Knowledge Resource Center for Ecological Environment in Arid Area
| 我国典型城市大气降水物质来源及其环境效应 | |
| 其他题名 | Sources of Chemical Components in Precipitation and Environmental Effects of Typical Cities in China |
| 武瑶 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 徐志方 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 酸雨是目前人类所面临的主要环境问题之一，近些年中国已成为继欧洲和北美之后的世界上第三大酸雨区。现阶段我国受酸雨影响的地区约占总国土面积的30%，并呈现出加重和蔓延的趋势，给我国的经济建设和人民生活造成了巨大的损失，严重影响了我国经济、社会的可持续发展。大气降水化学组成、物质来源及其贡献是酸沉降研究的重要内容，可以为研究酸雨成因、发展趋势和制定相应政策提供依据。近年来，学者们对全国各地大气降水中雨水的酸度、基本化学组成和酸沉降量进行了大量的研究。但是对于降水中碱性离子含量、沉降通量及其中和能力的相关研究报道较少，对于降水中碱性物质的来源、贡献比例等方面研究就更为缺乏，使得我们在酸雨研究工作中缺乏大气中碱性物质减少所带来的连锁反应方面的相关数据和研究基础。同时，硫（δ34S）和锶（87Sr/86Sr）稳定同位素地球化学理论和方法为我们更好的理解和阐明降水中硫和钙的来源及其物质贡献量提供了重要的技术手段，但目前为止，我国关于大气降水中锶同位素组成特征的研究十分薄弱，缺乏大尺度长时间的研究，也缺乏锶和硫同位素联合应用的研究。为此，本研究选取兰州、北京、天津、池州、贵阳和杭州六座典型城市作为研究区，进行为期一年的降水采样，测定降水样品的酸度、主微量元素含量和δ34S、87Sr/86Sr，以此来了解我国典型城市的降水化学和硫、锶同位素组成特征，运用相关性分析、富集系数、气流后向轨迹模拟和同位素示踪等方法对各研究区降水中物质的来源及其相对贡献进行辨识和定量评估，在对降水的酸度与其中酸、碱离子的相关关系进行分析的基础上，对各研究区降水中碱性离子的中和作用进行评估和对比，得出如下认识和结论：（1）我国南、北方城市降水的酸度和化学特征呈现出明显的区域差异，北方城市降水的pH值和离子浓度要明显高于南方城市。由于各地不同的污染物排放源和气候条件不同，各研究区降水的酸度呈现出不同的季节变化趋势。各研究区降水中的离子组成相似，Ca2+和NH4+是主要阳离子，SO42-是主要阴离子，表明目前我国降水仍然以硫酸型污染为主。（2）兰州、北京的酸沉降有加重趋势，降雨无论是酸度还是酸雨频率都逐年增加，这与当地实施各项环保措施导致大气中碱性颗粒物大量减少有关。而贵阳地区，由于近年来实施的SO2减排措施，降雨酸度有所减弱，酸雨频率有所降低。杭州降水的酸度虽然没有明显增强，但是离子浓度水平有所升高，大气污染问题同样不容忽视。（3）北京、天津、池州、贵阳和杭州大气降水的硫同位素组成存在明显差异，各地区降水的硫同位素组成与当地使用的燃煤有关。各地降水的δ34S值均表现出冬季高夏季低的波动现象，其中北京和天津降水的这种季节性变化特征可能与冬季燃煤排放污染物增多以及同位素平衡分馏的温度效应有关，池州、贵阳和杭州降水的这种季节性变化特征则可能是由夏季生物成因硫的大量释放和同位素平衡分馏的温度效应导致的。（4）由于各地所处地区岩性、气候条件和人为活动等情况各不相同，各研究区降水的锶同位素组成特征和季节性变化存在差异。兰州和贵阳降水的锶同位素组成分别与当地的黄土沙尘和碳酸盐岩接近，且不具有明显的季节变化趋势；北京和天津降水的锶同位素组成在春季受到了来自北方黄土、沙漠沙尘的影响，具有较高的87Sr/86Sr值；池州和杭州降水中的锶受到人为活动的显著影响，其87Sr/86Sr值均不具有规律性的的季节变化。（5）根据离子化学组分特征可以初步判断降水中各物质的来源，其中各研究区降水中的Cl-均受到海洋来源的影响；绝大部分SO42-和NO3-来自人为源输入，与自化石燃料的燃烧密切相关；几乎全部的K+、Ca2+、Mg2+都源自陆相来源，主要来自岩石和土壤风化；NH4+则主要来自农业活动、生物质燃烧和动物粪便等。利用硫同位素数据进一步计算得出人为来源硫在北京、天津、池州、贵阳和杭州降水中的平均贡献率分别为92%、86%、74%、72%和77%。降水的锶同位素组成特征和化学组分数据表明，兰州降水中的锶主要来自周围黄土沙尘，同时西北和北部沙漠沙尘也有一定贡献；贵阳降水中的锶主要受当地碳酸盐岩风化影响，同时人为活动输入也有一定贡献；北京和天津降水中的锶受海洋、北部沙漠和黄土沙尘以及人为活动排放的共同影响；杭州降水中的锶主要来自海水和人为排放；池州降水中的锶则主要为人为活动输入。（6）各研究区降水中的酸性物质均受到了碱性离子不同程度的中和作用，各地降水中的主要中和离子是Ca2+，其次是NH4+，它们对兰州、北京、天津和贵阳降水中酸的中和比例分别为88.0%、86.8%、86.3%和83.4%，要明显高于池州和杭州降水中的比例。 |
| 英文摘要 | At present, acid rain is one of the most serious environmental problems in the world. In recent years, China has become the third largest heavy acid rain region in the world, behind Europe and North America. Nowadays, areas affected by acid rain account for approximately 30% Chinese area, and it is gradually expanding. Acid rain has caused great damage to economic construction and people’s life, it has also seriously affected the sustainable development of national economy and society. It is of great importance to study the chemical compositions, sources and their relative contribution of precipitation, which can provide scientific references for controlling the development trend of acid rain and formulating the corresponding policies.In recent years, researchers have made a lot of studies on rainwater’s acidity and chemical composition as well as the amount of acid deposition. However, few studies have reported the amount, deposition fluxes and neutralizing capacity of alkaline ions in rainwater, and there are even fewer studies focused on the sources and their relative contributions of