Knowledge Resource Center for Ecological Environment in Arid Area
| 典型城市及区域背景点有机气溶胶组成、来源、粒径分布及形成机理 | |
| 其他题名 | Molecular distributions, sources, size distributions and formation mechanisms of organic aerosols from typical megacities and background site in China |
| 任艳芹 | |
| 出版年 | 2017 |
| 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 | 我们分析了西安和广州2013年冬夏两季四个粒径段的颗粒相的多环芳烃（PAHs）和氧代多环芳烃（OPAHs）的浓度和分子组成，并且把细粒子上的含量与2003年的做了对比。结果表明，在冬季，14PAHs的TSP当量浓度在西安和广州分别为57±20和18±23 ng m-3，比夏季要高出5-10倍。两个城市的PAHs，夏季的时候以5环和6环为主，主要是因为交通排放的缘故，但是到冬季则是以4环和5环为主，这主要是因为冬季家用燃煤排放加强，还有就是半挥发性PAHs气固分配的作用。冬季我们检测到7个OPAHs，但是夏天只检测到了1个OPAH。在冬季，7OPAHs的TSP当量浓度在西安和广州分别为54±15 和 23±32 ng m-3 ，并且以5环为主。粒径分布的结果表明，在冬季，西安和广州大气细粒子(<3.3 μm)上以4环和5环的PAHs和OPAHs为主。而3环的PAHs和OPAHs的相对丰度随着颗粒物粒径的增大而增加，占总质量浓度的百分比从最小粒子 (<1.1 μm) 上的1% 到最大粒子上的90% (> 9.0μm)。PAHs的毒性评估结果表明，大气粒子的毒性，在冬季要比夏季的毒性强很多，而且，细粒子的毒性要比粗粒子的毒性强。与2003年的结果相比，冬季两个城市细粒子上的PAHs和OPAHs减少了50-90%，主要是因为我国天然气取代煤这一政策的广泛实施。在2013年的沙尘暴期间，我们在西安同时采集了TSP和分粒级的样品，并且分析了其中的一次和二次有机气溶胶。在沙尘和非沙尘期间，正构烷烃（n-alkanes）都是最主要的一类物质，接着是脂肪酸。人为源的一次和二次有机物的时间变化趋势一致，基本都是沙尘期低，非沙尘期高，这表明它们主要来自于本地/区域源，如煤和生物质燃烧。但是生物二次有机气溶胶则主要来自于长距离传输，比如戈壁沙漠的植物源。类似的，海藻糖在非沙尘期的浓度很低，但是在沙尘期的浓度却很高，并且，海藻糖和Ca及Na2SO4有很好的线性相关，表明了它也主要来自于长距离传输，同时进一步证明了Na2SO4来自于戈壁沙漠的地表土壤。分子组成，特殊比值和粒径分布的结果进一步证明了大分子量的有机气溶胶在沙尘期主要来自于戈壁区域的植被，而且沙尘期的气溶胶更加老化。Phe和DBP在非沙尘期是双模态，但是沙尘期的时候粗模态会显著增加，这主要是因为它们的饱和蒸气压比较大，易于挥发造成的。相反的，BeP和BPA的粒径分布在沙尘期变化就比较小，这是因为它们的饱和蒸气压比较小，不易挥发。二次有机物质在沙尘期主要分布在粗粒子上，主要是因为凝聚和/或它们分配到沙尘表面的液相造成的。为了调查清洁能源的利用对城市大气气溶胶中有机物的影响，我们分析了乌鲁木齐“煤改气”前后的两个供暖季（供暖季?: 2012年1月 – 2012年3月和供暖季II: 2014年1月– 2014年3月）的分级样品。讨论了其中的n-alkanes，PAHs和OPAHs。结果表明，与供暖季?相比，n-alkanes，PAHs和OPAHs的总浓度 (PM1.1, PM1.1?3.3 和PM3.3?9上的浓度之和) 在供暖季II分别降低了74%, 74% 和 82%。源解析结果表明，在乌鲁木齐的供暖季，煤燃烧，交通排放和生物质燃烧是这些有机物的主要来源。交通排放是这个城市中n-alkanes的主要来源。在供暖季?，煤燃烧是PAHs和OPAHs的主要来源，但是到供暖季II，交通排放变成它们的主要源。由于供暖燃煤被天然气的取代，煤燃烧对n-alkanes，PAHs和OPAHs的相对贡献从供暖季?的21?75% 降到了供暖季 II的 4?21%。健康风险评估的结果进一步表明，在乌鲁木齐的供暖季，受利于“煤改气”工程，由PAHs暴露引起的肺癌人数，在供暖季 II将比供暖季?降低73%。总之，我们的结果表明，家用供暖期间，清洁能源取代煤的措施，将会显著的缓解大气污染问题，并且有利于人体健康。论文最后还分析了背景点和城市点TSP中异戊二烯和单萜烯的光氧化产物的示踪物。所检测的所有生物二次有机气溶胶（BSOA）的浓度都是城市点高于背景点，夏天高于冬天。而且，所有的BSOA与硫酸盐有很好的正相关性(R2=0.52-0.9)，表明硫酸盐能够促进BSOA的生成。粒径分布的结果还表明，除了蒎酮酸和顺蒎酸，大部分的BSOA都分布在细模态(<1.1μm)。夏天，城市点异戊二烯与单萜烯的比值 (Riso/mono) 要比高山点和森林点的低。异戊二烯和单萜烯对OC的贡献夏天要高于冬天，而且，单萜烯氧化产物的浓度大于异戊二烯氧化产物的浓度。这些结果表明在我国的城市点，单萜烯是比异戊二烯更重要的一种BSOA前体物。 |
| 英文摘要 | Concentrations and compositions of PAHs and oxygenated PAHs (OPAHs) in four size ranges of ambient particles collected in Xi’an and Guangzhou, two megacities of China, during the winter and summer of 2013 were measured and compared with those in 2003. The TSP-equivalent concentrations of Σ14PAHs in Xi’an and Guangzhou are 57±20 and 18±23 ng m-3 in winter, 5?10 times higher than those in summer. PAHs in both cities are dominated by 5- and 6-ring congeners in summer due to the predominance of traffic emissions, but dominated by 4- and 5-ring congeners in winter due to enhanced emissions from domestic coal burning and increased gas-to-particle phase partitioning of the semi-volatile PAHs. Seven OPAHs