Molecular Composition of Organic Peroxides in Secondary Organic Aerosols Revealed by Peroxide-Iodide Reactivity

Organic peroxides are recognized as major contributors
to the toxicity
and adverse health effects of secondary organic aerosols (SOA). However,
their molecular composition and chemical properties in SOA remain
largely unexplored. Here we develop a novel analytical strategy for
the molecular characterization of organic peroxides in α-pinene
SOA, combining iodometry kinetic experiments with liquid chromatography–high-resolution
mass spectrometry. Using non-targeted analysis, we identify over 300
organic peroxides in α-pinene SOA, showing a wide range of reactivities
with iodide, spanning 4 orders of magnitude. The structures of 12
organic peroxides derived from stabilized Criegee intermediates are
further proposed and discussed. Our findings present a reliable, standard-free
methodology for identifying previously uncharacterized organic peroxides
in SOA at the molecular level, offering new avenues for investigating
formation pathways and health impacts of this large, diverse, yet
rarely explored compound class. Additionally, we propose peroxide-iodide
reactivity as a novel metric for future predictions of oxidative potentiala
key indicator of toxicityand for elucidating the structure
of individual organic peroxides in SOA.