[Impacts of Rainfall Characteristics and Occurrence of Pollutant on Effluent Characteristics of Road Runoff Pollution].

Urban road runoff contains pollutants such as particulate matters, organic chemicals, heavy metals, nutrients, oil and grease that can cause significant degradation of receiving water quality. Eliminating the pollutant mass loading of road runoff and protecting the receiving water bodies have been the focuses in environmental field in recent years. To accomplish pollutant reduction and develop a cost-effective treatment method, knowledge of water quality characteristics, as well as the pollutant effluent characteristics of road runoff is required. In order to investigate the impacts of rainfall characteristics and occurrence of pollutant on the variation of pollutant concentrations during the duration of runoff events and pollutant load effluent characteristics of road runoff, 207 road runoff samples in the durations of 13 storm events occurred at Taibai Interchange of the south second-ring road in Xi'an, Shaanxi province from July 2014 to September 2015 were collected by the manual time-interval sampling method, and concentrations of SS, COD, dissolved COD, Cu, dissolved Cu, Pb, dissolved Pb, Cr, dissolved Cr, Cd and dissolved Cd of the samples were determined. The results indicated that, the road runoff of Xi'an city was seriously polluted by SS and COD, which were the main contaminants in road runoff. Meanwhile, concentrations of Pb and Cr in road runoff were also at a high level. The variation of pollutant concentrations during the duration of runoff was closely related to rainfall characteristics and occurrence states of the pollutants. Emission of the dissolved pollutants was not affected by the type of rainfall. The concentration of the dissolved pollutants in the runoff reached a peak in the initial duration of runoff, and then, decreased continuously. However, the peak concentration of particulate pollutants in the runoff only occurred after the peak of sufficiently large rainfall intensity. The concentration of particulate pollutants in the runoff fluctuated sharply with the variation of rainfall intensity, and impacted by the rainfall duration and rainfall depth as well. Rainfall characteristics didn't have a great impact on the load emission of the dissolved pollutants, therefore, had a significant influence on the load emission of the particulate pollutants. Compared with the rainfall type Ⅲ, first flush effects of pollutant loads of SS, COD, Cu, Pb, Cr, Cd in rainfall type Ⅰand type Ⅱ were more obvious. Besides, first flush effect of pollutant loads was not ubiquitous. All the pollutants in the monitoring 13 runoff events didn't exhibit an obvious first flush effect. The descending order of the first flush effect of those pollutants was COD, SS, dissolved COD, Cu, Pb, Cr, dissolved Cu, Cd, dissolved Pb, dissolved Cr, dissolved Cd.