| 题名 | 我国近海大气汞的时空分布及海-气交换研究 |
| 作者 | 王纯杰 |
| 学位类别 | 博士 |
| 答辩日期 | 2016-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 张晓山 |
| 关键词 | Atmospheric mercury, Air-sea exchange, Wet and dry deposition, Chinese marginal seas, Changdao 大气汞，海-气交换，干湿沉降，中国近海，长岛 |
| 其他题名 | Spatial-temporal distributions and air-sea exchange of atmospheric mercury in Chinese marginal seas |
| 学位专业 | 环境科学 |
| 中文摘要 | 汞的特殊性质（如长距离输送、迁移转化和强富集性等）使得它成为一种全球性的污染物。大气中汞的物理化学特性和迁移转化过程决定了它们在大气中的存留时间和对环境的效应。大气中的汞按操作上的定义可分为三种形态：气态元素汞（GEM）、活性气态汞（RGM）和颗粒态汞（HgP），大气汞可以通过光致氧化还原等方式从一种形态转化为另外一种形态。由于 GEM 具有较高的挥发性、较低的水溶性和较低的化学特性，所以它在大气中可以长时间（0.3 1年）存留；尽管 RGM和 HgP占大气总汞（TAM）的比例还不到 5%，但它们在大气汞干湿沉降方面发挥着非常重要的作用，而干湿沉降是大气汞进入海洋的重要方式。东亚地区是全球人为汞排放量最大的地区，中国是世界上人为汞排放量最大的国家，由于工业经济的发展，其汞的排放量还在逐年增加。高的人为汞排放量可能会导致我国及周边地区较高的大气汞浓度和干湿沉降通量。然而目前对我国近海大气汞的时空分布及海-气交换的研究还非常有限。 本研究通过结合海岸站点（长岛气象站）的长期观测和依托科考船对我国近海（黄渤海、东海和南海）的随航观测，系统地研究了我国近海及长岛地区的大气汞及其海-气交换。我们分别于 2013 年的夏季和秋季对东海进行了两次科学考察，于 2014 年的春季和秋季对黄渤海进行了两次科学考察，又于 2015年的秋季对南海进行了一次科学考察。本研究的目的是揭示我国近海不同形态大气汞的时空分布，探讨大气汞与气象参数之间的关系，估算我国近海汞的海-气交换通量和大气汞的干湿沉降通量，最后估算我国近海及长岛地区汞的收支。我国近海的观测结果表明，南海 GEM的浓度（1.52 ± 0.32 ng m3）和一些开阔大洋海域的浓度相当，黄海和东海的浓度稍高于南海的浓度，而渤海的浓度（2.51 3.64 ng m3）明显高于黄海、东海和南海，说明渤海在一定程度上受到了人为污染的影响。长岛地区 GEM的浓度表现出明显的季节变化特征：冬、春、夏、秋四个季节 GEM的浓度依次降低，分别为 3.11 ± 1.89，2.40 ± 1.33，2.31 ± 1.01和 1.96 ± 1.02 ng m−3，说明长岛地区 GEM的浓度和渤海海域的浓度相当，但高于黄海、东海和南海海域的浓度。黄渤海和南海的观测结果显示，黄渤海 RGM 的浓度相差不大，南海海域RGM 的浓度明显高于黄渤海，这可能是由于南海较高的光照和气温有利于RGM 的产生。长岛地区 RGM 的浓度表现出明显的季节变化特征：夏季 > 春秋季 > 冬季，而细颗粒态汞（HgP2.5）的季节变化特征与 RGM 相反。相关性分析结果表明，RGM与光照和气温呈显著正相关关系，而与湿度呈显著负相关关系。此外，研究期间 RGM 的浓度都表现为白天明显高于夜间，说明光照对RGM 的产生有促进作用。渤海 HgP2.5的浓度高于其它海域，HgP2.5的浓度在黄海和南海都表现为近岸高于远海。我们还分析了不同粒径范围内（< 0.4 10 µm，九级）颗粒态汞的浓度，结果表明，总颗粒态汞（用 HgP10 表示）的浓度以及细颗粒态汞（HgP2.1）与 HgP10的比例（即 HgP2.1/ HgP10）都表现为近岸高于远海，说明近岸受人为影响明显；长岛地区 HgP10的浓度高于我国近海，并且 HgP10的浓度和 HgP2.1/ HgP10的值都表现出明显的季节变化特征。 不管在我国近海还是长岛地区，RGM的干沉降通量都远高于 HgP的干沉降通量，RGM的干沉降通量占 TAM干沉降通量的比例在 85%以上。粗颗粒态汞（HgP2.1 10）在 HgP10的干沉降方面发挥决定作用。长岛观测站 HgP10和 RGM的干沉降通量都高于我国近海，并且长岛 HgP10 的干沉降通量表现出明显的季节变化特征：冬季 > 春季 > 夏季 > 秋季，而 RGM干沉降通量的季节变化特征 与 HgP10相反。我国近海大气 RGM和 HgP10的干沉降通量分别为 5.68和 0.69gm 2 yr 1，长岛大气 RGM和HgP10的干沉降量通量分别为 11.0和1.74 g m2 yr 1。长岛大气汞的湿沉降通量为 1.80 g m2 yr1。 根据表层海水中溶解性气态汞（DGM）和近海面大气中 GEM的浓度，我们利用气液交换模型估算了我国近海汞（主要为 Hg0）的海-气交换通量。结果表明，Hg0的海-气交换通量在空间上变化不大。长岛近岸海水中 DGM 的浓度和 Hg0的海-气交换通量都表现出明显的季节变化特征：夏季 > 秋季 > 春季 >冬季。东海海域 Hg0的年排放量为 27.6吨，大约占全球海洋年均汞排放量的比例为 0.98%，但是东海的面积占全球海洋面积的比例 0.21%。我们在黄渤海和南海也发现了相似的趋势，即各海域汞排放通量与全球海洋汞排放通量的比例高于各海域面积与全球海洋面积的比例，表明我国近海是大气汞的重要再排放源。 |
| 英文摘要 | The special characteristics of mercury (Hg), such as the long-range atmospheric transport, transformation and biomagnification, and the role as a neurotoxin, make it a ubiquitous and potent pollutant of global concern. Once Hg is released into the atmosphere, its physical and chemical properties and transformation processes will determine its subsequent fate and transport. Hg in the atmosphere exists in three major operationally defined forms: gaseous elemental Hg (GEM or Hg0), reactive gaseous Hg (RGM), and particulate Hg (HgP). Hg can be transformed from one species to another via photo-oxidation, photo-reduction, reactions with halides, and other oxidation or reduction reactions. Generally, GEM is very stable in the atmosphere with a residence time of 0.31 year due to its high volatility, low solubility, and chemical stability. RGM and HgP play an important role in Hg deposition