title: Oxidative potential and chemical speciation of size-resolved particulate matter (PM) at near-freeway and urban background sites in the greater Beirut area.
abstract: To assess particle oxidative potential in the greater Beirut area, size-resolved PM10-2.5, PM2.5-0.25 and PM0.25 samples were collected at near-freeway and urban background sites. Metals and trace elements, including Mn, Cr, Cu, Ba, Mo and Sb, displayed increased levels and crustal enrichment factors at the roadway, indicating their vehicular origin. These elements in addition to Co, V, Ni and Zn were mostly distributed in PM2.5-0.25 and PM0.25 at both sites, with moderate-to-high water-solubility (>30%). The presence of these metals, mainly air toxics, in small size ranges constitutes an added health risk. Of particular concern are elements with strong correlations (R ≥ 0.70) with reactive oxygen species (ROS)-activity, measured by a cellular assay. In PM10-2.5, road dust component Mn and soil-related element Co were highly correlated with ROS-activity. In PM2.5-0.25, vehicular abrasion element Cu and soil-derived component Co were highly associated with ROS-activity. In PM0.25, V and Ni, originating from fuel oil combustion, strongly correlated with ROS formation. ROS-activity displayed a particle-size dependency, with lowest activity associated with PM10-2.5. On a per air volume basis, size-resolved ROS-activity was 1.5-2.8 times greater at the roadside than background location, indicating that exposure to redox-active species may be greatest near the freeway. Size-fractionated PM intrinsic activity (i.e. PM mass-normalized) was comparable at both sites, possibly suggesting a similarity in the sources of ROS-active species. Relative to other urban settings, while the intrinsic redox activity of PM10-2.5 in Beirut is comparable to that measured at an urban site in Los Angeles (LA), its PM0.25-induced ROS-activity is ~2.3-fold greater. Moreover, the intrinsic ROS-activity of ambient PM2.5 in Beirut is comparable to that reported in Milan-Italy, but 3.1-times PM2.5 activity in the heavily-polluted Lahore-Pakistan. Lastly, findings suggest a dominant role of transition metals in generating ROS compared to organic carbon in the LA area.
authors.affiliation: University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, USA.
authors.forename: Nancy
authors.initials: N
authors.lastname: Daher
authors.affiliation: American University of Beirut, Department of Chemistry, Beirut, Lebanon.
authors.forename: Najat A
authors.initials: NA
authors.lastname: Saliba
authors.affiliation: American University of Beirut, Department of Mechanical Engineering, Beirut, Lebanon.
authors.forename: Alan L
authors.initials: AL
authors.lastname: Shihadeh
authors.affiliation: American University of Beirut, Department of Chemistry, Beirut, Lebanon.
authors.forename: Malek
authors.initials: M
authors.lastname: Jaafar
authors.affiliation: American University of Beirut, Department of Chemistry, Beirut, Lebanon.
authors.forename: Rima
authors.initials: R
authors.lastname: Baalbaki
authors.affiliation: University of Wisconsin-Madison, Environmental Chemistry and Technology Program, Madison, WI, USA.
authors.forename: Martin M
authors.initials: MM
authors.lastname: Shafer
authors.affiliation: University of Wisconsin-Madison, Environmental Chemistry and Technology Program, Madison, WI, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Schauer
authors.affiliation: University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, USA. Electronic address: sioutas@usc.edu.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sioutas
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution; D002947:Cities; D004784:Environmental Monitoring; D007861:Lebanon; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D014186:Transportation; D001335:Vehicle Emissions / Q000032:analysis
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D001335:Vehicle Emissions
keywords: Beirut; Metals; Near-freeway; Redox activity; Size-resolved particulate matter; Urban settings