## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c} \hline \hline \(\upmu\)g/g & \multicolumn{2}{c}{**Olive Pollen**} \\ \hline
**Soluble Ionic Fraction** & **Mean** & **Standard Deviation** \\ \hline NO\({}_{3}\)\({}^{-}\) & 117 & 49 \\ PO\({}_{4}\)\({}^{3-}\) & 3392 & 2875 \\ Total metallic fraction & & \\ Cr & 0.15 & 0.15 \\ Mn & 5 & 5 \\ Fe & 57 & 57 \\ Co & \textless{}LOD * & \\ Ni & \textless{}LOD * & \\ Cu & 1 & \\ Zn & \textless{}LOD * & \\ Pb & \textless{}LOD * & \\ Cd & \textless{}LOD * & \\ \hline \hline \end{tabular} \({}^{*}\) Limit of detection of the analytical procedure.  
\end{table} 
Table 1: _Cont._In light of the promising results obtained, and in order to validate the new system of passive sampling, we replicated the experiment in 2021, exposing pollen samples to atmospheric pollutants for 7 and 15 days. In Table S2 are shown the POL and CNT fluxes calculated for the soluble ionic and metallic fractions, expressed in ug\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\). After 7 days, the POL fluxes of soluble ionic and metallic fractions were always similar or greater than those of the CNT, except for Na, Ca, and Fe at MM; Ca at PG; and Cr, Fe, Co, Ni, Pb, Ba, Al at TR. Furthermore, for the 15-day exposure time, we observed higher controls than sample fluxes for Na and Br at MM and for Ca, F, Cr, Fe, Ni, and Al at TR. The different deposition fluxes detected in 2019 and 2021 at the three sites were probably due to the circulation of air masses characterized by different chemical composition, and in the rural background MM site also to the perturbation of aerosol mass concentrations induced by increasing height of the boundary layer, which is observable in the summertime [39]. \begin{table}
\begin{tabular}{c c c c c c} \hline Air Exposition Test & 2019 & & & 2021 & \\ \hline  & & Mean & \
\begin{tabular}{c} Standard \\ Deviation \\ \end{tabular} & Mean &
\begin{tabular}{c} Standard \\ Deviation \\ \end{tabular} \\ \hline Temperature (\({}^{\circ}\)C) & & & & & \\  & TR & 26.8 & 2.2 & 27.7 & 1.4 \\  & PG & 24.2 & 2.7 & 26.6 & 1.5 \\  & MM & 20.9 & 2.8 & 22.4 & 1.6 \\ Wind speed (km h\({}^{-1}\)) & & & & & \\  & TR & 0.4 & 0.2 & 2.1 & 0.1 \\  & PG & 1.1 & 0.2 & 1.1 & 0.5 \\  & MM & 4.5 & 1.5 & 6.3 & 3.1 \\ Relative humidity \% & & & & & \\  & TR & 50.2 & 6.4 & 43 & 5.5 \\  & PG & 64.6 & 6.9 & 56 & 3.3 \\  & MM & 66.7 & 13.5 & 50 & 11.7 \\ Precipitations (mm) & & & & & \\  & TR & 0.3 & 0.7 & 0.01 & 0.05 \\  & PG & 1.4 & 3.4 & 0.1 & 0.4 \\  & MM & 1.3 & 3.1 & 0.2 & 0.6 \\  & TR & 31.9 & 14.2 & 43.5 & 9.3 \\  & PG & 16.7 & 6.8 & 18.8 & 0.9 \\  & MM & 14.1 & 6.1 & 17.9 & 5.1 \\ PM\({}_{2.5}\) (ug m\({}^{-3}\)) & & & & & \\  & TR & 19.2 & 8.0 & 20.7 & 9.1 \\  & PG & 9.4 & 3.1 & 8.6 & 2.3 \\  & MM & 9.4 & 3.1 & 7.5 & 3.0 \\ Ozone (ug m\({}^{-3}\)) & & & & & \\  & TR & 83.5 & 12.1 & 137.1 & 18.6 \\  & PG & 70.2 & 12.5 & 79.5 & 7.4 \\  & MM & 98.4 & 14.3 & 116.6 & 13.5 \\ NO\({}_{2}\) (ug m\({}^{-3}\)) & & & & & \\  & TR & 34.4 & 15.9 & 50.6 & 17.0 \\  & PG & 27.7 & 10.6 & 32.3 & 19.0 \\  & MM & 6.1 & 2.5 & 4.6 & 2.1 \\ \hline \end{tabular}
\end{table} 
Table 2: Average values of meteorological and air-quality parameters detected during the study periods. Figure 3: Scanning electron microscopy images (SEM) of olive pollen samples after exposure to air for 15 days (2019 experiment; (**a**), Monte Martano; (**b**), Perugia; (**c**), Terri. The daily surface deposition fluxes of the main soluble and insoluble metals and ionic species deposited on pollen were used to calculate the bioaccumulation factors (BFAs) and bioaccumulation indexes over time (BAIts). The BAF index characterizes the bioaccumulation of natural or anthropogenic elements in organisms living in natural ecosystems. When an organism is born into a given natural matrix, bioaccumulation takes place from birth to death or to the moment when the organism is sampled for measurement [44]. In these conditions, the concentration of a given element in the tissues of the organism is related only to the concentration in the natural matrix.