光化学污染过程大气汞的形态转化机理量子化学研究及模拟

Photochemical reaction is one of the most important ways to determine the fate of mercury in the atmospheric environment. Despite the experimental confirmation of atmospheric photochemical oxidation, reduction and methylation of gaseous elemental, reactive gaseous and particle bounded mercury species, the exact reaction mechanism remains poorly understood. This study would be conducted under varying degrees of photochemical pollution, and compared by none-photochemical pollution conditions in Shanghai, and apply quantum chemistry theory, combined with site monitoring, laboratory simulation experiments and related model simulation to explore the mechanism of atmospheric photochemical reduction, oxidation and methylation of different mercury species, besides, the concentration and proportion of GEM, RGM and TPM under non-photochemical pollution and varying degrees of photochemical pollution conditions would be analyzed, additionally, this study would seek to illuminate multiphase photochemical reactions mechanism of mercury species on the surface and cover layer of the secondary organic aerosols, further, this research would also attempt to figure out the influential factors of mercury transportation and deposition under photochemical pollution conditions by demonstrating reaction mechanism of TMP accumulation. Implementation of this project would provide scientific basis for further research on regional transportation and global circulation of atmospheric mercury.

光化学反应是决定大气汞环境归趋的重要途径之一。有关大气中气态元素汞、活性气态汞、颗粒态汞等各形态汞的光化学反应已通过实验方式得到证实，但其反应机理尚不明确。本申请拟以上海不同程度光化学污染作为研究背景，选择非光化学污染作为对照，采用量子化学理论，结合现场监测、实验室模拟实验及相关模型，探讨大气不同形态汞光化学氧化、光化学还原、光化学甲基化等典型光化学反应过程中各形态汞量子化学机理，明确非光化学污染和不同程度光化学污染期间各形态汞的浓度水平和浓度占比变化特征，初步阐明大气各形态汞在二次有机气溶胶表面及包裹层的多相光化学反应动力学过程，阐明具有较好沉降作用的颗粒态汞积累的反应机制，明确光化学污染期间影响大气汞迁移沉降的影响因素。该项目的实施可为进一步明确汞的区域迁移和全球汞循环提供科学支持。

本申请以不同程度光化学污染作为研究背景，选择非光化学污染作为对照，结合现场监测、实验室模拟实验及相关模型，探讨大气不同形态汞光化学氧化、光化学还原、光化学甲基化等典型光化学反应过程中各形态汞量子化学机理。结果如下：. 研究区域大气中GEM和PBM的浓度分别为3.89±9.60 ng/m3和1590±1681 pg/m3，GEM与城市大气水平较为接近而PBM高于城区环境的1~4个数量级。大气中O3的小时浓度范围为14.9~381.1 μg/m3，其氧化GEM的速率为8.20±20.34 molecule/(cm3·s) (0.01±0.02 ng/(m3·h))。 Na+、NO3-等较多时会促使二价汞分配到PBM中，而较高的NH4+和SO42-浓度会引起二价汞向RGM分配。积聚态和粗颗粒态PBM的沉降通量分别为687.67和16255.50 pg/(m2·d)，9.90~18.00 μm粒径PBM的沉降通量约占总沉降通量的71.07%，且PBM的总沉降速率为0.56 cm/s。大气中O3、OH·、NO3·和Br·氧化而引起GEM的消耗量为0.34~6.39 ng/m3，对汞的气粒分配产生动态影响。SO2和NO2氧化为SO42-和NO3-过程中，生成的气溶胶成分也影响着汞的气粒分配。VOCs氧化生成的SOA能为汞的液相非均相反应提供较大反应比表面积，能促进活性汞向PBM形态分配。