Ambient fine particulate matter (PM 2.5 ) continues to pose significant environmental and public health challenges, with increasing evidence that emerging organic contaminants enhance its toxicity. One such contaminant, the tire-derived transformation product N-(1,3-dimethylbutyl)-N′-phenyl-p-benzoquinone (6PPD-Q), has garnered attention due to its high aquatic toxicity and redox activity. This study examined the seasonal patterns, sources, and oxidative potential of PM 2.5 at a rural site in South Korea, which is influenced by both agricultural and urban emissions. We analyzed a year-long dataset of PM 2.5 (from March 2023 to February 2024) for its chemical composition, including tracers from biomass and plastic burning, metals, and 6PPD-Q, alongside quinone-normalized dithiothreitol oxidative potential (QDTT-OP). Through Positive Matrix Factorization, five major sources were identified: vehicle emissions, agricultural residue burning, long-range transport, secondary nitrate, and secondary sulfate. Vehicle emissions were the primary source overall and particularly during the summer, while agricultural residue burning contributed significantly in the spring and autumn. 6PPD-Q levels peaked during warmer months and showed a strong correlation with vehicle emissions, oxidative potential, transition metals (Ni, V), sulfate, and aerosol acidity. These results indicate that the formation of 6PPD-Q is influenced not only by the availability of oxidants but also by the catalytic and acidic conditions of aerosol microenvironments. Our findings underscore the crucial roles of non-exhaust traffic emissions and agricultural burning in driving the oxidative burden of PM 2.5 and the associated health risks. • Vehicle and agricultural burning contribute to the seasonal levels of PM 2.5 mass and toxicity. • 6PPD-quinone peaks during warm seasons and correlates with traffic sources. • Ni, V, and acidity accelerate the formation of oxidative 6PPD-Q.
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