Wind tunnel experiments on dust emissions from different landform types

The measurement and assessment of dust emissions from different landforms are important to understand the atmospheric loading of PM10(particulate matter ≤10 μm aerodynamic diameter) and to assess natural sources of dust; however, the methodology and technique for determining the dust still present significant research challenges. In the past, specialized field observation and field wind tunnel studies have been used to understand the dust emission. A series of wind tunnel tests were carried out to identify natural sources of dust and measure the magnitudes of dust emissions from different landforms. The method used in this study allowed the measurement of the PM10 emission rate using a laboratory based environmental boundary layer wind tunnel. Results indicated that PM10 emissions demonstrated strong temporal variation and were primarily driven by aerodynamic entrainment. Sand dunes, playa, and alluvial fans had the largest dust emission rates(0.8–5.4 mg/(m~2·s)) while sandy gravel, Gobi desert and abandoned lands had the lowest emission rates(0.003–0.126 mg/(m~2·s)). Dust emissions were heavily dependent on the surface conditions, especially the availability of loose surface dust. High dust emissions were a result of the availability of dustparticle materials for entrainment while low dust emissions were a result of surface crusts and gravel cover. Soil surface property(surface crusts and gravel cover) plays an important role in controlling the availability of dust-sized particles for entrainment. The dust emission rate depended not only on the surface conditions but also on the friction velocity. The emission rate of PM10 varies as a power function of the friction velocity. Although dynamic abrasion processes have a strong influence on the amount of dust entrainment, aerodynamic entrainment may provide an important mechanism for dust emissions. Large volumes of dust entrained by aerodynamic entrainment cannot only occur at low shear velocity without saltation, but may dominate the entrainment process in many arid and semi-arid environments. So it may also be responsible for large magnitude dust storms. Playa and alluvial fan landforms, prior to developing a surface crust, may be the main sources of dust storms in Qinghai Province.     

策勒绿洲-荒漠过渡带风沙前沿近地表沙尘水平通量观测

沙漠地区近地表水平输送的沙尘物质通量及其随高度的变化是沙尘输送过程的重要表现特征。在塔克拉玛干沙漠南缘策勒绿洲-荒漠过渡带风沙前沿平坦沙地的风沙观测场,利用BSNE集沙仪对近地表（2 m）不同高度沙尘物质的水平输送进行了观测,对其随高度变化特征进行了分析,并对近地表水平运动的沙尘通量进行了计算。结果表明：观测点沙尘物质的水平通量随高度的增加而减小,与高度的关系可用幂函数和指数函数表示;55%～58%的沙尘量在地表0.5 m高度以内传输;73%～75%在地表1 m高度以内传输;87%～89%在地表1.5 m高度以内传输;2010年5月25日至2011年5月24日,通过0～2 m高度的单宽总输沙量为1 846.7 kg•m^-1;其中PM80、PM50的输送量分别为1 192.0 kg•m^-1、387.9 kg•m^-1。     

Effect of stones on the sand saltation threshold during natural sand and dust storms in a stony desert in Tsogt-Ovoo in the Gobi Desert,Mongolia

Non-erodible elements such as stones and vegetation are key to controlling wind erosion and dust emission in drylands. Stony deserts are widely distributed in the Gobi Desert, but the effect of stones on wind erosion and dust emission have not been well studied, except under artificial conditions. In this study, we evaluated the effect of stones on wind erosion and dust emission by measuring the sand saltation threshold in a stony desert in Tsogt-Ovoo in the Gobi Desert, Mongolia, under natural surface conditions during sand and dust storms. We quantified the amount of stones by measuring the roughness density, and determined the threshold friction velocity for sand saltation by measuring wind speed and sand saltation count. Our results showed that the threshold friction velocity increased with the roughness density of stones. In the northern part of the study area, where neither a surface crust nor vegetation was observed, the roughness density of stones was 0.000 in a topographic depression (TD), 0.050 on a northern slope (N.SL), and 0.160 on the northern mountain (N.MT). The mean threshold friction velocity values were 0.23, 0.41, and 0.57 m/s at the TD, N.SL, and N.MT sites, respectively. In the southern part of the study area, the roughness density values of stones were 0.000 and 0.070-0.320 at the TD and southern slope sites, respectively, and the mean threshold friction velocities were 0.23 and 0.45-0.71 m/s, respectively. We further compared the observed threshold friction velocities with simulated threshold friction velocities using Raupach's theoretical roughness correction and the measured roughness density values, and found that Raupach's roughness correction worked very well in the simulation of threshold friction velocity in the stony desert. This means that the results of our stone measurement can be applied to a numerical dust model.     

