## 3 Results  
### Air Pollution Concentration in Lisbon  
All air pollutants present a seasonal pattern with high winter levels and low summer levels--only summer and winter are shown because these seasons have the extreme climatic conditions considering temperature and humidity--except in the cases of O\({}_{3}\) and PM\({}_{10}\) (Table 6). In O\({}_{3}\), the summer higher values are explained by adequate weather conditions for its formation (sunlight, warm temperatures, and high emission of precursor pollutants (nitrogen oxides and volatile organic compounds) lead to high levels of this atmospheric oxidant during the summer season [107]. As for PM\({}_{10}\) the average and standard deviation values are higher in wintertime; however, the minimum and maximum values are higher in summertime. This variation can be justified by the seasonality of PM\({}_{10}\), which sees an increase in dust production in the spring and summer months compared to winter months (especially in dry years), this is due to the intrusion of Saharan particles. Also, another source of particulate matter is the natural increase in atmospheric moisture (water vapor) during the summer [108]. In general, differences between minimum and maximum are quite large, as was expected, consequently standard deviations are high, nonetheless the average and median are similar indicating a data normality. When analyzing the values in Table 7 according to the European air quality guidelines suggested in Directive 2008/50/EC, it is possible to verify that, over the period in the study: (1) daily averages of PM\({}_{10}\) concentrations exceeded the limit of 50 \(\upmu\)g m\({}^{-3}\); (2) O\({}_{3}\) concentrations in Amadora and Lisbon \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Pollutant**} & \multirow{2}{*}{**Municipality**} & **Period:** & \multirow{2}{*}{\(\overline{\mathbf{X}}\)} & \multirow{2}{*}{\(\sigma\)} & **Minimum** & **Maximum** \\  & & **2005-2015** & & & & \\ \hline \multirow{8}{*}{PM\({}_{10}\)} & Amadora & Summer/winter & 23.2/30.5 & 13.9/15.4 & 1.1/1.8 & 206.1/100.0 \\  & & total & 26.5 & 14.4 & 0.0 & 206.1 \\  & Lisbon & Summer/winter & 30.7/35.1 & 16.3/18.1 & 8.0/4.7 & 222.4/117.9 \\  & & total & 32.0 & 15.5 & 4.7 & 222.4 \\  & & Summer/winter & 24.6/29.6 & 13.8/15.2 & 4.0/2.6 & 223.6/109.0 \\  & & total & 26.5 & 13.4 & 2.6 & 223.6 \\  & & Summer/winter & 61.0/42.6 & 17.1/19.3 & 15.8/2.8 & 123.2/92.7 \\  & & total & 52.3 & 21.0 & 1.6 & 123.2 \\  & & Summer/winter & 60.9/41.7 & 17.0/18.2 & 18.3/4.0 & 119.5/87.0 \\  & & total & 52.5 & 20.4 & 3.6 & 119.5 \\  & & Summer/winter & 63.0/48.5 & 16.0/17.0 & 22.5/3.1 & 129.7/99.7 \\  & & total & 57.1 & 17.8 & 3.1 & 129.8 \\  & & Summer/winter & 24.5/41.8 & 15.7/19.6 & 4.3/4.0 & 106.1/102.1 \\  & & total & 34.2 & 19.1 & 4.0 & 112.7 \\ NO\({}_{2}\) & Lisbon & Summer/winter & 29.8/44.7 & 14.3/17.2 & 8.5/9.3 & 100.5/111.0 \\  & & total & 38.1 & 16.9 & 8.5 & 122.8 \\  & & Summer/winter & 21.8/35.2 & 10.6/15.3 & 1.8/4.8 & 78.4/98.3 \\  & & total & 29.4 & 14.5 & 1.8 & 125.2 \\  & & Summer/winter & 12.5/32.0 & 10.0/33.0 & 0.0/1.2 & 76.5/278.1 \\  & & total & 23.1 & 26.2 & 0.0 & 278.1 \\ NO & Lisbon & Summer/winter & 11.8/30.4 & 6.4/26.6 & 0.6/0.7 & 53.2/156.0 \\  & & total & 21.0 & 20.4 & 0.6 & 156.0 \\  & & Summer/Winter & 10.0/22.8 & 5.4/20.0 & 0.3/1.6 & 39.6/164.6 \\  & & Total & 16.3 & 15.3 & 0.3 & 164.7 \\  & & Summer/winter & 0.3/0.5 & 0.1/0.3 & 0.0/0.2 & 1.3/1.5 \\  & & total & 0.4 & 0.2 & 0.0 & 1.5 \\ CO & Lisbon & Summer/winter & 0.2/0.4 & 0.1/0.1 & 0.1/0.1 & 1.2/1.2 \\  & & total & 0.3 & 0.1 & 0.1 & 1.2 \\  & & Summer/winter & 0.2/0.3 & 0.1/0.2 & 0.1/0.1 & 0.9/1.1 \\  & & total & 0.3 & 0.1 & 0.07 & 1.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary statistics of air pollutants’ daily average concentrations (\(\upmu\)g m\({}^{-3}\), CO is in mg m\({}^{-3}\)) for the 2005–2015 period.