Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原大气气溶胶的理化特征及其来源解析 | |
| 其他题名 | Characteristics and source apportionment of aerosol particles over Qinghai-Tibetan Plateau |
| 赵竹子 | |
| 出版年 | 2015 |
| 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 | 青藏高原地区是气候变化的敏感区和脆弱区，近几十年来，青藏高原气溶胶污染物不断增加，严重影响到区域气候及生态环境。本研究通过在青藏高原东南缘（鲁郎）、东北缘（青海湖）开展为期一年的大气颗粒物监测，获取鲁郎和青海湖不同季节大气颗粒物质量浓度、碳气溶胶、离子和元素的浓度水平，了解青藏高原不同区域大气颗粒物季节变化特征及其影响因素；探讨青藏高原背景点不同类型污染事件的成因、来源及其对青藏高原的影响；最后利用源解析方法判断不同因子及潜在源区对采样点的贡献率。 青海湖PM2.5年均浓度为38.9 ± 25.8μg m-3，且其最主要的组成成分是矿物粉尘。采样期间八种水溶性离子之和的浓度变化范围为1.0- 41.5 μg m-3, 占PM2.5的30%，其中含量最高的组分为SO42-，其次为NO3?，第三是Ca2+。青海湖的有机碳（1.0 - 8.2 μg m-3）和元素碳（0.2 -2.3 μg m-3）在PM2.5中占的比例较低，大约占PM2.5的10%和2%。OC/EC的比值四季变化并不显著，表明碳气溶胶有着较稳定和简单的源。WSOC（0.5 - 4.3 μg m-3）大约占OC的47.8%，OC和WSOC同时和K+具有较好的相关性，表明其可能受到了生物质燃烧排放的影响。WSOC和EC的相关性在冬春两季优于夏秋两季，这可能是由于在寒冷季节生物质燃烧排放增加的结果。将大气样品和牛羊粪燃烧的源样品的源谱进行对比，结果显示两者具有很大的差异性，说明大气样品受到牛羊粪燃烧排放源的影响不大。另外大气样品的SO42-/OC要远远高于源样品，这表明大气样品很可能是受到了化石燃料燃烧的影响。尽管不同季节青海湖的主导季风不同，但在剔除了沙尘事件数据下（正常天气下），不同季节的OM、EC、 K+、 NH4+、NO3-和矿物粉尘在相对含量上反而差异不大，这说明在没有特殊事件的影响下，青海湖四季污染源相对稳定，不会有突发的增加或改变，且相对人为污染源而言，自然源对青海湖的影响相对更大（矿物粉尘约占PM2.5的~40%）。 最后使用PSCF对影响青海湖PM2.5质量浓度污染的潜在源区进行分析，得出造成青海湖高PM2.5质量浓度的潜在源区分布于新疆南部的塔里木盆地（塔克拉玛干沙漠）、新疆东部的吐鲁番盆地及青海、新疆、甘肃交界的沙漠地区、青海湖西边的柴达木盆地地区、甘肃的河西走廊部分地区、青海湖东部城市地区。 青海湖的四次沙尘事件及三次冬季烧草事件对青海湖大气颗粒物浓度和组成成分产生了重要影响。四次沙尘暴事件质量浓度的平均值达到99.73μg m-3，四次沙尘事件具有不同的特点，结合源区数据的对比以及后向轨迹分析，我们推测第四次沙尘事件时类似于“气团置换”的过程，为一次较为“原始”的沙尘事件。这说明在下游地区监测到的沙尘事件所携带的SO42-、NO3-并不全是由于和沙尘颗粒和污染物的反应产生，可能是直接来自源区，且这种贡献是不可忽视的。冬季烧草事件下，青海湖的PM2.5的平均浓度达到75.33μg m-3，从相对浓度上看，增高最大的组分是SNA（SO42-/NO3-/NH4+），占质量浓度的44%，是所有组分中所占比例最高的，而K+和EC则相对浓度变化不大，说明在青海湖地区，开放生物质燃烧产生的二次污染物，其产生的影响要远比一次排放污染物高的多。 藏东南鲁朗站点TSP、OC、EC、K+、NO3-和SO42-在季风前期浓度达到最高，除OC外，TSP及相关组分的最低浓度出现在季风期，而OC的最低值出现在冬季，这种化学组分清晰的季节变化可用不同季节下大气环流差异解释。通过深入分析高质量浓度载荷（> 35μg m-3），并通过后向轨迹将其分为两种类型，一种富含沙尘指示物（Fe和Ca2+），另一种则富含OC、EC、SO42-、NO3- 和Fe，和正常天气相比，大气颗粒物的载荷往往会升高3~6倍，且主要化学组分在这两类事件下往往会升高数倍。通过MODIS AOD和NCEP/NCAR的再分析资料，得出第一种事件下的气团运动轨迹主要来源于中国的西北部区域，人烟稀少，从而导致此类事件的地壳相关元素很高，人为污染源则相对较低，而第二种事件时气团运动轨迹主要来自来自西南方向，传输路径上经过了高人口密度的印度-恒河平原，因此人为污染源在此类污染事件中大幅度升高。 藏东南PMF解析结果显示，藏东南TSP主要有以下四种源贡献：（1）混合污染物（沙尘与燃烧）贡献率达33.8%；（2）矿物粉尘源，达28%；（3）二次有机碳及海盐，22%；（4）二次污染物16.5%。那些对源具有高贡献率的样品和污染事件具有很好的一致性，且PMF的解析结果又能够被气团的运动轨迹同时结合MODIS AOD所印证。 本研究提供了复杂的化学证据证明周围区域的自然和人为气溶胶会干扰青藏高原地区大气。 |
| 英文摘要 | The Qinghai-Tibet Plateau is a sensitive and vulnerable area for climate change. In recent decades, the rapid increase in the aerosol pollution in Qinghai-Tibet Plateau has seriously affected the climate and ecological environment. Bulk aerosol samples were collected at two different sites in Tibetan Plateau (TP)—the Qinghai Lake Obsevatory on the northeast and the Lulang site on the southeast of TP. We report aerosol mass levels and the concentrations of selected elements, carbonaceous species, and water-soluble inorganic ions, objectives were to determine chemical characteristics of the aerosol and identify its major sources. The cause, source and influnce of different types of pollution events in TP were explored in this study. Finally, source apportionment methods were used to identify presumptive sources and potential source regions to the sampling sites. The PM2.5 ranged from 5.7 to 149.7 μg m-3 in Qinghai Lake, and it was predominately crustal material (~40% on average). The combined mass of eight water-soluble inorganic ions ranged from 1.0 to 41.5 μg m-3, with the largest contributions from SO42-, NO3?, and Ca2+. Low abundances of organic carbon (OC, range: 1.0 to 8.2 μg m-3) and elemental carbon (EC, 0.2 to 2.3 μg m-3) were found in QHL. Weak seasonality in the OC/EC ratio (4.5 ± 2.0) indicated simple and stable sources for carbonaceous particles. The water-soluble ions, OC and EC accounted for ~30%, 10% and 2% of the PM2.5, respectively. Water-soluble organic carbon (WSOC, range: 0.5 to 4.3 μg m-3) accounted for 47.8% of the OC. Both OC and WSOC were positively correlated with water-soluble K+ (r = 0.70 and 0.73 respectively), an indicator of biomass burning. Higher WSOC and stronger correlations between WSOC and EC in spring and winter compared with summer