## 3 Results  
### Evolution of PM\({}_{10}\) Pollution during Traffic Restrictions and Normal Conditions  
The following analysis provides a detailed examination of PM\({}_{10}\) pollution behavior in Bucharest, Brasov, and Iasi during the traffic restrictions imposed in 2020 compared with 2022, which was considered a normal traffic year. Figure 2 presents the monthly averages of 24 h PM\({}_{10}\) mass concentrations derived from raw time series collected in 2020 and 2022 at traffic monitoring locations across all three cities. Figure 2: Monthly average PM\({}_{10}\) values for traffic stations from Bucharest (**a**,**b**), Brasov (**c**,**d**), and Iasi (**e**). The black line represents the PM\({}_{10}\) monthly mean for 2020; the red line represents the PM\({}_{10}\) monthly mean for 2022. Error bars represent SEM. At the Bucharest B-3 traffic station (Figure 2a), the highest PM\({}_{10}\) concentration in 2020 was recorded in March at 53.46 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), coinciding with the COVID-19 lockdown period. In comparison, the maximum concentration in 2022 was 38.58 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), recorded in November. Similar values for both years were observed only in June, corresponding to the Alert 1 restrictions. Starting in March, which marks the beginning of the national lockdown, there was a noticeable decrease in monthly average PM\({}_{10}\) concentrations in 2020 compared with 2022. The annual PM\({}_{10}\) trends for both years are similar, though with slight variations, with the minimum concentrations recorded in May 2020 (22.55 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)) and January 2022 (21.55 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)). Data from the B-6 traffic station (Figure 2b) reveal a maximum PM\({}_{10}\) concentration of 44.16 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\) in March 2020, while the maximum in 2022 was 38 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\) in November, consistent with the trends observed at the B-3 station. The lowest concentrations were recorded in May 2020 (19.85 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)) and January 2022 (19.22 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)). A clear decline in PM\({}_{10}\) concentrations was evident during 2020, particularly during the COVID-19 restrictions, mirroring the trend observed at the B-3 station. At the Brasov BV-1 traffic station (Figure 2c), the maximum PM\({}_{10}\) concentration in 2020 was 46.46 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), recorded in January before the COVID-19 restrictions during BAU the period. In 2022, the maximum concentration was 35.41 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), which was recorded in March. Similar values for both years were measured as early as June, corresponding to the Alert 1 restrictions. For the Brasov BV-3 traffic station (Figure 2d), the maximum PM\({}_{10}\) concentration in 2020 was 49.25 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), which was recorded in January before the COVID-19 restrictions during the BAU period. In 2022, the maximum concentration was 37.94 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\), which was recorded in March. Figure 2e shows averaged data from the Iasi IS-1 traffic station, with monthly PM\({}_{10}\) behavior like those in Bucharest. Lower concentrations were measured in 2022 compared with 2020. The lowest PM\({}_{10}\) concentrations were recorded in May 2020 (19.95 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)) and June 2022 (25.17 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\)). Due to missing data for the last five months of 2022, a comparison for the Alert 2 period is not possible. After analyzing the raw data for the years 2017 to 2019, it was discovered that the PM\({}_{10}\) values were significantly higher than those of the pandemic year 2020 [40] and comparable to the year 2022, which was also shown as an example in Figure 3.  
However, the direct comparison of monthly averages between these two years does not provide conclusive evidence of lower PM\({}_{10}\) concentrations in 2020 compared with 2022.