## 3 Results
### PM\({}_{10}\), PM\({}_{2.5}\), and PM\({}_{1}\) Analysis  
Table 3 shows the analytical data of each element investigated in this study. First, the concentrations of the three PM fractions should be noted: the mean levels of PM\({}_{10}\) and PM\({}_{2.5}\) were below the law limit values (PM\({}_{10}\) daily average 50 \(\upmu\)g m\({}^{-3}\), PM\({}_{10}\) annual average 40 \(\upmu\)g m\({}^{-3}\), and PM\({}_{2.5}\) annual average 25 \(\upmu\)g m\({}^{-3}\)) [40] whereas no limits were reported for PM\({}_{1}\). For this last fraction, very few data are present in the literature: [PERSON] and [PERSON] [41] reported PM\({}_{1}\) levels ranging between from 20 \(\upmu\)g m\({}^{-3}\) to 26 \(\upmu\)g m\({}^{-3}\) for the background, street, and motorway sites in the Netherlands; [PERSON] et al. [42] confirmed the scarce presence of PM\({}_{1}\) data on levels and speciation and reported a mean level of 19 \(\upmu\)g m\({}^{-3}\) in Barcelona from October 2005 to October 2006; [PERSON] et al. [43] showed levels of 29-34 \(\upmu\)g m\({}^{-3}\) in Milan; [PERSON] et al. [44] measured 11-12 \(\upmu\)g m\({}^{-3}\) in Helsinki; and the same levels were also found by [PERSON] et al. [45] in rural areas in Germany. The situation was quite different as determined by [PERSON] and [PERSON] [46]: they found hourly average PM\({}_{1}\) concentrations ranging between 32 and 66 \(\upmu\)g m\({}^{-3}\) near an urban roadway in Chennai city (India), where the levels depend on the meteo-climatic conditions (post-monsoon period, winter and summer seasons). Therefore, the concentrations found in this paper could be considered as quite good, considering the environmental conditions present in the area. First, among the 36 elements investigated, their distribution in the three different fractions was not regularly distributed: for instance, Au, Ca, Cd, Co, Eu, Fe, La, Mo, Na, Ni, Sm, Sn, Ta, and Tb showed decreasing levels passing from PM\({}_{10}\) to PM\({}_{1}\), whereas Ce, Hg, Sc, and Zn did not show any significant difference in any of the three fractions. Other elements were instead distributed between PM\({}_{10}\), PM\({}_{2.5}\), and PM\({}_{1}\) in different ways (e.g., As was at 1.0 \(\upmu\)g m\({}^{-3}\), 0.38 \(\upmu\)g m\({}^{-3}\), and 1.1 \(\upmu\)g m\({}^{-3}\) in PM\({}_{10}\), PM\({}_{2.5}\) and PM\({}_{1}\), respectively). With the exception of Cd and U (their levels were below the respective LODs), our attention only focused on some elements: As, Au, Br, Ce, Co, Cr, Cs, Fe, Hg, Ni, Sb, Sc, Se, Th, and Zn. Their importance is due to different reasons such as the toxicological point of view, the identification of the anthropogenic or natural sources, or the possible common origin between them. In this way, an important example is described by bromine: its level in the atmosphere is essentially due to natural, (i.e., marine aerosol) and anthropogenic (i.e., auto-vehicular traffic, sources) [1; 47]: the levels of this element were 0.22 ng m\({}^{-3}\), 0.17 ng m\({}^{-3}\), and 0.52 ng m\({}^{-3}\), respectively in PM\({}_{10}\), PM\({}_{2.5}\) and PM\({}_{1}\) with a coefficient of variation (CV%) varying between 43.5%, 55.8%, and 7.5%, respectively. It should be noted that the CV% for each element shows its concentration level variability across the whole sampling period. As can be seen, the minimum CV% is related to the PM\({}_{1}\) fraction, meaning a low data dispersion for this size. The Br level in PM\({}_{10}\) (0.22 ng m\({}^{-3}\)) was really below the level found in downtown Rome (22.2 ng m\({}^{-3}\)) [2] and the level in PM\({}_{2.5}\) (0.17 ng m\({}^{-3}\)) was really below that found in the same city (17.1 ng m\({}^{-3}\)) [1], whereas the correlation (\(r\)) with another important element, Sb, was very good for PM\({}_{10}\) (0.9998), good for PM\({}_{1}\) (0.761), and less good for PM\({}_{2.5}\) (0.156). This occurrence (i.e., the high correlation between Br and Sn within PM\({}_{10}\) and low within PM\({}_{2.5}\)) suggests a different contribution to Br levels.