and autumn are evidence for primary biomass burning aerosols. The concentrations of mass and major compositions were 2~10 times higher than those for some TP or continental background sites but much lower than urban areas. Compared with particles produced from burning yak dung (a presumptive source material), PM2.5 had higher SO42-/OC ratios. The higher ratios were presumed as a result of fossil fuel combustion. After excluding data for dust storms events (Normal days), the relative percentages of OM, EC, K+, NH4+, NO3- and mineral dust showed little difference among seasons despite different monsoons dominated in four seasons; implying that the PM2.5 sources were relatively stable. The results from Qinghai lake evidently reflect regional characteristics of the aerosol. Potential source contribution function (PSCF) model was used to evaluate the potential source region of Qinghai Lake PM2.5 mass concentration. There were six potential source regions that had effect on PM2.5concentration in Qinghai Lake, including Tarim Basin (Taklimakan desert), Turpan Basin in Xinjiang, the junction areas of Qinhai, Xinjiang and Gansu, Qaidam Basin in Qinghai, Hexi Corridor in Gansu Province, and the urban zones in the eastern of Qinghai Lake. Four dust storm events (DS) and three open biomass burning events (OB) had significant impact on aerosol population and concentrations in Qinghai Lake. The averaged mass concentrations of dust storms reach 99.73μg m-3. Combined with backward trajectory analysis and data comparison with source region, we assumed that “air masses replacement” make the fourth DS event seems like a “fresh/pure” one. The dust strom carried significant quantities of pollutants (such as sulfate/nitrate) may be directly from the source region, not always caused by the reactions on the surface of dust particles with pollutants. In OB events, the averaged mass level reach 99.73μg m-3. On the relative contributions of major chemical species to the aerosol mass,.SNA (SO42-/NO3-/NH4+) was the most abundant species, accounting for 44% of the mass, while K+ and EC concentrations had no significant changes during the episode. After excluding the pollution events (Normal days), the percentages of OM, EC and mineral dust in four seasons showed no significant difference, which implied the pollution sources in Qinghai Lake were relatively stable. Dramatic increase or change of pollution sources may not occur in Qinghai Lake. Natural sources have significant impact on the sampling site relative to anthropogenic sources. Significant buildup of aerosol mass and chemical species (organic carbon, element carbon, nitrate, and sulfate) occurred during the premonsoon, while lower concentrations were observed during the monsoon in Lulang. Seasonal variations in aerosol and chemical species were driven by precipitation scavenging and atmospheric circulation. Two kinds of high-aerosol episodes were observed: one was enriched with dust indicators (Fe and Ca2+), and the other was enhanced with OC, EC, SO42_, NO3-, and Fe. The TSP loadings during the latter were 3 to 6 times those on normal days. The greatest aerosol optical depths (National Centers for Environmental Protection/National Center for Atmospheric Research reanalysis) occurred upwind, in eastern India and Bangladesh, and trajectory analysis indicates that air pollutants were transported from the southwest. Northwesterly winds brought high levels of natural emissions (Fe, Ca2+) and low levels of pollutants (SO42-, NO3-, K+, and EC); this was consistent with high aerosol optical depths over the western deserts and Gobi. Our work provides evidence that both geological and pollution aerosols from surrounding regions impact the aerosol population of the TP. |
| 中文关键词 | 青藏高原 ; 气溶胶污染 ; 来源解析 |
| 英文关键词 | Qinghai-Tibet Plateau aerosol pollution source apportionment. |
| 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/2XILL650/287501 |
| 推荐引用方式 GB/T 7714 | 赵竹子. 青藏高原大气气溶胶的理化特征及其来源解析[D]. 中国科学院大学,2015. |
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