## 3 Results and Discussion
### Seasonal Variations  
PM\({}_{10}\) emissions during the analyzed period were higher in the winter season. In January, concentrations ranged from 11.92 ug/m\({}^{3}\) in Szczecin to 26.25 ug/m\({}^{3}\) in Katowiec (Figure 5). In December, the highest concentration was also recorded in Katowiec (35.85 ug/m\({}^{3}\)), and the lowest in Szczecin (15.19 ug/m\({}^{3}\)). This phenomenon is associated with increased combustion of fossil fuels for heating purposes during the winter season. In spring, PM\({}_{10}\) levels decrease compared to winter but remain relatively high in some locations. High concentrations of particulate matter in May and June were observed at two stations in Szczecin and Gdansk. Summer months typically show lower levels of particulate pollution, which may be due to unfavorable weather conditions (lack of wind, high humidity, or thermal inversion phenomena) that can limit the dispersion of pollutants in the atmosphere. Analyzing the year 2023 in relation to meteorological conditions, it can be seen that in Poland, the colder months of the year were humid and the warmer ones were dry. The only exception was the extremely humid August. January, February, and November were very humid months in terms of pluvial conditions, and October and December were extremely humid. May and September were very dry months, and June was a dry month. Particularly in coastal areas, variable conditions can cause pollutants to persist in the air for longer periods. Additionally, Gdansk and Szczecin are among the largest ports in Poland, and the summer season is associated with increased port and maritime activity. Cargo handling, exhaust emissions from vessels, and emissions from port operations can lead to periodic increases in particulate concentrations, especially under unfavorable weather conditions. Summer PM\({}_{10}\) concentrations are at their lowest levels for the year due to better dispersion conditions and reduced emissions from heating. In July, the lowest concentrations were recorded, ranging from 12.64 ug/m\({}^{3}\) (Olsztyn) to 19.41 ug/m\({}^{3}\) (Katowice). In this case, precipitation had no effect on the PM\({}_{10}\) value (Tables S7 and S8, Supplementary Materials). With the start of the heating season in the fall, PM\({}_{10}\) concentrations increased again. No statistically significant differences were observed between the cold and warm seasons for PM\({}_{10}\) (\(p<0.05\)), which was the result of higher concentrations in certain locations during the summer months due to specific processes, such as dusting or changes in the transport of pollutants, which is also observed in other Central European countries. For PAHs, the lowest concentrations were also observed during the summer season, while the highest values of total PAH concentrations were recorded in the winter season (34.50 ng/m\({}^{3}\)), followed by spring (16.19 ng/m\({}^{3}\)), autumn (14.22 ng/m\({}^{3}\)), and the lowest in summer (2.21 ng/m\({}^{3}\)) (Figure 3). A similar seasonal pattern was observed for BaP, with the highest concentration occurring in winter (6.20 ng/m\({}^{3}\)), followed by spring (4.81 ng/m\({}^{3}\)), autumn (2.71 ng/m\({}^{3}\)), and summer (0.33 ng/m\({}^{3}\)). [PERSON] et al. (2007) studied the air pollution levels of PAHs in Xiamen, where the BaP concentration ranged from 0.04 ng/m\({}^{3}\) to 1.5 ng/m\({}^{3}\). According to EU standards, as outlined in Directive 2004/107/EC [24], the permissible annual concentration of benzo(a)pyrene in the air was not exceeded only during the summer season. Higher concentrations of PAHs in the molecular phase in winter/autumn than in summer are probably related to lower temperature, weaker radiation intensity, and more emission sources. Figure 5: Concentration of PM\({}_{10}\) and individual PAHs; (**a**) station 1; (**b**) station 2; (**c**) station 3; (**d**) station 4; (**e**) station 5; (**f**) station 6; (**g**) station 7; (**h**) station 8.