我国城市大气细颗粒物中甲基汞的富集及其影响因素

Atmospheric fine particle pollution is really serious in urban areas of China with its complicated formation process and unclear toxic components. Atmospheric mercury pollution in China is a siginificant issue, and it should be great concern to the toxicity contribution of mercury species to atmospheric fine particulate matter. Recent our investigation shown that it is an inevitable problem for the enrichment of Methylmercury(MeHg) in fine particles, and the systematic research need to be urgently conducted to clarify the enrichment characteristics and environment process of MeHg in atmospheric fine particles, which will benefit to comprehensive evaluation of the environmental health effects of MeHg. The main objective of this project is investigate the enrichment of MeHg in atmospheric fine particles and its influence factors in urban areas with serious air pollution and high frequent of haze event. Thus the efforts will perform on (i) optimizing the sampling system for gas and particle phase MeHg in the atmosphere, (ii) the systematic observation on the speciated atmospheric mercury, atmospheric species, chemical components of atmospheric fine particles and meteorological factors to clarify the characteristics of enrichment and temporal variation, the gas-particle ratio of MeHg in atmospheric fine particles, and (iii) combining with the gas-particle partitioning models to explore the possible source of MeHg in fine particles and the key effect factors on the enrichment of MeHg and its gas-particle partitioning. These are valuable for systematically study the health effect of air fine particulate matter, and comprehensively understanding environmental risks of mercury emissions.

我国城市大气细颗粒物污染严重，其来源和成因复杂且毒性组分不清；我国大气汞环境问题突出，各种形态大气汞对于大气细颗粒物污染及其毒性的贡献值得关注。我们初步的观测分析表明，作为最具毒性的汞形态—甲基汞在大气细颗粒物中的富集不容忽视，有必要对其变化特征和环境过程开展系统研究，以全面评价其环境健康效应。本项目拟在我国区域大气复合污染严重和雾霾频发的典型城市开展大气细颗粒物中甲基汞的富集特征及其影响因素的研究。发展和优化大气中气相-颗粒相甲基汞分离采集系统，系统观测不同形态大气汞及相关大气物种和要素的分布特征和变化规律，深入认识大气细粒子中甲基汞的富集特征和气-粒分配关系；结合气-粒分配模型，研究大气细颗粒物中甲基汞富集的关键影响因素。本项目对全面评价我国汞排放的风险和大气细颗粒物的环境健康效应有明显的现实意义和学术价值。

本项目围绕我国城市大气细颗粒物污染严重，其来源和成因复杂且毒性组分不清这一当前核心科学问题，通过发展和优化大气中颗粒相甲基汞采集与分析系统，利用综合观测大气细粒子甲基汞、不同形态大气汞及相关大气物种和要素，系统获得北京大气汞形态基础资料；率先认识了典型城市地区大气细粒子中甲基汞和大气不同形态汞的富集水平、特征和分配关系；发现甲基汞在大气细粒子中具有高富集度，且随着PM2.5浓度的增加，大气细颗粒物中甲基汞的浓度逐渐升高，但是质量分数显著降低；洁净天时甲基汞在大气细颗粒物中的富集程度高，随着污染程度的增加，甲基汞在大气细颗粒物中的富集程度逐渐下降，表明大气中可能存在甲基汞的生成过程。揭示了大气活性汞浓度随大气细粒子水平增加而减小的现象，获得不同季节大气活性汞气-粒分配系数，发现大气温度、湿度和颗粒物组分（氯离子和黑碳）是影响大气活性汞气-粒分配的关键因子，建立了大气活性汞气-粒分配系数（Kp）与大气温度（T）和相对湿度（RH）在不同季节的多元回归响应模型。在以上基础上，结合大气细粒子全元素分析，利用受体模型对北京城市大气细颗粒物中甲基汞的潜在来源进行探究，提出大气二甲基汞降解和表面甲基汞挥发（47.8%）、燃烧和海洋（18.7%）是大气细粒子甲基汞主要来源，扬尘（16.4%）和非均相反应（13.2%）贡献稍低。本项目顺利完成为今后进一步完善大气汞模型，和全面评价我国汞排放的风险和大气细颗粒物的环境健康效应提供基础数据和科学依据，具有明显的现实意义和学术价值。