西安市某文教区典型下垫面径流污染特征

Characteristics of runoff pollution of different underlying surfaces in typical cultural and educational area of Xi'an

在西安市某文教区路面、屋面和绿地设置径流采样点,采用人工时间间隔采样法对2016年8月～2017年2月的3场降雨径流和2场融雪径流全程采样,测试径流过程SS、COD、TN、TP、Pb、Zn、Cu、Cd、Ni、Cr、PAHs、溶解态COD、溶解态重金属和溶解态PAHs的浓度以及颗粒物粒径d_(50),研究各下垫面降雨径流污染水平及出流规律,比较不同下垫面降雨径流和融雪径流污染特征.结果表明,各类下垫面降雨径流主要污染物均为SS、COD、TN、Pb、Cr,路面和绿地径流中SS的EMCs均超过《污水综合排放标准》二级标准,3类下垫面降雨径流COD、TN、Pb、Cr的EMCs均超出《地表水环境质量标准》Ⅲ类标准,PAHs与国内相关研究相比属于中等污染水平,路面、屋面和绿地径流的EMC分别为266.8～389.8ng/L、254.9～303.0ng/L和231.2ng/L.路面径流SS、COD、Zn、Pb、Cu、PAHs浓度高于屋面径流,而TN、TP、Cr等指标则相反,表明径流中TN、TP、Cr主要源于大气干湿沉降,而交通排污对SS、COD、Zn、Pb、Cu、PAHs等有较大输入贡献.3类下垫面降雨径流污染浓度输出规律差异显著,路面径流污染物初期浓度较大,受雨期交通排污影响中后段波动剧烈,屋面径流污染物浓度随径流历时持续降低且趋于稳定,绿地径流污染物浓度沿程变化相对较小.降雨强度对总量污染物浓度输出的影响大于溶解态污染物,表现为d_(50)与降雨强度呈现良好的相关性.因降雪期间污染物持续累积且径流量较小,路面融雪径流污染物浓度远大于降雨径流,而屋面融雪径流因流量较小导致携带污染物的能力较弱故水质优于降雨径流.

In order to investigate rainfall runoff pollution level and effluent characteristics of different underlying surfaces in urban community, three kinds of underlying surfaces, such as road, roof and grass land at a cultural and educational area in Xi＇an, Shaanxi province were selected as sampling areas, and runoff samples over the whole time range of 3 storm events and 2 snowmelt events were collected by the manual time-interval sampling method from Aug. 2016 to Feb. 2017. The concentrations of SS, COD, TN, TP, Pb, Zn Cu, Cd, Ni, Cr, PAHs, dissolved COD, dissolved heavy metals and dissolved PAHs, as well as particulate matters size d_（50） of samples were determined. Pollution characteristics were compared between rainfall runoff and snowmelt runff. The results showed that the main contaminants of urban surface runoff were SS, COD, TN, Pb and Cr. The average event mean concentrations（EMCs） of SS in road and grass land rainfall runoff exceeded grade two level of integrated wastewater discharge standard, and the EMCs of COD, TN, Pb and Cr exceeded grade Ⅲ level of environmental quality standards for surface water. The event mean concentration（EMC） of PAHs in road, roof and grass land rainfall runoff were 266.8～389.8 ng/L, 254.9～303.0 ng/L and 231.2 ng/L respectively, which were at medium pollution level compared with domestic related research. The concentrations of SS, COD, Zn, Pb, Cu and PAHs in road runoff were higher than which in roof runoff. However, the concentrations of TN, TP and Cr in road runoff were slightly lower than roof runoff, which indicated that TN, TP and Cr mainly derived from atmospheric dry and wet deposition,while the main sources of SS, COD, Zn, Pb, Cu and PAHs were traffic pollution emission. Pollutants effluent characteristics of these three kinds of underlying surfaces rainfall runoff were different obviously. The pollutants concentration of road runoff were rather high in the initial duration of runoff, and fluctuated violently affected by traffic pollution emission in the later runoff. However, the pollutants concentration of roof runoff continuously decreased with runoff time and finally tended stablely. While the pollutants concentration of grass land runoff were rather stable during the whole time. The impact of rainfall intensity on the total pollutants concentration emission were greater than on the dissolved pollutants, and d_（50） showed a good correlation with rainfall intensity. Pollutants concentration of road snowmelt runoff were far greater than rainfall runoff, due to pollutants accumulated continuously during the snowfall events and snowmelt runoff flow was rather small. Nevertheless, water quality of roof snowmelt runoff was better than rainfall runoff, owing to the ability of carrying contaminants of snowmelt runoff were more weak than rainfall runoff.