## 2 Materials and Methods
Since the period in which the instruments gathered data was exceptionally rainy and with numerous days with considerable cloudiness, only the days when the cloud cover was less than 4/8 were considered. Cloud cover data were collected from Iowa Environmental Mesonet. MODIS (Moderate Resolution Imaging Spectroradiometer) satellite imagery was used to fill the existing flaws in the data. Through these images, if at 12:00 p.m., more than 4/8 of the sky was covered with clouds, that day was excluded. For the analysis of air temperature data, hourly averages were calculated on each day, to understand the behavior of this variable in the study area. The collected data allowed comparing the registered air temperature in two streets with opposite exposures to the prevailing wind direction in Lisbon (north and northwest). Using an infrared thermal camera (FLIR B425) the surface temperatures of the facades and different materials were collected. Table 2 summarizes the input parameters of the thermal camera on all the days that fieldwork was carried out. Thermal images were collected in 2018 at different times: in the winter, on February 21, in the spring, on June 18, and in the summer, on July 7. In the summer period, images were collected at four different times of the day: 09:00 a.m., 1:00 p.m., 3:00 p.m., and 7:00 p.m. Regarding the afternoon period we chose two different times to collect images, to \begin{table}
\begin{tabular}{c c c c c c} \hline
**Groups of Buildings** & **Exposure of the Facades** & **Pink** & **White** & **Gray** & **Windows** \\ \hline \multirow{2}{*}{1} & East & 36.7\% & 39.8\% & - & 23.5\% \\  & South & 80\% & 5\% & - & 15\% \\ \hline
2 & West & 52\% & 39\% & - & 9\% \\ \hline
3 & North & 70\% & 10\% & 5 & 15\% \\ \hline \end{tabular}
\end{table} 
Table 1: Facades covered by different colors and materials (as a % of the total facades). Figure 3: Thermo-hygrograph (Hobo No 3—see Figure 3) in Telheiras. register the temperature variation from when the air temperature is higher and when the incident solar radiation is lower. Since different urban surfaces present different emissivity values, we chose to collect all images with a constant value of 0.98. Given the characteristics of the studied streets, the distance between the camera and the facades was \(\pm\)25 m to collect the thermal images of the facades with exposure to east and west. In the case of north and south facades, the distance was \(\pm\)17 m. To guarantee the stability of the thermal infrared camera, a tripod was used (around 1.67 m high). The ground floor was not included, since it was covered by windows and glazed doors, and because there were always parked cars in front of them (heat sources that can influence the obtained measurements). To collect the thermal images, the scheme shown in Figure 4 was followed. In addition to the facades, thermograms were collected from different surfaces in the study area: asphalt, tile floor, and sidewalk. All collected thermograms (summer period) were analyzed using FLIR Tools software [19]. It was decided not to consider the values registered in windows, since, being translucent surfaces, they present different emissivity values when compared to the materials used in the facades. In addition, the temperature of these surfaces can be influenced by the interior of the apartments. The decision to not consider these surfaces also depended on the existence of different types of conditions where there were windows with interior or exterior blinds. Finally, we also did not consider the values obtained in \"strange\" objects that could be framed in the thermal images, such as lamps, plants on the balconies of each apartment, and people who were sometimes outside. In order to be able to compare different thermograms, as well as to perceive in which colors and types of surfaces the highest and lowest temperatures were recorded, two scales were used: one for the thermal images of the facades and one for the horizontal surfaces.