at the UA due to the geographical differences in their locations. In the case of the WS, it was more frequently between 1 and 3 m/s. During spring and summer, high wind gusts could reach up to 10 m/s. The RH exhibited a typical pattern for an interior desert area influenced by the coast. In winter, spring, and autumn, the RH showed drier values, with a majority frequency around 10%. However, in these three seasons, the RH levels could also reach 100%.