though they generally account for < 5% of total atmospheric Hg (TAM),and atmospheric Hg (mainly RGM and HgP) deposition is identified as the dominant source of atmospheric Hg to the ocean. Atmospheric Hg emissions from East Asia were much higher than those from other continents in global emission inventories.China is the largest contributor to global atmospheric Hg, where anthropogenic Hg emissions are likely to further increase with the development of industrial ecomomy. Higher Hg emissions in China may result in elevated atmospheric Hg concentrations and deposition levels, and then cause Hg pollution in the surrounding regions. But we have little knowledge on the atmospheric Hg speciation and air-sea exchange of gaseous Hg in the Chinese marginal seas due in part to sparse data from these regions. Based on the long-term measurements at a coastal station (Changdao Meterological Observatory) and the cruises covering the majority areas of Chinese marginal seas (i.e., Bohai Sea: BS, Yellow Sea: YS, East China Sea: ECS, and South China Sea: SCS), this thesis systemically investigated the cycling of Hg in the atmosphere and air-sea exchange of Hg in the Chinese marginal seas (including Changdao Observatory). Two oceanographic cruises were carried out in the ECS during the summer and fall of 2013; another two oceanographic cruises were carried out in the BS and YS during the spring and fall of 2014; finally, an oceanographic cruise was carried out in the SCS during the fall of 2015. The main objectives of these cruises are to identify the spatial-temporal distributions of speciated atmospheric mercury (GEM, RGM, and HgP) in air, to explore the relationships between speciated atmospheric Hg and meteorological parameters, and to estimate the air-sea Hg0 flux and the wet and dry depositon flux of atmospheric Hg in the Chinese marginal seas, and finally estimate the mass balance of Hg in Chinese marginal seas and Changdao Observatory. The measurements in the Chinese marginal seas suggested that the GEM concentrations in the SCS (1.52 ± 0.32 ng m3) were comparable to those of the open oceans, and the GEM concentratios in the YS and ECS were slightly higher than those in the SCS, while the GEM values in the BS were significantly higher than those in the YS, ECS, and SCS, indicating that the BS was polluted. The GEM concentrations at Changdao exhibited distinct seasonal variation with the order of winter (3.11 ± 1.89 ng m−3) > spring (2.40 ± 1.33 ng m−3) > summer (2.31 ± 1.01 ngm−3) > fall (1.96 ± 1.02 ng m−3). The results show that GEM concentrations at Changdao were comparable to those in the BS, while higher than those in the YS,ECS and SCS. The results showed that there was no significant difference in RGM concentrations in the BS and YS, but the RGM concentrations in the SCS were generally higher than those in the BS and YS. This was probably due to the higher solar radiation and air temperature in the SCS. The RGM concentrations at Changdao exhibited significant seasonal variation with the order of summer > spring or fall > winter, while the HgP2.5 concentrations also exhibited significant seasonal variation with the order of winter > spring or fall > summer. The correlation analysis revealed that RGM positively correlates with solar radiation and air temperature while negatively