沙漠地区不同下垫面近地表沙尘水平通量研究

沙漠地区近地表水平输送的沙尘物质通量及其随高度的变化特征直接影响着沙尘的输送过程。选择塔克拉玛干沙漠腹地塔中地区的典型沙丘、平沙地为观测点,利用BSNE集沙仪,对2008-2009年11次典型沙尘天气过程中近地表0～200 cm不同高度层沙尘物质的水平输送进行了测量,对其随高度变化特征进行分析,计算近地表水平运动的总沙尘通量。结果表明：近地表0～200 cm范围内,在沙丘顶部和平沙地沙尘水平通量均随高度呈显著降低趋势,在这2种下垫面条件下,沙尘水平通量随高度的变化均较好地符合幂函数关系;在沙丘顶部,通过100 cm（宽度）×200 cm（高度）空间断面的总沙尘水平通量为3 721.0 kg,平沙地通过相同大小断面的沙尘水平通量为2 252.9 kg,比沙丘顶部减少了39.5%;沙丘顶部与平沙地PM80的总水平通量分别为996.8 kg和678.9 kg。     

边界层参数化方案对一次西北地区沙尘天气过程影响的数值模拟研究

使用耦合化学模块的高分辨率中尺度数值模式WRF-Chem3.4,结合近地层观测资料评估YSU、MYJ、QNSE、MYNN2.5和BouLac共5种边界层参数化方案对2007年3月27日西北地区一次沙尘天气过程模拟效果的影响,结果显示5种边界层参数化方案均可模拟出此次沙尘天气的发展演变过程,其中YSU和BouLac方案模...     

Near-surface sand-dust horizontal flux in Tazhong-the hinterland of the Taklimakan Desert

Tazhong is the hinterland and a sandstorm high-frequency area of the Taklimakan Desert. However, little is known about the detailed time-series of aeolian sand transport in this area. An experiment to study the sand-dust horizontal flux of near-surface was carried out in Tazhong from January to December 2009. By measuring the sand-dust horizontal flux throughout sixteen sand-dust weather processes with a 200-cm tall Big Spring Number Eight (BSNE) sampler tower, we quantitatively analyzed the vertical variation of the sand-dust horizontal flux. And the total sand-dust horizontal flux of different time-series that passed through a section of 100 cm in width and 200 cm in height was estimated combining the data of saltation movement continuously recorded by piezoelectric saltation sensors (Sensit). The results indicated that, in the surface layer ranging from 0-200 cm, the intensity of sand-dust horizontal flux decreased with the increase of the height, and the physical quantities obeyed power function well. The total sand-dust horizontal flux of the sixteen sand-dust weather processes that passed through a section of 100 cm in width and 200 cm in height was about 2,144.9 kg, the maximum of one sand-dust weather event was about 396.3 kg, and the annual total sand-dust horizontal flux was about 3,903.2 kg. The high levels of aeolian sand transport occurred during daytime, especially from 13:00 to 16:00 in the afternoon. We try to develop a new method for estimation of the detailed time-series of aeolian sand transport.     

