中国沙尘源区和典型城市大气汞的污染特征和来源及其对东海输入的贡献

Mercury pollution has attracted international attention again in its pollution level, migration manner, and transformation mechanism, which has become the global environmental problems, especially in atmospheric environment. The release of mercury after its dry and wet deposition is also an important source of atmospheric mercury. Serious anthropogenic emission of mercury leads to the increase of mercury concentration both in atmosphere and its deposition, which makes that mercury from atmosphere to aquatic environment is as important as that from surface runoff, and even more serious in certain area. This research presents the observation of mercury and other chemical species in aerosols over the Central Asian desert of Taklimakan and Gobi, as well as typical urban areas and the East China Sea situated in the pathways of dust downstream, to explore the contribution of dust mercury from the desert area to the atmosphere, and reveal the characteristic of mercury in the atmosphere in respect of space-time distribution, morphological transformation, source and transmission mechanism. The mercury in the typical river, lake, coastal water, and precipitation samples over Shanghai and Huaniao Island are also determined to evaluated the atmospheric deposition flux of mercury to the Eastern China Sea, and show the contribution of mercury pollution in the aquatic environment from atmospheric deposition, which could explain the pathway of the global biogeochemical cycle of mercury and provide scientific basises for controlling measures in mercury pollution.

汞在我国乃至全球环境中的污染水平及其迁移、转化和传输机制再次引起国际广泛关注，汞污染成为全球性环境问题，特别是大气环境。人为排放导致大气汞浓度升高，而大气汞通过干湿沉降后的再释放也是大气汞的重要来源。大气汞浓度及其沉降的增加，使得经大气长途传输与沉降导致的水体汞污染已经严重到与径流输入污染并重，有时甚至超过径流输入。本研究利用对塔克拉玛干和蒙古戈壁两大中亚沙漠源区以及沙尘传输途经的下游典型城市气溶胶样品以及东部典型河口、湖泊、近海水体和降水中的汞及其它化学组分的观测，探究作为自然源的沙尘输出对大气汞的贡献，给出我国中部大气汞的污染水平、理化特征、时空分布、形态转化以及源汇和传输机制，获得中国东部近海等水域大气汞沉降通量，评估大气干湿沉降对水体汞污染的影响，为探讨汞的全球生物地球化学循环以及汞污染的防治提供科学依据。

大气长距离传输导致全球各介质中汞本底浓度逐年增加。《水俣公约》实施后世界各地人为汞排放量逐渐减少。项目对城市、沙源地及近岸海三类型地域大气汞的区域性长期观测，评估汞污染控制措施的成效，为未来减排政策的制定和实施提供科学依据；探讨地表自放对汞生物地球化学循环的贡献；分析陆地和海域汞迁移的变化特征及影响；获得汞的时空分布及传输机理。.主要结果如下：.1. GEM空间分布和变化趋势。2015-2018年间中国东部GEM的年下降比率为 10.54±1.26 %，而欧洲西部和北美洲分别为 3.7±1.4%和4.29±1.68 %，下降趋势也较过去更为明显。.2.中国东部大气汞的来源、形成机制和区域传输特征。上海GEM, PBM和GOM的平均浓度分别为2.77 ng/m3、60.8 pg/m3和82.1 pg/m3。当区域/长程传输占主导时GEM浓度较高。GEM的人为来源及贡献为煤燃烧和生物质燃烧（53%）、船舶（21%）、钢铁（11%），机动车（10%）和水泥（6%）。船舶排放是仅次于煤和生物质燃烧的第二大人为来源。.3.地表释放汞的定量。利用地表释放指示物并将其引入PMF模型，建立定量评估地表释放对GEM贡献的方法，发现从2015-2018年地表释放对GEM贡献的年均值为1.00~1.13 ng/m3。人为源对GEM贡献明显降低，地表释放对GEM的相对贡献从2015年的41%增加到2018年的57%，贡献量逐渐超过了人为源。.4. 颗粒汞的时空分布。上海和北京的PBM最高，分别为146.7 pg/m3和274.7 pg/m3；多伦、榆林、和田、塔中、花鸟岛PBM分别为39.7 pg/m3、67.3 pg/m3、61.0 pg/m3、23.5 pg/m3、43.6 pg/m3。上海和花鸟岛的季节变化是冬天>秋天≈春天>夏天，而塔中为春季>冬季>夏季>秋季，塔中大气也受到人为污染汞源的侵入。.5. 沙尘传输对下游区域大气汞的影响。沙尘爆发期间多伦PBM达到160.7 pg/m3，两天后上海和花鸟岛PBM分别达到123.5 pg/m3和74.4 pg/m3，同时其它化学组分也大幅度提高。除了人为排放，亚洲沙尘和海洋源对东海颗粒汞都有贡献。花鸟岛颗粒汞的干沉降通量为1.70µg m-2 yr-1。