【作者】 李娟；

【导师】 庄国顺；

【作者基本信息】 复旦大学 ， 环境科学， 2009， 博士

【摘要】 大气气溶胶通过影响大气辐射、大气化学及云和降水过程，改变地水气系统内部的辐射能量收支和水循环，对全球气候和环境变化产生巨大影响。气溶胶长距离输送被认为是全球生物地球化学循环的重要途径之一，研究大气气溶胶即是研究大气圈、水圈、生物圈以及人类圈之间的生物地球化学平衡，对人类自身具有生死攸关的重大意义，已成为研究全球环境和气候变化的重要领域。大气气溶胶可远距离洲际输送，横跨太平洋、大西洋，因而大气气溶胶同时对区域气候异常及全球气候环境变化有着极其重要的影响。大气污染已成为全球性问题。亚洲中部的沙漠和黄土高原是太平洋上空气溶胶的主要来源。深入研究亚洲沙尘源区沙尘气溶胶的时空分布，理化特性及其来源有利于全面认识亚洲沙尘气溶胶特性，探究其与污染气溶胶相互混合和作用的机理，不仅是促进我国经济发展和改善人们生活质量的亟需，也是正视全球生态危机和全球环境变化问题的亟需。本研究的主要成果有：1．揭示了中亚沙尘源区各典型地区沙尘气溶胶的理化特性，来源，形成机制及其对下游我国东部沿海城市地区乃至全球变化的可能影响。中亚沙尘的两大主要源区之一，世界第二大沙漠，塔克拉玛干沙漠沙尘气溶胶具有高浓度，高硫，高钙的鲜明特性。发现了塔克拉玛干沙漠气溶胶及其主要来源，塔克拉玛干沙漠的表层沙土中90％以上的总硫含量是以可溶性的硫酸盐形式存在。同时，气溶胶中的硫酸盐与Na⁺，Cl^-，K⁺都具有非常好的正相关。显示了塔克拉玛干沙漠沙尘气溶胶具有明显的古海洋源的特性。大气气溶胶的研究正好补充论证了地质学研究的重要成果，即塔克拉玛干沙漠是5．3M万年的古海洋隆起后干涸并经历长期风化而成。2．发现了塔克拉玛干沙漠Ca／Al比值高达1．5以上，这与蒙古戈壁沙尘中Ca／Al比值仅有0．5左右形成鲜明对比。这一发现使得Ca／Al比值成为区分我国两大沙尘源区和判断下游地区外来沙尘来源的最可靠的判据。3．塔克拉玛干沙漠每年输出约1．69*10⁷吨沙尘（TSP），其中PM₁₀约5．40*10⁶吨，2．1*10⁵吨硫酸盐(PM_2．5中)，同时又有6．2*10⁴吨黑碳气溶胶。由于本研究揭示了塔克拉玛干沙漠所产生的沙尘中的硫大多在一次气溶胶中就已经以硫酸盐的形式存在，中亚沙尘中所含的硫酸盐的总量会大大超过以前许多研究的估计。基于硫酸盐可能导致的降温效应和黑碳可能导致的增温效应，显然，中业沙尘的长途传输不仅会对我国东部地区包括北京上海等大城市的大气质量产生影响，同时会对全球的气候与环境变化产生重大影响。4．中亚沙尘源区的重要城市乌鲁木齐的空气污染非常严重。除夏季外其出现严重灰霾的天数高达60-80％，且具有浓度高，形成迅速，发生频繁三大特点。乌鲁木齐已是我国大气污染最严重城市之一。通过比较气溶胶、降尘和表层土壤中有关元素丰度和Ca／Al比值，证实乌鲁木齐气溶胶中高浓度硫酸盐来自于：1．城区工业排放的大量SO₂转化形成的硫酸盐2．来自准格尔盆地南缘农业带含高浓度硫酸盐的土壤沙尘；3．周边盐湖地区含有高浓度硫酸盐的表层土壤。人为污染源与外来沙尘的相互混合和作用是导致乌鲁木齐严重空气污染的的主要成因。乌鲁木齐气溶胶中水可溶性离子的总量及具有强吸水性的铵盐分别占细颗粒物总质量的百分比高达57．8％和51．0％。这一至今为止在任何地区前所未见的高浓度水可溶性离子，尤其是所包含的高浓度铵盐（主要是硫酸铵）是形成乌鲁木齐严重灰霾的主要机制。5．在我国西部渺无人烟的塔克拉玛干沙漠的气溶胶和尘土中均含有某种程度的污染元素As，Pb，Cd．。污染元素As，在天山气溶胶中的富集系数竟然高达5800，其它污染元素如Pb，Cd的富集系数也高于20。天山及其周边表层土壤中As，Zn，Cd浓度高出地壳平均浓度约1．4-15．7倍。这些发现强烈地显示，我国主要能源燃煤产生的大气污染物，经由大气颗粒物的长途传输，已经污染了我国几乎所有地区的大气和土壤。我国各地区、各城市的大气污染不仅都来自于本地污染源，同时也都来自于外地沙尘及污染源的长途传输。气溶胶的长途传输，即元素或有关化合物的生物地球化学循环成为我国大气气溶胶的来源和形成机制的主要特点。更多还原

