Knowledge Resource Center for Ecological Environment in Arid Area
| 我国高海拔地区二元羧酸类二次有机气溶胶的组成、来源及形成机理 | |
| 其他题名 | Molecular distributions, sources and formation mechanisms of dicarboxylic acids and related SOA from high altitude regions in China |
| 孟静静 | |
| 出版年 | 2014 |
| 学位类型 | 博士 |
| 导师 | 王格慧 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 二元羧酸是二次有机气溶胶的重要组分之一，影响气溶胶的吸湿性，改变大气颗粒物的粒径分布特征及云凝结核（CCN）活性。二元羧酸还可以改变成云过程，影响云寿命及降雨模式，进而对太阳辐射平衡、全球气候变化及人体健康产生重要影响。在高海拔地区，由于太阳辐射强、昼夜温差大，使二次有机气溶胶的分子组成、来源及形成机理与近地面地区存在着显著的差异。因此，全面阐明我国高海拔地区二次有机气溶胶的组成特征及形成机理，对了解区域内大气污染的程度及来源具有更加明确的指示意义，并对大气污染控制对策的制定提供理论依据。 本文选择青海湖（海拔：3200 m）和华山（海拔：2060 m）分别作为大陆背景点、高山点采集大气气溶胶样品，并对气溶胶中二元羧酸类有机化合物、碳组分及无机离子进行分析。结果表明：青海湖夏季大气颗粒物PM2.5中草酸（C2）的浓度最高，其次是丙二酸（C3）、丁二酸（C4）和壬二酸（C9）。青海湖气溶胶中二元羧酸（231±119 ng m-3）、酮羧酸（8.4±4.3 ng m-3）及α-二羰基化合物（2.7±2.1 ng m-3）的浓度比平原地区低20%–40%，表明青海湖二次有机气溶胶的浓度水平较低，受污染源影响较小。与地表城市与海洋地区相比，青海湖气溶胶中C2/DCAs与DCAs-C/WSOC的比值较高，表明青海湖气溶胶氧化程度更深，这是因为高原地区太阳辐射较强。二次有机气溶胶的分子构成与后向轨迹分析结果表明青海湖气溶胶中的二元羧酸类化合物主要来自长距离传输。大气环境中的C2/Lev、Gly/Lev与mGly/Lev的比值比由牛粪燃烧直接排放的气溶胶高30?400倍，表明在大陆背景点生物质燃烧对草酸（C2）、乙二醛（Gly）及甲基乙二醛（mGly）等二次气溶胶的生成影响甚微。 另外，通过对华山山顶大气气溶胶冬、夏季PM10中化学组分的季节变化特征分析，发现无论是冬季还是夏季，华山山顶有机气溶胶中草酸（C2）浓度最高，其次是丙二酸（C3）、丁二酸（C4），与青海湖以及地表城市地区的分子组成特征相似。夏季大部分水溶性二次有机化合物的浓度高于冬季，但是冬季己二酸（C6）和邻苯二甲酸（Ph）的浓度是夏季的2倍，表明在冬季自由对流层大气气溶胶受平原地区人为污染源的影响更大。冬季乙二醛（Gly）与甲基乙二醛（mGly）的浓度高于夏季，与二元羧酸的季节变化特征相反，乙二醛（Gly）与甲基乙二醛（mGly）均是二元羧酸的重要前体物，因此本文认为夏季高山对流层气溶胶的氧化性比冬季强。冬季草酸（C2）与左旋葡萄糖苷（Levoglucosan）呈显著的线性相关关系，而夏季草酸（C2）与异戊二烯、单萜烯的氧化产物间的相关性较强。主成份分析（PCA）结果进一步表明华山冬季SOA主要来自由生物质及煤燃烧排放的前体物经二次氧化产生的，但是夏季SOA主要是经异戊二烯、单萜烯的氧化产物等生物二次有机气溶胶（BSOA）进一步氧化产生的。利用气溶胶无机模型（Aerosol Inorganic Model (AIM)），对华山夏季PM10气溶胶的实际酸度（pHIS）及气溶胶中液相水含量（LWC）进行计算，结果表明草酸（C2）的浓度与pHIS相关性（R2=0.60）较强，但与LWC相关性（R2=0.11）很弱，表明颗粒物酸度（pHIS）增强能够促进气溶胶中草酸（C2）的生成，这是因为草酸（C2）主要是经酸催化反应二次形成的。 最后，通过对比沙尘期、非沙尘期西安与华山气溶胶中化学组分的差异，分析沙尘暴对地表城市与高山地区气溶胶的影响，得出以下结论：沙尘期西安大气中WSON/WSTN的比值约是非沙尘期的2倍，这是由于在沙尘暴期水溶性有机氮大量增加。另外，沙尘期西安大气中矿物粉尘占PM10质量浓度的相对含量约是非沙尘期的2倍，而无机离子、EC和OM的相对含量仅是非沙尘期的55%，说明沙尘暴严重影响了城市大气的化学组分。沙尘期华山气溶胶OC的浓度显著增高，其主要因为来自戈壁沙漠源区的气溶胶中含有大量的有机物。但是沙尘期EC的浓度仅是非沙尘期的一半，可能是因为沙尘暴带来的强风对当地的EC有稀释作用。华山非沙尘期二元羧酸类SOA的总浓度约是非沙尘期的3倍，而在西安沙尘期SOA的总浓度约是非沙期1–2倍，说明沙尘暴对二元羧酸有一定的稀释作用，且对高山地区的稀释作用比地表城市更强烈，同时也表明非沙尘期西安和华山大气中的二元羧酸主要来自本地源，而非来自长距离传输。西安、华山大气溶胶在沙尘期均比非沙尘期的老化程度深，表明来自戈壁沙漠源区的气溶胶在长距离传输过程中逐渐老化。 |
| 英文摘要 | Dicarboxylic acids are important components of secondary organic aesosols (SOA), which can change the hygroscopic properties and size distributions of ambient particles, and thus influence the atmospheric radiative forcing through acting as cloud condensation nuclei (CCN). Moreover, dicarboxylic acids can change the process of cloud formation, and further significantly influence the solar radiation balance, global climate change and in addition to the impact on humuan health. Molecular compositons, sources and formation mechanisms of water-soluble SOA from high altitude aerosols are greatly different from those on ground surface due to stronger solar radiation and more significant variation in temperature of the atmospheric environment. Therefore, it’s necessary to explore the molecular characteristics and formation mechanisms of SOA in high altitude regions in China, because most observations on aerosols have been conducted on ground surface and characteristics of aerosols in high altitude areas are poorly understood. In this work, Qinghai Lake (3200 m a.s.l) and Mt. Hua (2060 m