Contribution of underlying terrain to sand dunes: evidence from the Qaidam Basin,Northwest China

Underlying terrain strongly influences dune formation. However, the impacts of underlying terrain on the dune formation are poorly studied. In the present research, we focused on dunes that formed in the alluvial fans and dry salt flats in the Qaidam Basin, Northwest China. We quantified the dunes' sediment characteristics on different types of underlying terrain and the terrain's effects on the surface quartz grains by analyzing grain-size distribution, soluble salt contents and grain surface micro-textures. Results showed that barchan dunes were dominated by medium sands with a unimodal frequency distribution, whose peak corresponded to the saltation load. Linear dunes were mainly composed of fine sands with a bimodal frequency distribution, whose main peak represented the saltation load, and whose secondary peak represented the modified saltation or suspension load. Sand was transported from source area by running water (inland rivers) over short distances and by wind over relatively longer distances. Thus, quartz grains had poor roundness and were dominated by sub-angular and angular shapes. Surface micro-textures indicated that dune sands were successively transported by exogenic agents (glaciation, fluviation and wind). Soluble salt contents were low in dunes that developed in the alluvial fans, which represented a low-energy chemical environment, so the grain surface micro-textures mainly resulted from mechanical erosion, with weak micro-textures formed by SiO₂ solution and precipitation. However, soluble salt contents were much higher in dunes that developed in the dry salt flats, which indicated a high-energy chemical environment. Therefore, in addition to micro-structures caused by mechanical erosion, micro-textures formed by SiO₂ solution and precipitation also well developed. Our results improve understanding of the sediment characteristics of dune sands and the effects of underlying terrain on dune development in the Qaidam Basin, China.     

冷锋天气过程大气边界层特征与颗粒物污染

利用兰州大学半干旱气候与环境观测站边界层铁塔梯度观测、湍流观测和PM₁₀浓度资料,分析一次典型冷锋天气过程兰州大气边界层结构和湍流输送特征及其与PM₁₀浓度的关系。结果表明：冷锋过境前边界层有逆温层出现。随着锋面过境,逆温层完全被破坏、消失,混合层迅速发展,边界层低层温度和湿度垂直梯度变得很小,风速垂直梯度则明显增大;PM₁₀浓度先升后降。冷锋过境时垂直湍流输送强烈,经向和纬向动量均向下输送。动量下传使地表尘沙大量扬起,造成冷锋过境初期颗粒物浓度骤升。     

Effects of aeolian processes on nutrient loss from surface soils and their significance for sandy desertification in Mu Us Desert,China: a wind tunnel approach

Mu Us Desert, a region with high aeolian activity, is at extremely high risk of sandy desertification. Using surface soil samples collected from Mu Us Desert of northern China, we evaluated the effects of aeolian processes on nutrient loss from surface soils by employing wind tunnel experiments. The experiments were conducted using free-stream wind velocities of 14, 16, 18 and 22 m/s. Our results showed that the fine particles(50 μm in diameter; 12.28% of all transported materials) carrying large nutrient loadings were exported outside the study area by aeolian processes. After the erodible fine particles were transported away from the soil surfaces at low wind velocity(i.e. 14 m/s), the following relatively high wind velocity(i.e. 22 m/s) did not have any significant effect on nutrient export, because the coefficients of variation for soil organic matter, total phosphorus, total nitrogen and available potassium were usually 5%. Our experimental results confirmed that aeolian processes result in a large amount of nutrient export, and consequently increase the risk of sandy desertification in arid and semi-arid ecosystems.     

