【作者】 牛贺文；

【导师】 何元庆；

【作者基本信息】 兰州大学 ， 自然地理学， 2014， 博士

【摘要】 冰冻圈在气候系统中扮演着重要的角色,它对太阳辐射有较高的反射率、低的热传导率和大的热容量并且在驱动深海环流中具有关键性的作用。全球和区域气候变化是当前众所关注的重大问题之一,大气环境污染及雾霾天气是当前影响人类社会健康稳定发展的现象之一。作为影响气候变化的一个重要因子,大气粉尘气溶胶对气候环境的影响需要深入研究。高海拔地区雪冰中沉积的粉尘微粒的研究能够提供对地理圈层之间相互作用的新认识,同时有助于对物质迁移转化机理的深入理解。雪冰是大气中各种物质的存储库,大气粉尘信息能够被很好地记录和保存在雪冰中。沉积在高海拔地区雪冰中的粉尘微粒可以很好的反映和指示大气环境状况,冰芯不溶粉尘微粒的研究对气候环境变化的恢复和重建具有重要作用。大气中粉尘气溶胶是重要的大气组成部分,能够影响地球表面的辐射平衡,中和降水中的酸性物质,作为地球气候系统的辐射强迫因子,同温室气体、太阳辐射以及地表特征的变化等因素一道扮演着改变地球系统能量收支平衡的重要角色,是气候变化的驱动因子。玉龙雪山地区位于青藏高原东南缘、横断山的最南端,区域气候环境特殊,同时受到西南季风和东南季风及西风环流等多种环流系统的影响。分布于该地区的冰川及大气降水对气候环境变化非常敏感,而雪山之巅发育的冰川更是重要的水资源(俗称“固体水塔”),对该地区冰川粉尘沉降的研究很有科学价值和现实意义。大气中的粉尘从源区开始搬运、传输、沉降,经过距离远近不同的地区时表现出不同的特征。因此,在玉龙雪山地区开展雪冰和大气降水中沉积的粉尘微粒及特征研究,并于北半球其它地区已有的相关研究进行比较,对于完善和拓展大气粉尘循环和沉降机制显得尤为重要。本研究主要对玉龙雪山地区典型冰川积雪中以及大气降水中的粉尘微粒含量及沉降特征进行了研究,并分析了雪冰化学、大气降水化学。雪冰中粉尘微粒特征分析表明,表层雪和积雪以及其它水体中微粒的数量浓度、质量浓度和体积粒径分布的众数都表现出空间差异和变化,且不同季节时期,水体中微粒的含量差异很大。不同水体中微粒含量的差异显示了区域环境对粉尘沉降的影响。雪坑中微粒浓度剖面和典型粉尘离子的相关性分析表明,玉龙雪山积雪中存在着明显的污化层位；微粒体积—粒径对数正态分布粒径众数3-21μm之间,显示了单一的分布模式。冰川积雪剖面及污化层揭示了非季风季节粉尘浓度的峰值及沉积数量上较大的年际变化,意味着玉龙雪山地区雪冰中粉尘沉积对大气环境变化的敏感性。总体上,玉龙雪山积雪中微粒含量(数量浓度)相对较低,而质量浓度较大,数量较少的粗颗粒对微粒的质量浓度贡献较大。玉龙雪山积雪中沉积的微粒的粉尘浓度和粒径与墓士塔格、达索普冰川、祁连山老虎沟冰川、天山山区、以及全球其它区域雪冰中的微粒浓度具有较好的可比性和相似性；然而微粒质量浓度和粒径分布远大于极地地区Penny冰帽和Devon冰帽等的研究结果。表层雪和新降雪中的主要离子浓度显示,非季风期的化学离子含量远远高于季风期的离子含量,显示了明显的季节性变化。季风期前雪冰中离子含量8042-的最高,而季风后期Ca2+和Mg2+含量最高。大气降雨中微粒含量随时间的迁移显示,在季风期末,微粒的数量浓度随着降雨频率和降雨量的减少而逐渐升高,即降雨中微粒的含量具有明显的季节变化特征。季风期前的水体样品中,雪山南端的水体中沉积的微粒含量最高,而在季风期采集的样品中,雪山西端的水体中沉积的微粒浓度最高。同时显示了水体中微粒含量的时空差异。雨水化学研究可以揭示玉龙雪山地区大气污染状况,分析结果表明,降水中粉尘颗粒物的浓度、粒径分布及化学组成在两个采样点都具有明显的季节变化特征。不同于积雪和地表水体中沉积的微粒,雨水中微粒的含量相对较低,可以反映出丽江市较好的大气环境质量。雨水中粒径d<1μm的微粒浓度与总微粒浓度的变化趋势极为一致,并且粒径d<1μm的微粒浓度变化可以更敏感的反映高空中悬浮的大气颗粒物(浮沉)状况。雨水pH频率分布接近正态分布,有73%的降雨事件的pH介于5.6～7.0之间,有大概23%的降雨事件的pH值在4.5和5.6之间,表明该地区部分雨水呈现微弱的酸性。降水中pH值和电导率的变化很大程度上受到粉尘活动的影响。Ca2+和8O42-分别是玉龙雪山地区大气降水中监测出的含量最高的阳离子和阴离子,分别占降水中总离子质量的40%和25%,该地区大气降水中离子含量总体显示相对低值。SO42-, NO3-和NH4+以及Ca2+之间的相关性揭示了大气降水中,酸碱中和后在雨水中以CaSO4、(NH4)2SO4和NH4NO3化合物的形式呈现,同时也表明雨水中其它化学离子对降雨的酸化和中和过程的贡献是可以忽略的。因子分析和聚类分析有助于解释雨水特征,强调了人类活动和地壳源颗粒物对该地区雨水化学的贡献和影响。此外,季风携带的海盐气溶胶离子对玉龙雪山地区雨水中的C1-和部分Na+具有一定的贡献,但对该地区大气降水中典型粉尘微粒的沉降没有贡献。玉龙雪山地区降水化学的研究揭示出地区差异、海拔高度的不同,以及当地不同程度的人类活动等因素可以解释该区域各采样点降水化学组成的差异。雪冰和雨水化学研究揭示了玉龙雪山为研究和分析中国西南地区大气和环境状况提供了独特的介质条件。后向轨迹HYSPLIT-4模型对大气降水和粉尘颗粒的来源进行验证,结果表明玉龙雪山地区非季风季节与季风季节大气粉尘来源不同：分别来源于西北和西南方向,且再分析资料(Re-analysis data)计算结果显示,研究区两个季节的水汽来源和空气湿度差别很大,这对大气中粉尘微粒的传输和沉降有很大的影响。此外,非季风时期离子浓度高值主要是由频繁的沙尘事件导致的离子沉降。玉龙雪山上裸露的基岩和来自岩石风化的矿物粉尘颗粒物也是沉积在该地区积雪中粉尘微粒的重要来源。更多还原

【Abstract】 The cryosphere plays a vital role in the global climatic system, it has high reflectance to the solar radiation, low thermal conductivity, and huge calorific capacity, as well as plays important roles in droving deep-sea circulations. At present, global and regional climate change is a hot topic and attracting many scientists concerning it. Atmospheric pollution and haze are significantly affecting human health and social sustainable development. As one of the vital factors affecting climate change, the effects of atmospheric dust aerosols on climate and environment need deep research. Study on dust particles deposited in the snow and ice can provide a new cognition on the interrelations of geographical spheres, and is helpful for the deep understanding of dust migration and transformation mechanisms. Snow or ice is the storage tank for atmospheric materials, dust aerosols can be well recorded and preserved in the snow or ice. Dust particles deposited in the high mountain snow and ice can well reflect and indicate atmospheric environment