雾霾颗粒物不同赋存形态汞同位素组成研究

Aerosols are the main carriers of atmospheric active mercury. In recent years, the frequent severe haze events in major urban regions in China imply dramatical increase in particulate mercury in the atmosphere, which may not only impact the biogeochemical cycle of mercury, but also aggravate the ecological and environmental detriments. At present, the "3-D" mercury isotope system (mass-dependent fractionation, mass-independent fractionation of odd and even isotopes) has been successfully applied to accurately apportion the sources of total mercury in haze particulate matter. However, as mercury may exist in different chemical forms (species), haze particulate matters may thus contain a mixture of species of mercuric compounds, and it is not yet possible to analyze the isotope compositions of mercury species. This renders it very difficult to accurately apportion the sources of all species of mercuric compounds, especially the active mercury and organic mercury that can be directly incorporated into human body, and determine their ultimate ecological effect and health threat. The main bottleneck is the lack of a method for the effective separation of species of mercuric compounds. Here we intend to fill up this gap and devote to develop a method for measuring isotope ratios of mercury species. The main objectives of the project are: 1) to establish the isotope analysis method of species of mercuric compounds in haze particulate matter based on the existed sequential selective extraction, 2) to figure out the mercury isotopic distribution characteristics and influencing factors of species of mercuric compounds of haze particles in different sizes of haze particulate matters collected from Beijing-Tianjin-Hebei region seasonally, on the basis of collecting samples, and 3) to apportion the sources of all species, and to identify the mechanisms of their transformation in the atmosphere. Upon the success, this project will surely provide the key scientific evidence for the research and refinement of regional atmospheric mercury pollution in China.

气溶胶是大气活性汞的主要载体。近年来，我国京津冀等主要城市圈频繁发生严重的雾霾事件，预示着大气中颗粒汞的含量剧增，这不仅会改变大气汞的生物地球化学行为，还会加剧区域空气污染的环境健康危害。当前，汞的“三维”同位素体系（质量分馏，奇数和偶数非质量分馏）能够对雾霾颗粒中总汞进行源解析。但是雾霾颗粒汞成分复杂，是多种形态汞及其化合物的混合物，由于无法测定各种形态汞的同位素组成，造成气溶胶汞源解析具有很大不确定性，更无法准确判定不同形态汞的环境归趋和健康危害，尤其是能被人体直接吸收的二价汞和有机汞。其主要瓶颈是缺乏有效分离不同形态汞的方法。申请人拟在改进选择提取法的基础上，建立适用于雾霾颗粒各种形态汞的同位素分析方法，在采集样品的基础上，明确不同季节、粒径雾霾颗粒形态汞的同位素分布特征及影响因素，判定相应的贡献源及迁移转化机制，尝试从方法和实例上为我国大气汞污染研究和精细化防控提供关键科学证据。

汞的“三维”同位素体系（质量分馏，奇数和偶数非质量分馏）能够对雾霾颗粒中总汞进行源解析。但是雾霾颗粒汞成分复杂，是多种形态汞及其化合物的混合物，由于缺乏有效分离不同形态汞的方法无法测定各种形态汞的同位素组成，造成气溶胶汞源解析具有很大不确定性，更无法准确判定不同形态汞的环境归趋和健康危害。在青年基金的支持下，项目组建立基于同位素要求的雾霾颗粒物形态汞的分离方法，在京津冀地区开展了雾霾颗粒物各形态汞同位素组成研究，取得了系列代成果：1）讨论了天津市四季大气颗粒态汞的粒径分布特征及季节性差异，颗粒态汞在 PM＜0. 5、PM0. 5～ 1粒径中明显富集，并且细粒径带来的健康风险值显著高于粗粒径，具有很强的生态环境危害；2）识别了天津市重度雾霾过程颗粒态汞主要人为排放源，发现燃煤、金属冶炼、水泥厂、扬尘等一次排放源对雾霾期间PBM的含量增加具有一定贡献；3）探究了不同季节典型污染过程下颗粒态汞的贡献源，发现春季以人为排放和自然粉尘的混合输入为主，秋季存在生物质燃烧贡献，冬季以煤炭燃烧为主；4）揭示了颗粒物上水溶性有机碳促进液相二价汞光还原产生偏正的奇数MIF，量化得约21%（高达46%）的二价汞被光还原为单质汞释放至大气中；5）提出了大气偶数汞同位素潜在机制，进一步揭示大气Hg偶数MIF的全球分布特征。.项目资助发表SCI论文2篇，中文核心2篇，正在撰写SCI论文3篇。期间，培养硕士生3人（1人已毕业），博士生2人（1人已毕业）。项目投入经费27万元，支出20.43万元，各项支出基本与预算相符。剩余经费6.57万元，剩余经费将按计划继续用于本项目后续研究。