| 中国西南地区大气降水中低分子有机酸研究（以贵阳市和尚重镇为例） | |
| Alternative Title | Studies on the Low Molecular Weight carboxylic acids in the rainwater of Guiyang City and Shangzhong Town, Southwest of China |
| 徐刚 | |
| 2007-12-19 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 地球化学研究所 |
| Degree Name | 博士 |
| Keyword | 低分子有机酸 甲醛 大气降水 富集系数 中和常数 后推径向轨迹 大气光氧化反应 直接来源 间接来源 沉降通量 干沉降 湿沉降 |
| Abstract | 近几年随全球变暖和大气污染的加剧，有机气溶胶对气候和环境的影响引起了广泛的关注。其中低分子有机酸由于易溶于水，易挥发等特性可以改变大气颗粒物吸湿性、粒径分布以及形成云凝结核活性，进而改变全球的水循环和辐射平衡，而日益成为大气化学研究的重要内容。低分子有机酸极强的水溶性使雨水成为研究大气有机酸的理想载体。有机酸进入降水后是降雨的酸度重要贡献者，尤其是边远地区有机酸对降水酸度贡献高达65%。传统的大气降水研究主要侧重无机离子，认为硫酸和硝酸是降水酸度的主要贡献者，而忽略对降水中有机组分的研究。以贵阳和重庆等为代表的西南地区是我国酸雨污染的重灾区，该地区是典型喀斯特地形地貌区，生态环境具有极端的脆弱性和破坏后难以恢复性，在该地区研究酸雨形成和影响因素具有特殊的重要意义。本研究选取典型酸雨区(贵阳市)和人为污染较少黔东南州黎平县尚重镇为研究对象，2006-4～2007-4期间，收集大气降水样品221个，测定了大气降水中7种有机酸和主要阴、阳离子。对有机酸对酸雨的贡献及大气降水中无机离子和有机酸的浓度分布、变化规律、主要来源和沉降通量进行研究。主要得到了以下几点认识： 1、建立了离子色谱同时测定雨水中有机酸和无机酸分析条件。以戴安AS11-HC为分离柱、AG11-HC为保护柱，RFC-30淋洗液发生器在线产生KOH淋洗液，主要梯度条件为1mmol ( 0～6min) 、1mmol～30mmol (6～31min)。淋洗液流速1.5ml/min，柱温39℃。此条件下主要有机酸线性相关系数0.9992~0.9999，RSD%≤5%，精密度RSD%≤5%(丙酮酸RSD%=13.8%)，样品的加标回收率在80~120%之间，满足分析测试要求。 2、 贵阳市降水样品pH值的分布范围为2.49～6.92，年均值为3.28。雨水酸化率为73.8%，其中pH值小于4.0雨水占样品总数42%。尚重镇降水样品pH值的分布范围为5.01～6.50，年均值为5.83，降水的酸雨率为18.4%。贵阳市酸雨污染仍十分严重，重酸雨尤为突出(pH<4.0)，尚重镇酸雨污染较轻。 贵阳市降水样品电导率在10～1028μS/cm之间，平均值为248μS/cm，降水电导率高反映了贵阳市大气污染显著。尚重镇降水样品电导率在2.2～52.8μS/cm之间，平均值为18.1μS/cm，降水电导率低反映大气污染较轻。 3、贵阳市大气降水主要无机离子是SO42-、NO3-、H+、Ca2+、NH4+，雨量加权平均浓度分别为154.1μmol/L、33.9μmol/L、520.7μmol/L、226.4μmol/L和158.3μmol/L。采样期间，贵阳市H+年沉降通量为496.9mmol/m2/yr，夏季H+沉降占全年沉降总量的78%，贵阳市SO42-年沉降通量达到151.5mmol/m2/yr，有195.3mmol/m2/yr的Ca2+沉降。NH4+、Mg2+、Na+、K+、NO3-、Cl-的沉降通量分别为138.7mmol/m2/yr、50.9mmol/m2/yr、26.8mmol/m2/yr、11.4mmol/m2/yr、32.3mmol/m2/yr和12.6mmol/m2/yr。 尚重镇贵阳市大气降水主要无机离子是SO42-、NO3-、Ca2+、NH4+，其雨量加权平均浓度分别为43.1μmol/L、19.3μmol/L、33.0μmol/L和49.5μmol/L。采样期间，尚重镇[H+]年沉降通量为0.5mmol/m2/yr。SO42-、Ca2+和NH4+是发生沉降主要离子，分别为13.9mmol/m2/yr、10.6mmol/m2/yr和15.9mmol/m2/yr。Mg2+、Na+、K+、NO3-、Cl-的沉降通量分别为2.1mmol/m2/yr、5.9mmol/m2/yr、3.0mmol/m2/yr、6.2mmol/m2/yr和3.2mmol/m2/yr。 4、在贵阳市、尚重镇大气降水中共检测出7种低分子有机酸，分别是甲酸、乙酸、草酸、丙酮酸、丙酸、甲烷磺酸和乳酸。其中甲酸、乙酸和草酸是三种主要的有机酸。贵阳市甲酸、乙酸和草酸年平均浓度分别为14.24μmol/L、9.35μmol/L和2.79μmol/L，而在尚重镇它们浓度分别为4.95μmol/L、1.35μmol/L和2.31μmol/L。根据酸平衡常数计算法，贵阳市有机酸对自由酸贡献分别为：甲酸-7.9%，乙酸-4.7%，草酸-6.1%，三种主要有机酸贡献了18.7%的自由酸；尚重镇有机酸对自由酸贡献分别为：甲酸-25.1%，乙酸-7.5%，草酸-25.5%，有机酸对自由酸贡献率为58.1%。贵阳市有机酸占阴离子比值1.7～19.2%，平均值为6.6%。尚重镇有机酸对阴离子的贡献为0.5～92.2%，平均值为13.2%。有机酸对酸雨形成和大气降水化学起不可忽视的重要作用。 采样期间，贵阳市甲酸、乙酸和草酸的湿沉降通量分别为13.5mmol/m2/year 、8.9mmol/m2/year和2.6mmol/m2/year，甲酸和乙酸干沉降通量分别为26.7mmol/m2/year 和14.5mmol/m2/year，干沉降和湿沉降是贵阳市有机酸的主要沉降形式。尚重镇甲酸、乙酸和草酸的湿沉降通量分别为1.59mmol/m2/year 、0.43mmol/m2/year和0.04mmol/m2/year，甲酸和乙酸干沉降通量分别为0.1mmol/m2/year 和0.17mmol/m2/year，湿沉降是尚重镇有机酸的主要沉降形式。 5、尚重镇大气降水有机酸生长季节浓度高于非生长季节浓度，说明生长植物或土壤的释放可能是尚重镇大气有机酸的主要来源。贵阳市大气降水中有机酸非生长季节浓度高于生长季节浓度，主要原因是贵阳市降雨主要发生在夏季，降雨量的增加加大了对大气中微量气体的淋滤作用，降低了大气中有机酸浓度，同时夏季降雨pH值较低也不利于雨水对大气有机酸的溶解吸收。气象条件是影响有机酸浓度的重要因素。贵阳市大气有机酸主要在降雨初期进入降水并被清除的，降雨初期(1～2h)对大气有机酸清除占总清除的50～80%。随降雨的进行雨水中有机酸浓度逐渐降低，降雨后期略有升高，大降雨量对雨水中有机酸浓度起稀释的作用。尚重镇降雨量对有机酸浓度影响作用不明显，说明有机酸浓度不受雨量稀释作用控制，在降雨过程可能存在有机酸的液相来源。不同来源气团对贵阳市雨水中有机酸浓度影响不同，其中以北面方向气团降水中有机酸最高，与我国内陆大气污染较重有关。而源于海洋方向的东南气团雨水中有机酸浓度最低。 