Study on ambient concentrations of PM 10, PM 10–2.5, PM 2.5 and gaseous pollutants. Trace elements and chemical speciation of atmospheric particulates

Abstract

This study provides the first comprehensive report on mass concentrations of particulate matter of various sizes, inorganic and organic gas concentrations monitored at three sampling sites in the city of Palermo (Sicily, Italy). It also provides information on the water-soluble species and trace elements. A total of 2054 PM 10 (1333) and PM 2.5 (721) daily measurements were collected from November 2006 to February 2008. The highest mass concentrations were observed at the urban stations, average values being about two times higher than those at the suburban (control) site. Time variations in PM 10 and also PM 10–2.5 were observed at the urban stations, the highest concentrations being measured in autumn and winter. CO, NOx, NO 2, benzene, toluene and o-xylene concentrations peaked in autumn and winter, a pattern similar to those recorded for PM 10 and PM 10–2.5 mass levels, indicating the importance of traffic emissions in urban air pollution. 91% and 51% of the benzene measurements exceeded the limit of 5 μg m −3 at the two urban monitoring sites. Trace elements (As, Ba, Cr, Cu, Mo, Pb, Sb) suspected of being introduced into the atmosphere mainly by anthropogenic activities, were highly enriched with respect to local soil. Results indicate that a large fraction of PM 10 (31–47% in weight) and PM 2.5 (29% in weight) is made up of water-soluble ions. Ammonium sulphate and nitrate particles accounted for 14–29 wt% of particulate matter mass concentrations. Crustal and marine components, combined, account for 41% and 49% in PM 2.5 and PM 10, respectively. The calculated deficits in Cl - and NH 4 + ions suggest that a proportion of these ions are lost, via the formation of gaseous NH 4Cl or HCl and NH 3.