correlates with relative humidity. Additionally, the RGM concentrations in the daytime were significantly higher than those in the nighttime during the whole study period. The above results indicated that solar radiation was conductive to the production of RGM. The HgP2.5 concentrations in the BS were higher than those in the YS and SCS, and the spatial distribution of HgP2.5 generally reflected a gradient with high levels near the coast of China and low levels in the open sea, suggesting the significant atmospheric mercury outflow from China. A cascade impactor was used to collect HgP in nine size fractions ranging from 10 µm to < 0.4 µm (nine stages). The concentrations of HgP in PM10 (hereafter referred to as HgP10) also tended to decrease from the land to the open sea except the measurements in the BS. Additionally, the ratios of HgP2.1 to HgP10 in the nearshore area were higher than those in the open sea. Moreover, there was a distinct seasonal variation of HgP10 concentrations and the ratios of HgP2.1/HgP10 at Changdao, and the HgP10 concentrations at Changdao were higher than those in Chinese marginal seas. The dry deposition flux of RGM was significantly higher than that of HgP10 both in Chinese marginal seas and at Changdao Observatory. The RGM contributed more than 85% of the total dry deposition of RGM and HgP10. Moreover, the coarse HgP (HgP2.110) plays an important role in the dry deposition of HgP10 due to the higher dry deposition velocities of coarse particulate matters. The dry deposition fluxes of RGM and HgP10 at Changdao Observatory were all higher than those in the Chinese marginal seas. The dry deposition flux of HgP10 exhibited distinct seasonal variation with the order of winter > spring > summer > fall, while the dry deposition flux of RGM exhibited seasonal variation with the order of summer > fall > spring > winter. The annual dry deposition flux of RGM and HgP10 in Chinese marginal seas were 5.68 and 0.69 g m2 yr1, which were lower than those estimated at Changdao Observatory (RGM: 11.0 g m2 yr1, HgP10: 1.74 g m2 yr1). The annual wet deposition flux at Changdao Observatory was 1.80 g m2 yr1. The air-sea fluxes of Hg0 in Chinese marginal seas were estimated using a thin film gas exchange model. The results show that the dissolved gaseous Hg (DGM)concentrations in surface seawater of the nearshore area were higher than those in the open sea except the measurements in the BS, while there was no significant difference in Hg0 fluxes between the nearshore area and open sea. The DGM concentrations and Hg0 flux at Changdao Observatory exhibited distinct seasonal variation with the order of summer > fall > spring > winter. The emission flux of Hg0 from the ECS was estimated to be 27.6 tons yr−1, accounting for ~ 0.98% of the global Hg oceanic evasion though the ECS only accounts for ~ 0.21% of global ocean area, indicating that the ECS plays an important role in the oceanic Hg cycle,moreover, we can get similar results in the BS, YS and SCS. The above results indicated that the Chinese marginal seas were the main sources for the global aomospheric Hg. |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/36969]  |
| 专题 | 生态环境研究中心_大气环境科学实验室 |
| 推荐引用方式 GB/T 7714 | 王纯杰. 我国近海大气汞的时空分布及海-气交换研究[D]. 北京. 中国科学院研究生院. 2016. |
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