Seasonal Dynamics of 6PPD and 6PPD-Quinone in Road Dust: Effects of Winter Tire Use and Precipitation in a Snowy Region of Japan

Seasonal variations of the tire-derived antioxidant N -(1,3-dimethylbutyl)- N '-phenyl- p -phenylenediamine (6PPD) and 6PPD-derived quinone (6PPDQ) in road dust were investigated in a snowy region of Japan during 2024. Concentrations of 6PPD and 6PPDQ ranged from 12–625 ng g⁻ 1 (median: 164 ng g⁻ 1 ) and 6.2–834 ng g⁻ 1 (median: 107 ng g⁻ 1 ), respectively. The median 6PPD concentration across six sampling sites showed a U-shaped seasonal pattern, with higher concentrations in February and December and lower concentrations from June to August. In contrast, 6PPDQ exhibited a high-concentration phase from February to June and a low-concentration phase from August to December. Exploratory multiple regression analysis revealed that the median concentration of 6PPD was associated with winter-tire usage rate and precipitation (Z = 0.77Z winter-tire usage rate − 0.26Z precipitation ), with a significant positive coefficient observed for the winter-tire usage rate (95% confidence interval: 0.11 to 1.4, p -value = 0.034). For 6PPDQ, a similar analysis showed a significant negative association between its median concentration and precipitation (Z = − 0.72Z winter-tire usage rate − 1.3Z precipitation , 95% confidence interval: − 2.4 to − 0.16, p -value = 0.036). The relative abundance of 6PPDQ [6PPDQ/(6PPD + 6PPDQ)] peaked in June. Least absolute shrinkage and selection operator (LASSO) retained solar radiation as the only predictor in the final model for the 6PPDQ ratio (standardized β = 0.67). Solar radiation had the highest bootstrap selection frequency (93%), although its 95% bootstrap percentile interval included zero (0–0.77). Collectively, these findings indicate that seasonal concentrations in this snowy urban environment may reflect a balance among tire-wear inputs, precipitation-related removal or redistribution, and environmental transformation processes.