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贵阳市中心城区大气中不同形态汞的研究
其他题名Atmospheric Mercury Species in the Central Urban Area of Guiyang
郑伟
2007-01-11
学位授予单位中国科学院地球化学研究所
学位授予地点地球化学研究所
学位名称博士
关键词 大气 形态 中心城区 贵阳市
摘要汞,是一种人体非必需的有毒重金属元素,一种全球性污染物,其全球生物地球化学循环演化规律的研究是目前环境科学领域的热点问题。汞在大气中的行为对其全球生物地球化学循环起着极其重要的控制作用。因此,关于大气汞循环演化规律的研究已经成为目前汞全球生物地球化学研究的热点问题。大气中的汞主要分为三类,即气态单质汞(GEM)、活性气态汞(RGM)和颗粒态汞(TPM)。各种形态汞的物理化学性质不同,在大气中的行为存在显著的差异。研究大气中不同形态汞的分布特征,对于正确认识汞在大气中的循环演化规律意义重大。目前中国是全球人为活动向大气释汞最多的国家,而城市区域是人为活动的中心地带,城市大气汞污染形势严峻。因此,开展城市大气中不同形态汞的研究对于评价与预测城市环境汞污染特征以及正确认识大气汞的局地、区域、全球循环演化规律具有重要的理论与实际意义。 本论文选取贵州省省会贵阳市的中心城区作为研究区域。贵阳市(东经106º07´~107º17´,北纬26º11´~27º22´)位于中国西南地区正好处在环太平洋汞矿化带中,能源消耗以煤炭为主,大气环境污染属煤烟型污染,常年影响大气环境质量的主要污染物是二氧化硫和可吸入颗粒物。本论文的研究工作包括:⑴2004年4月~12月在中国科学院地球化学研究所建立与完善了大气中气态总汞(TGM)、GEM、RGM、TPM的采集与分析方法,并测定了大气和雨水中不同形态汞的含量,对大气汞的干、湿沉降通量进行了估算;⑵2005年4月~2006年1月在贵阳市中心城区的居民区、商业区、工业区、游览区4个功能区各设1个研究点,农村设1个对照点,按春、夏、冬3个季节研究了大气中GEM、RGM、TPM的分布特征,估算了贵阳市中心城区大气汞的干沉降通量,并利用高分辨透射电子显微镜(HR–TEM)分析技术对冬季各采样点TPM的来源作了定性识别;⑶测量了中心城区表层土壤和某些植物的总汞(THg)含量,探讨了大气汞对中心城区地表生态系统的污染效应。通过本论文的研究,得出以下主要结论: 1.在国内外研究基础上,建立了金捕汞管–冷原子荧光光谱法(CVAFS)测定大气中TGM的方法、微型捕集管–CVAFS测定大气中TPM的方法、镀KCl直形扩散管–金捕汞管串联采集RGM与GEM的方法。每种形态汞的测量技术水平都在pg•m-3量级。并在国内首次实现了对城市大气中GEM、RGM、TPM的同步测量。 2.2005 ~ 2006年间贵阳市中心城区大气中GEM、RGM、TPM的平均浓度分别是9.11 ng•m-3、132.4 pg•m-3、1.02 ng•m-3,均为对照点的1.5倍,都显著高于全球背景参考值1.5 ~ 2.0 ng·m-3、< 10 pg•m-3、1 ~ 86 pg•m-3。3种形态汞的季节、昼夜与空间分布特征如下:⑴GEM:①季节平均浓度表现为冬季>夏季>春季,居民采暖燃煤释放是造成冬季GEM浓度高的主要原因。②春、夏非采暖季受释放源及其排放方式、自身物理化学性质与气候条件等因素的影响一般是夜间高于白天;冬季则受居民白天采暖燃煤影响主要表现为白天高于夜间。③年平均浓度,工业区>居民区>商业区>游览区>对照点。⑵RGM:①季节平均浓度表现为春季>夏季>冬季,气候条件对RGM的影响较大。②受白天释放源、自身物理化学性质、大气氧化强度与气候条件等因素的影响,春、夏、冬3季一般都为白天高于夜间。③年平均浓度,商业区>工业区、居民区>游览区、对照点。⑶TPM:①季节平均浓度表现为冬季>夏季>春季,居民采暖燃煤释放是造成冬季TPM浓度高的主要原因。②受释放源及其排放方式、自身物理化学性质与气候条件等因素的影响,春、夏、冬3季一般都为夜间高于白天。③年平均浓度,工业区>居民区>商业区>对照点>游览区。④TPM受局地释放源的影响显著,而燃煤释放是其冬季的普遍来源。 3.2005 ~ 2006年间不同形态汞在贵阳市中心城区大气中的含量分布为GEM(89.8 %)> TPM(8.8 %)> RGM(1.5 %),其中(RGM + TPM)占大气总汞(TAM)的比例略高于对照点的10.0 %,但显著高于全球背景参考值1 ~ 5 %,说明贵阳市中心城区大气汞向地表生态系统的沉降通量相对背景区较大。因为尽管RGM、TPM在大气中的含量很低,但正是它们控制了大气汞向地表生态系统的沉降速率。 4.2005 ~ 2006年间贵阳市中心城区各功能区及对照点大气中不同形态汞日均浓度的相关关系大多数都表现为不显著,表明在贵阳市中心城区及对照点大气中不同形态汞的来源可能是多元化的。 5.2005 ~ 2006年间贵阳市中心城区大气中GEM、RGM、TPM的干沉降通量平均值分别为28.7 μg•m-2•yr-1、10.4 μg•m-2•yr-1、160.9 μg•m-2•yr-1,均为对照点的1.5倍,其中TPM控制了大气汞向地表生态系统的干沉降通量;TAM干沉降通量平均值为200.1 μg•m-2•yr-1,其时空差异表现为冬季>春季>夏季和工业区>居民区>商业区>对照点>游览区。 6.经估算,2005 ~ 2006年间在贵阳市中心城区面积范围内大气汞干、湿沉降总量为54.7 kg•yr-1,它仅占燃煤向大气排汞量(以2003年为例,贵阳市中心城区燃煤向大气排汞量为334 kg•yr-1)的16.4 %,说明贵阳市中心城区的大部分大气汞仍然停留在大气中,最终将经由大气进行长距离迁移,散布到更广的区域。 7.在中国科学院地球化学研究所,2000 ~ 2006年间的大气TGM污染程度呈逐年递增趋势;2004年大气汞的干沉降通量为16.5 ng•m-2•h-1,高于湿沉降通量12.2 ng•m-2•h-1。 8.贵阳市中心城区及对照点不同类型土壤THg含量的几何平均值分别是0.370和0.276 mg•kg -1,都高于贵阳市土壤汞背景值0.201 mg•kg -1。土壤释汞是贵阳市大气气态总汞的一个重要自然源,而土壤THg含量是土壤释汞的最主要影响因子。因此,为了提高城乡居民的生活环境质量,更为了保护城乡居民的健康,非常有必要采取防治措施来降低贵阳市中心城区及对照点的土壤汞污染。 9.贵阳市中心城区苔藓THg平均含量为0.258 mg•kg -1,为对照点的1.5倍;中心城区某些常见的木本植物叶片THg含量范围是 0.068 ~ 0.181 mg•kg -1,木本植物叶片吸收大气汞的能力表现为落叶植物>常绿植物。苔藓、梧桐叶片中的THg含量与其生长时期的大气汞浓度密切相关,能够指示区域大气汞的污染现状与空间分布规律。
