基于粒径阈值的街尘重金属污染指数研究

Road-deposited sediments (RDS) on urban surfaces are ubiquitous and important carriers of contaminants. A right risk assessment for contaminants associated with RDS is crucial for urban diffuse pollution control. In the case study, three different types of cities were selected such as Beijing, Shijiazhuang and Cangzhou in North China, which could affect significantly the environmental characteristic of RDS. Based on the investigation of the regional spatial pattern of the quantity, grain size, and particle mobility of RDS and the experiments of natural and simulated rainfall washoff, we will build the probability density function by grain size between the heavy metal risk and the factors of quantity, grain size, and particle mobility of RDS. The grain size threshold for RDS pollution was calibrated by the probability density function. We will classify levels and assigned level values of the risk factors according to our measured values. The pollution index of heavy metal in RDS based on grain size was calculated by the above-mentioned risk factors. The grain size threshold for RDS pollution, the pollution index of heavy metal in RDS was verified and calibrated by RDS washoff pollution from the indoor simulation and on-site detection. The new methods above will be simple and effective to assess heavy metal pollution in RDS at rainfall event scale and provide an important scientific basis for the source control pollution caused by RDS washoff.

街尘是引起城市面源污染分布最为广泛的重要污染载体，街尘及其负载污染物风险的正确评估，对于评价和有效控制城市地表径流污染有着重要意义。以华北地区三个街尘环境特征差异明显的城市北京、石家庄和沧州为例，在调查区域街尘单位面积质量、颗粒物粒径组成、重金属含量及赋存形态的空间分异规律基础上，结合人工降雨模拟街尘冲刷试验与天然降雨冲刷定位观测，采用变量探索的数理统计手段，构建粒径与街尘重金属面源污染风险因子的多种概率密度分布函数，多角度综合探寻能够表征街尘重金属面源污染风险的粒径阈值。同时，利用街尘重金属污染风险因子的实测值进行因子等级划分和权重赋值，构建基于粒径的街尘重金属污染指数。最后，利用天然和人工降雨情景下的地表径流污染对街尘污染粒径阈值和街尘重金属污染指数进行验证与校准，确立降雨事件尺度的简明有效地评估城市区域街尘重金属面源污染的方法，为我国街尘降雨冲刷污染的源头控制提供重要科学依据。

地表街尘是引起城市面源污染分布最广泛的重要污染物载体，其与城市地表径流污染联系紧密。本项目构建了具有指示与预测城市面源污染功能的街尘污染指数模型（RDSindex），它由源因子和迁移因子构成。该指数模型考虑了街尘的单位面积质量、粒径组成、可迁移性和重金属浓度等特征。它包含具有识别污染源强度（RDSindex，strength）和估算污染负荷的功能（RDSindex，strength）两个子模型。以上两个子模型用来评估北京市不同城乡环境梯度单元的街尘重金属污染强度和负荷。实际应用证明，该指数模型简单易操作、同时受数据缺乏制约较小的街尘重金属污染指数，能对区域性街尘重金属的城市面源污染进行评价和预测。