AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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The Relative Importance of Tailpipe and Non-tailpipe Emissions on the Oxidative Potential of Ambient Particles in Los Angeles, CA
FARIMAH SHIRMOHAMMADI, Sina Hasheminassab, Dongbin Wang, James Schauer, Martin Shafer, Ralph J. Delfino, Constantinos Sioutas, University of Southern California
Abstract Number: 244 Working Group: Source Apportionment
Abstract This study examines the associations between the oxidative potential of ambient PM$_(2.5) and PM$_(0.18), measured by means of the dithiothreitol (DTT) assay, and their chemical constituents and modeled sources. Particulate matter (PM) samples were collected during 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 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 PM$_(0.18) versus PM$_(2.5) 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, 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. This was also reflected in DTT activity levels’ comparison with previous studies conducted in Central LA for PM$_(2.5) and PM$_(0.18) in the past decade. The trends revealed a reduction in PM$_(0.18) DTT activity, while a slight increase was observed for PM$_(2.5) size range.