title: The relative importance of tailpipe and non-tailpipe emissions on the oxidative potential of ambient particles in Los Angeles, CA.
abstract: This study examines the associations between the oxidative potential of ambient PM2.5 and PM0.18, measured by means of the dithiothreitol (DTT) assay, and their chemical constituents and modeled sources. Particulate matter (PM) samples were collected from 2012-2013 in Central Los Angeles (LA) and 2013-2014 in Anaheim, California, USA. Detailed chemical analyses of the PM samples, including carbonaceous species, inorganic elements and water-soluble ions, were conducted. Univariate analysis indicated a high correlation (R > 0.60) between the DTT activity and the concentrations of carbonaceous species at both sites. The strongest correlations were observed between DTT and organic tracers of primary vehicle tailpipe emissions including polycyclic aromatic hydrocarbons (PAHs) and hopanes as well as EC, with higher correlations for PM0.18versus PM2.5 components. Moreover, metals and trace elements (e.g., Ba, Cu, Fe, Mn, Pb and Sb) in both size ranges were also associated with DTT activity. Multiple linear regression (MLR) analysis was performed on DTT activity and PM sources identified by a Molecular Marker-Chemical Mass Balance (MM-CMB) model (i.e. major carbonaceous sources: vehicle tailpipe emissions, wood smoke, primary biogenic and secondary organic carbon) together with other typical sources of ambient PM (i.e. crustal material, vehicular abrasion, secondary ions and sea salt). Overall, our findings illustrate the relative importance of different traffic sources on the oxidative potential of ambient PM. Despite major reductions of tailpipe emissions, the lack of similar reductions (and possibly an increase) in non-tailpipe emissions makes them an important source of traffic-related PM in Los Angeles and their increasing role in the overall PM toxicity raises concerns for public health.
authors.affiliation: University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA. sioutas@usc.edu.
authors.forename: Farimah
authors.initials: F
authors.lastname: Shirmohammadi
authors.affiliation: University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA. sioutas@usc.edu.
authors.forename: Sina
authors.initials: S
authors.lastname: Hasheminassab
authors.affiliation: University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA. sioutas@usc.edu.
authors.forename: Dongbin
authors.initials: D
authors.lastname: Wang
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 Wisconsin-Madison, Environmental Chemistry and Technology Program, Madison, WI, USA.
authors.forename: Martin M
authors.initials: MM
authors.lastname: Shafer
authors.affiliation: University of California, Irvine, Department of Epidemiology, School of Medicine, Irvine, CA, USA.
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: Delfino
authors.affiliation: University of Southern California, Department of Civil and Environmental Engineering, Los Angeles, CA, USA. sioutas@usc.edu.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sioutas
mesh_terms: D016014:Linear Models; D015141:Los Angeles; D008670:Metals / Q000737:chemistry; D010084:Oxidation-Reduction; D052638:Particulate Matter / Q000032:analysis*; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry; D017382:Reactive Oxygen Species / Q000378:metabolism; D014315:Triterpenes / Q000737:chemistry; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D008670:Metals; D052638:Particulate Matter; D011084:Polycyclic Aromatic Hydrocarbons; D017382:Reactive Oxygen Species; D014315:Triterpenes; D001335:Vehicle Emissions; C025206:hopane