Estimation of the quantity of aeolian saltation sediments blown into the Yellow River from the Ulanbuh Desert,China

The Ulanbuh Desert borders the upper reach of the Yellow River.Every year,a mass of aeolian sand is blown into the Yellow River by the prevailing wind and the coarse aeolian sand results in serious silting in the Yellow River.To estimate the quantity of aeolian sediments from the Ulanbuh Desert blown into the Yellow River,we simulated the saltation processes of aeolian sediments in the Ulanbuh Desert.Then we used a saltation submodel of the IWEMS(Integrated Wind-Erosion Modeling System)and its accompanying RS(Remote Sensing)and GIS(Geographic Information System)modules to estimate the quantity of saltation sediments blown into the Yellow River from the Ulanbuh Desert.We calibrated the saltation submodel by the synchronous observation to wind velocity and saltation sediments on several points with different vegetation cover.The vegetation cover,frontal area of vegetation,roughness length,and threshold friction velocity in various regions of the Ulanbuh Desert were obtained using NDVI(Normalized Difference Vegetation Index)data,measured sand-particle sizes,and empirical relationships among vegetation cover,sand-particle diameters,and wind velocity.Using these variables along with the observed wind velocities and saltation sediments for the observed points,the saltation model was validated.The model results were shown to be satisfactory(RMSE less than 0.05 and|Re|less than 17%).In this study,a subdaily wind-velocity program,WINDGEN,was developed using this model to simulate hourly wind velocities around the Ulanbuh Desert.By incorporating simulated hourly wind-velocity and wind-direction data,the quantity of saltation sediments blown into the Yellow River was calculated with the saltation submodel.The annual quantity of aeolian sediments blown into the Yellow River from the Ulanbuh Desert was 5.56×106t from 2001 to 2010,most of which occurred in spring(from March to May);for example,6.54×105tons of aeolian sand were blown into the Yellow River on 25 April,2010.However,in summer and winter,the saltation process occasionally occurred.This research has supplied some references to prevent blown sand hazards and silting in the Yellow River.     

Large scale sand saltation over hard surface:a controlled experiment in still air

Saltation is the major particle movement type in wind erosion process. Saltating sand grains can rebound up to tens of times larger in length and height over hard surface(such as gravel surface) than over loose sand surface. Gravels usually have different faces, causing distinct response of the impacting grains, but the effects of the grain and gravel-surface contact angle on grain rebound are not yet well quantified. We performed full-range controlled experiments of grain saltation using different contact angles, grain sizes and impact speeds in still air, to show that contact angle increases the height of representative saltation path but decreases particle travel length. The results were compared with outputs from the COMprehensive numerical model of SALTation(COMSALT). Large saltation height of 4.8 m and length of 9.0 m were recorded. The maximum and representative saltation height over the gravel surface were found to be about 4.9 times and 12.8 times those over the loose sandy surface, respectively. The maximum saltation length may be reduced by 58% and the representative saltation height may be increased by 77% as contact angle increases from 20° to 40°. We further showed that the collision inertia contributes 60% of the saltation length, and wind contributes to the other 40%. These quantitative findings have important implications for modeling saltation trajectory over gravel surface.     

An experimental study on the influences of water erosion on wind erosion in arid and semi-arid regions

Complex erosion by wind and water causes serious harm in arid and semi-arid regions. The interaction mechanisms between water erosion and wind erosion is the key to further our understanding of the complex erosion. Therefore, in-depth understandings of the influences of water erosion on wind erosion is needed. This research used a wind tunnel and two rainfall simulators to investigate the influences of water erosion on succeeding wind erosion. The wind erosion measurements before and after water erosion were run on semi-fixed aeolian sandy soil configured with three slopes(5°, 10° and 15°), six wind speeds(0, 9, 11, 13, 15 and 20 m/s), and five rainfall intensities(0, 30, 45, 60 and 75 mm/h). Results showed that water erosion generally restrained the succeeding wind erosion. At a same slope, the restraining effects decreased as rainfall intensity increased, which decreased from 70.63% to 50.20% with rainfall intensity increased from 30 to 75 mm/h. Rills shaped by water erosion could weaken the restraining effects at wind speed exceeding 15 m/s mainly by cutting through the fine grain layer, exposing the sand layer prone to wind erosion to airflow. In addition, the restraining effects varied greatly among different soil types. The restraining effects of rainfall on the succeeding wind erosion depend on the formation of a coarsening layer with a crust and a compact fine grain layer after rainfall. The findings can deepen the understanding of the complex erosion and provide scientific basis for regional soil and water conservation in arid and semi-arid regions.     