6、利用统计分析方法(相关性分析、主成分分析和聚类分析)和有机酸来源判别方法结合不同的来源释放有机酸通量得出：尚重镇大气中有机酸主要来源植物或者土壤直接或间接释放，而贵阳市有机酸来源相对复杂，其中植物的直接释放和机动车辆尾气排放不是大气有机酸的主要来源，生物质燃烧直接释放以及植物和人类活动向大气排放大量的不饱和有机物大气氧化可能是大气有机酸的重要来源。 7、从大气降水的电导率和pH值对比来看，贵阳市大气污染严重，雨水酸化率高，尚重镇大气污染较轻，雨水酸化率低。贵阳市大气降水中水溶性离子浓度是尚重镇的2～5倍左右，尚重镇地区酸沉降只有贵阳市0.1%，酸沉降对尚重镇不会造成太大影响。有机酸占贵阳市大气降水自由酸的19%，而尚重镇有超过1/2的自由酸是来源于低分子有机酸，是边远地区大气降水酸度的主要贡献者。来源分析表明尚重镇有机酸主要为生物源，贵阳市有机酸为人为源和生物源并重。 8、 传统的大气降水化学研究主要侧重于无机离子的研究，而忽略了对大气降水中有机组分的研究。本文第一次较全面、系统的研究了西南典型酸雨污染区大气降水化学组成以及降水酸度的来源，指出有机酸组分是西南地区大气降水化学的重要组成部分，对酸雨形成有不可忽视的影响。 |
| Other Abstract | In recent years, Due to the change of climate and the worsen of the atmosphere quality, there has been an increasing focus on the effect of organic aerosol on regional climate and enviromental response. Low molecular weight(LMW for short) carboxylic acids have benn identified as major constituents of the organic aerosol. These acids are water-soluble and volatile compounds, it has been suggested they may alter the hygroscopic properties of atmospheric particles and act as more acitive cloud condensation nuclei in atmosphere, As a result, they become more and more importan in atmospheric chemistry.The high solubility of LMW carboxylic acids makes rain an ideal scavenging medium. Entering the aqeuous phase, they made major contribution to rainwater acidity. In remote area, they constituents 65% of the free acidity.Southwest of China, such as Guiyang and Chongqing, is one of the most serious areas of acid rain in our country. The ecosystem of this region is more fragility and irreverseble after disturbed because they belong to Karst region in the world. It is more important to research the acid rain and possible reasons in such region. Guiyang city,typical of acid rain area,and Shangzhong town,less human activities’s region were selected as the research rrgion. From 2006-4 to 2007-4, 221 rainwater sample were collected and seven LMW carboxylic acids and formaldehyde were determined,in addition, the major inorganic anions and cations were analyzed to elucidate their occurrence, variation, possible sources and deposition.By the way,the origin of free acidity in rainwater especially LMW carboxylic acids contributions were evaluated for enviromental policy. The main conclusions are as follows: 1、Seven LMW carboxylic anions and inorganic anions were simultaneously determined by ICS-90 chromatography combined with RFC-30(eluent generator) about 30min. The Dionex anoin separator column(250×4mm) IonPac AS11-HC and it’s corresponding guard column(50×4mm)AG11-HC were used. The conductivity of eluent was chemically suppressed by a self-regenerating suppressor(ASRS ULTRA II 4mm) that used the column effluent to supply the proton generated by water electrolysis.The eluent KOH was generated by RFC-30(Reagent free controllor) on line with 1mmol/L(0～6min) and 1mmol/L～30mmol/L (6～31min). The flow of eluent was 1.5ml/min and column temperature was kept at 39℃ by CTS-10. Under this chromatography condition,the linear correlation coefficients in the range of 0.9995~0.9999. The relative standard deviations(RSD%) were below 5%. Quantitative recoveries of spiked samples ranged from 80~120% .This method has been effectively applied to the determination of these anions in rain samples in GuiZhou province. 