其他摘要Mercury (Hg) is a global pollutant and a toxic heavy metal that is non-essential for human beings. The cycling and transformation of mercury on the global scale is one of the hotspot fields in environmental science research at present. The behaviors of mercury in the atmosphere play a significant controlling role in global mercury biogeochemical cycles, so researching on the cycling and transformation of atmospheric mercury has been significant in the territory of mercury science. In the air, the main three forms of Hg are: gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and total particulate mercury (TPM). The atmospheric behaviors of different mercury species are obviously different due to their chemical and physical properties. When evaluating the global transport of environmentally cycled mercury, a critical data is the atmospheric distribution of mercury among various forms. China is regarded as one of the largest anthropogenic Hg emission countries over the world, and the atmospheric Hg pollution problem in metropolitan cities which are the center district of human activity may be very serious. Thus, the researches on atmospheric speciation have important theoretical meaning and application value for forecasting and assessing Hg pollution characteristics in urban areas and for understanding the atmospheric mercury cycling at local, regional and global scale. The sampling sites were located in downtown Guiyang. Guiyang (26º11´~27º22´ N, 106º07´~107º17´ E), the capital of Guizhou Province, is located in southwestern China and the Circum-Pacific Global Mercuriferous Belt. SO2 and particulate matter emitted mainly from coal combustion, which is the main energy source in Guiyang, are the main airborne pollutants in Guiyang. In this thesis, the three main research were performed. Firstly, the methods for sampling and analysis of total gaseous mercury (TGM), GEM, RGM and TPM were developed, and the different mercury species concentrations in the air and precipitation were determined, and the atmospheric mercury dry and wet deposition fluxes were estimated in the Institute of Geochemistry, Chinese Academy of Sciences (IGCAS) from April to December, 2004. Secondly, three seasonal measurement campaigns of spring, summer and winter were carried out to determine GEM, RGM and TPM in ambient air of four study districts including a residential district, a business district, an ordinary industrial district and a tourism district in central urban area and one contrast site in rural area of Guiyang from April 2005 to January 2006. The atmospheric mercury species dry deposition fluxes were estimated, and qualitative analyses of the particulate matters were performed by a high-resolution transmission electron microscope (HR–TEM) in order to elucidate the source of TPM in winter in downtown Guiyang. Furthermore, the distribution characteristics of total mercury (THg) in surficial soil and some plants at all sampling sites were investigated to evaluate the amount of atmospheric mercury deposition and subsequent watershed contamination. Through the researches mentioned above, some main conclusions were obtained as follows: 1.Based on the systematic literature review of the overseas and domestic studies, the procedures to determine TGM and TPM in ambient air by a gold trap coupled with cold vapour atomic fluorescence spectrometry (CVAFS) and a miniaturized trap coupled with CVAFS were developed, and the synchronous collection of RGM and GEM in ambient air was performed using