【Abstract】 Atmospheric aerosol would have tremendous impact on the global environmental andclimate change through influencing radiation,atmospheric chemistry,andcloud/precipitation processes and shifting the balance of the radiation energy andwater cycle.The long-range transport of aerosol has been regarded as the importantpath of the global biogeochemical cycle.The study on the atmospheric aerosol is thestudy on the balance of the global biogeochemical cycling among atmosphere,hydrosphere,biosphere,and human-sphere,which has been of the vital significance tohuman being,and it has been the important domain of the study on the globalenvironmental and climate change.Atmospheric aerosol can travel across over Pacific and Atlantic,and it would exertgreat influence on both the regional environment and the global climate change.Theair pollution has been global issue.Those deserts located in the center of Asia andLoess Plateau is the major sources of those aerosols over Pacific.To investigatedeeply into the temporal and spatial distribution,the physicochemical characteristics,and sources of Asian dust would understand the mechanism of the mixing and theinteraction of mineral with pollution aerosols,which has been the urgent need indeveloping economy and improving the life quality of human being.The major results of this study are as below:1.The physic-chemical characteristics,sources,and the formation mechanism of thedust aerosol from those typical areas of Central Asian Dust as well as theirpossible impact on the regional environment of the downstream urban cities aswell as the global climate change were revealed.The aerosols from Taklimakandesert,one of the two major sources of Asian dust storm,which also is the secondgreat desert over the world,are characterized of high mass concentration,highcontent of sulfur and calcium.It was found that 90% of the sulfur in the aerosolsover Taklimakan desert and in the soil collected from the desert is in the form ofsulfate.Additionally,the sulfate in the aerosols shows a high positive relation withthose ions of sodium,chlorine,and potassium,which indicated evidently thatthose components in the aerosols were from the paleo-marine source.Theseresults were the evidence to support the hypotheses that Taklimakan desert wasused to be the ocean～5.3 millions year ago. 2.It was found that the ratio of Ca/Al in the aerosols over Taklimakan is over 1.5,whereas it is only～0.5 in Gobi located in Mongolia and Inner Mongolia.Thisdistinct difference makes the ratio of Ca/A1 be used as excellent tracer todistinguish the two major source areas of Asian dust and to distinguish the out-citysources of those local urban areas.3.The annual transport of dust from Taklimakan desert is 1.69*10⁷ ton,whichincludes 2.1*10⁵ ton of sulfate and 6.2*10⁴ ton of black carbon.As most ofsulfur in the dust aerosol and soil of Taklimakan was found to be in the form ofsulfate,the amount transported out from this second largest desert would be muchmore than previously estimated.Those sulfate emitted and transported fromTaklimakan desert would have great impact on the regional atmosphericenvironment and the global climate change.4.Urumqi is one of the heavy polluted cities in the world,as the days of hazespanned over one third of the year and accounted for 60-80% of the heating periodfor the past six years.High aerosol concentration of fine aerosols,frequentoccurrence of haze,and rapid formation of heavy haze were the three maincharacteristics.With comparison of the pollution elements,As,Cd,and S,and theratio of Ca/Al in aerosols and soils in those sites located on the south of JunggerBasin as tracers,it was found that As,Cd,and S highly enriched in the aerosolsover urban Urumqi were not only derived from the re-suspended road dust butalso from the soil transported from south of the Jungger Basin.Different from themost cities in China,the high concentration of sulfate in Urumqi was partiallyfrom the primary soil dust transported from the surrounding areas.The mixing ofthe local anthropogenic aerosols with the soil transported from outside the citywas the main source of the high sulfate concentration.Equivalent ammoniumconcentration were higher than the summed equivalents of SO₄^2-,NO₃^-,and Cl^- inUrumqi and much higher than that in other Chinese cities.The total water solubleions and the total ammonium salts were as high as 57.8% and 51.0% in PM_2.5.Thehigh concentration of soluble salts with high hygroscopicity,especiallyammonium and sulfate salts,were the main factors contributing to the heavy hazeover Urumqi.5.It was found that there is a certain degree pollution of As,Pb,Cd even in such adesolate area,Taklimakan desert.The enrichment factor of As in the aerosolsover Tianshan mountain was as high as 5000,while those of Pb and Cd were over 20.In the soil of Tianshan and its surrounding areas the content of As,Zn,Cd was1.4-15.7 times higher than the average in crust content of the world.Theseresults strongly indicated that the air-pollutant in aerosol originally from the heavycoal burning have spread everywhere over China due to the long-range transport.The air-pollution in many urban cities was not only from local pollution sources,but also from the long-range transport out of the cities.The long-range transportof aerosols,i.e.the biogeochemical cycle has been one of the major sources andone of the main characteristics of air-pollution in China.更多还原