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Catalytic role of atmospheric constituents in the formation of 6PPD-Quinone in a Korean Metropolitan Region
Summary
This research investigates how atmospheric constituents such as reactive gases, UV radiation, and oxidants act as catalysts in the physical and chemical degradation of larger plastic debris into secondary microplastics. Understanding these atmospheric pathways is important for modeling microplastic formation rates and developing strategies to reduce their accumulation in terrestrial and aquatic environments.
N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-quinone) is an oxidation product of the tire antioxidant 6PPD and has recently emerged as a toxic environmental contaminant. Although the transformation of 6PPD to 6PPD-quinone through ozone has been documented, the influence of other atmospheric constituents as catalysts remains inadequately characterized. This study assessed whether specific airborne elements promote the conversion of 6PPD to 6PPD-quinone. From 7 to 26 June 2024, total suspended particles were sampled at the National Institute of Environmental Research in Incheon, Republic of Korea. The elemental composition of collected samples was determined using energy-dispersive X-ray fluorescence, while 6PPD-quinone levels were measured by liquid chromatography–tandem mass spectrometry. Particle number and volume concentrations were recorded in parallel with a scanning mobility particle sizer and an optical particle sizer, along with real-time detection of black carbon, nitrogen dioxide, and ozone. Mean daytime 6PPD-quinone concentrations were measured at 0.12 ± 0.08 ng m− 3, displaying significant temporal variability (0.001–0.519 ng m− 3). Multivariate regression analysis identified bromine and vanadium as principal predictors of 6PPD-quinone abundance. Notably, strong correlations with particle characteristics indicated that these elements may act not only as markers of emissions but also as catalysts facilitating atmospheric transformation of 6PPD. This study offers the first mechanistic insight in Korea into the contribution of traffic-associated elements to 6PPD-quinone formation, which has important implications for urban air quality management and the assessment of ecological risks.