## 3 Air Quality Assessment Methodology
### Human Health Risk Index  
The health risk generated by the effects of pollutants is realized by assessing the carcinogenic and non-carcinogenic risks, following several stages presented below. The applicability of the formulas and the scenario used can be found in Section 4. There was another formula used for this index, which also included the PEF parameter (pollution emission rate) but according to the EPA the use of that equation is no longer recommended. Thus, the new formula does not consider this factor anymore. The first step is to determine the daily inhaled dose according to the updated Equation (3) [37; 38]:  
\[\mathrm{ADD_{inh}}=\frac{\mathrm{C_{i}}\times\mathrm{InhR}\times\mathrm{ET} \times\mathrm{EF}\times\mathrm{ED}}{\mathrm{BW}\times\mathrm{AT}} \tag{3}\]  
Equation (3). Average daily inhaled dose formula.  
where:  
* \(\mathrm{ADD_{inh}}\left(\frac{\mathrm{mg}}{\mathrm{kg}},\frac{1}{\mathrm{day}}\right)\): average daily inhaled dose;
* \(\mathrm{C_{i}}\) \(\left(\frac{\mathrm{mg}}{\mathrm{m}^{3}}\right)\): air concentration of a pollutant--in our case, we used the value of the aggregate index for each individual pollutant, after converting all units of measure into \(\mathrm{mg/m^{3}}\), in order to have the same measurement unit, according to the formula;
* \(\mathrm{InhR}\left(\frac{\mathrm{m^{3}}}{\mathrm{hour}}\right)\): volume of inhaled air;
* \(\mathrm{ET}\) \(\left(\frac{\mathrm{hours}}{\mathrm{day}}\right)\): exposure time;
* \(\mathrm{EF}\) \(\left(\frac{\mathrm{days}}{\mathrm{year}}\right)\): frequency of exposure;
* \(\mathrm{ED}\) (years): duration of exposure;
* \(\mathrm{BW}\) (kg): body weight;
* \(\mathrm{AT}\) (days): \(\mathrm{ED}\) \(\times\) 365 (days)--average exposure time.  
Furthermore, in order to characterize the non-carcinogenic risks, the hazard coefficient (HQ) was determined, the calculation formula of which is represented by Equation (4) [39]:  
\[\mathrm{HQ}\ =\frac{\mathrm{ADDinh}}{\mathrm{RfD}} \tag{4}\]  
Equation (4). Hazard coefficient formula.  
where:  
* HQ: hazard coefficient;
* \(\mathrm{ADD_{inh}}\): daily dose that can be inhaled;
* RfD: daily reference dose (as shown in Table 3)--the values were taken from the IRIS and RAIS databases [40; 41].  
\begin{table}
\begin{tabular}{c c} \hline
**PLI Scale** & **Classification** \\ \hline \(\mathrm{PLI}<1\) & Unpolluted air \\ \(1\leq\mathrm{PLI}<2\) & Unpolluted to moderately polluted \\ \(2\leq\mathrm{PLI}<3\) & Moderately polluted \\ \(3\leq\mathrm{PLI}<4\) & Moderately to highly polluted \\ \(4\leq\mathrm{PLI}<5\) & Highly polluted \\ \(\mathrm{PLI}\geq 5\) & Very highly polluted (excessive) \\ \hline \end{tabular}
\end{table}
Table 2: Classification of the pollution load index.  
Equation (5) presents the calculation formula for the hazard index (HI), with the help of which the impact generated by the non-carcinogenic effects can be estimated [39]:  
\[\text{HI }=\sum_{n=1}^{i}\text{HQ}n \tag{5}\]  
Equation (5). Hazard index formula.  
Thus, the hazard index is characterized as follows:  
* If HI \(<\) 1, there are no health risks;
* If HI \(>\) 1, there are possible health risks, depending on the value of the index--the higher it is, the higher the risk [39].