alkaline substances in rainwater. Thus, we lack the relevant data and research bases to study the chain reactions caused by the decrease of alkaline ions in rainwater. Meanwhile, the geochemistry theory and methods of stable sulfur (δ34S) and strontium isotope (87Sr/86Sr) provide us an important way to get a better understanding and description of the sources and their contributions to sulfur and calcium in rainwater. But until now, there are few researches focused on strontium isotope characterization of rainwater in China, lacking of studies at large scale and over long time period. At the same time, there are also lack studies applying both stable sulfur and strontium isotope.Therefore this study chose six Chinese typical cities (Lanzhou, Beijing, Tianjin, Chizhou, Guiyang and Hangzhou) as study area, we collected rainwater samples systemically for almost one year in all the six cities, and then analyzed the acidity, concentration of major and trace elements, δ34S and 87Sr/86Sr, to get understanding of the characterizations of chemical composition and stable isotopes of rainwater in typical cities of China. We combined methods such as correlation analysis, enrichment factors, back trajectory of air masses and tracer isotopes to distinguish the sources of substances in rainwater and quantitative evaluated their relative contributions. Moreover, we analyzed the correlations between acidity and acid-base ions, then evaluated and compared the neutralizing effects in rainwater of different study areas. Through our work, we find:(1) There were obvious differences of acidity and chemical characterizations between rainwaters in South China and North China, rainwaters in North China had higher pH and ion concentrations. Due to different sources of pollutants and climate conditions, the acidity of rainwater in different areas showed different seasonal variations. The chemical compositions were quite similar among all the study areas, Ca2+and NH4+ were the most abundant cations, SO42- was the most abundant anion, indicating sulfate are still the main pollutants in rainwater of China.(2) Acid deposition in Lanzhou and Beijing showed an increasing trend, both the acidity and the frequency of acid rain were increasing year by year, it may be due to the decrease of alkaline particles in the air which caused by the application of environmental measures. While, both the acidity and the frequency of acid rain were decreasing in rainwater of Guiyang, due to the application of SO2 reducing measures. Although the acidity of rainwater at Hangzhou did not increase obviously, the level of ion concentrations became higher, indicating the air pollutions cannot be ignored.(3) The characterizations of sulfur isotope in rainwater were quite different among Beijing. Tianjin, Chizhou, Guiyang and Hangzhou, the sulfur isotopic composition in these sites were similar with the local coals. The results showed striking seasonality between summer and winter δ34S values of rainwater among all the sampling sites. The seasonal pattern of δ34S values of precipitation in Beijing and Tianjin may be explained by the coal combustion in winter and the temperature dependence of the isotope equilibrium fractionation associated with SO2 oxidation reaction during sulfate formation in the atmosphere. While, the seasonal pattern of δ34S values of precipitation in Chizhou, Guiyang and Hangzhou may be attributed to the greater relative contribution of biogenic sulfur during the summer and the temperature dependence of the isotope equilibrium fractionation.