Unveiling the Hidden Role of Zinc in Aerosol Oxidative Potential: From Coordination Competition to Metal Specific Interplay

Previous studies have shown that the oxidative potential (OP) of fine particulate matter (PM2.5) is mainly driven by redox-active transition metals and organic compounds. Although multiple studies have found that the non-redox-active metal zinc (Zn), which is enriched in PM2.5, is associated with OP, the OP activity it exhibits is limited and its mechanistic role has not been fully elucidated. Although Zn itself does not directly participate in electron transfer, it has a relatively strong binding affinity for molecules such as dithiothreitol (DTT). In this study, the reactive behavior of Zn was systematically evaluated under controlled conditions, and its interactions in the DTT depletion system with redox-active transition metals (Cu, Fe, Mn) and quinone compounds (phenanthrenequinone, 1,4-naphthoquinone, and 1,2-naphthoquinone) present in PM2.5 components were quantitatively analyzed. The results confirmed that Zn itself has negligible intrinsic redox activity in the DTT detection system. However, in complex systems where other metals or organic components coexist, Zn significantly regulates the overall OP and exhibits clear metal and organic specificity. This differential interaction pattern indicates that Zn profoundly interferes with the oxidation process through indirect mechanisms. Its potential mechanisms may involve competition for DTT coordination sites, the formation of new metal ligand complexes, and changes in the speciation of catalytically active metals. In addition, potential interactions between Zn and organic components in PM2.5 suggest that it may further alter the reaction kinetics of electron transfer through ligand-mediated pathways. To reveal the molecular basis of these complex interactions, mass spectrometry (MS) will be used to investigate the formation of reaction intermediates and molecular transformation pathways. Detailed kinetic modeling and deeper mechanistic elucidation will be presented at the conference.