TY - JOUR
T1 - Oxidative potential of on-road fine particulate matter (PM2.5) measured on major freeways of Los Angeles, CA, and a 10-year comparison with earlier roadside studies
AU - Shirmohammadi, Farimah
AU - Wang, Dongbin
AU - Hasheminassab, Sina
AU - Verma, Vishal
AU - Schauer, James J.
AU - Shafer, Martin M.
AU - Sioutas, Constantinos
N1 - Funding Information:
The present project was supported by grant numbers 4R01AI065617-16 from the National Institute of Allergy and Infectious Disease (NIAID), and 1R01ES024936-01 from the National Institute of Environmental Health Sciences, U.S. National Institutes of Health (NIH). The authors wish to thank the staff of the Wisconsin State Laboratory of Hygiene (WSLH) for their assistance with the chemical analysis. We also acknowledge the support of University of Southern California Provost PhD fellowship.
Publisher Copyright:
© 2016 Elsevier Ltd
PY - 2017/1/1
Y1 - 2017/1/1
N2 - This study describes on-road measurements of fine particulate matter (PM2.5) using a mobile instrumentation platform to assess the chemical composition and oxidative potential of PM2.5, using the dithiothreitol (DTT) assay, over three representative roadways in the Los Angeles Basin: the I-110 and I-710 freeways, the Wilshire/Sunset boulevards as well as the main campus of the University of Southern California (USC), used as a reference urban background site. Samples were chemically analyzed for elemental carbon (EC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs) and 50 elements. The cumulative mass fraction of the measured PAHs was highest on the freeways (0.16 ± 0.01 and 0.15 ± 0.01 ng/μg PM, on I-110 and I-710, respectively); which on average 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, tracers of vehicular abrasion, were 3.8 ± 0.8 times higher on both freeways in comparison to Wilshire/Sunset. The observed intrinsic (normalized per PM mass) DTT activity was greatest on freeways, averaging 30.13 ± 3.15 nmol/min mg PM and being roughly 1.9 and 2.1 times higher than the values obtained at Wilshire/Sunset and USC, respectively. Furthermore, comparison of our results with previous on-road and roadside studies conducted in the last decade in Los Angeles indicated an overall reduction in the contribution of carbonaceous species and PAHs (important tracers of exhaust emissions) to PM mass, especially on I-710 freeway with the higher heavy-duty diesel vehicle fraction, indicating the effectiveness of diesel vehicle emissions control policies implemented in recent years in California. In contrast, greater contributions of certain groups of metals and trace elements that are indicators of non-tailpipe emissions compared to previous studies provide evidence on the increasing importance of non-tailpipe emissions to the oxidative potential of on-road PM2.5 as vehicular exhaust emissions becomes cleaner. This finding was also reflected in the increased levels of on-road DTT activity by factors of 1.4–1.5 in comparison to the DTT activity of vehicular emissions estimated in previous dynamometer studies.
AB - This study describes on-road measurements of fine particulate matter (PM2.5) using a mobile instrumentation platform to assess the chemical composition and oxidative potential of PM2.5, using the dithiothreitol (DTT) assay, over three representative roadways in the Los Angeles Basin: the I-110 and I-710 freeways, the Wilshire/Sunset boulevards as well as the main campus of the University of Southern California (USC), used as a reference urban background site. Samples were chemically analyzed for elemental carbon (EC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs) and 50 elements. The cumulative mass fraction of the measured PAHs was highest on the freeways (0.16 ± 0.01 and 0.15 ± 0.01 ng/μg PM, on I-110 and I-710, respectively); which on average 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, tracers of vehicular abrasion, were 3.8 ± 0.8 times higher on both freeways in comparison to Wilshire/Sunset. The observed intrinsic (normalized per PM mass) DTT activity was greatest on freeways, averaging 30.13 ± 3.15 nmol/min mg PM and being roughly 1.9 and 2.1 times higher than the values obtained at Wilshire/Sunset and USC, respectively. Furthermore, comparison of our results with previous on-road and roadside studies conducted in the last decade in Los Angeles indicated an overall reduction in the contribution of carbonaceous species and PAHs (important tracers of exhaust emissions) to PM mass, especially on I-710 freeway with the higher heavy-duty diesel vehicle fraction, indicating the effectiveness of diesel vehicle emissions control policies implemented in recent years in California. In contrast, greater contributions of certain groups of metals and trace elements that are indicators of non-tailpipe emissions compared to previous studies provide evidence on the increasing importance of non-tailpipe emissions to the oxidative potential of on-road PM2.5 as vehicular exhaust emissions becomes cleaner. This finding was also reflected in the increased levels of on-road DTT activity by factors of 1.4–1.5 in comparison to the DTT activity of vehicular emissions estimated in previous dynamometer studies.
KW - Dithiothreitol (DTT) assay
KW - EC and OC
KW - Metals and elements
KW - Oxidative potential
KW - Particulate matter
KW - Tailpipe and non-tailpipe emissions
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U2 - 10.1016/j.atmosenv.2016.10.042
DO - 10.1016/j.atmosenv.2016.10.042
M3 - Article
AN - SCOPUS:84995471886
SN - 1352-2310
VL - 148
SP - 102
EP - 114
JO - Atmospheric Environment
JF - Atmospheric Environment
ER -