## 2 Materials and Methods  
The locations of the deposimeters (Figure 1) have been identified, taking into account the characteristics of the territory, distributing them on the various municipalities around Civitavecchia (North Latium, Central Italy). The location of Rocca Respampani, in the territory of Viterbo, very far from any known industrial/urban emission source, has been identified as a background location. The monitoring network installed for the study consisted of:  
* Location #1: area not affected by industrial and urban sources; positioning: at the Roccaccia Business Center, Tarquinia Agricultural University;
* Location #2: area characterized by the absence of settlements; positioning: Enel Sant'Agostino electrical power station;
* Location #3: area characterized by medium population density; positioning: at the environmental monitoring station of the Management Consortium of the Environmental Observatory of Civitavecchia, at Allumiere;An ambient air monitoring network was installed consisting of four stations equipped with total bulk deposimeters (Figure 1b) for determining the atmospheric deposition rate. The determinations of organic (PCDD/Fs, DL-PCBs and PAHs) and inorganic (metals and metalloids) micro-pollutants at (ultra-)trace levels were carried out on all the samples collected. The sampling started at the four sites from June and continued for a whole year, each lasting about 30 days. Each sampling was performed following the indications reported in the Italian Legislative Decree no. 155/2010 [50]: UNI EN 15980:2011 for organic micropollutants [51] and UNI EN 15841:2010 for metals and metalloids [52]. Pyrex glass deposimeters were used for the determination of PCDD/Fs, PCBs and PAHs, while high-density polyethylene (HDPE) deposimeters were used for metals and metalloids.  
The samples were filtered on a membrane filter in mixed cellulose esters, diameter 47 mm and porosity 0.45 mm for metals, and in glass fiber, diameter 47 mm, without organic binders, for organic compounds. The mixed cellulose ester filter was then mineralized in a microwave digestion system using concentrated nitric acid and 5% hydrogen peroxide, and the acidified filtrate with high purity concentrated nitric acid for trace analysis, whereas the glass fibers and the filtrate were subjected to extraction with high purity organic solvent for trace analysis (dichloromethane, DCM), respectively, by ultrasound and in a separating funnel. The acid solution coming from the mineralization and the acidified filtrate were analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), using the procedure described in UNI EN 15841:2009 [52], whereas the extracts with the solvent were combined, dried, concentrated and analyzed for determining PCDD/Fs by means of gas chromatography coupled with mass spectrometry (GC-MS) according to UNI EN 1948-2:2006 [53], UNI EN 1948-3:2006 [54] and UNI EN 1948-4:2010 [55], and for determining PAHs by means of high performance liquid chromatography-MS (HPLC-MS) according to UNI EN 15980:2011 [51]. In the analytical results, the concentration values below the limit of  
Figure 1: (**a**) Location of the four sampling sites around Civitavecchia and neighboring municipalities; (**b**) total bulk deposimeter sampler used in this campaign.  
detection (LOD) are expressed as 50% of the LOD, as indicated in [32]. The LODs for each compound/metal investigated are reported in Table S1 of the Supplementary Material.