conditions, research on insoluble dust particles deposited in the ice cores has important roles in recovering and rebuilding climate and environment change. Dust particles are the important components of atmosphere, and can affect radiation balance of earth surface, neutralizing acidic materials in precipitation, as one of radiative forcing factors of earth system, dust particles, combined with greenhouse gases and solar radiation, as well as variations of earth surface features, they are driving factors of climate change, which playing important roles in changing earth system’s energy balance. Yulong Snow Mountain （Mt. Yulong） is located in the southeastern Tibetan Plateau and southernmost Hengduan Mountains. The climate of the Mt. Yulong area is special and simultaneously suffered from the influence of many circulation systems, i.e. southwest and southeast winds, and the westerlies. Glaciers and atmospheric precipitation distributed in the Mt. Yulong area are very sensitive to climate change, and the glaciers developed at the summit of the Mt. Yulong are important water resources （or solid water tower）, thus the study on dust deposition has great scientific values and practical significance. Atmospheric dust first transferred from source areas, then in the transportation processes dust aerosol experienced transmission, deposition, and exhibited different characteristics when passed through distant and adjacent areas. Therefore, conduct the research on microparticles deposited in snow and atmospheric precipitation in the Mt. Yulong region, and make comparison with relevant researches carried out in the Northern Hemisphere and other areas, is profound to complete and expand the atmospheric circulation and deposition mechanisms.This study mainly analyzed the micoparticle concentrations and deposition characteristics in the typical snow and atmospheric precipitation in the Mt. Yulong region, and also analyzed snow chemistry and rainfall chemistry. Results of microparticles analysis showed that the number concentrations, mass concentrations of microparticles and the modes of volume size distributions performed great differences at the spatial and temporal scales. The difference of microparticles in the water bodies exhibited the influences of regional environment on the dust deposition. Correlations among dust concentrations and the typical dust ions at lateral direction of the snowpits revealed that there exist distinct dust layers in the snowpit. Volume size distributions of dust particles in water bodies showed mono-modal structure having a volume median diameter of3-21μm, comparable with the modal size of micro-particles in other sites. Dust concentration peaks and high number concentrations of microparticles in non-monsoon season revealed that there exists big inter-annual variation, and also signifies that dust deposition in the Mt. Yulong snow was sensitive to atmospheric environment change. Overall, the number concentrations of microparticles in the snow of Mt. Yulong was relatively low, and few coarse particles made big contributions to the higher mass concentrations. Dust concentrations of microparticles deposited in the Mt. Yulong snow were comparable to that detected in Dasuopu, Laohugou glacier, Tienshan area, while the mass concentrations were significantly higher than that measured in Penny ice cap, Devon Ice cap.Ion concentrations of surface snow and fresh snow showed that non-monsoon ion concentrations were substantially higher than that monsoon