【作者】 王鑫；

【导师】 黄建平；

【作者基本信息】 兰州大学 ， 气象学， 2009， 博士

【摘要】 沙尘暴天气是我国西北地区频发的一种强灾害性天气,沙尘天气的发生对社会发展和经济发展都造成了严重的危害,虽然近年来国内外很多科学家对当前发生的沙尘天气有较深入的研究,但是多集中在局地沙尘天气和单个站点的研究,对于我国黄土高原半干旱地区发生的沙尘天气研究较少。而我国黄土高原半干旱地区由于降水量较少,生态环境脆弱,容易导致大范围的沙尘天气过程,此外,由于人类社会发展对大气造成的污染,使大气中的黑碳气溶胶也急剧增加,黑碳气溶胶能强烈吸收太阳辐射,是影响全球气候变化的一个重要因子,基于以上分析,本文主要对黄土高原半干旱地区的沙尘气溶胶与黑碳气溶胶的物理化学特征及其光学属性进行了深入分析,论文研究内容主要包括以下几个方面:（1）首先利用中国气象局提供的我国1960年-2000年701个气象站点的沙尘天气发生频次资料,重点分析了近年来我国沙尘天气空间分布的背景特征,通过研究发现,我国存在新疆塔克拉玛干沙漠与内蒙古戈壁沙漠两大主要沙尘源区。利用两个沙尘源区不同类型沙尘天气的发生次数,建立了一个新的沙尘气溶胶指数,通过相关统计方法以及利用TOMS卫星气溶胶吸收指数对比发现,新的沙尘气溶胶指数能够较好的反映我国北方地区沙尘天气的变化特征。（2）通过对黄土高原地区2007年5月2日一次大范围的沙尘天气过程分析,对沙尘天气发生过程前后沙尘气溶胶的物理及其光学属性进行了深入的讨论,结果显示,这次沙尘天气的源地主要是南疆地区和内蒙古的戈壁沙漠地区,当沙尘天气发生时,大气中粗模态的气溶胶明显增加,气溶胶质量浓度达到2484.72 ug/m³,是沙尘暴天气发生前气溶胶质量浓度的13倍,同时沙尘天气还伴随着大风降温天气的发生,气象资料显示这次沙尘气溶胶主要来源于南疆与内蒙古戈壁沙漠两个地区,同时通过对比污染气溶胶与矿物气溶胶的光学特征可以发现,污染气溶胶能更好的反映气溶胶散射和吸收属性,背景大气气溶胶的散射和吸收系数平均为150-200Mm^-1和5-15Mm^-1,而沙尘气溶胶的散射系数和吸收系数平均值低于150 Mm^-1和3 Mm^-1。（3）利用SACOL气候站上黑碳仪、RP1400、积分浊度仪以及太阳光度计等仪器,分析黄土高原地区气溶胶的物理特征及其光学属性,通过研究发现,黄土高原地区的大气气溶胶来源比较复杂,造成的大气污染较为严重。分析粒径小于1um和10um的气溶胶的数浓度可以发现,冬季粒径小于1um的气溶胶数浓度最高,夏季最低,其中,在背景天气条件下,大气中主要以细颗粒的人为污染气溶胶为主,气溶胶粒子半径主要小于1um,根据太阳光度计观测的结果分析表明,气溶胶的平均光学厚度冬季最高,春季次之,夏季最低。说明,兰州市冬季由于燃煤取暖等原因导致冬季大气污染最严重。（4）最后,本文对2002年春季兰州市、武威市和皋兰县三个地区的大气TSP进行采样分析,通过分析表明,2002年春季是近20年以来沙尘天气最为严重的一年,2002年沙尘天气对我国整个北方地区的影响较为严重。当发生沙尘天气时,沙尘气溶胶从沙漠地区起沙开始,不断地向下游地区传输,在这个过程中不断吸附城市地区的污染物,导致矿物气溶胶中Hf、Ta、Ag、Cr、Hb等微量元素浓度明显增加,沙尘气溶胶自身的物理化学特征也发生了明显的改变。通过相关分析以及因子分析等方法对兰州市春季大气气溶胶质量浓度进行了统计,对采集的沙尘气溶胶进行化学微量元素分析。结果表明,兰州市沙尘天气发生时,气溶胶除来源于沙尘源地的外来矿物气溶胶以外,还包括了大量的本地扬尘,以及本地燃煤造成的污染尘和大量的水泥石灰尘。更多还原

