AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Aerosol-mediated ROS Production: Roles of Functional Groups and Reaction Kinetics
HUANHUAN JIANG, Jin Chen, C.M. Sabbir Ahmed, Zixu Zhao, Haofei Zhang, Ying-Hsuan Lin, University of California, Riverside
Abstract Number: 82 Working Group: Health-Related Aerosols
Abstract The toxicity of organic aerosols has been largely ascribed to the generation of reactive oxygen species (ROS), which could subsequently induce oxidative stress in biological systems. Dithiothreitol (DTT) assay is an acellular assay widely used to determine the oxidative potential (the ability to generate ROS) of different types of PM at a laboratory benchtop scale. Both inorganic (i.e., transition metals) and organic species (i.e., quinones, organic hydroperoxides and electron deficient alkenes) in PM have been recognized as the main contributors to DTT responses. Conventionally, the reaction of DTT with redox-active species in PM has been assumed to be pseudo-first order, and the oxidative potential of PM is represented by the DTT consumption per minute of reaction time per µg of PM. However, inconsistency of DTT results among different studies has been reported. Recent studies have shown that the DTT consumption rate of PM decreased significantly with reaction time, which highlights the necessity of taking the reaction kinetics and mechanisms of DTT assay into consideration when interpreting DTT results. In this study, we investigated the reaction kinetics of DTT with model organic compounds with various functional groups. We observed that the DTT consumption rate largely depends on the initial sample and DTT concentrations. The reaction order of DTT with non-catalytic reactive species (e.g., conjugated carbonyls and organic hydroperoxides) is higher than first order. The reaction of DTT with different functional groups have significantly different rate constants. A predictive multiple linear regression model is developed to estimate the contributions of aerosol functional groups to oxidative potential using the measured reaction rate constants. This model will be applied to the DTT measurements of primary (e.g., e-cigarette smoke particles and diesel exhaust particles) and secondary organic aerosols (e.g., isoprene and toluene SOA). This study will provide molecular insights into the interpretation of DTT-based aerosol oxidative potential.