Redox activity and chemical speciation of size fractioned PM in the communities of the Los Angeles-Long Beach harbor S. Hu1, A. Polidori1, M. Arhami1, M. M. Shafer2, J. J. Schauer2, A. Cho3, and C. Sioutas1 1University of Southern California, Department of Civil and Environmental Engineering, 3620 South Vermont Avenue, Los Angeles, CA 90089, USA 2University of Wisconsin-Madison, Environmental Chemistry and Technology Program, 660 North Park Street, Madison, WI 53706, USA 3University of California, Los Angeles, School of Medicine, Los Angeles, CA 90095, USA
Abstract. In this study, two different types of assays were used to quantitatively
measure the redox activity of PM and to examine its intrinsic toxicity: 1)
in vitro exposure to rat alveolar macrophage (AM) cells using dichlorofluorescin
diacetate (DCFH-DA) as the fluorescent probe (macrophage ROS assay), and: 2)
consumption of dithiothreitol (DTT) in a cell-free system (DTT assay).
Coarse (PM10–2.5), accumulation (PM2.5–0.25), and quasi-ultrafine
(quasi-UF, PM0.25) mode particles were collected weekly at five
sampling sites in the Los Angeles-Long Beach harbor and at one site near the
University of Southern California campus (urban site). All PM samples were
analyzed for organic (total and water-soluble) and elemental carbon, organic
species, inorganic ions, and total and water-soluble elements. Quasi-UF mode
particles showed the highest redox activity at all Long Beach sites (on both
a per-mass and per-air volume basis). A significant association (R2=0.61)
was observed between the two assays, indicating that macrophage ROS
and DTT levels are affected at least partially by similar PM species.
Relatively small variation was observed for the DTT measurements across all
size fractions and sites, whereas macrophage ROS levels showed more
significant ranges across the three different particle size modes and
throughout the sites (coefficients of variation, or CVs, were 0.35, 0.24 and
0.53 for quasi-UF, accumulation, and coarse mode particles, respectively).
Association between the PM constituents and the redox activity was further
investigated using multiple linear regression models. The results showed
that OC was the most important component influencing the DTT activity of PM
samples. The variability of macrophage ROS was explained by changes in OC
concentrations and water-soluble vanadium (probably originating from ship
emissions – bunker oil combustion). The multiple regression models were
used to predict the average diurnal DTT levels as a function of the OC
concentration at one of the sampling sites.
Citation: Hu, S., Polidori, A., Arhami, M., Shafer, M. M., Schauer, J. J., Cho, A., and Sioutas, C.: Redox activity and chemical speciation of size fractioned PM in the communities of the Los Angeles-Long Beach harbor, Atmos. Chem. Phys., 8, 6439-6451, doi:10.5194/acp-8-6439-2008, 2008.