AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Oxidative Potential of Ambient Ultrafine Particulate Matter in the Los Angeles Air Basin: Possible Impact of Atmospheric Aging
ARIAN SAFFARI, Sina Hasheminassab, Dongbin Wang, Martin Shafer, James Schauer, Constantinos Sioutas, University of Southern California
Abstract Number: 90 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract There is growing literature supporting the hypothesis that the most important pathway underlying the adverse health effects of exposure to particulate matter (PM) is the oxidative stress derived from the interaction of PM with cells. Differences in the chemical and physical properties of particles from secondary and primary sources can potentially lead to differences in their oxidative potential. The effect of aging on PM oxidative potential, measured by chemical (abiotic) assays (e.g. DTT assay), has been investigated in previous chamber studies and increased ROS activity for photochemically-aged particles compared to fresh particles was reported. Other than smog chamber measurements, previous dynamometer studies imply the possible effect of aging on the ROS activity as well. This study aims to investigate the effect of atmospheric aging on the oxidative potential using field measurement techniques, in order to provide much-needed insight regarding the toxicity of airborne particles in the real-world urban atmosphere rather than laboratory conditions. To this end, ultrafine particles were collected at 3 locations along the prevailing air trajectory across the Los Angeles south coast air basin at three specific time periods of the day (morning rush hour at the source location, followed by mid-day and afternoon at the two further downwind regions) and oxidative potential of the particles were quantified. Furthermore, comprehensive chemical analysis was conducted on the collected samples, followed by source apportionment of organic carbon (OC) using Chemical Mass Balance (CMB) Receptor Modeling. Secondary organic aerosol (SOA) and vehicular emissions were by far the two most dominant sources of OC at all three locations, with increased concentration of SOA at the downwind regions. Univariate and Multivariate regression analysis between the ROS activity and the CMB-derived sources indicated an increased contribution from SOA as the particles move along the basin and get aged throughout the mid-day and afternoon periods.