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

Abstract

As part of a monitoring programme conducted by the Institute of Environment and Development (IDAD) and supported by the regional municipal solid waste (MSW) management authorities, an extensive database of trace metals (TMs) concentrations in ambient air was collected in two sites, Leça do Balio (LB) and Vila Nova da Telha (VNT), located in Porto's metropolitan area, north of Portugal. Since 2004, concentrations of As, Cd, Pb, Cu, Cr, Mn, Hg, Ni and Zn were measured in PM10. In addition, total gaseous mercury (TGM) was monitored since 2008. These measurements were used to assess long-term trends of concentrations. Statistical analysis was used to search for the possible origin of the TMs.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.