## 4 Results and Discussion  
### Concentrations of PM\({}_{2.5}\) and Its Related Main Chemical Compounds  
The concentrations of PM\({}_{2.5}\) registered both at rural (Table 1) and urban background stations (Table 2), varied within wide range of values. Considering data for the former type of stations, it can be observed that the concentrations of PM\({}_{2.5}\) in Zloty Potok were visibly higher compared to the values registered on most of the European rural sites, especially during the heating period. This suggests that the main factor determining the concentration of PM\({}_{2.5}\) in the investigated area was the emission from anthropogenic sources, especially fossil fuels and biomass combustion in households (low-level emission sources) [25; 27; 31; 32; 49; 69]. The average concentrations of the main components in PM\({}_{2.5}\) from Zloty Potok were also higher, which is particularly evident in the case of the carbonaceous aerosol, which was the predominant PM\({}_{2.5}\) component from mentioned station (TC = 10.07 \(\mu\)g\(\cdot\)m\({}^{-3}\), _Ep_), as well as other rural stations located in different parts of Poland. However, it is worth to note that TC concentrations in Zloty Potok and Raciborz were higher compared to stations located in the central and north-eastern part of the country (Zielonka, Puszcza Borecka) (see also [31]). PM\({}_{2.5}\) concentrations and associated carbon compounds from stations located in north-western European countries were clearly lower, for example, Uto (Finland) (PM\({}_{2.5}\) = 6.55 \(\mu\)g\(\cdot\)m\({}^{-3}\), _Ep_), Waldhof (Germany) (PM\({}_{2.5}\) = 11.45 \(\mu\)g\(\cdot\)m\({}^{-3}\); TC = 2.71 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Cabauw-Zijdeweg (the Netherlands) (PM\({}_{2.5}\) = 11.45 \(\mu\)g\(\cdot\)m\({}^{-3}\); TC = 2.86 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Paris (France) (PM\({}_{2.5}\) = 12.60 \(\mu\)g\(\cdot\)m\({}^{-3}\); TC = 3.40 \(\mu\)g\(\cdot\)m\({}^{-3}\)). This also applies to the rural background stations located in Mediterranean area, for example, Finokalia (Greece) (PM\({}_{2.5}\) = 12.00 \(\mu\)g\(\cdot\)m\({}^{-3}\); TC = 1.69 \(\mu\)g\(\cdot\)m\({}^{-3}\)), Monte Martano (Italy) (PM\({}_{2.5}\) = 10.09 \(\mu\)g\(\cdot\)m\({}^{-3}\); TC = 2.48 \(\mu\)g\(\cdot\)m\({}^{-3}\)) or Montseny (Spain) (PM\({}_{2.5}\) = 11.96 \(\mu\)g\(\cdot\)m\({}^{-3}\); TC = 1.91 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), where the proportion of PM\({}_{2.5}\) in PM\({}_{10}\) reaches relatively lower values, due to the higher load of crustal species and sea spray in PM mass [91; 92; 93]. In the case of concentration of secondary inorganic ions (SO\({}_{4}\)\({}^{2-}\) + NO\({}_{3}\)\({}^{-}\) + NH\({}_{4}\)\({}^{+}\)), regarded as secondary inorganic aerosol (SIA), the situation was more diversified. The SIA concentrations in Zloty Potok (SIA = 4.36 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_) was lower compared to the values recorded at many rural background stations in Europe, for example, Kosecite (the Czech Republic) (SIA = 6.57 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Rise (Denmark) (SIA = 6.43 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Cabauw-Zijdeweg (the Netherlands) (SIA = 7.89 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Paris (France) (SIA = 5.30 \(\mu\)g\(\cdot\)m\({}^{-3}\)), Neelgobsov (SIA = 5.25 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_) as well as other German stations (with exception to Schauinsland). However, it was higher than the SIA concentrations registered in: Rucava (Latvia) (SIA = 1.17 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Uto (Sweden) (SIA = 0.85 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Harwell (United Kingdom) (SIA = 2.17 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Chaumont (Switzerland) (SIA = 3.70 \(\mu\)g\(\cdot\)m\({}^{-3}\)), Iskrba (Slovenia) (SIA = 1.78 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Ispra (Italy) (SIA = 2.97 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_), Monte Martano (Italy) (SIA = 3.28 \(\mu\)g\(\cdot\)m\({}^{-3}\)) and Montseny (Spain) (SIA = 1.88 \(\mu\)g\(\cdot\)m\({}^{-3}\); _Ep_).