Influence of Rainfall Pattern and Traffic Variability on the Occurrence of PAHs in Road Surface Runoff

This study aims to investigate the phase distribution, structure characteristics and ecological risk of Polycyclic Aromatic Hydrocarbons (PAHs) in runoff from typical traffic roads, as well as the influences of rainfall pattern and traffic variability. An improved wash-off calculation method of PAHs, which incorporates the total number of vehicles, was established. Seventy-five runoff samples in 35 rainfall events were collected and analyzed in a suburban freeway (JJ) and an urban traffic road (CB) in Shanghai. Results showed that the average event mean concentrations (EMCs) and load densities (LDs) of Σ 16 PAHs in the runoff in JJ were 22.8 times and 37.2 times those in CB, mainly due to the high proportion of coaches and trucks, the dry antecedent time before rainfall events and the high traffic volume in JJ. LDs of PAHs in runoff were predominantly present in the particulate phase (69%-98%) with 4–6 rings (83%-86%). Among the 16 individual PAHs in CB and JJ, those of high ecological risk accounted for 15% and 74%, respectively. The factors influencing the EMCs and LDs of Σ 16 PAHs during a rainfall included the total rainfall depth, rainfall duration, dry antecedent time, and total traffic volume. According to dry antecedent time, total rainfall depth, rainfall duration and traffic volume for each event in 2020, the total LDs for the Σ 16 PAHs in CB and JJ were calculated at 653 μg∙m −2 and 17,619 μg∙m −2 , respectively, using the improved wash-off load calculation method. This indicated that PAHs in JJ runoff have a more cumulative pollution effect on the surrounding farmland and the ecological risk cannot be ignored. Intercepting particles of traffic runoff is very important for the control of PAHs.