## 3 Results and Discussion
### Seasonal Variations and Congeners' Contributions  
In Tables 1-4, the results were divided by their seasonality in order to reveal any possible variation between measurements during cold and warm periods. The Mann-Whitney test was applied in each dataset for this purpose. Regarding PAHs, seasonal variations were observed for PAHs with 4 or more rings in their molecules. These high molecular weight PAHs presented significantly higher concentrations during cold months (\(p<0.05\)). PAHs' seasonal variations are described also in Figure 2 and it is worth mentioning that \(\Sigma\)PAHs was 4 times higher during cold months (8.44 ng m\({}^{-3}\) compared to 2.01 ng m\({}^{-3}\)), and the most carcinogenic among the compounds, BaP, exceeded the target limit of the European Commission with an average value of 1.03 ng m\({}^{-3}\), while during warm period, it was 0.57 ng m\({}^{-3}\). Such differences can be explicated by the increased direct emissions sources (fossil fuel combustion, biomass burning, etc.) during cold months, and by the enhanced condensation of PAHs in the particulate matter due to the lower temperatures [41], whereas increased solar radiation and atmospheric oxidants during warm months lead to PAHs' degradation [65]. Similar seasonal trends, especially for high molecular weight PAHs, have also been reported in other studies in Greece [36; 47; 66] and globally [21; 39; 41]. In Figure 3, the relative contribution of each compound is presented for both sampling periods. Obviously, 5-6 rings PAHs were the most abundant species during cold period, accounting for about 80% of the \(\Sigma\)PAHs, while the percentage is about 30.4% in the warm period dominating by the low molecular weight PAHs. This inversion may be a result of the decreased emissions from combusti  
Figure 2: PAH seasonal variations in ng m\({}^{-3}\) (* outliers and \({}^{\circ}\) values above 3 rd quartile). related with central heating during the warm period. The dominance of petrogenic low molecular weight PAHs, especially with 3-4 rings, in the warm period may be affected also by emissions from petroleum depositories from oil refineries and cargo ships [49; 67; 68] that both constitute a constant factor in the area working all year long. The most abundant PAH during the cold period was BbkF 27.5% followed by BaP 12.2%, while in summer BaP remained the dominant PAH with 28.2% relative abundance, followed this time by petrogenic ANT and PHE with 13.9 and 13.5%, respectively (Figure 3). BbkF and BaP were also the most abundant compounds in other studies in Aspropirgos [36], Athens [66], Volos [49], Greece, in Dunkirk, France [31], and Sao Paolo, Brazil [41]. As for the indPCB's seasonal variations, none of the six congeners presented statistically significant differences (\(p\) values were \(>\)0.05) between the cold and warm periods, with the concentrations for both seasons being included in Table 2. The indPCBs also did not present any alteration regarding their relative abundance, with PCB28 being the most abundant congener in both sampling periods (41.7 and 46.0%, respectively) (Figure 4). The indPCBs profile also indicates a marked decrease in concentration with increasing chlorination for different congeners. The same outcome was highlighted also by [PERSON] et al. (2013) in the highly industrialized city of Brescia, in northern Italy [23]. Figure 3: Relative abundance among PAH compounds for the cold and warm periods. Seasonal variations of dioxins are presented in Figure 5 and according to the Mann-Whitney test only 1,2,3,4,6,7,8-HpCDD, 1,2,3,4,7,8-HxCDF were found significantly higher during the cold period. Table 2 and Figure 5 show that there was not a clear seasonal pattern, with some compounds like OCDD (warm: 192 fg m\({}^{-3}\), cold: 151 fg m\({}^{-3}\)) and OCDF (warm: 429 fg m\({}^{-3}\), cold: 128 fg m\({}^{-3}\)) being relatively higher during the warm period.