## 4 Results and Discussion  
### Air Pollution Index  
The results of the air pollution index calculated for the last 11 years, for four cities in Romania, are presented in Table 4.  
According to Table 2 and the results on the air pollution load index in Table 3, the air quality in the four cities falls into the \"unpolluted\" scenario. This is possible because all values for this index are less than 1, even if the alert threshold was exceeded in some situations. At the same time, it is important to mention that in this paper, only three pollutants (PM\({}_{2.5}\), As, CO) were considered, but in one city, they are much more diversified. Therefore, the highest value calculated for the air pollution load index was found in lasi, while Brasov, has the lowest value. The value of the pollution load index depends a lot on the specifics of the area under analysis. This is also supported by a 2022 study on the risk assessment of potentially toxic elements in the Indonesia region. Thus, in this case, values higher than 1 were obtained for PLI, this value increasing more and more with the proximity to industrial areas, being also influenced by winds, which transport the dust to populated areas [42].  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**City** & **Indicator** & \begin{tabular}{c} **AT\({}_{\text{Adults}}\)** \\ **(Days)** \\ \end{tabular} & \begin{tabular}{c} **AT\({}_{\text{Children}}\)** \\ **(Days)** \\ \end{tabular} & \
\begin{tabular}{c} **ADD\({}_{\text{Inh Adults}}\)** \\ **(mg/kg/Day)** \\ \end{tabular} &
\begin{tabular}{c} **ADD\({}_{\text{Inh Children}}\)** \\ **(mg/kg/Day)** \\ \end{tabular} & **RfD** & **HQ\({}_{\text{Adults}}\)** & **HQ\({}_{\text{Children}}\)** \\ \hline \multirow{3}{*}{Brasov} & PM\({}_{2.5}\) & \multirow{3}{*}{8760} & \multirow{3}{*}{2190} & 0.00112 & 0.00415 & 0.035 & \multirow{3}{*}{0.03200} & \multirow{3}{*}{0.11857} \\  & CO & & & 0.01720 & 0.06351 & 9 (RAIS) & 0.00191 & 0.00705 \\  & As & & & 0.22942 \(\times\)\(10^{-7}\) & 0.84690 \(\times\)\(10^{-7}\) & 0.0003 & \multirow{3}{*}{0.00007} & \multirow{3}{*}{0.00028} \\  & PM\({}_{2.5}\) & \multirow{3}{*}{8760} & \multirow{3}{*}{2190} & 0.00114 & 0.00421 & \multirow{3}{*}{0.035 (RAIS)} & \multirow{3}{*}{0.03257} & \multirow{3}{*}{0.12028} \\  & CO & & & 0.01656 & 0.06116 & 9 (RAIS) & 0.00184 & 0.00679 \\  & As & & & 0.34414 \(\times\)\(10^{-7}\) & 1.27035 \(\times\)\(10^{-7}\) & 0.0003 & \multirow{3}{*}{0.00011} & \multirow{3}{*}{0.00042} \\  & PM\({}_{2.5}\) & \multirow{3}{*}{8760} & \multirow{3}{*}{2190} & 0.00145 & 0.00536 & \multirow{3}{*}{0.035 (RAIS)} & \multirow{3}{*}{0.04142} & \multirow{3}{*}{0.15314} \\  & CO & & & 0.01784 & 0.06587 & 9 (RAIS) & 0.00198 & 0.00731 \\  & As & & & 0.50984 \(\times\)\(10^{-7}\) & 1.88200 \(\times\)\(10^{-7}\) & 0.0003 & \multirow{3}{*}{0.00016} & \multirow{3}{*}{0.00062} \\  & PM\({}_{2.5}\) & \multirow{3}{*}{8760} & \multirow{3}{*}{2190} & 0.00093 & 0.00346 & \multirow{3}{*}{0.035 (RAIS)} & \multirow{3}{*}{0.02657} & \multirow{3}{*}{0.09885} \\  & CO & & & 0.01784 & 0.06587 & 9 (RAIS) & 0.00198 & 0.00731 \\  & As & & & 0.59269 \(\times\)\(10^{-7}\) & 2.18783 \(\times\)\(10^{-7}\) & 0.0003 & \multirow{3}{*}{0.00019} & \multirow{3}{*}{0.00072} \\  & & & & & (IRIS) & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Calculation of the average daily dose (ADD\({}_{\text{inh}}\)) and the hazard coefficient (HQ).  
The pollution sources in the case of PM\({}_{2.5}\), can be mentioned as the incomplete burning of fuels by car engines, combustion processes (such as waste burning or residential heating), some industrial processes, and also road wear or construction sites. The incomplete combustion of fossil fuels, as well as traffic or some industrial processes, is also a source of carbon monoxide and arsenic emissions [34].