Tire Rubber-Derived Cyclic Amines in Urban Ambient Particulate Matter in Shanghai

Tire wear compounds (TWCs) and their byproducts have raised increasing environmental and health concerns due to their widespread production and release. In this study, a custom-designed versatile aerosol concentration enrichment system coupled with HPLC-Q-TOF-MS was employed to conduct a nontargeted screening of suspect TWCs in urban PM_2.5, followed by the targeted quantification of ten selected TWCs, providing high temporal resolution data across summer, autumn, and winter in Shanghai. The total TWC concentrations (∑TWCs) exhibited distinct seasonal variations. The highest levels were observed in autumn, with an average concentration of 15.53 ng/m³ (ranging from 1.39 to 58.67 ng/m³), followed by summer with an average of 7.44 ng/m³ (2.22 to 25.39 ng/m³), and the lowest levels observed in winter, with an average of 5.74 ng/m³ (1.56 to 17.83 ng/m³). The seasonal contributions of ∑TWCs were 73.9% in the autumn, 18.6% in the summer, and 7.5% in the winter. The diurnal pattern showed elevated nighttime concentrations compared with morning and evening rush hours. This study marks the first to investigate the diurnal variation in the ratio of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) to its parent compound, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), in the atmospheric particle phase. The ratio showed a similar daily pattern, peaking in the afternoon and reaching 3.64 in the summer and 6.55 in the autumn, in alignment with temperature and ozone patterns. Correlation analysis showed weak relationships between ∑TWCs and temperature (R = 0.12) as well as a weak negative correlation with humidity (R = -0.04). These findings highlight the need for further research into the toxicological and epidemiological impacts of TWCs, especially considering the heightened levels of nighttime exposure among night workers.