积雪中不溶微粒与Mg~（2＋）的沉积特征和相互关系

为了探究不溶微粒和Mg2＋在雪冰沉积过程中的相关性,对采自乌鲁木齐河源1号冰川海拔4 130 m处的雪冰样品进行不溶微粒和Mg2＋浓度的分析。表层雪中不溶微粒和Mg2＋浓度的季节变化具有较好的一致性,在6～8月的降水频发期和局地风盛行时,两者都达到一年中的最大值。粗微粒（直径大于10μm）和Mg2＋浓度在雪层剖面中的垂...     

全球变暖背景下中国北方沙尘暴变化及其对黄土高原成壤的影响研究

黄土的风成说表明粉尘黄土沉积及其成壤与沙尘暴之间存在着密切的联系,作为粉尘搬运的典型:沙尘暴是一种在强冷空气条件下粉尘快速而大规模被搬运和沉降事件,而长时间尺度的沙尘暴事件受全球气候变化的控制和影响;同时,沙尘暴发生的频次和强度变化进而会影响黄土高原地区的黄土粉尘沉积及其成壤强度的变化。本文是在考察中国北方沙尘暴成因机制与黄土高原粉尘沉积和成壤之间关系的基础上,探讨了在全球持续变暖背景下中国北方沙尘暴的发生频次变化及其对黄土高原地区粉尘沉积和成壤强度的可能影响。主要结论是:在全球持续变暖的背景下,虽然粉尘沉积区的降水并没有显著增加,但粉尘源区气候趋于暖湿化,导致中国北方沙尘暴有逐年减少的趋势,使得黄土高原粉尘堆积的速率减小,因而,黄土高原地区将进入一个成壤相对强的时期。     

与长途输送和当地污染物排放有关的大气悬浮物中的Cd/Pb和Zn/Pb比例特征(英文)

1.IntroductionAsiandustparticlesaretransportedoverlongdistancesbythewesterlywindsannuallyinlatewinterandspringandaffecttheairqualityofdownwindregionsandcountries.AnumberofinvestigationshavebeenconductedondiverseaspectsofAsiandust,includingchemical,physica…     

Impact of utility-scale solar photovoltaic array on the aeolian sediment transport in Hobq Desert,China

Deserts are ideal places to develop ground-mounted large-scale solar photovoltaic (PV) powerstation. Unfortunately, solar energy production, operation, and maintenance are affected bygeomorphological changes caused by surface erosion that may occur after the construction of the solar PVpower station. In order to avoid damage to a solar PV power station in sandy areas, it is necessary toinvestigate the characteristics of wind-sand movement under the interference of solar PV array. The studywas undertaken by measuring sediment transport of different wind directions above shifting dunes andthree observation sites around the PV panels in the Hobq Desert, China. The results showed that the twoparameterexponential function provides better fit for the measured flux density profiles to the near-surfaceof solar PV array. However, the saltation height of sand particles changes with the intersection anglebetween the solar PV array and wind direction exceed 45°. The sediment transport rate above shifting duneswas always the greatest, while that around the test PV panels varied accordingly to the wind direction.Moreover, the aeolian sediment transport on the solar PV array was significantly affected by wind direction.The value of sand inhibition rate ranged from 35.46% to 88.51% at different wind directions. When theintersection angle exceeds 45°, the mean value of sediment transport rate above the solar PV array reducesto 82.58% compared with the shifting dunes. The results of our study expand our understanding of theformation and evolution of aeolian geomorphology at the solar PV footprint. This will facilitate the designand control engineering plans for solar PV array in sandy areas that operate according to the wind regime.     

