## 4 Results and Discussion
### Concentrations of PM\({}_{2.5}\) and Its Related Main Chemical Compounds
Taking into account the rural background stations in Poland, the SIA concentration in Zloty Potok was \(\sim\)2 times lower than the concentration of SIA in Raciborz (SIA = 8.36 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), while comparable to the values registered in Zielonka and Puszcza Borecka (in both cases: SIA = 4.32 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), which applies also to other averaging periods (Table 1). Moreover, it was comparable to the SIA concentration from the measurement station at Ayia Marina (Cyprus) (SIA = 4.28 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_) and Seville (Spain) (SIA = 4.25 \(\mu\)g\(\cdot\)m\({}^{-3}\)), however in the first case higher concentration levels were recorded in the non-heating season (opposite to Zloty Potok). Generally, fine particulate matter concentrations recorded at urban and urban background stations (Table 2) are higher than the PM\({}_{2.5}\) concentrations from the rural background station (Table 1). As an example, the following could be mentioned:- Urban background station in Paris (PM\({}_{2.5}\) = 14.8 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) and station in its suburbs (PM\({}_{2.5}\) = 12.6 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) (France);
* Urban station in Thessaloniki (PM\({}_{2.5}\) = 25.9 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\) and 37.7 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\) (_Ep_)) and rural background stations in Finokalia (PM\({}_{2.5}\) = 12.00 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) and Penteli (PM\({}_{2.5}\) = 23.8 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) (Greece),
* Urban background station in Prague (PM\({}_{2.5}\) = 29.6 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) and regional background station in Kosetiec (PM\({}_{2.5}\) = 22.5 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\) (_Ep_)) (the Czech Republic, heating period). The exceptions to the above rule could be explained by the different research period (e.g., PM\({}_{2.5}\) concentrations in the summer season in Budapest (14 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) and K-Puszeta (23.32 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)), Hungary) and the location conditions of measurement stations [31; 71]. This is clearly visible on the basis of the results obtained in the earlier mentioned research project (Section 3)--lower values of PM\({}_{2.5}\) concentrations were recorded in Szczecin compared to Zloty Potok, due to the location of the former station in a relatively \"clean\" coastal area [27; 47; 32; 49]. Similarly, the concentrations of the selected main constituents of PM\({}_{2.5}\) from urban areas (Table 2) are generally higher compared to the values obtained in rural background stations (Table 1). The exceptions concern mainly concentrations of secondary inorganic ions and as an example such situation could be observed in:  
* Poland: SIA concentrations in Szczecin (SIA = 5.42 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\); _Ep_) was closer to the value recorded in Zloty Potok (SIA = 4.36 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\); _Ep_) than in Trzebinnia (SIA = 7.35 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\); _Ep_);
* Germany: similar levels of the SIA concentrations from rural background stations located in Waldhof (SIA = 6.06 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\); _Ep_) and Neuglobosw (SIA = 5.25 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\); _Ep_) and urban background station in Duisburg (SIA = 5.80 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\));
* The Netherlands: higher SIA concentrations from rural background station in Cabauw-Zijdeweg (SIA = 7.89 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\); _Ep_) in comparison with urban background station in Rotterdam (SIA = 4.10 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)). Regarding the concentrations of PM\({}_{2.5}\) main constituents, urban background station in Szczecin generally differed significantly compared to Trzebinnia (Table 2), which information was mentioned in the Section 3. Therefore, the comparison of the concentrations of these components with the values recorded at other urban and urban background stations in Europe should be performed separately.