AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Increased Oxidative Potential of Fine Particulate Matter (PM2.5) Measured On-road of Major Freeways of Los Angeles, CA
FARIMAH SHIRMOHAMMADI, Dongbin Wang, Sina Hasheminassab, Vishal Verma, James Schauer, Martin Shafer, Constantinos Sioutas, University of Southern California
Abstract Number: 242 Working Group: Health Related Aerosols
Abstract This study describes a series of on-road sampling campaigns conducted using a mobile instrumentation platform to assess the chemical composition and oxidative potential of fine particulate matter (PM$_(2.5)) on three representative roadway environments in Los Angeles: 1) I-110, a highly trafficked freeway, consisting of almost exclusively light-duty vehicles (LDVs); 2) I-710, a freeway with higher fraction of heavy-duty vehicles (HDVs), which serves as the main corridor to and from the Ports of Los Angeles and Long Beach, and; 3) Wilshire/Sunset boulevards, which are two of the busiest surface streets in Los Angeles. Sampling was also conducted at the main campus of the University of Southern California (USC), representing an urban stationary reference site. The PM$_(2.5) samples were chemically analyzed for elemental carbon (EC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs) and 50 elements. PM$_(2.5) oxidative potential was also quantified using the dithiothreitol (DTT) assay. The cumulative mass fraction of the measured PAHs on the freeways was 3 and 3.3-fold higher than at Wilshire/Sunset and USC site, respectively. Mass fractions of Ba, Cr, Cu, Mn, Ni, Pb, Sb and Zn as common tracers of vehicular abrasion were 3.8±0.8 times higher on both freeways in comparison to surface streets (Wilshire/Sunset). The observed PM mass-normalized DTT activity was greatest on freeways, roughly 1.9 and 2.1 times higher than the values obtained at Wilshire/Sunset and USC, respectively. This observation underscores the important role of both tailpipe and non-tailpipe traffic emissions on the overall oxidative potential of urban PM. The higher freeway DTT activity levels (i.e. by a factor of 1.5-1.6) measured in our study compared to those in dynamometer facilities reflected the additional contribution of non-tailpipe emissions (e.g. re-suspended road dust and vehicular abrasions of brake and tire wear) to the PM$_(2.5) oxidative potential.