持续霾污染期间羟基自由基对大气汞非生物甲基化行为的影响研究

Mercury is one of the metals which can be methylated. Great progress has been made in the study of the abiotic methylation behavior of mercury in the environmental media of sediments, water, and soil at home and abroad. The research will be taken during the haze pollution in Shanghai, and the non-haze period will be considered as comparison. The previous study funded by National Natural Science Foundation of China has monitored the atmospheric aerosol and analyzed the physical and chemical properties, structures of functional groups, and oxidative activities of particles with different diameters. The process and characteristics of generation, growth of secondary particles has also been analyzed. The study will first conduct the on-site continuous supplementary sampling and monitoring. The supplementary samples will then be determined and analyzed. The hydroxyl radicals, methyl mercury, and the methylation donors of small molecules (acetone, acetic acid, propionic acid, acetaldehyde, etc) will be analyzed. Moreover, the results will be verified by simulation experiments of photochemical oxidation, homogeneous oxidation and liquid-phase oxidation in the laboratory. Finally, the synchrotron radiation photoionization mass spectrometric technology will be adopted to study the reaction rate constants of free radical reactions and the dynamics principle of free radical reactions. This project will mainly carry out the research work of the following aspects: (1) to screen out the related factors of abiotic methylation behavior of atmospheric mercury during continuous haze pollution period; (2) to analyze the dynamic variation characteristics of hydroxyl radicals and methyl mercury during continuous haze pollution period; (3) to analyze the role and characteristics of the hydroxyl radicals in the process of transformation of zero-valent mercury and bivalent mercury during continuous haze pollution period, and the results will be verified by simulation experiments; (4) to analyze the impact of the hydroxyl radicals on the secondary generation of methylation donors with small molecules (acetone, acetic acid, propionic acid, pyruvic acid, aldehyde, etc.) and to analyzed the characteristics of interaction of hydroxyl radicals and small molecule methylation donors during continuous haze pollution period, and the results will be verified by simulation experiments. (5) to do simulation experiments in the laboratory in the simulation box, in which are methylation donors with small molecules, mercury, hydroxyl radicals, etc. The simulation experiments are conducted to simulate the role and comprehensive reaction characteristics of hydroxyl radicals on the abiotic methylation behavior of atmospheric mercury. The implementation of the project will provide new ideas about the mercury cycle during haze period and a scientific basis to further clarify the abiotic methylation mechanism of atmospheric mercury.

汞是可以进行甲基化的重金属之一。关于汞在沉积物、水和土壤介质中非生物甲基化行为研究取得很好的进展。本申请拟在上海霾污染期间开展研究，并与非霾作为对照，在前一个国家基金研究的基础（如：现场连续检测分析了霾期间大气气溶胶和不同粒径颗粒物的理化特征、二次颗粒物生成、成长过程等）上，补充检测霾期间羟基自由基、甲基汞和小分子甲基化供体（丙酮、乙酸、丙酸、乙醛等）。筛选霾期间大气汞非生物甲基化相关因子；分析霾期间羟基自由基与甲基汞的相互关系。结合实验室模拟实验，探讨霾期间羟基自由基在零价汞与二价汞转化过程中、以及羟基自由基在小分子甲基化供体二次形成及与其相互反应中的作用；阐明羟基自由基在汞/甲基化供体共存情况下的反应特征。并利用同步辐射光电离质谱技术，研究自由基反应速率常数，探讨自由基反应动力学原理。该项目实施可为进一步了解霾期间汞循环过程提供新的思路，为深入阐明大气汞非生物甲基化机制提供科学依据.

本项目通过对持续霾污染期间大气中总汞、甲基汞变化特征分析，结合大气中VOCs、无机元素、可溶性离子、有机组分、EC/OC等，探讨了持续霾污染期间汞的非生物甲基化影响因素。结果表明，冬季甲基汞浓度是其他季节甲基汞最大值的50~100倍。污染天颗粒物上存在的甲基供体（乙酸、乙醛等），与二价汞共存于水溶液，为甲基化提供了良好的水环境，并在日光照射下或催化剂作用下更容易产生甲基汞。丙酮等VOCs能够为GEM的非生物甲基化提供烷基，在太阳光辐射下生成甲基汞MeHg，乙苯等芳香烃与GEM的负相关关系暗示着其可能作为甲基供体参与了汞的非生物甲基化过程。OH将GEM氧化为RGM以及MeHg的浓度范围为0.27~2.05 ng/m3，占对应的GEM被氧化去除浓度的34.22%~63.16%，OH对大气中GEM的光化学转化具有一定的作用。案例分析发现，钢铁企业排放对其周边环境造成一定的汞污染；大气氧化剂能迅速将GEM动态氧化为RGM或PBM，且Br·是最主要的氧化剂；气溶胶中OC、EC、SO42-、NO3-、NPOCs及VOCs均能对汞的气粒分配行为产生影响。