Research advance in the characterization and source apportionment of pollutants in urban roadway runoff

As a major part of urban surface runoff, urban road runoff has drawn extraordinary attention due to its large magnitude of pollution and severe influence on surface water bodies. By summarizing the results of previous studies on water quality of road rainfall runoff, it can be found that the concentration of COD, TP, TN and Pb were 239.59, 0.46, 6.29 and 0.14 mg·L-1, respectively, and exceeded the Ⅴ class of surface water. The concentration of TSS was 552.86 mg·L-1. Therefore, the COD, TP, TN, Pb and TSS were the main pollutants of urban road runoff. The concentration of Pb, Cu and Zn are higher in the highway than the other road. But, the concentration of TSS and COD are lower in the highway than the other road. When Comparing domestic studies with the other countries', the pollutants concentration of road rainfall runoff are higher in China. The most researchers found that the concentration of pollutants and rainfall volume have negative correlation. The steeper slope of the road could produce higher runoff concentrations of pollutants due to the greater friction between vehicle tire and road and more burnt fuel. The road sweeping could have adversely affected to the concentration of pollutants mainly due to releasing the fine material from the fixed load but not having enough suction to remove them. However, there are contradicting reports in the literature as to the correlation of the concentration of pollutants with rainfall intensity, antecedent dry period, rainfall duration and average daily traffic. By summarizing the data in existing studies, it is found that the concentration of COD, TSS, Pb and Cu in road runoff at the traffic volume ≥30 000 were 2.5, 4.3, 1.4 and 5.1 times respectively, compared with the concentration at the traffic volume 30 000. In the road runoff, the heavy metals were mainly come from vehicle's exhaust, the organic pollutants mainly sourced from vehicles activities and road material and the nutrition-related pollutants mainly sourced from atmospheric dry and wet deposition. The following aspects should be carried out in future research: To take the polycyclic aromatic hydrocarbons and Escherichia coli into the research program; Deep analysis of the factors affecting rainfall runoff water quality and the interaction between factors, and to utilize the isotope tracing techniques to indentify the pollution source of the urban road runoff.