Aeolian transport over a developing transverse dune

The spatial and temporal changes in aeolian transport over a dune are fundamental factors that control the morphology of the dune.In the present study,we obtained direct field observations of aeolian transport over a developing transverse dune at the Shapotou Aeolian Experiment Site in the southeastern part of China’s Tengger Desert.The transport rate versus wind speed relationship is complicated over a developing dune compared with the relationships over flat surfaces and over dunes that are in equilibrium with the wind.We obtained trend lines for transport rate over the transverse dune versus distance.The transport rate generally increased from the toe to the crest above the stoss slope,but the difference in transport rate between the crest and the toe was smaller than those that have been proposed for taller dunes.The crest/toe ratio for transport rates therefore seems to depend greatly on dune height.Flux density profiles for different points above the dune at different wind speeds were well described by the exponential decay law,as has been proposed for saltation flux density profiles.Coefficients in the flux density profile function can be defined in terms of the transport rate and wind speed.However,the dependence of relative decay rate with height and average saltation height on wind speed was weaker than that observed in a wind tunnel and above a flat surface.The preliminary results obtained in this study require more evidence from field observations to fully describe aeolian transport above developing dunes.     

不同砾石盖度戈壁床面动力学特征研究

利用野外车载移动式风洞,对莫高窟顶不同砾石盖度戈壁床面的动力学特征进行了实地模拟实验。结果表明：砾石盖度直接决定戈壁床面的粗糙元数量和分布状况,进而影响近地表风速廓线、摩阻速度、床面粗糙度和剪切力;随着风洞进口指示风速的增加,摩阻速度呈线性递增,而动力学粗糙度在波动中呈下降趋势;相同高度,随着砾石盖度的增加,近地表风速逐渐降低,而摩阻速度、动力学粗糙度和剪切力呈线性增加;当床面盖度增加至35%时,动力学粗糙度达到0.30 cm,摩阻速度相应提高到0.93 cm/s,床面剪切力增加至1.11 N/cm。     

干涸湖床不同类型盐土地表净风吹蚀实验研究

以内蒙古东乌珠穆沁旗及浑善达克沙地区域干涸湖床3种不同形态的盐土原状土为对象,通过风洞模拟实验,研究了干涸湖床不同类型盐土地表的净风吹蚀速率。对比风洞实验测定结果发现,3种盐土净风吹蚀速率依次是:蓬松盐霜盐土(14.44 g·m^-2·min^-1)>普通盐土(1.00 g·m^-2·min^-1)>结皮盐土(0.42 g·m^-2·min^-1)。风蚀过程中,不同类型盐土的近地表物质输移主要集中分布在0~10 cm的高度范围内,初始运动中,实验盐土风蚀颗粒物质以就地滚动和近距离跃移为主。实验观测发现,随着风速的增大,更多、更大的表面物质会受到更强烈的撞击与磨蚀作用,形成较细小的粉尘物质释放于空中,因此,干旱区盐土地表是形成区域盐碱浮尘或含盐沙尘天气的重要物源。不同类型盐土近地表物质输移总量从大到小依次是:蓬松盐霜盐土(3.17 g)、结皮盐土(0.42 g)、普通盐土(0.35 g)。     

“4.24”民勤特强沙尘暴过程初步分析

特强沙尘暴是干旱区一种破坏性极大的灾害性天气现象,文中分析了2010年4月24日民勤特强沙尘暴过程中地面气象要素和近地面沙尘浓度的变化,同时对大气动力、热力学参数进行了计算和分析。结果表明:在强沙尘暴过境时地面水平风风向经历了从稳定到多次调整,再到稳定,最后崩溃的演变。风向调整时,风速减弱,而调整之后,风速加大,同时伴有很强的上升气流。强沙尘暴使地表发生非常严重的风蚀起沙现象,近地面沙尘浓度迅速升高200多倍。沙尘暴天气来临前,地面空气呈干热状态处于低气压控制之下,而在沙尘暴过境时和过境后,地面空气显得相对湿冷,地面气压急剧上升,并处于高压控制之下。沙尘暴的强度与相对风暴螺旋度有很好的对应关系。