## 3 Results and Discussion
### Temporally Dependence of Pollutant Concentrations  
The main result of the cross-correlation analysis is that the pollutant concentration trend of Roma Green Band is the same in the other suburbs or provinces areas. For this reason, the following analysis is focused on the mean values of contaminants of each station of Roma Green Band, that will be representative of the pollutant concentrations trend in all the monitoring station of the Lazio region. Figure 2 shows the trends from 2006 to 2015 of pollutant concentrations in Rome. In this analysis, the values of the period from July to August aren't taken into account, because the urban traffic values are very low due to the summer holidays that lead people outside the cities. The blue line of Figure 2 identifies the average pollutant concentration in winter taking into consideration the data from November to April in which the heating systems are turned on (based on DPR n.412/1993 [52]). The red line referred to the average pollutant concentration in spring and autumn in which the heating systems are turned off (period from April to June and from September to November). It is possible to notice that the values of most of the pollutants are decreasing in the years due to the update of the laws of pollutant emissions. Only the ozone concentration has a rising trend during the years and has a higher value in spring and autumn than in winter, because of its dependence on solar radiation. Considering the difference of winter and spring-autumn values there is an average percentage deviation of about 58.8% with a range from 20.1% to 127.4% excluding the [O\({}_{3}\)] that have an opposite trend despite the other pollutant concentrations. This result indicates that there is an average pollutant level increase of 58.8% from spring-autumn, in which the main anthropogenic pollutant source is urban traffic, to winter where there are heating systems are turned on. This highlights the importance to take some policy strategies to decrease the pollutant emissions from heating systems. Focusing on all the pollutant concentrations excluding the [O\({}_{3}\)], that have an opposite trend despite them, the average difference of pollutant level year after year is about \(-1.6\%\) for winter and \(-4.1\%\) for spring-autumn with a range from 1.3% to \(-3.2\%\) in winter and from \(-1.4\%\) to \(-6.2\%\) in spring-autumn. These results indicate that there is a decrease year after year of pollutant concentrations both in winter and in spring-autumn. Nevertheless, the range for spring-autumn, which is directly related to urban traffic, has only negative \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & **[C\({}_{6}\)H\({}_{6}\)]** & **[CO]** & **[NO\({}_{\chi}\)]** & **[NO\({}_{2}\)]** & **[NO]** & **[O\({}_{3}\)]** & **[SO\({}_{2}\)]** & **[PM\({}_{10}\)]** & **[PM\({}_{2,5}\)]** \\ \hline Average & 0.43 & 0.45 & 0.59 & 0.59 & 0.56 & 0.75 & 0.18 & 0.88 & 0.87 \\ Maximum & 0.69 & 0.72 & 0.82 & 0.78 & 0.81 & 0.93 & 0.50 & 0.96 & 0.97 \\ Minimum & 0.13 & 0.08 & 0.15 & 0.23 & 0.05 & 0.31 & \(-0.24\) & 0.57 & 0.72 \\ \hline \end{tabular}
\end{table} 
Table 13: Cross-correlation average, maximum and minimum values between Roma Green Band and suburbs or province stations of all pollutant concentrations in 2015. \begin{table}
\begin{tabular}{c c c c c c} \hline  & **Monitoring** & **From July to** & **From April** & **From September** & **From November** \\  & **Station** & **August** & **to June** & **to November** & **to April** \\ \hline  & Guidonia & 0.93 & 0.90 & 0.97 & 0.92 \\  & C. di Guido & 0.89 & 0.89 & 0.95 & 0.95 \\  & Cavaliere & 0.91 & 0.89 & 0.97 & 0.94 \\  & Malagrotta & 0.75 & 0.72 & 0.86 & 0.93 \\ \hline  & Latina & 0.87 & 0.84 & 0.92 & 0.76 \\  & Frosinone & 0.87 & 0.85 & 0.91 & 0.87 \\  & Rieti & 0.84 & 0.82 & 0.91 & 0.80 \\  & Viterbo & 0.87 & 0.83 & 0.85 & 0.79 \\ \hline \end{tabular}
\end{table}