Temperature as a key driver of PM_2.5 tire additive pollution: Seasonal variability and climate-driven elevation of...

Tire and road wear particles (TRWPs) generated during vehicle use are an emerging non-exhaust source of fine particulate matter (PM_2.5). Due to its small aerodynamic diameter and high surface area, PM_2.5 can efficiently carry organic additives originating from tire formulations, including benzothiazoles (BTHs) and substituted p-phenylenediamines (PPDs), as well as their transformation products. While vehicle ownership in Korea continues to increase, long-term characterization of these tire-derived additives in ambient PM_2.5 has not yet been reported. Here, we collected 74 PM_2.5samples in Daegu, Korea (October 2024-July 2025) and conducted, to our knowledge, the first long-term qualitative and quantitative analysis of tire additives in Korean urban air, accompanied by a preliminary inhalation risk assessment. Nine additives were identified, and four compounds (benzothiazole, 2-hydroxybenzothiazole, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine,2-anilino-5-(4-methylpentan-2-ylamino)-1,4-benzoquinone) were quantified. These compounds showed high detection rate, with three detected in 100% and one in 96% of the 74 samples, and concentrations ranging from single digit pg/m³ to several hundred pg/m³. Among them, 2-hydroxybenzothiazole (OTH) exhibited positive correlations with daily maximum temperature (R² = 0.69), indicating sensitivity to seasonal conditions and suggesting that climate warming may enhance its atmospheric burden. Risk assessment yielded low non-carcinogenic risk (HQ and RCR), but the estimated carcinogenic risk for OTH (CR = 3.72 × 10^-3) far exceeded the U.S. EPA benchmark (1 × 10^-6), warranting further evaluation. These findings provide an evidence base for monitoring and regulatory consideration of tire-additive emissions under increasing traffic and climate-driven stressors, particularly in the context of global warming.