one, which exhibited distinct seasonal variation. SO42-and Ca2+with the highest concentrations in the pre-monsoon and post monsoon snow, respectively. At the end of monsoon season, dust concentrations in the atmospheric precipitation were gradually increased with the decrease of precipitation amount and the frequency of rainfall events. As for the spatial distribution of dust concentrations in water bodies in the Mt. Yulong area, the southern and pre-monsoon water bodies with the highest microparticle concentrations. While in monsoon season the western water bodies with the highest concentrations of microparticles, which simultaneously exhibited spatial and temporal variations of microparticles in the water bodies in Mt. Yulong area.Precipitation chemistry can reveal air conditions of the Mt. Yulong area, results showed that concentrations of microparticles, volume-size distribution, and chemical composition of precipitation performed distinct seasonal variations. Different with the scenarios found in snow cover and surface water bodies, the concentrations of microparticles in atmospheric precipitation were relatively low, which can reflect preferable air quality of the Lijiang city. Micro-particles with d＜1μm and total number concentration of particles in each rainfall sample display amazing consistent variation over the entire rainy season, though it seems that particles with d＜1μm are more sensitive to reflect the variations of atmospheric particles suspended in the rainfall.The frequency of pH values resulted in a nearly log-normal distribution, with73%of the rain events with a pH value between5.6and7.0, and23%with a pH value ranged from4.5to5.6, indicating that the majority of rainwater had a neutral or alkaline character in the study area. Ca2+and SO42-were the most abundant cations and anions among the detected nine ion species in the rainwater, accounting for40%and25%of the total ion mass, respectively. The association of SO42-,NO3-with NH4+and Ca2+revealed the neutralization of rainwater by CaSO4,（NH4）2SO4and NH4NO3, and the contribution of other ion species in the acidification and neutralization processes in rainwater was negligible.The application of factor and cluster analysis facilitates the interpretation of rainwater characteristics, highlighting the contribution of anthropogenic activities and crustal sources. In addition, monsoon-carried sea salts made up a minor contribution to the origins of Cl-and part of Na+in the rainwater of the Mt. Yulong region. Our studies on rainwater chemistry revealed that elevation differences and the different extents of local anthropogenic activities might account for the differences in the chemical composition of rainwater.The atmospheric backward trajectories calculated with HYSPLIT₄transport model show that the origins of dust aerosols were different in monsoon and non-monsoon seasons, i.e. originated from western and southwest directions of the Mt. Yulong. Re-analysis data calculation indicated that the moisture origins and air moistures of the two seasons with big difference, which has huge influence on the mircroparticles transmission and deposition in the atmosphere. Moreover, high concentrations of major ions during the non-monsoon seasons may due to the frequent dust events occurred in those seasons. It is also noteworthy that the bare rock of snow-free terrain on the Mt. Yulong and mineral dust particles from rock weathering are important sources for the dust in the water bodies there.更多还原