a KCl coated tubular denuder and a gold trap. The detection limit of each method was in the order of pg•m-3. For the first time in urban areas of China, the simultaneous measurements of GEM, RGM and TPM in ambient air were carried out. 2.The yearly average GEM, RGM and TPM concentrations in central urban Guiyang in the year of 2005 - 2006 reached up to 9.11 ng•m-3, 132.4 pg•m-3 and 1.02 ng•m-3, respectively, which were 1.5 times of those at the contrast site and significantly elevated compared to the respective global background: 1.5 ~ 2.0 ng·m-3, < 10 pg•m-3 and 1 ~ 86 pg•m-3. The seasonal, diurnal and spatial distribution patterns of GEM, RGM and TPM concentrations were observed as follows: ⑴The seasonal mean GEM concentrations were: winter > summer > spring. The high GEM concentrations in winter could be attributed to household heating using coal. The nighttime GEM concentrations were generally larger than that of daytime in spring and summer seasons, while in winter the opposite GEM diurnal distribution pattern was observed. The diurnal patterns of GEM in spring and summer seasons were mainly influenced by sources and their emission form, its chemical and physical characteristics, meteorological conditions, whereas the winter exhibited patterns that could be attributed to household heating using coal in the daytime. The yearly mean GEM concentrations were: an ordinary industrial district > a residential district > a business district > a tourism district > a rural district. ⑵The seasonal mean RGM concentrations were: spring > summer > winter. RGM concentrations were likely to be highly variable and highly related to meteorological conditions. The daytime RGM concentrations were generally larger than that of nighttime in all seasons. The diurnal patterns of RGM depended upon many factors: daytime sources, its chemical and physical characteristics, oxidant levels, and meteorological conditions. The yearly mean RGM concentrations were: a business district > an ordinary industrial district, a residential district > a tourism district, a rural district. ⑶The seasonal mean TPM concentrations were: winter > summer > spring, and The high TPM concentrations observed in winter could be attributed to the household heating using coal. The nighttime TPM concentrations were generally larger than that of daytime in all seasons. The factors of sources and their emission form, its chemical and physical characteristics, meteorological conditions impacted on the diurnal patterns of TPM. The yearly mean TPM concentrations were: an ordinary industrial district > a residential district > a business district > a rural district > a tourism district. Local emission sources contributed significantly to TPM contamination, and coal combustion in winter posed influences on the TPM concentrations at all sampling sites. 3.On the average, the atmospheric mercury apportioned in the central urban air in the year of 2005 - 2006 as follows: GEM (89.8 %) > TPM (8.8 %) > RGM (1.5 %). Measured (RGM + TPM)/TAM ratios were fewer than the contrast site of 10.0 % and greater than the global background of 1 ~ 5 % and therefore would lead to even greater amounts of deposition of mercury to the local environment. Despite both RGM and TPM constitutes a small percentage of TAM, they have chemical and physical properties which make them likely to govern a substantial part of the total deposition of atmospheric mercury. 