## 3 Results and Discussion
### Relationship between PAH and Trace Metals Concentrations and Household Characteristics
#### 3.2.2 Metals  
The location of the house seems to be an important factor in the presence of Zn (\(p\) = 0.083), Fe (\(p\) = 0.071), and Sr \(p\) = 0.071) in house dust, with houses located in urban areas having higher concentrations. Figure 1 illustrates the elevated concentrations of the aforementioned elements detected in urban areas, which are lower in suburban areas and especially in rural areas. This observation is explained by the common emission sources of these elements, which are traffic emissions and road dust resuspension. Also, houses located close to a highway (<200 m) indicated higher concentrations of Se (1.3 vs. 0.6 \(\mu\)g/g, \(p\) = 0.073).  
Figure 1: Concentrations of Fe, Zn and Sr in urban, suburban and rural areas.  
Residences located either on the ground floor or the first floor indicated higher Hg concentrations with respect to those at higher floors (0.62 vs. 0.16 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)). The age of the house was found to affect the levels of Sr, as higher concentrations in homes older than 20 years (128 vs. 77 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)) were observed. In houses with a total area of less than 100 m\({}^{2}\), higher concentrations of Fe (6928 vs. 2526 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)), Al (2691 vs. 1562 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)), V (10.6 vs. 5.7 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)) and Ba (327 vs. 133 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)) were found. This fact can be related to the lower number of openings (windows and doors) to houses of smaller total area, which consequently leads to lower infiltration rates. Houses that used fireplaces as the main source of heating indicated significantly higher concentrations of Pb (343 vs. 32 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)), probably due to the burning of painted or treated wood [33; 34], while those that were heated using electricity were associated with significantly higher concentrations of Fe (10729 vs. 3529, \(p<0.05\)) and V (12.8 vs. 7.3 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p=0.059\)), likely due to dust resuspension occurring during the operation of air conditioning. In houses that remained closed (without the presence of occupants) for several hours during the day, higher values of As (8.7 vs. 2.5 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)) and Sr (152 vs. 93, \(p<0.05\)) were detected in household dust. The type of glazing appeared to affect Pb levels in household dust, as higher concentrations were observed in homes with single glazing compared to those with double glazing (57.8 vs. 46.2, \(p=0.078\)). In terms of glazing on indoor Pb concentrations, we believe that the effect is not directly related to the type of glazing (or to be more accurate not only related to that) but on the type of the windows used. Double glazed windows are of newer technology and have been found in previous studies to significantly reduce the infiltration rates [35]. Since Pb is emitted from outdoor anthropogenic activities and resides in the fine fraction, it is expected that its indoor concentrations will be attributed mainly to infiltration. Finally, as with PAHs, the habit of residents wearing shoes inside their dwelling significantly affected the levels of Al (2684 vs. 1850 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p=0.076\)) and Ba (275 vs. 217 \(\mathrm{\SIUnitSymbolMicro g}\)/g, \(p<0.05\)) in house dust. As both elements can be found in urban dust, there are transferred inside the residents by the dust that is found on their shoes.