Size distribution of airborne particulate matter and associated heavy metals in the roadside environment

The size distributions of airborne particulate matter (PM) and associated heavy metals Pb, Cd, Ni, Cr, V, Mn, Cu and Fe in different inhalable fractions (<0.8 μm, 0.8-1.3 μm, 1.3-2.7 μm, 2.7-6.7 μm and >6.7 μm) were determined at a traffic-orientated urban site in the city of Thessaloniki, northern Greece. The airborne PM displayed a bimodal distribution with most of the mass (52%) contained in the submicron size range (<0.8 μm) and an additional minor mode (20%) in the coarse size fraction (>6.7 μm). Characteristic size distributions of heavy metals allowed identification of three main behavioral types: (a) metals whose mass was resided mainly within the accumulation mode (Pb, Cd), (b) those which were distributed between fine, intermediate and coarse modes (Ni, Cu, Mn), and (c) those which were mainly found within particles larger than 2.7 μm in diameter (Fe). The mean mass median aerodynamic diameter (MMAD) of PM was found at 0.85 ± 0.71 μm, while the mean MMADs of heavy metals followed the order Pb (0.96 ± 0.71 μm) < Cd (1.14 ± 0.82 μm) < V (1.38 ± 0.63 μm) < Ni (1.45 ± 0.88 μm) < Cu (2.04 ± 0.77 μm) < Mn (2.61 ± 1.23 μm) < Cr (2.91 ± 1.40 μm) < Fe (3.82 ± 0.88 μm). The measured distributions are believed to result from a combination of processes including local anthropogenic and natural sources, such as traffic, industrial emissions and resuspension of road dust.