## 2 Materials and Methods
### Environmental Acoustic Patterns  
To evaluate the environmental acoustic behavior of a site, European Directive 2002/49/ EC [2] recommends the use of the \(L_{\text{Aeq}T}\) indicators corresponding to day, evening, and night periods over 24 h for a specific station on every day during one year, denoted as \(L_{\text{d1y}}\), \(L_{\text{e1y}}\) and \(L_{\text{n1y}}\), respectively, and the overall assessment period noise indicator DEN (day, evening, night), represented by \(L_{\text{den}}\). To take into account the temporal variability of the sound pressure level values during the different periods of the day, the yearly standard deviation of \(L_{\text{den1d}}\), denoted \(sd_{\text{1y}}(L_{\text{den1d}})\), has been proposed to describe the variability or volatility of the sound pressure level of the nodes during a year [5; 6]. In these previous works of ours, four environmental acoustic patterns were recognized using these four noise indicators, calculated from the described dataset as inputs of several unsupervised learning techniques. Therefore, the nodes of BCN's WASN were classified into one of these patterns, and are shown in Figure 1 in different colors together with their locations. Table 1 shows the average values of the four previously defined noise indicators for the different pattern categories that allow the description of their behaviours. Analytically, there are three pattern categories in which day and evening sound pressure level values are similar and in which both are higher than night sound pressure level values by a statistical significance amount. The first pattern category, shown by the 23 nodes with the black color tag in Figure 1, has higher sound pressure values (\(L_{\text{d1y}}\), \(L_{\text{e1y}}\) and \(L_{\text{n1y}}\)) than the second pattern category, shown by the 27 nodes with the magenta color tag in Figure 1. Both categories have higher sound pressure values than the fourth category, which includes the 11 nodes shown with the brown color tag in Figure 1. Therefore, these pattern categories represent nodes with high, medium, and low values of sound pressure with the described behavior. Moreover, a negative correlation between sound pressure levels indicators and variability (\(sd_{\text{1y}}(L_{\text{den1d}})\)) can be observed, i.e., the fourth category is the one with the highest variability, followed by the second and first categories, in this order. The remaining third category, indicated by the blue color tag, contains nine nodes. This category shows a different behavior than the others, with evening sound pressure level value being higher than the other periods, which all have similar values. Moreover, this third category presents the highest variability of all categories. These environmental acoustic patterns can be contextualized by features such as the type of roads, use of the area, and noise sources. Interpretation of these characteristics \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pattern** & \multirow{2}{*}{\(L_{\text{d2019}}\)**(dB)**} & \multirow{2}{*}{\(L_{\text{e2019}}\)**(dB)**} & \multirow{2}{*}{\(L_{\text{n2019}}\)**(dB)**} & \multirow{2}{*}{\(sd_{\text{2019}}\)**(\(L_{\text{den1d}}\))**} & \multirow{2}{*}{**Nodes**} & \multirow{2}{*}{**Color**} \\
1 & 70.74 & 70.79 & 66.39 & 1.50 & 23 & black \\
2 & 66.40 & 66.04 & 62.28 & 2.06 & 27 & magenta \\
3 & 66.05 & 68.25 & 66.71 & 3.78 & 9 & cyan \\
4 & 61.11 & 60.57 & 56.24 & 2.61 & 11 & brown \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Environmental acoustic pattern classification of BCN WASN (adapted from [PERSON], [PERSON], and [PERSON] [5]). Figure 1: Map showing location and pattern category (indicated by different colors) of the nodes of the WASN of BCN. Category 1 in black, Category 2 in magenta, Category 3 in cyan and Category 4 in brown. allows for a deeper understanding and appreciation of the behavior patterns of different city areas. This can be valuable for residents, tourists, businesses, and city managers.