were detected in winter while only one OPAH was detected in summer. TSP-equivalent Σ7OPAHs during winter are 54±15 and 23±32 ng m-3 in Xi’an and Guangzhou and dominated by 5-ring OPAHs. Size distribution results showed that 4- and 5-ring PAHs and OPAHs in Xi’an and Guangzhou are the dominant species in fine particles (<3.3 μm) during winter. Relative abundances of 3-ring PAHs and OPAHs increased along with an increase in particle sizes, accounting for from about 1% of the total PAHs or OPAHs in the smallest particles. The toxicity of PAH assessment indicated that atmospheric particles in winter are much more toxic than those in summer and fine particles are more toxic than coarse particles. Compared to those in 2003, fine particulate PAHs and OPAHs in both cities during winter decreased by 50?90%, most likely due to the replacement of coal by natural gas in the country.TSP and 9-stage size-segregated samples are simultaneous collected in Xi’an during spring 2013 and some primary and secondary organic aerosols are detected by using the TMS derivatization and GC/MS quantification technique. During both the dust storm and non-dust storm periods, n-alkanes are detected as the dominant compound class, followed by fatty acids. The anthropogenic primary and secondary organic aerosols display similar variation patterns with lower in the dust storm event and higher in the non-dust period, indicating they are mostly originated from local/regional sources, e.g. coal burning and biomass emissions. While biogenic secondary organic aerosols are largely originated from long-range transport such as Gobi desert plants. Similarly, trehalose shows a very low concentration during the nonevent time, but much higher in the dust storm period with good linear correlations with Ca and Na2SO4, indicating it is derived from long-range transport and further suggesting Na2SO4 directly originate from Gobi desert surface soil. The changes of molecular compositions, special ratios and size distributions further indicate that high molecular weight organic aerosols during the dust are mostly originated from plants in Gobi regions with dominant in coarse particles, and aerosols are more aged in the event. Phe and DBP show a bimodal size distribution during the nonevent and the coarse pattern significantly increase when dust present because of their high vapor pressures. In contrast, there are no clearly changes in size distributions of BeP and BPA generally with a fine mode due to their low volatility. Secondary organic compounds in Xi’an are predominantly enriched on the coarse particles in the presence of the dust storm due to the coagulation or/and a partitioning into the aqueous-phase of dust particles surface.Size-segregated aerosols were collected in Urumqi, a megacity in northwest China, during two heating seasons before (heating season ?: January – March 2012) and after the project “shifting coal to natural gas” (heating season II: January – March 2014), and determined for n-alkanes, PAHs