Photooxidative Fate of Atmospheric Methylated Selenium Compounds

ERIN BOWEY, Yumeng Cui, Roya Bahreini, Kunpeng Chen, Linhui Tian, Michael Lum, Ying-Hsuan Lin, Don Collins, University of California, Riverside

     Abstract Number: 281
     Working Group: Aerosol Chemistry

Abstract
Atmospheric oxidation of methylated selenium compounds can lead to formation of secondary organic aerosols (SOAs). The nature and degree of the toxic effects of Se-containing organic compounds in the environment and on human health depend largely on their oxidation state and gas-particle partitioning potential. To explore this, photooxidation experiments of dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe) precursors under low NOx conditions were carried out in an environmental chamber. An aerosol mass spectrometer (mAMS), a Scanning Electrical Mobility Spectrometer (SEMS), and a chemical ionization mass spectrometer (I- ToF-CIMS) were used to investigate online aerosol composition, size distribution, and gas phase concentration of the formed products. A denuder and filter pack system was also used to collect gaseous and particulate samples both before and after the peak in SOA mass concentration was reached for offline analysis of carbonyls. This allows the evolution of the products’ oxidation state and partitioning behavior over time to be followed. The denuders and filters were coated with the derivatizing agent, O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) which converts the carbonyl species into their oxime derivatives for immediate extraction post-sampling and analysis with GC-MS. It is expected that higher carbon oxidation states will be observed after peak mass loading is reached than before, and that the gas phase samples will be dominated by small carbonyls while the particle phase will contain large carbonyls containing Se in their backbone. Lastly, PTFE filter samples were collected near the end of each experiment to obtain molecular information of the formed SOAs by offline analysis on FIGAERO-ToF-CIMS (I-). Results from these various measurements will be synthesized to improve our understanding of atmospheric chemistry of methylated Se species under low NOx conditions.