4.The fact that most of the correlation between every two atmospheric mercury species daily average concentrations was not significant on the basis of the whole sampling periods observation in the year of 2005 - 2006 suggested the presence of a multitude of sources for these species in both the central district and the contrast district of Guiyang. 5.The mean GEM, RGM and TPM dry deposition fluxes in central urban Guiyang in the year of 2005 - 2006 reached up to 28.7 μg•m-2•yr-1, 10.4 μg•m-2•yr-1 and 160.9 μg•m-2•yr-1, respectively, which were 1.5 times of those at the contrast site. TPM governed dry deposition of atmospheric mercury to the local environment. The mean TAM dry deposition fluxes were 200.1 μg•m-2•yr-1, while its seasonal and spatial distribution patterns was observed as follows: winter > spring > summer and an ordinary industrial district > a residential district > a business district > a rural district > a tourism district. 6.The total dry and wet deposition fluxes of TAM in central urban Guiyang were estimated to be 54.7 kg•yr-1 in the year of 2005 - 2006, which only constituted 16.4 % of the annual Hg emission from coal combustion to the ambient air in 2003 which was calculated to be 334 kg. Most of atmospheric mercury still resided in the air, and was likely to be transported over very long distances from the central urban district of Guiyang. 7.We observed TGM concentrations in the ambient air of IGCAS with years from 2000 to 2006. TAM dry deposition fluxes to ecosystems of IGCAS were 16.5 ng•m-2•h-1 in 2004, higher than 12.2 ng•m-2•h-1 of wet deposition fluxes. 8.The geometric mean THg concentrations in surficial soil from the central district and the contrast district of Guiyang were 0.370 and 0.276 mg•kg -1, which were much elevated compared to the Guiyang’s background of 0.201 mg•kg -1. In Guiyang, natural emissions from soil contribute significantly to the elevated TGM concentrations in the ambient air, and soil Hg concentrations were used to scale up Hg emission from soil. So we should take strong measures against the Hg pollution in soil for protecting human health in Guiyang. 9.The mean of THg concentrations in moss from the central urban area of Guiyang was 0.248 mg•kg -1, which was about 1.5 times of that in the contrast site. THg concentrations in leaves of the central urban woody plants ranged from 0.068 to 0.181 mg•kg -1. Mercury uptake by leaves was in the order of: deciduous plants > evergreen plants. THg in both naturally growing mosses and leaves of Frimiana simplex were controlled by Hg concentrations in the ambient air, and were able to reflect the present pollution level and the spatial distribution pattern of regional atmospheric mercury.
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语种中文
文献类型学位论文
条目标识符http://ir.gyig.ac.cn/handle/352002/3200
专题研究生_研究生_学位论文
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郑伟. 贵阳市中心城区大气中不同形态汞的研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2007.
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