Long-term monitoring of trace metals in PM10 and total gaseous mercury in the atmosphere of Porto, Portugal

During the monitoring period, the mean TMs concentrations followed the order: Zn > Cu > Pb > Mn > Cr > Ni > As ≈ Hg > Cd, and have not exceeded the current air quality guidelines values. Concentrations of As, Cd, Pb, Mn, and Hg have slightly decreased during the measurement period despite already being at historically low levels. The concentrations range of Zn, Cd, Pb and As suggests a seasonal variability for these elements in ambient air, for both sites. Average TGM levels were 1.93 and 1.35 ng m−3, for LB and VNT respectively. In terms of seasonality, a statistical difference was found in TGM concentrations between winter and summer for LB. A daily pattern was also observed in TGM with minimum concentrations during the night and early morning.