a.s.l) are regarded as representatives of remote continetal background and mountainous area, respectively, in which dicarboxylic acids, ketocarboxylic acids, dicarbonyls, carbonaceous fraction and water-soluble inorganic ions in the aerosol samples were analysed to investigate the molecular distributions, sources and formation mechanisms of atmospheric aerosols from the tropospheres over the above high alitude regions. Oxalic acid (C2) is the dominant dicarboxylic acid in the samples, followed by malonic, succinic and azelaic acids. Total dicarboxylic acids (231±119 ng m-3), ketocarboxylic acids (8.4±4.3 ng m-3), and α-dicarbonyls (2.7±2.1 ng m-3) at the Tibetan background site are 2?5 times less than those detected in lowland areas such as 14 Chinese megacities. Compared to those in other urban and marine areas enhancements in relative abundances of C2/total diacids and diacids-C/WSOC of the PM2.5 samples suggest that organic aerosols in the Tibetan region are more oxidized due to strong solar radiation. Molecular compositions and air mass trajectories demonstrate that the above secondary organic aerosols in the Qinghai Lake atmosphere are largely derived from long-range transport. Ratios of oxalic acid, glyoxal and methylglyoxal to levoglucosan in PM2.5 aerosols emitted from household burning of yak dung, a major energy source for Tibetan in the region, are 30?400 times lower than those in the ambient air, which further indicates that primary emission from biomass burning is a negligible source of atmospheric oxalic acid and α-dicarbonyls at this background site. PM10 aerosols from the summit of Mt. Hua (2060 m a.s.l) in central China during the winter and summer of 2009 were analyzed for dicarboxylic acids, ketocarboxyli acids and α-dicarbonyls. Molecular composition of dicarboxylic acids (C2?C11) in the free tropospheric reveals that oxalic acid is the most abundant species in both seasons, followed by malonic (C3) and succinic (C4) acids, being consistent with those at the Qinghai Lake site and other ground level sites. Most of the diacids are more abundant in summer than in winter, but adipic (C6) and phthalic (Ph) acids are twice lower in summer, suggesting more significant impact of anthropogenic pollution on the wintertime alpine atmosphere. Moreover, glyoxal (Gly) and methylglyoxal (mGly) are also lower in summer than in winter. As both dicarbonyls are major precursor of C2, their seasonal variation patterns, which are opposite to those of the diacids, demonstrating that the mountain troposphere is more oxidative in summer. C2 showed strong linear correlations with levoglucosan in winter and oxidation products of isoprene and monoterpene in summer. PCA analysis further suggested that the wintertime C2 and related SOA in the Mt. Hua troposphere mostly originate from photochemical oxidations of anthropogenic pollutants emitted from biofuel a |
| 中文关键词 | 二次有机气溶胶 ; 草酸 ; 二元羧酸 ; 乙二醛与甲基乙二醛 ; 高海拔地区 |
| 英文关键词 | Secondary organic aerosols Oxalic acid Dicarboxylic acids Glyoxal and methyglyoxal High altitude regions |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 环境科学 |
| 来源机构 | 中国科学院地球环境研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287367 |
| 推荐引用方式 GB/T 7714 | 孟静静. 我国高海拔地区二元羧酸类二次有机气溶胶的组成、来源及形成机理[D]. 中国科学院大学,2014. |
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