(4) The characterizations and seasonal variations of strontium isotopic composition in precipitation were relate to the local rocks, climate conditions and anthropogenic activities, thus they were quite different among all the sampling sites. The strontium isotopic composition of rainwater in Lanzhou and Guiyang was to the loess dusts and carbonate rocks respectively, and they did not show obvious seasonal variations. Due to the dusts from loess and deserts in North and Northwest China, the strontium isotopic composition of rainwater at Beijing and Tianjin had higher 87Sr/86Sr ratios in spring. Because of the significant influences of anthropogenic activities, the strontium isotopic composition of rainwater in Chizhou and Hangzhou did not fluctuated regularly.(5) According to the chemical characterizations of major ions, we concluded the sources of components in the rainwater primarily. Cl- was influenced by sea salts at all the sampling sites; the majority of SO42- and NO3- came from anthropogenic inputs, and possibly from fuel combustion; almost all the K+, Ca2+ and Mg2+ came from terrestrial sources, mainly the weathering of rocks and soils; NH4+ mainly originated from agricultural activities, biomass burning and animal waste. We use the quantity equilibrium model to calculate the relative contribution of anthropogenic inputs to sulfates in rainwater, the results showed that anthropogenic inputs contributed 92%, 86%, 74%, 72% and 77% to sulfates in rainwater of Beijing, Tianjin, Chizhou, Guiyang and Hangzhou, respectively. When coupled with chemical composition data, strontium isotope systematics can be used to investigate the mixing of different strontium sources. Results showed that strontium in Lanzhou rainwater mainly originated from the surrounding losses, and the dusts from deserts in North and Northwest China also had some influences on it; strontium in Guiyang rainwater mainly came from weathering of local carbonate, and anthropogenic activities made significant contribution to it; strontium in Beijing and Tianjin rainwater can be interpreted in terms of three mixing sources: seawater, dusts from losses and deserts in North China and anthropogenic inputs; strontium in Hangzhou rainwater mainly derived from seawater and anthropogenic inputs; strontium in Chizhou rainwater was mainly influenced by anthropogenic inputs. (6) The acids in rainwater were neutralized by alkaline ions to some extent at all the sampling sites. Ca2+ was the main neutralizing ions, following by NH4+. The proportions of acids neutralized by Ca2+ and NH4+ in rainwater of Lanzhou (88.0%), Beijing (86.8%), Tianjin (86.3%) and Guiyang (83.4%) were obviously higher than that in rainwater of Chizhou and Hangzhou. |
| 中文关键词 | 大气降水 ; 物质来源 ; 硫同位素 ; 锶同位素 ; 中和效应 |
| 英文关键词 | precipitation sources of substances sulfur isotope strontium isotope neutralizing effects |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 地质工程 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287877 |
| 推荐引用方式 GB/T 7714 | 武瑶. 我国典型城市大气降水物质来源及其环境效应[D]. 中国科学院大学,2017. |
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