and oxygenated PAHs to investigate the impact of the replacement by natural gas on organic aerosols in the urban atmosphere. Our results showed that compared to those in heating season I concentrations of n-alkanes, PAHs and OPAHs (the sum of PM1.1, PM1.1?3.3 and PM3.3?9) decreased by 74%, 74% and 82% in heating season II, respectively. Source apportionment analysis showed that coal combustion, traffic emission and biomass burning are the major sources of the determined organics during the heating seasons in Urumqi. Traffic emission is the main source for n-alkanes in the city. Coal combustion is the dominant source of PAHs and OPAHs in heating season ?, but traffic emission become their major source in heating season ?I. Relative contributions of coal combustion to n-alkanes, PAHs and OPAHs in Urumqi decreased from 21?75% in heating season I to 4?21% in heating season II due to the replacement of coal with natural gas for house heating. Health risk assessment further showed that compared with that in heating season I the number of lung cancer related to PAHs exposure in Urumqi decreased by 73% in the city during heating season II due to the project implementation. Our results suggest that replacing coal by clean energy sources for house heating will significantly mitigate air pollution and improve human health in China.Polar organic tracers of isoprene and monoterpene photooxidation in TSP (the sum of 9 Anderson size-segregated aerosols) collected in Qinghai Lake (as background site) and five cities of China were measured using gas chromatography/mass spectrometry (GC/MS). All the biogenic secondary organic aerosol (SOA) tracers showed higher concentrations in cities than the background site with higher during summer than winter. Moreover, concentrations of biogenic SOA positively correlated with sulfate (R2=0.52-0.9), which suggesting sulfate could enhance SOA formation. The size distribution measurements showed that most of the determined SOA tracers are enriched in the fine mode (<1.1μm) except cis-pinic acid plus cis-pinonic acid presenting a bimodal pattern. In summer, the average ratio of isoprene to monoterpene oxidation products (Riso/mono) was much little in the aerosols of urban than those reported in mountains and forests of China. Both of the carbon fractions for isoprene and monoterpene to OC increased during summertime and the contributions of monoterpene SOA tracers were much higher than those of isoprene SOA tracers. These phenonmenones suggests that monoterpene is a more significant precursor for biogenic SOA than isoprene in urban of China. |
| 中文关键词 | 一次和二次有机气溶胶 ; 分子组成 ; 粒径分布 ; 来源解析和形成机制 ; 健康评估 |
| 英文关键词 | Primary and secondary organic aerosols Molecular composition Size distribution Source and formation Health risk assessment |
| 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/2XILL650/287829 |
| 推荐引用方式 GB/T 7714 | 任艳芹. 典型城市及区域背景点有机气溶胶组成、来源、粒径分布及形成机理[D]. 中国科学院大学,2017. |
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