Roles of Functional Groups in ROS Production by Fresh and Aged Aerosols

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. Both catalytic reactive (e.g., quinones) and non-catalytic reactive species (e.g., organic hydroperoxides and Michael acceptors) in particulate matter (PM) have been recognized as the main contributors to ROS generation. Recently, the aging process has been found to have a significant effect on the oxidative potential (the ability to generate ROS) of PM. However, the connection between dynamic change of chemical compositions of PM and its oxidative potential during the aging process has not been fully unveiled yet. Recent studies proposed that the dynamic change of oxidative components in PM contribute to the corresponding change of oxidative potential. In this study, to compare the ROS generation ability of fresh and aged PM, we measured the oxidative potential of anthropogenic and biogenic secondary organic aerosols using dithiothreitol (DTT) assay and characterized the chemical compositions using both chemical assays and gas chromatograph mass spectrometry. We observed that quinones are not important contributors to the DTT reaction rates of secondary organic aerosols (SOA) derived from isoprene or toluene. The oxidative potential of SOA in different aging stages was largely determined by the concentration of organic hydroperoxides (e.g. isoprene hydroxy hydroperoxide-derived components) for isoprene SOA and reactive Michael acceptors for toluene SOA. These results will provide molecular insights into the interpretation of the aging process on adverse health effects of SOA in respect to their ROS production ability.