Aqueous Processing of Volatile Organoselenium-derived Secondary Aerosols Results in Reactive Oxygenated Species Production
MICHAEL LUM, Ying Zhou, Erin Bowey, Lillian Tran, Linhui Tian, Wonsik Woo, Dimitri Niks, Aiden Pianalto, Yiwen Zhu, Yujie Men, Don Collins, Roya Bahreini, Ying-Hsuan Lin, University of California, Riverside
Abstract Number: 149
Working Group: Aerosol Chemistry
Abstract
Dimethyl selenide (DMSe) and dimethyl sulfide (DMS) are major organoselenium and organosulfur species that are released from phytoplankton in marine environments and undergo atmospheric oxidation to form secondary aerosols (SA). Prior studies indicate that DMSe-derived secondary aerosols exhibit elevated oxidative potential. However, the role of Se and the underlying processes responsible for reactive oxygen species (ROS) production along with the impact on aqueous environmental systems remain unclear. In this study, we used electron paramagnetic resonance spectroscopy (EPR) to detect, quantify, and contrast ROS produced by DMSe- and DMS-derived secondary aerosols in aqueous solutions and X-ray photoelectron spectroscopy (XPS) to confirm oxidation state changes for Se elements before and after dissolution. DMSe-derived aerosols and DMS-derived aerosols produced 9.0 ± 2.1 nmol ·OH/µg SA and 0.29 ± 0.11 nmol ·OH/µg SA, respectively. The average 33-fold difference in ·OH produced by each system implies different dominating mechanism of formation. The sulfur-containing system will form ·OH through peroxide decomposition, while the selenium-containing system is capable of producing ·OH through Fenton-like chemistry in addition to potential peroxide decomposition. Se was observed to cycle between oxidation states Se(0), Se(IV), and Se(VI) when exposed to water, catalyzing the production of ·OH. Selenate (SeO42-), selenite (SeO32-), selenium dioxide (SeO2), and methane seleninic acid (CH4O2Se) were confirmed to be redox-active compounds within DMSe-derived secondary aerosols driving the production of ·OH radicals. This study highlights the redox cycling of atmospheric particulate Se species in the production of ·OH radicals in aqueous environments, which has important implications for atmospheric aqueous chemistry and biogeochemical cycling.