EPFR-mediated enhancement of atmospheric oxidants dominates the photochemical transformation of acenaphthylene on mineral dusts

Abstract

Polycyclic aromatic hydrocarbons (PAHs) and mineral dusts are the key toxic and reactive components of atmospheric particulate matter (PM_2.5). Their synergistic conversion poses significant adverse environmental concerns but remains underexplored, especially for photoactive particles. Here, we conduct an in-depth study of the photochemical transformation mechanism of acenaphthylene (ACY), a common atmospheric PAH, on the surface of typical mineral dusts. Notably, TiO₂ induces the formation of environmentally persistent free radical (EPFR) upon the “cation-π” interaction with ACY, thereby promoting the generation of atmospheric oxidants and significantly enhancing the photochemical conversion of ACY. In contrast, Fe₂O₃ and SiO₂ primarily serve as inert carriers with minimal effect. EPFR-mediated hydroxyl radical (·OH) is identified to be the dominant reactive species in the photochemical transformation of ACY, driving nearly 100% conversion. Oxygenated PAHs (OPAHs), which likely aggravate the formation of secondary organic aerosols (SOA), are the main products. In addition, the enhanced ACY transformation has also been verified on the natural kaolinite, underscoring the universality of this mechanism in atmospheric chemistry. This work proposes a new pathway for the photochemical transformation of PAH on the surface of photoactive mineral particles mediated by EPFR, providing unique perspectives and deep insights into the enhanced atmospheric oxidizing capacity and the photochemical transformation from organic carbon (OC) into SOA.

Graphical abstract

Keywords

Atmospheric photochemical reaction / Photoactive mineral dust / Environmental persistent free radicals / Photocatalysis / Polycyclic aromatic hydrocarbon

Highlight

	● The photochemical transformation of ACY was greatly enhanced on photoactive mineral particles.
	● PTR-TOF-MS revealed OPAHs as the main products.
	● OH mediated by EPFR through the “O2 →·O2−→H2O2→·OH” pathway was the dominant factor that directly resulted in almost 100% conversion of ACY.

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