Authors
Jiejing Kong, Mingzhu He, Jintao Liu, Xinke Wang, Sebastien Perrier, Taicheng An, Christian George
Published in
Journal of environmental sciences (China). Volume 168. Pages 448-455. Epub Oct 25, 2025.
Abstract
Brown carbon (BrC) profoundly influences secondary organic aerosol (SOA) formation via photosensitized reactions in atmospheric condensed phases, yet the intrinsic oxidative power of its excited triplet state remains mechanistically unresolved. We reveal that the BrC proxy 1,4-naphthoquinone (NQ) undergoes dual photochemical pathways in deoxygenated aqueous systems, simultaneous self-photoconversion and substrate oxidation, enabled by two distinct, long-lived triplet states (3NQ* and 3OH-NQ*) with 3(n, π*) configurations generated under 355 nm irradiation. Crucially, 3NQ* acts as an endogenous oxidant, driving efficient hydrogen abstraction from key organic classes without requiring external oxidants. Oxidation kinetics exhibit a striking hierarchy governed by bond dissociation energies and one-electron oxidation potentials: alkanes (104 M-1s-1) < oxygenated alkanes (105 M-1s-1) < phenols (106 M-1s-1). Radical intermediates (alkyl, alkoxyl, phenoxy) dehydrogenate into stable products (e.g., benzoquinone from phenol), while the self-photoconversion product OH-NQ regenerates a secondary triplet (3OH-NQ*), amplifying oxidative cascades. This establishes 3BrC* as the dominant sink for phenols in BrC-rich haze, particularly under acidic, O2-limited conditions. Our findings provide kinetic and mechanistic benchmarks for integrating triplet-state chemistry into atmospheric models, advancing predictions of SOA formation in regions plagued by severe particulate pollution.
PMID:
42680402
Bibliographic data and abstract were imported from PubMed on 02 Sep 2026.
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