## 3 Results
### Human Health Risk  
The hazard quotient (HQ) values were estimated for the adult group to determine the non-carcinogenic risk associated with PM\({}_{10}\) in the ambient air of Bucharest, Brasov, and Iasi. The human health risk was calculated based on exposure concentrations from 2017 to 2022. Two scenarios are presented in Figure 5 and Figure S2 considering the new WHO recommendations [45] and EU limit for PM\({}_{10}\). Higher values were observed when the toxicity value was set according to the 2021 WHO recommendation for PM\({}_{10}\) (HQ2). In line with previous studies, values greater than 1 are associated with potential non-carcinogenic chronic health risks [40; 41]. Figure 5a illustrates an example of the human health risk assessment, focusing on the Bucharest metropolitan area, using data from traffic stations B-3 and B-6, as well as background station B-8.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Period/Station** & **B-3** & **B-6** & **BV-1** & **BV-3** & **IS-1** \\ \hline BAU & 0.750 & 0.057 & 0.129 & 0.621 * & 0.167 \\ LOCKDOWN & 0.001 * & 0.022 * & 0.022 * & 0.000 * & 0.000 * \\ ALERT 1 & 0.932 & 0.006 * & 0.008 * & 0.000 * & 0.436 * \\ ALERT 2 & 0.038 * & 0.000 * & 0.189 & 0.016 * & 0.030 * \\ \hline \end{tabular}
\end{table}
Table 5: The \(p\)-value of the Kruskal-Wallis test between the year 2020 and the period of Business as Usual in the reference years 2017–2019 and 2021–2022, through the ratio of the traffic stations and the background stations from the metropolitan cities of Bucharest, Brasov, and Iasi. Asterisks indicate statistical significance.  
Figure 5: Hazard quotient (HQ2) in Bucharest, WHO recommendations.  
In accordance with EU regulations, the hazard quotient (HQ1) values for Bucharest were calculated as follows: between 0.69 and 1.14 in 2017, 0.62 and 1.16 in 2018, 0.62 and 1.13 in 2019, 0.58 and 0.97 in 2021, and 0.52 and 0.94 in 2022, and these are presented in Figure S2. At station B-3, the reference value was exceeded in February and August 2017, April, August, and October 2018, and October 2019. However, it is noteworthy that the reference level was not surpassed in the years following the COVID-19 pandemic. Similarly, at station B6, the benchmark was exceeded in April and October 2018 and November 2019, with the same pattern observed at station B-3 in 2021 and 2022. In Bucharest, during 2020, HQ1 > 1 was obtained in January, before the implementation of COVID-19 restrictions, and in March.  
In the worst-case scenario (HQ2), determined using the WHO recommendation, the benchmark was exceeded every month for traffic station B-3 in Bucharest. A similar pattern was observed at station B-6, with a few minor exceptions in April 2017, May and July 2020, and January 2022. Furthermore, exceedances were recorded at the background station in at least two of the months examined. For station B-3, the HQ2 values ranged from 1.03 to 2.28 in the research years, with a maximum value of 2.56 in March 2020. For station B-6, the HQ2 values ranged from 0.92 to 2.24. At the background station, HQ2 values of less than 1 were recorded in 8 months during 2020, indicating lower pollution levels.  
The positions of stations B-3 and B-6 differ significantly, with B-3 located next to a large avenue and B-6 situated in a canyon-like area surrounded by tall buildings. In accordance with EU regulations and WHO recommendations, it is observed that station B6 exhibits lower values of HQ < 1. Although PM\({}_{10}\) levels are mostly within the legislative limits, the high HQ computed based on the WHO toxic limit reveals a serious potential risk for chronic pathologies. In 2020, lower HQ values were obtained in both scenarios, suggesting a potential benefit from traffic restrictions. However, these reductions were not sufficient to significantly improve the potential risk related to non-carcinogenic chronic health effects. For all cities, a higher risk is recorded during the cold season, which is associated with an increased concentration of PM\({}_{10}\).