## 3 Results and Discussion  
The average chemical composition of the olive pollen used in the study is reported in Table 1. Olive pollen showed considerable amounts of potassium, calcium, sodium, and magnesium; minor quantities of manganese, iron, copper, and chromium; and high ion concentrations of PO43-, SO42-, Cl-, NH4+, C2O42-, and NO3-. \begin{table}
\begin{tabular}{c c c} \hline \hline \(\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{\text  
The meteorological and air-quality parameter values detected in the exposure periods are shown in Table 2. Meteorological factors, such as wind speed, wind direction, humidity, rainfall, and mean temperature, affect PM deposition. However, in field studies, it is difficult to isolate the effects of single meteorological parameters because monitoring periods typically last for days or weeks, whereas the weather conditions vary continuously [45]. During the two study periods (summers of 2019 and 2021), the average meteorological conditions registered at the monitoring sites, although belonging to different climatic zones, were similar, and we considered that the influence of meteorological parameters on deposition fluxes was comparable in all sites. PM concentrations also affect the deposition fluxes. Similar concentration values were detected for particles with diameter less than 10 \(\upmu\)m (PM\({}_{10}\)) and for particles with diameter less than 2.5 \(\upmu\)m (PM\({}_{2.5}\)) in the exposure periods at Perugia and Monte Martano sites. Higher values were detected at the Terni industrial site. During the summer of 2019, a first exploratory experiment was carried out, and pollen grains were exposed to air in the three sites for 15 days. The daily deposition fluxes of the main soluble and insoluble metals and major ionic species were determined. In Table S1, the POL and CNT fluxes expressed in \(\upmu\)g\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\) are reported. At the MM regional background site (a mid-altitude station for air-quality monitoring distant from any pollution source) and at the PG urban site (located in a residential and commercial district characterized mainly by traffic pollution), the deposition fluxes of soluble ionic and total metallic fractions on POL samples were always greater or similar to those of the CNTs. However, the TR industrial site, situated near the AST (Acciai Special Terni) factory, one of the oldest steel plants in Europe and one of the largest in Italy, registered the highest fluxes. At TR, the fluxes in POL and CNT samples were similar except for some pollutants associated with steel production, namely calcium, fluoride, formate, and sulfate, which were higher in the CNT collector dish [36]. At the end of the exposure time, olive pollen grains selected from the passive samplers exposed in the three sites were observed by SEM. The bioaccumulation and interaction of the constituents of the atmospheric particulate with olive pollen were revealed by the microscope images, which showed, in some cases, significant morphological anomalies on the grain surfaces. In particular, the granules exposed at the industrial TR site, and, to a lesser extent, those exposed at the urban PG site, presented an anomalous thinning of the walls of the reticulum of the exine (Figure 3), suggesting chemical damage was induced by the interaction with the pollutants. The morphological damage was more evident at TR probably due to the presence of specific pollutants generated by the steel plant and due to the site's geographical location. The town of Terni is located in a vast plain area surrounded by medium-range geographical elevations (average elevation 800-1200 m a.s.l. ), which limit the dispersion of locally generated air pollutants [37].