2、The pH of rainwater in Guiyang city ranged from 2.49 to 6.92 with an annual volume weighted average(VWA for short) 3.28 which is typical acidic value.About 73.8% of the rainwater had a pH of less than 5.6 and 42% of the rainwater showed a pH of less than 4.0 which indicate acidic rain severely polluted the atmosphere in Guiyang city. By contrast, the VWA concentration of H+ is 5.83 in Shangzhong Town. The pH of rianwater ranged from 5.01 to 6.50 with 18.4% of the sample’s pH below 5.6. The conductivity of rainwater in Guiyang city ranged 10～1028μS/cm with a mean 248μS/cm which showed the serious air pollution in this region. In Shangzhong Town, the conductivity of rainwater ranged 2.2～52.8μS/cm with a mean 18.1μS/cm which showed the slight air pollution in this region. 3、SO42-、NO3-、H+、Ca2+ and NH4+ were the dominate ions in rainwater in Guiyang city, their VWM concentration were 154.1μmol/L、33.9μmol/L、520.7μmol/L、226.4μmol/L and 158.3μmol/L respectively. The annual wet deposition of H+ was 496.9mmol/m2/yr and 78% of H+ deposited in sumertime. The annual wet deposition of SO42-、Ca2+、NH4+、Mg2+、Na+、K+、NO3-、Cl- were 151.5mmol/m2/yr、195.3mmol/m2/yr、138.7mmol/m2/yr、50.9mmol/m2/yr、26.8mmol/m2/yr、11.4mmol/m2/yr、32.3mmol/m2/yr和12.6mmol/m2/yr respectively. In Shangzhong Town,SO42-、NO3-、Ca2+ and NH4+ were the dominate ions in rainwater , their VWM concentration were 43.1μmol/L、19.3μmol/L、33.0μmol/L and 49.5μmol/L respectively. The annual wet deposition of H+ was 0.5mmol/m2/yr much lower than that in Guiyang city. The annual wet deposition of SO42-、Ca2+、NH4+、Mg2+、Na+、K+、NO3-、Cl- were 13.9mmol/m2/yr、10.6mmol/m2/yr、15.9mmol/m2/yr、2.1mmol/m2/yr、5.9mmol/m2/yr、3.0mmol/m2/yr、6.2mmol/m2/yr and 3.2mmol/m2/yr respectively. 4、Seven LMW carboxylic acids were determined in rainwater, they are formic acetic oxalic pyruvic propanic methanesulfonic and lactic acid.Formic acetic and oxalic acids were found to be the three dominate carboxylic acids with the VWM concentrations 14.24μmol/L、9.35μmol/L and 2.79μmol/L in rainwater in Guiyang city and 4.95μmol/L、1.35μmol/L and 2.31μmol/L in the rainwater in Shangzhong town. Carboxylic acids were estimated to account for 18.7% of the free acidity in rainwater in Guiyang city. In Shangzhong town, this contribution is much bigger, 58.1% of the free acidity was originated from LMW carboxylic acids. During research period, the wet deposition of formic acetic and oxalic acids were 13.5mmol/m2/yr 、8.9mmol/m2/yr and 2.6mmol/m2/yr repectively. It was deposited 26.7mmol/m2/yr and 14.5mmol/m2/yr for formic and acetic acids through dry deposition in Guiyang city. There were 1.59mmol/m2/yr 、0.43mmol/m2/yr and 0.04mmol/m2/yr wet deposition for formic acetic and oxalic acids, 0.1mmol/m2/yr and 0.17mmol/m2/yr dry deposition for fromic and acetic acids in Shangzhong town. 5、The town Shangzhong also witnessed higher concentratin of the acids in the summer season than in the winter. Direct emissions from growing vegetations or from soils account for the main provenance of the acids in the rural area. This is, however, not the