## 3 Results and Discussion
In comparison, other areas with a lot of road traffic and common use of solid fuels for home heating showed more consistent metal levels that followed clearer seasonal and weather patterns, like thermal inversions and low air movement. It should also be noted that the concentration of the analysed pollutants--Pb, Ni, Cd, As, and \(\Sigma\)PAHs--can reach 1.69 mg per gram of PM\({}_{10}\) (Figure 3). An extreme case was recorded in Upper Silesia in 2022, where the Pb content alone reached 0.97 mg per gram of PM\({}_{10}\). Unfortunately, PM\({}_{10}\) in Upper Silesia is rich in heavy metals and PAHs, with total pollutant concentrations ranging from 1.26 to 1.69 mg per gram. Similar pollutant levels, exceeding 1000 ppm, were observed in Wroclaw (2018-2021) and Szczecin (2018-2019). In the case of Szczecin, the elevated concentration levels observed during this period can be attributed to the fact that measurements covered less than 80% of the annual total. In general, across Poland, lead and polycyclic aromatic hydrocarbons constitute the largest share of pollutants in PM\({}_{10}\). Based on cluster analysis using [PERSON]'s method, the agglomerations were grouped according to the similarity of the PM\({}_{10}\) and PM\({}_{10}\)-bound Pb, Ni, Cd, As and PM\({}_{10}\)-bound PAH concentrations for the period 2018-2022. The application of this method made it possible to distinguish three statistically distinct groups of agglomerations: cluster I--Upper Silesia, Wroclaw; cluster II--Warsaw, Lodz, Lublin, Cracow; cluster III--Tricity, Szczecin (Figure 4). This procedure made it possible not only to confirm cluster differences but also to determine the degree of variability, the level of environmental pressure, and potential emission sources. The first cluster includes agglomerations: Wroclaw and Upper Silesia which have much higher pollution levels, especially for lead (14.97 \(\pm\) 7.27 \(\mathrm{rg}\cdot\mathrm{m}^{-3}\)), arsenic (1.73 \(\pm\) 0.60 \(\mathrm{ng}\cdot\mathrm{m}^{-3}\)), cadmium (0.49 \(\pm\) 0.28 \(\mathrm{ng}\cdot\mathrm{m}^{-3}\)) and \(\Sigma\)PAHs (15.53 \(\pm\) 6.44 \(\mathrm{ng}\cdot\mathrm{m}^{-3}\)) with average concentrations of these metals being 2-3 times greater than in clusters II and III. These agglomerations are characterised by the highest pollution levels and high daily and seasonal variability. This situation may be due to the strong industrialisation of these regions, the high proportion of low emissions, and the significant impact of traffic emissions. Similar results have been obtained in studies conducted in Romania, Malaysia, and China, where urban agglomerations with a dominant share of industrial and road emissions showed high levels of metals in \(\mathrm{PM}_{10}\)[102; 103; 104]. The second cluster is formed by agglomerations: Warsaw, Cracow, Lodz, and Lublin. Although the average \(\mathrm{PM}_{10}\) concentrations (29.36 \(\pm\) 6.57 \(\mathrm{ug}\cdot\mathrm{m}^{-3}\)) are comparable to group I, the levels of metals and \(\Sigma\)PAHs are noticeably lower. This variation indicates a different structure of the pollution profile--the dominant role is most likely played by traffic-related emissions, low emissions during the winter season, and dense urban development. Despite geographic differences, the similarity of urban layout and local emission sources leads to similar pollution levels and structure. Other researchers [82; 105; 106; 107] found similar trends, showing that the \(\mathrm{PM}_{10}\) levels were mainly influenced by local factors like building designs and transportation intensity, leading to a consistent pattern in urban areas where road emissions are the main source. The third cluster is formed by the Szczecin and Tricity agglomerations, which show substantial similarity among themselves, as well as significant distinctiveness in relation to the other cities.