Understanding petroleum hydrocarbon pollution characteristics on urban roads

Accurate characterization of urban road pollution is imperative for safeguarding stormwater quality in harvesting or discharge scenarios. Petroleum hydrocarbons (PHCs, including volatile (VOCs), semi-volatile (SVOCs), and non-volatile organic compounds (NVOCs)), primarily from traffic emissions, tire wear, and fuel leakage, pose significant environmental and health risks. This necessitates understanding the spatiotemporal distribution of VOCs, SVOCs, and NVOCs to guide mitigation. This study characterized dry-period PHC deposition on urban roads, analyzing determinants including total solids (TS) load, land use, season, traffic volume, and road condition. Size-resolved PHC deposition loads (μg/m²) were quantified across particulate fractions. Results identified TS load and seasonal variation as primary factors. For instance, fine particles (<75 μm), comprising only approximately 10 % (summer) and 25 % (winter) of TS mass, adsorbed 78.2 % and 70.8 % of ΣPHCs, respectively. SVOCs and NVOCs persistently associated with fines across seasons, while VOCs showed thermally mediated adsorption: fines dominated in summer (promoting volatilization), shifting to coarse fractions (≥300 μm) in winter (enhancing deposition). Precipitation and temperature drove these seasonal patterns. Lower temperatures and less rainfall promoted greater deposition in winter, resulting in an over 150 % increase in ΣPHC loads compared to that in summer. Therefore, the particle-size-resolved data demonstrate that the interplay between PHC volatility, particle size, and seasonality is a critical driver of PHC fate. Conventional mass-based methods for TS assessment, which do not account for this interplay, are therefore insufficient. These findings collectively highlight the need for particle-size-resolved and seasonally adaptive modelling approaches and mitigation strategies applicable to PHCs of varying volatility.