Widespread Occurrence of Tire Wear p-Phenylenediamines and Their Quinones in Cloud Water

P-Phenylenediamines (PPDs), widely used tire antioxidants, undergo oxidation to form toxic quinones (PPD-Qs). Despite their detection in diverse environmental media, the role of cloud water in environmental fate remains unknown. This study employed ultrahigh-performance liquid chromatography-Orbitrap mass spectrometry to investigate ten PPDs and PPD-Qs in cloud water collected from Tianmu Mountain in China─a remote background site with minimal industrial/human activity. The concentrations of PPDs (3.0-43.7 ng/L) are markedly exceeding their transformation products (PPD-Qs, 0.2-11.5 ng/L), with IPPD and 6PPD dominating. PPDs exhibited greater accumulation in water-insoluble organic matter (WISOM) than in water-soluble organic matter (WSOM), with enrichment factors (concentration of PPDs in WISOM/concentration of PPDs in WSOM) ranging from 1.13 to 1.88, indicating a stronger tendency for particle-phase partitioning. Significant positive correlations linked PM_2.5 levels with the deposition fluxes of both PPDs and PPD-Qs in WSOM and WISOM, demonstrating cloud water's key role in their atmospheric transport and wet deposition. This study presents the first characterization of PPDs and their quinone derivatives' distribution and environmental behavior in cloud water, revealing clouds' significant role in the fate of rubber-derived pollutants. The findings reveal clouds as pivotal reactors for tire-derived pollutants, driving oxidation and multiphase portioning, previously overlooked in global contaminant cycling.