Effect of Mineral Dust Transition Metal Oxides on Photochemistry of Secondary Organic Aerosols
ANTHONY JUE, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 572
Working Group: Aerosol Chemistry
Abstract
Secondary Organic Aerosol (SOA) makes up a significant fraction of particles in our atmosphere. Volatile organic compounds emitted by biogenic and anthropogenic sources oxidize in the atmosphere through different gas phase reactions and condense into the particle phase, where they can further transform through photochemical processes from solar UV radiation. These processes generate a variety of organic products, resulting in different physical and chemical properties of the resulting aerosol. In addition, organic and aqueous phase compounds can mix with insoluble materials such as mineral dust particles. Mineral dust can contain a variety of transition metal compounds such as metal oxides of iron and titanium, possibly acting as a photocatalytic surface resulting in different chemical transformations during photochemical aging. Soluble iron has been shown to participate in photocatalytic systems such as the Fenton and photo-Fenton cycle, as well as isomerization, oligomerization, and photodegradation reactions. Similarly, titanium dioxide has been shown to be photocatalytic in the UV range, breaking down SOA components. The objective of this study is to determine whether the insoluble mineral dust components such as Fe2O3 (hematite), TiO2 (anatase) and Arizona Test Dust could act as heterogeneous photocatalysts with complex mixtures of lab-generated SOA from α-pinene ozonolysis and naphthalene photooxidation, as well as other single molecules commonly found in SOA. These were modeled in lab solutions with mineral dust slurries photoaged under UV-B light sources and analyzed with UPLC-HRMS to identify the products resulting from these different aging environments. Results have shown that while titanium dioxide behaves as expected in breaking down organic species, hematite does not show the same ability, having little to no effect on the overall product distribution.