Secondary Aerosol Formation and Potential Reaction Pathways of the Photooxidation of Dimethyl Selenide with and without NO x

Abstract Once methylated selenium (Se) compounds such as dimethyl selenide (DMSe) are emitted into the troposphere by marine or terrestrial plants and microbes, they are subject to photooxidation by OH radicals during the day. It has been reported that atmospheric processing of these compounds can produce oxidized organic and inorganic gaseous pollutants and Se-containing secondary aerosol particles. However, the details of the involved reactions and their dependence on other pollutants such as NOx, the intermediate and product identities, and chemical properties of the resulting aerosol remain understudied, limiting our ability to accurately predict their environmental fate, transport, and impacts. This study aims to investigate the identities of gas- and particle-phase reaction products as well as the bulk properties of the aerosol particles generated by DMSe oxidation by OH radicals in an environmental chamber, in the absence or presence of NOx, using a suite of on- and offline mass spectrometry techniques. Differences in particle number concentration and observed products were shown between the two conditions. Identified products included but are not limited to inorganics such as selenium dioxide (SeO2), selenous acid (H2SeO3), and selenic acid (H2SeO4) under both oxidative conditions, as well as organics such as dimethyl selenone ((CH3)2SeO2), methaneselenonic acid (CH4SeO3), and hydroperoxymethylselenoformate (HPMSeF) by OH-dominated oxidation, and nitrogen-containing species such as CHSeNO4 and CH3SeNO5 only under the NOx-influenced oxidation.