Role of Selenium in Production of Reactive Oxygen Species from Aqueous Processing of Dimethyl Selenide-Derived Secondary Aerosols.

Dimethyl selenide (DMSe) is the simplest volatile organoselenium compound that can undergo atmospheric oxidation to form secondary aerosols. While the oxidative potential of DMSe-derived aerosols has been shown to be greater compared to that of ambient aerosols from various sources, the role of selenium (Se) in processes governing reactive oxygen species (ROS) production remains unclear. Utilizing dimethyl sulfide (DMS) as a chemical analogue and mechanistic control of DMSe, we detected, quantified, and contrasted ROS produced by DMSe- and DMS-derived aerosols in aqueous solutions and confirmed the changes in Se oxidation state after dissolution. DMSe- and DMS-derived aerosols produced 9.0 ± 2.1 nmol ·OH/μg-aerosol and 0.29 nmol ± 0.11 ·OH/μg-aerosol, respectively. The average 33-fold difference in ·OH produced in these systems implies different dominating mechanisms of formation. DMS-derived aerosols can generate ·OH through organic hydroperoxide decomposition, whereas DMSe-derived aerosols are additionally capable of producing ·OH through Fenton-like reactions by cycling among Se(0), Se(IV), and Se(VI). Selenate (SeO₄²⁻), selenite (SeO₃²⁻), selenium dioxide (SeO₂), and methane seleninic acid (CH₄O₂Se) were redox-active compounds confirmed within DMSe-derived aerosols. This study highlights the redox cycling of particulate Se and the production of aqueous ·OH, which have important implications for atmospheric aqueous chemistry and Se biogeochemical cycles.