上海区域微环境中典型POPs土气交换机制及其输运负荷估算

Air-soil exchange is a key process of POPs migration in the environment and drives the environmental fate of those pollutants on regional and global scales. At present, many researches quantified the fugacities of POPs in air and soil based on prediction and lab measurement and calculated diffusive exchange flux of these pollutants by fugacity model. This method, to large extent, weakened effects of local micro-environmental meteorological condition, physical and chemical properties of soil, and local aboveground vegetation, which reduced reliability of source-sink recognition and precision of diffusive exchange flux in air-soil exchange process of POPs. This study plans 1) to select three typical POPs and investigate vertical distribution of those pollutants in urban microenvironment close to the ground surface, 2) to analyze the effects of urban microenvironmental meteorological condition, physical and chemical properties of soil, and aboveground vegetation, 3)to develop an in-situ passive sampling method for source-sink recognition in air-soil exchange process of target compounds, 4) to estimate the overall mass transfer velocity of targets in vertical direction and calculate diffusive exchange flux based on the molecular diffusion and turbulent diffusion models; to analyze temporal and spatial variation of the diffusive flux and to estimate those mass load to the surface soil through air-soil exchange process over Shanghai. The key scientific issue in this study involves the precise estimation of air-soil diffusive exchange flux of POPs under real conditions. The novel perspective of this project is to identify accurately transport direction in air-soil diffusive exchange based on the in-site passive sampling technology.

土气交换是持久性有机污染物（POPs）在环境中迁移的关键过程，驱动污染物在区域及全球尺度下的环境行为。目前许多研究采用预测和实验室测量表征土壤和空气中目标物逸度，采用逸度模型计算气态交换通量，该方法忽略了现场气象条件、土壤理化性质和地表植被的影响，降低了土气交换源汇识别的可靠性和气态交换通量计算的准确性。本研究拟选取三种典型POPs，开展近地面微环境中目标物的垂直分布研究，分析近地面微环境气象条件、土壤理化性质和地表植被对土气交换过程的影响，建立基于原位被动采样技术的土气交换源汇识别方法。通过分子扩散和湍流扩散模型，估算它们垂直方向的迁移速率，量化真实环境中土气气态交换通量，分析上海区域环境中土壤气态交换通量的时空差异，估算土气交换过程对土壤污染的输运负荷。关键科学问题：土气交换通量量化评估。创新表现为：利用原位被动采样技术表征土气介质中目标物的逸度，消除分配系数误差，提高源汇识别准确性。

土气交换是持久性有机污染物（POPs）在环境中迁移的重要过程，驱动污染物在区域及全球尺度下的环境行为。目前许多研究采用预测和实验室测量表征土壤和空气中目标物逸度，采用逸度模型计算气态交换通量，该方法忽略了现场气象条件、土壤理化性质和地表植被的影响，降低了土气交换源汇识别的可靠性和气态交换通量计算的准确性。本研究以多环芳烃（PAHs）和有机氯农药（OCPs）为典型POPs，利用被动采样技术，分别在实验室模拟条件下和真实环境场地条件下对目标污染物的逸度进行对比，参照传统分配模型逸度评估结果，建立了真实场地条件下目标污染物的化学活度（逸度）的原位表征方法。结合现有较成熟的空气中目标污染物逸度原位表征方法，构建了PAHs土气交换源汇识别方法，不确定分析结果表明该方法具有较好的源汇识别准确性。以上海中心城区某城市绿地为研究场地，基于场地土壤理化性质评估目标污染物在表层土壤中的迁移速率，基于近地面温度场的在线监测数据估算近地面空气中目标污染物的垂直紊流扩散系数及距地面不同高度污染物的垂直迁移速率，分别采用了逸度模型方法和微气象方法量化评估了土气交换过程中目标污染物的迁移通量。分别在上海市中心城区（同济新村）和区域背景点（长兴岛）、江苏省海门市农村、浙江省舟山市洋山港（岛屿）和嘉兴市新城区（新兴城市）共5个场地开展目标污染物的土气交换过程长期观测，在2018~2021共采集了8批次的成组样品，多环芳烃交换通量在242~1497 ng/m2/day，低环多环芳烃呈现为从空气向土壤的沉降过程，高环多环芳烃多为动态平衡，有机氯农药呈现出从土壤向大气中挥发趋势，最大可达4.77 ng/m2/day。多环芳烃空气干湿沉降年均通量为791~4830 ng/m2/day，以3~4环PAHs为主，远高于气态交换输入负荷，是表层土壤PAHs重要输入途径。为了识别出空气沉降PAHs的污染源区，研发了基于3D-CWT多点联合定位技术，确定了潜在的区域输运源区，即经河北、天津、山东和江苏从上海北部输入和经安徽从上海西部输入2条污染源区。发表论文6篇，其中IF>10 SCI论文4篇；授权发明专利1项；项目负责人成功晋升正高。