Dependence of Reactive Oxygen Species Formation on Oxidation State of Biogenic Secondary Organic Aerosols

KASEY EDWARDS, Lena Gerritz, Manjula Canagaratna, Anita Avery, Mitchell Alton, Andrew Lambe, Sergey Nizkorodov, Manabu Shiraiwa, University of California, Irvine

     Abstract Number: 474
     Working Group: Aerosol Chemistry

Abstract
Reactive oxygen species (ROS) play a central role in chemical aging of organic aerosols and adverse aerosol health effects upon respiratory deposition. Previous research has shown that reactive compounds such as hydroperoxides and alcohols that are present in biogenic secondary organic aerosols (SOA) form ROS. However, the influence of aging and/or SOA oxidation state on ROS yield has not been systematically investigated. In this study we quantify ROS yield in limonene SOA generated in an oxidation flow reactor (OFR) at equivalent atmospheric aging times ranging from approximately 1 to 10 days. Aqueous ROS is quantified in limonene SOA filter samples collected from the OFR using electron paramagnetic resonance (EPR) spectroscopy combined with a spin-trapping technique. We also analyze the detailed molecular composition of the SOA samples with high-resolution mass spectrometry. We observe a ~50% decrease in ROS yield when the oxygen-to-carbon ratio (O:C) of limonene SOA increases from 0.5 to 1. Similarly, the ROS yield in limonene SOA is reduced by up to 90% following 30 hrs of on-filter photoirradiation. Overall, our results suggest that the ROS yield in “fresh” limonene SOA, generated at low photochemical age, decreases due to aging-induced fragmentation and/or photolysis of species such as organic hydroperoxides that contribute to ROS formation.