## 4 Results and Discussion
### Human Health Risk Index  
In this paper, the determination of the health risk index was carried out following the method presented by USEPA [38; 43]. The specific parameters (InhR and ED) used to quantify the health hazards are in accordance with the literature. According to the previous studies, the EF was considered 350 days/year and ET 8 h/day [44; 45; 46]. For this purpose, two scenarios were considered: the first corresponded to adults weighing 65 kg (BW\({}_{\text{Adults}}\)), and the second to children weighing 15 kg (BW\({}_{\text{Children}}\)). The results are presented in Tables 3 and 5. After calculating the indices presented in the previous tables, the determination of the hazard index followed, the results of which can be found in Table 6. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**City** & **Indicator** & **MAC** & **C\({}_{\text{i}}\)** & **PI** & **PLI** \\ \hline \multirow{3}{*}{Brasov} & PM\({}_{2.5}\) & 20 & 17.65 & 0.88 & 0.117 \\  & CO & 10 & 0.27 & 0.03 & (\(<\)1) \\  & As & 6 & 0.36 & 0.06 & (\(<\)1) \\ \hline \multirow{3}{*}{Cluj-Napoca} & PM\({}_{2.5}\) & 20 & 17.90 & 0.90 & 0.134 \\  & CO & 10 & 0.26 & 0.03 & (\(<\)1) \\  & As & 6 & 0.54 & 0.09 & (\(<\)1) \\ \hline \multirow{3}{*}{Iasi} & PM\({}_{2.5}\) & 20 & 22.81 & 1.14 & 0.164 \\  & CO & 10 & 0.28 & 0.03 & (\(<\)1) \\  & As & 6 & 0.80 & 0.13 & (\(<\)1) \\ \hline \multirow{3}{*}{Timisoara} & PM\({}_{2.5}\) & 20 & 14.74 & 0.74 & 0.153 \\  & CO & 10 & 0.28 & 0.03 & (\(<\)1) \\ \cline{1-1}  & As & 6 & 0.93 & 0.16 & (\(<\)1) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Calculation of the air pollution load index in Brasov, Cluj-Napoca, Iasi, and Timisoara. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**City** & **Indicator** & **C\({}_{\text{i}}\) (mg/m\({}^{3}\))** & \begin{tabular}{c} **InhR\({}_{\text{Adults}}\)** \\ **(m\({}^{3}\)/h)** \\ \end{tabular} & \begin{tabular}{c} **InhR\({}_{\text{Children}}\)** \\ **(m\({}^{2}\)/h)** \\ \end{tabular} & \begin{tabular}{c} **EF** \\ **(Days/Year)** \\ \end{tabular} & \begin{tabular}{c} **ED\({}_{\text{Adults}}\)** \\ **(Years)** \\ \end{tabular} & \
\begin{tabular}{c} **ED\({}_{\text{Children}}\)** \\ **(Years)** \\ \end{tabular} &
\begin{tabular}{c} **ET (h/Day)** \\ \end{tabular} \\ \hline \multirow{3}{*}{Brasov} & PM\({}_{2.5}\) & 0.01765 & & & & & & \\  & CO & 0.27 & 0.54 & 0.46 & 350 & 24 & 6 & 8 \\  & As & \(3.6\times 10^{-7}\) & & & & & & \\ \hline \multirow{3}{*}{Cluj-Napoca} & PM\({}_{2.5}\) & 0.01790 & & & & & & & \\  & CO & 0.26 & 0.54 & 0.46 & 350 & 24 & 6 & 8 \\  & As & \(5.4\times 10^{-7}\) & & & & & & \\ \hline \multirow{3}{*}{Iasi} & PM\({}_{2.5}\) & 0.02281 & & & & & & & \\  & CO & 0.28 & 0.54 & 0.46 & 350 & 24 & 6 & 8 \\ \cline{1-1}  & As & \(8\times 10^{-7}\) & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Specific values for the calculation of the health risk index. The graphical representation for the health risk index can be found in Figure 9 for all four cities, both for adults and children. We noticed that all values were below 1, which means that there are no health risks [47]. One difference is that in the case of children, the index is higher than that obtained for adults, which means that they are more exposed to the negative effects generated by air pollution [47]. This is also supported by the results of other studies with the same theme, with varying results, but always obtaining higher values of the index for children compared to adults, indicating children's vulnerability to the negative effects of pollution [48; 49]. Previous studies reported similar results in the case of HI, also highlighting the cumulative effect of heavy metals (arsenic, lead) and the low degree of tolerance to pollutants of children, as well as the variation of the index depending on the activities carried out in the area or the difference between the urban and rural environment [50]. Evaluations carried out in 2021 show higher values of the index in the urban environment compared to the rural area [51].