Oxidative Potential and ROS Speciation in Organoselenium Derived Secondary Organic Aerosols

MICHAEL LUM, Erin Bowey, Linhui Tian, Kunpeng Chen, Ningjin Xu, Ying Zhou, Alexa Canchola, Wonsik Woo, Don Collins, Roya Bahreini, Ying-Hsuan Lin, University of California, Riverside

     Abstract Number: 264
     Working Group: Aerosol Chemistry

Abstract
Trace levels of selenium (Se) are widespread and ubiquitous in the environment due to long-range transport processes through the atmosphere as alkylated organoselenium compounds or elemental Se produced from combustion. Dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe) are organoselenium compounds that produce secondary organic aerosols (SOA) through atmospheric oxidation. Prior laboratory experiments showed that Se-enriched SOA formed from the DMSe precursor had a higher oxidative potential than ambient urban aerosols. The resulting SOA contained a mixture of chemically reactive compounds, however, the presence and identities of radicals acting as reactive oxygen species (ROS) produced during this process have yet to be detailed. For this study, DMSe- and DMDSe-derived SOA samples from atmospheric oxidation under varying environmental conditions were collected and analyzed to determine their aerosol oxidative potential using the dithiothreitol (DTT) assay, as well as determine the identities and concentration of radical ROS using electron paramagnetic resonance (EPR) spectroscopy. The proportions of each radical species (e.g., hydroxyl radicals, superoxide or hydroperoxide radicals, alkyl radicals, and alkoxy radicals) normalized to the total radical concentration of each sample will be discussed. Though Se-rich aerosol has been shown to have higher oxidation potential, the results of this study will contribute to an improved understanding of the relative abundance and speciation of these ROS, which will have a large impact on possible secondary particle phase chemical reactions, major product identities, and oxidative stress in humans upon exposure.