| 08 Jul 2026
An Underappreciated Aqueous Pathway for Particle Oxidative Potential (OP): Mechanistic Insights into OP-Relevant Products from α-Dicarbonyl and Reduced Nitrogen Reactions
Abstract. Aqueous-phase reactions between α-dicarbonyls and reduced nitrogen species represent an understudied pathway generating secondary organic aerosols that exhibit oxidative potential (OP). In this study, we investigated the OP of products formed from methylglyoxal (MG) or glyoxal (GX) reacting with ammonium sulfate (AS) or glycine (Gly) under varying pH (3–7) and reaction times (4–144 h). OP was quantified using dithiothreitol (DTT) depletion and hydroxyl radical (•OH) production assays, while molecular composition was characterized using high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy. The results demonstrate that OP is strongly dependent on precursor identity, pH, and reaction time. Products from the MG+Gly system consistently exhibit the highest OPDTT and OPOH. Molecular analysis indicates that CHO species, including conjugated carbonyls and quinones, are primarily responsible for DTT activity, whereas N-heterocycles with unprotonated N-bases drive •OH formation. Electron-withdrawing substituents adjacent to the unprotonated N atoms enhance electron-transfer capability, thereby increasing the ability of N-heterocycles to generate •OH. N-heterocycles also act synergistically with quinone-like species to promote DTT oxidation, highlighting their dual role in modulating OP. Collectively, these findings reveal that aqueous reactions between α-dicarbonyls and reduced nitrogen species can produce secondary organic aerosols with substantial oxidative capacity, which may contribute to oxidative stress and cause adverse health effects. This work advances mechanistic understanding of aerosol OP and emphasizes the importance of considering aqueous-phase chemistry when evaluating the health-relevant oxidative properties of ambient particulate matter.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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