## 3 Results and Discussion  
Poland has experienced excessive air pollution for decades. According to the Institute of Environmental Protection--National Research Institute (IEP-PIB), a downward trend in the concentrations of PM\({}_{10}\) and other pollutants has been observed since 2010, affecting both annual and daily averages [78]. However, current concentrations of PM\({}_{10}\), PM\({}_{10}\)-bound PAHs, and PM\({}_{10}\)-bound metals (Pb, Cd, Ni, and As) remain significantly elevated, particularly in urban areas such as Upper Silesia, Cracow, Lodz, and Wroclaw [61]. The Concentration of PM\({}_{10}\) and PM\({}_{10}\)-Bound PAHs, and PM\({}_{10}\)-Bound Metals  
In major Polish urban agglomerations between 2018 and 2022, the annual mean PM\({}_{10}\) concentrations ranged from 17.42 to 43.20 \(\upmu\)g m\({}^{-3}\), depending on location and year (Table S3). Despite the observed downward trend recently, these values considerably exceed those reported in most other European countries [79; 80]. The results of other detailed studies conducted in various Polish cities confirm similar trends, indicating a decrease in air pollutant concentrations [81; 82]. In 2022, Poland's annual average PM\({}_{10}\) concentration reached 23.99 \(\upmu\)g m\({}^{-3}\), whereas in Slovakia, Lithuania, the Czech Republic, and Latvia--where these pollutants are also prevalent--the values were 20.91, 19.75, 19.00 and 18.09 \(\upmu\)g m\({}^{-3}\), respectively [54]. The highest multi-year mean PM\({}_{10}\) concentration (average of annual values for the period 2018-2022) was recorded in the Lodz (35.04 \(\upmu\)g\(\cdot\)m\({}^{-3}\)), Cracow (33.75 \(\upmu\)g\(\cdot\)m\({}^{-3}\)) and Upper Silesia (32.31 \(\upmu\)g\(\cdot\)m\({}^{-3}\)) agglomerations. The lowest levels were recorded in the Szczecin (19.73 \(\upmu\)g \(\times\) m\({}^{-3}\)) and Tricity (21.13 \(\upmu\)g \(\times\) m\({}^{-3}\)) agglomerations. In 2018, the average annual concentrations in the agglomerations of Cracow, Lodz and Upper Silesia exceeded the national limit value of 40 \(\upmu\)g\(\cdot\)m\({}^{-3}\)[83]. Compared to the WHO guideline of 15 \(\upmu\)g \(\times\) m\({}^{-3}\), exceedances occurred at all monitoring stations in all years (Figure 2). Additionally, the regulatory threshold of 50 \(\upmu\)g/m\({}^{3}\) is exceeded on more days per year than is permitted [83]. The maximum average daily concentration recorded in Cracow was 190.2 \(\upmu\)g \(\times\) m\({}^{-3}\), which is almost four times higher than the permissible limit. This highlights the seriousness of acute pollution episodes. Cracow's specific location in the Vistula River valley naturally weakens the influx of westerly winds, which are dominated by hills to the west. Consequently, wind speeds in the city tend to be much lower than in the surrounding areas, which limits the city's natural ventilation [84; 85]. In addition, a temperature inversion often forms over Cracow, leading to higher concentrations of PM\({}_{10}\), particularly on windless, cold days, mainly during the autumn and winter. While the presence of the Vistula River has a positive effect on local aeration, it is unable to completely negate the effects of the inversion and restricted air circulation. Poland has consistently recorded the highest average annual concentrations of B[a]P of all European countries. In 2022, the concentration of this representative compound from the PAH group reached 2.41 ng\(\cdot\)m\({}^{-3}\), whereas in Slovakia, the Czech Republic, and Croatia, where B[a]P levels are also elevated, the values were 1.51, 1.19, and 0.87 ng\(\cdot\)m\({}^{-3}\), respectively [54]. The presented study found that all major urban areas in Poland experienced peak B[a]P concentrations in 2018, ranging from 1.50 ng\(\cdot\)m\({}^{-3}\) in Warsaw to 4.89 ng\(\cdot\)m\({}^{-3}\) in Cracow, with similarly high levels observed in Upper Silesia (4.73 ng\(\cdot\)m\({}^{-3}\)).