case in the city Guiyang, where the organic acids were found higher in the non-growing season than in the growing season. This seasonal variation of the acids indicates their anthropogenic sources and the relatively weak scavenging effect of precipitation during the wintertime. Mteorological parameters have an important impact on the concentration levels of organic acids in precipitation. During the wet precipitation events, the rain fluxes of organic acids generally decreased as a function of time and the scavenging of atmospheric organic acids by wet precipitation mostly take place during the early stage of the precipitation. The air-mass back-trajectory anlysis indicated that rainwater in Guiyang city with inland back-trajectory coming from the north had the highest concentrations of organic acids whlie the marine back-trajectory coming from the southeast had the lowest concentrations. 6、From statistical analysis (such as correlation analysis,principal component analysis and classify analysis)and indicator of origin of LMW carboxylic acids in atmosphere, it was suggeted that the LMW carboxylic acids in Shangzhong town were mainly originated from the direct emissions from vegetations or soils. However, the origin of carboxylic acids in Guiyang were more complicated, and human being activity provided a large amount unsaturated hydrocarbons, which could be the precursor of carboxylic acids. 7、Guiyang city ,the acid rain belt, is the most severely polluted area in China from the pH and conductivity of the rainwater. By contrast, the town of Shangzhong received little air pollition and acid rain during research period. The Guiyang city data exhibits concentrations of water-soluable ions which are roughly 1～4 times higher than at Shangzhong town resulting in the significantly lower acidic deposition (about 99.9%) in Shangzhong town compared to Guiyang city. LMW carboxylic acids contribute 19% to the free acidity in rainwater in Guiyang city,on contrary, they were estimated to contribute 58% to the rainwater acidity in Shangzhong town which were the major acid contributor. From origin anlysis, it was suggested the biogenic emissions were main source in Shangzhong town and anthropogenic sources were equal important to LMW carboxylic acids in Guiyang city. 8、Extensive experiments have been conducted to study the inorganic anions in atmosphere precipitation especially sulfuric and nitric acids. However, little is known about the characteristaics and the role of organic compounds in rainwater. This is the first complete and systematically study on the chemical composition of rainwater and the possible sources of acid rain in Southwest of China, a severely acid rain polluted region. LMW carboxylic acids were found an important constituents to the rainwater and contribute a large fraction to the free acidity in rainwater especially in remote area. |
| Pages | 148 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3358 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 徐刚. 中国西南地区大气降水中低分子有机酸研究（以贵阳市和尚重镇为例）[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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