## 3 Results and Discussion
### Seasonal Variations and Congeners' Contributions
However, the WHOTEQ\({}_{2005}\) value was significantly higher in cold months, revealing that particulate PCDD/Fs pose a higher risk to human health during cold periods due to their higher concentrations (Figure 6). This outcome could be combined with our previous studies in this area [35; 36], where uncontrolled combustions in Thiassion Plain play a potential role in atmospheric degradation and the increased toxicity of the particles in the whole area, including Eleusis and Aspropirgos town (Figure 1). In particular, during cold months the wind direction is usually north, northeast (N, NE) in the sampling area and as a result the particulate matter is enriched by the site where uncontrolled combustions take part [35]. Comparing with other studies, in some of them, seasonal variations were observed with higher concentrations during cold months [38; 54; 64], assuming either elevated combustions for heating or relatively low boundary layer heights in cold weather [58] being the dominant reason for that outcome. Nevertheless, other studies did not describe any seasonal trend for PCDD/Fs [69]. Discussion on the congener profile of PCDD/Fs during the warm and cold periods will be based on Figure 7. The most toxic congener, 2,3,7,8-TCDD, was not detected in any sample. The congener profiles demonstrated the prevalence of OCDF, OCDD, 1,2,3,4,6,7,8,-HpCDF, and 1,2,3,4,6,7,8-HpCDD for the entire sampling period. The relative abundances of these four compounds were 19.7-58%, 23.1-26.0%, 8.7-29.6%, and 2.2-7.7%, respectively. The results are in agreement with those from other studies in industrial sites in Shanghai [55] and Anshan [38], China, in Seoul, Korea [64], and in Umm-Al-Aish oil field, Kuwait [20]. Figure 4: Relative abundance among indPCB congeners for the cold and warm periods. Figure 5: PCDD/F seasonal variations in pg m\({}^{-3}\) (* outliers and \({}^{\circ}\) values above 3 rd quartile). Figure 6: WHO-TEQ\({}_{2005}\) seasonal variations for PCDD/Fs and dlPCBs (* outliers and \({}^{\circ}\) values above 3 rd quartile). In regard to particle-bound dlPCBs, no seasonal pattern was observed during the sampling campaign (Table 3), with concentrations and WHOTEQ\({}_{2005}\) values for each congener (Figure 6) being quite similar between the cold and warm periods. This result is in agreement with other studies [20], although there are papers reporting elevated concentrations during warm periods for PCBs in gas phase [38; 64], assuming that PCBs evaporated more easily from soil to gaseous phase and could be transported long-range under high temperatures [38; 70; 71]. Although the sampling was performed only in the particulate phase, the dlPCBs congener fingerprint detected in our study complies with that reported in the literature. Thus, according to Figure 8, the most abundant congener was PCB118, accounting for 45.9-46.1% of the relative abundance followed by PCB105 (13.7-15.2%), PCB167 (8.1-16.7%), and PCB77 (5.1-5.7%). The outcome from our study matches the profile from other studies in both gas and particulate phase [6; 20; 23; 72], except for PCB167, reinforcing the conclusion that the dlPCBs' profile does not depend on the sampling location. Figure 8: Relative abundance among dlPCB congeners for the cold and warm periods. Figure 7: Relative abundance among PCDD/F congeners for the cold and warm periods.