Effects of Different Transition Metal Oxide Mineral Dusts on Secondary Organic Aerosol Photochemistry

Secondary organic aerosols (SOA) can undergo photochemical aging upon solar irradiation, changing their physical and chemical properties. Mineral dust particles internally mixed with SOA may act as a heterogeneous photocatalytic surface, altering the photochemical aging processes available to SOA compounds and changing their overall composition. We examined aqueous photodegradation of laboratory-generated α-pinene ozonolysis SOA in the presence of α-Fe2O3 (hematite), TiO2 (anatase), Arizona test dust (AZTD), and automotive ceramic brake pad dust. Anatase, a well-known photocatalyst, accelerated the photodegradation of SOA as expected. While hematite did not display the photocatalytic properties of anatase, its presence in solution did change the distribution of photoproducts for select SOA compounds such as cis-pinonic acid. Arizona test dust and brake wear dust behaved more similarly to hematite than anatase, displaying low photocatalytic activity but subtly changing the distribution of photodegradation products.