【Abstract】 Local and global responses of climate change to the aerosol depend strongly on its optical and physical properties.Aerosol is very effective in modifying the radiation field by absorbing and scattering solar and thermal radiation strongly modify the radiation budget at the surface of the earth as well as the cloud microphysical properties,precipitation rate and hydrological cycle. In recent years,blace carbon（BC）became more and more important because of its direct impace on radiation and its heating effect on climate,Additionally,BC can affect the climate by its indirect effects due to its action on cloud droplet and change the cloud proerties.China loess Plateau and the deserts in the arid and semi-arid regions of Northwest China are considered as the largest and most persistent dust sources and air pollution in the Northern Hemisphere However, due to the shortage of in situ observations in those regions,the detailed information on their physical and optical properties of dust and non-dust aerosol from those regions have not been well understood yet.Understandings on physical processes and its optical propertities of aerosols are important because atmospheric aerosols play key roles to affect the earth-atmosphere radiative system.The main objective of this paper is to identify detailed information of aerosol measurements conducted over China loess Plateau.The conclusions can be summarized as follows:（1）In order to examine the decadal variations of the dust events over East Asia,we analyze surface observations from 701 meteorological stations for the period 1960-2004 to obtain spatial and temporal distributions of dust events.Since the Taklamakan Desert in western China and the Gobi Desert in Inner Mongolia are the two major sources of dust storms,we have defined two dust indices,one for the Taklamakan Desert Index（TDI）and one for the Gobi Desert Index（GDI）, tocharacterize the statistical nature of the dust events over these two regions.Both of these indices are well correlated with the Total Ozone Mapping Spectrometer（TOMS）Absorbing Aerosol Index（AAI）.（2）The objective of this section is to understand the detailed characteristics and underlying mechanisms of dust aerosol at SACOL during dust plume.During dust plume,the mass concentration of PM₁₀can rise to～2484.72 ug/m³,～13 times as high as that in non-dust plume period.The meteorological analysis indicates that these polluted layers are not from local sources during dust plume and this large-scale transport of dust and pollutants remains a major uncertainty in quantifying the global effect of emissions from Northern China.Local air pollution can reflect the absorbing and scattering properties more effective than dust aerosol.（3）The objective of this section is to understand the detailed characteristics and underlying mechanisms of aerosol physical and optical parameters over China Loess Plateau and its potential impacts on the regional/global climate.To meet this goal,several ground instruments were performed from May 1 2007 to May 31,2008 at an integrated observational site of China （35.57N,104.08E）.Results indicate that The type of aerosol is more complicated over China loess Plateau.The seasonal and diurnal variations of the larger accumulation mode and the coarse mode particle number concentrations(N_0.5-1and N_1-20,respectively)exhibited a seasonal cycle with the highest values in winter-spring and the lowest value in summer-autumn.a two-year data set of aerosol optical properties obtained from the AERONET is analyzed focusing on the western part of China.The aerosol optical depth standard product（AOD at 500 nm）is employed to evaluate the inter-annual and seasonal variability of the aerosol properties over SACOL.The AOD shoms that the high value during winter period and low value in winter period.This result shows that the air pollution in winter is heavy by the biomass burning（clearing of agricultural land）.（4）Based on the available data from surface synoptic reports（8 times every day）,the temporal and spatial distribution characteristics of sand/dust storms in China in the spring of 2002 are analyzed.The results show that there were mainly twelve dust storm weather processes including five severe dust storm events in China, among which the event on March 18—22 had the largest area and highest intensity.It has been found that most dust storm weather processes concentrated in early spring（from March to mid April）of 2002.The chemical composion of dust aerosol was analysed during spring,2002 in Lanzhou、Wuwei and Gaolan, which is the key region for major dust plume frequently influenced during its transportation from the dust original regions.Results shows that the mass concentration of trace elements include Hf、Ta、Ag、Cr、Hb increase quickly during dust plume.更多还原