## 3 Results and Discussion
### PAH Sources in the Adriatic Sea  
Factor profiles obtained by the PMF modelling are shown in Figure 6. The application of the PMF revealed four main factors contributing to the pollution of PAH in the studied area. Each factor is considered as one of the specific sources of polycyclic aromatic hydrocarbons and is further discussed as such. Figure 4: Concentration of total PAH (T-PAH), 16 EPA priority PAH (16 EPA PAH), unsubstituted PAH (parent-PAH), methyl-substituted PAH (C-PAH), sulphur-containing-PAH (S-PAH) and oxygen-containing-PAH (O-PAH) at stations in Kastela Bay. Source 1 emits PAH mixtures enriched in unsubstituted PAH compounds. Dominant PAH compounds in the mixture are BFLs with a relative amount of 11.81% and BaA with a relative amount of 9.13%. Among the methyl-substituted compounds, C1-CHR (4.17%), C2-CHR (3.36%), C1-PHE (2.97%) and C2-PHE (3.43%) were the most abundant. The  
Figure 5: Concentration of total PAH (T-PAH), 16 EPA priority PAH (16 EPA PAH), unsubstituted PAH (parent-PAH), methyl-substituted PAH (C-PAH), sulphur-containing-PAH (S-PAH) and oxygen-containing-PAH (O-PAH) at stations in Siberik Bay. Figure 6: Factor (Source) profiles obtained by application of Positive Matrix Factorization. relative amounts of S-PAHs and O-PAH in the PAH mixture derived from this source were less than 1%. Unsubstituted parent-PAH compounds were the most abundant fraction of the PAH mixture emitted from Source 2. The relative amounts of BFLs, FL and Py were 14.53%, 11.61% and 9.65%, respectively. The predominant C-PAH compounds in the mixture were C1-P (5.66%) and C1-BFLs (4.19%), while the predominant heterocyclic aromatic compounds were C1-BNTs, DBTs and DBFs, with relative amounts of 1.18%, 0.65% and 0.30%. The unsubstituted parent-PAH compounds with more than three aromatic rings in the structure were the predominant compounds in the PAH mixtures emitted from both Source 1 and Source 2, indicating that both sources refer to high-temperature combustion [33; 34]. However, the mixture emitted from Source 1 contained lower amounts of unsubstituted PAH and higher amount of phenanthrene than the mixture emitted from Source 2. BFLs, BaP and BaA are compounds typically formed during gasoline combustion, while mixtures formed during diesel combustion are enriched in phenanthrene, fluoranthene, pyrene and chrysene. Comparing the obtained results with the literature data, it is observed that the PAH mixture emitted by Source 1 is similar to the composition of the PAH mixtures produced by the combustion of liquid fossil fuels in vehicle engines. In contrast, Source 2 emits PAH mixtures in which the amount of low-molecular weight PAH is significantly lower than the amount of high-molecular-weight PAH. PAH mixtures enriched in unsubstituted parent-PAH compounds, such as BFLs, BaA, FL, P and CHR resemble PAH mixtures typically formed during high-temperature combustion of crude fossil fuels in industrial furnaces or forest fires [2; 10; 33; 34]. The above-mentioned differences in the composition of the PAH mixtures emitted from these two sources indicate that Source 1 can be ascribed to inland and marine transport, while Source 2 represents high-temperature combustion of crude fossil fuels and biomass. PAH mixture emitted from Source 3 also contained a high proportion, but the contribution of the C-PAH fraction to the total concentration of PAH was higher than the contribution of the parent-PAH compounds. The PAH mixture contained higher relative amounts of methyl phenanthrenes, naphthalene and pyrenes, while the dominant heterocyclic compounds were C1-BNTs with a contribution of 1.18%. Comparison with the literature data suggests that Source 3 is a petrogenic PAH source, mostly associated with recent accidental leakage of unburned fossil fuels and other petroleum derivatives [2; 32; 37]. Source 4 emitted a PAH mixture enriched in C2-FEN (8.41%), A (7.33%) and PHE (6.17%).