Backward air mass trajectory frequencies were calculated during the coastal site sampling time by using the NOAA HYSPLIT database65 (link),66 (link). Trajectory frequencies (as number of endpoints per squared grid per number of trajectories) were calculated with frequency grid resolution 1.0° × 1.0°, starting 96 h before arrival time (00:00 UTC) and altitudes ranging from 0 to 99999 m a.g.l. During the sampling period, air mass trajectories were of typical oceanic contribution, passing on Atlantic Ocean through urbanized city centers and industrialized areas around the coast before arriving to our coastal sampling collection site (SI Fig. S1 ).
Multivariate statistical analyses, such as Pearson correlation, ternary correlation, Principal Component Analysis (PCA) and Agglomerative Hierarchical Clustering (AHC) were calculated for both dataset by using XLSTAT BASE software package version 19.5 for Microsoft Excel from Addinsoft Ltd (Paris, France). Ternary correlations were done by STATISTICA version 12.0 (Statsoft, USA).
Multivariate statistical analyses, such as Pearson correlation, ternary correlation, Principal Component Analysis (PCA) and Agglomerative Hierarchical Clustering (AHC) were calculated for both dataset by using XLSTAT BASE software package version 19.5 for Microsoft Excel from Addinsoft Ltd (Paris, France). Ternary correlations were done by STATISTICA version 12.0 (Statsoft, USA).
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