NUMBER CONCENTRATION, SIZE DISTRIBUTION AND FINE PARTICLE FRACTION OF TROPOSPHERIC AND STRATOSPHERIC AEROSOLS

1. Introduction The number concentration and size distribution of at-mospheric particles are the two major parameters for aerosol radiative forcing calculation, as the aerosol bur-dens affect the radiative transfer of solar and terrestrial emissions, while the size distribution of atmospheric aerosol is critical to all climatic influences (IPCC, 2001). However most measurements on the characteristics of the number-size distribution were carried out near the earth surface, with only a few exte…     

SEASONAL CHARACTERIZATION OF DUST DAYS, MASS CONCENTRATION AND DRY DEPOSITION OF ATMOSPHERIC AEROSOLS OVER QINGDAO, CHINA

1. Introduction Aerosols play an important role in affecting the atmos-pheric quality, cloud formation and precipitation, influenc-ing the energy balance of the earth-atmosphere system (Sokolik et al., 2001; Cao et al., 2003), although their concentration is very low. Recently, studies on atmospheric aerosols and their radiative forcing have been the inter-esting research area in global and/or regional environment and climate changes (Zhang et al., 2001; Menon et al., 2002). Among them, much…     

MODELING OF ORGANIC CARBON AEROSOL DISTRIBUTIONS OVER EAST ASIA IN THE SPRINGTIME

1. Introduction Atmospheric aerosols are a chemical mixture of solid and liquid particles suspended in ambient air. They range in size from the smallest superfine particles, having di-ameters of a few nano-meters (nm), to coarse mode parti-cles, with diameters of several micrometers (mm) or more. From a climatic point of view, probably the most critical subset of atmospheric aerosols are those in the fine or accumulation mode, having diameters ranging from about 0.1 mm to a few micrometers. Th…     

Simulation of atmospheric aerosols in East Asia using modeling system RAMS-CMAQ： Model evaluation

The modeling system RAMS-CMAQ is applied in this paper to East Asia to simulate the temporo-spatial concentration distributions of atmospheric aerosols. For evaluating its performances, modeled concentrations of aerosols such as sulfate, nitrate, ammonium, black carbon and organic carbon were compared with observations obtained in East Asia on board of two aircrafts in the springtime of 2001. The comparison showed generally good agreement, and, in particular, that the modeling system captured most of the important observed features, including vertical gradients of the aerosols of the Asian outflow over the western Pacific. The evaluation results provide us with much confidence for further use of the modeling system to investigate the transport and transformation processes of atmospheric aerosols over East Asia and to assess their impacts on the Earth＇s radiation budget.     

Surrogate atmospheric dust particles generated from dune soils in laboratory: Comparison with field measurement

Desert dust strongly influences the climate and the environment by altering the radiation budget, participating in atmospheric chemical reactions, and engaging the biogeochemical cycle. Studying its impacts requires knowledge of the physical and chemical properties of the original particles from the source origin. Unfortunately, the field collection of atmospheric samples in the desert is impractical. Fine surface soil is thus considered an alternative material from which to obtain the information applicable to dust particles from the desert soil. In this study, a laboratory system was set up to generate dust particles with simulated natural wind erosion processes from surface soils or directly from desert surfaces. Surface soils and field dust were simultaneously collected during a local blowing dust event. The comparison between the laboratory-generated dust and the field dust showed a consistent trend in particle size distribution and chemical composition. The chemical compositions were found to have explainable differences with the Certified Reference Materials for Asian dust (CJ-2). The laboratory-generated dust particles with the system could be applied as surrogates for soil-emitted dust in desert areas.     

NANOPARTICLE AEROSOL SCIENCE AND TECHNOLOGY： AN OVERVIEW

As a new scientific discipline, nanoparticle aerosol science and technology （NAST） deals with the formation, properties and behavior of nanoparticles in gases. Driven by its practical applications in many different fields, NAST has been undergoing rapid development. A conceptual framework of the discipline, with its own basic principles, experimental methods and computational techniques, is now taking shape. This paper presents an overview of the current status and research needs of the new discipline. The presentation begins with a discourse on the relationship among various particle systems, which occur frequently in nature and industry. The properties and behavior of nanoparticle aerosols are then discussed, with emphasis on the key roles played by particle size and morphology. Similar to fluid dynamics, NAST is an enabling discipline in the sense that it has provided the concepts and methodology needed for the development of many other fields. Applications of nanoparticle aerosol science and technology are highlighted in three important areas： （1） aerosol processes for synthesis of nanoparticles, （2） atmospheric nanoparticles and global climate, and （3） dosimetry of inhaled nanoparticles. These fields have features in common insofar as nanoparticie aerosols follow the same basic laws of physics and chemistry.     

Effects of physical properties of supercritical water on coarse graining of particle cluster

The coarse graining of particle cluster is of great significance to the study of a fluidized bed. The effects of variations in the physical properties of supercritical water on the coarse graining of particle cluster are investigated in this work. The drag coefficient distributions of the particle cluster are not influenced by the physical properties. However, the physical properties have effects on the values of drag coefficient. The effects of physical properties are weaker in the case of large particle concentrations. Furthermore, the physical properties lead to that the effect of particle cluster wake on the drag of downstream particles being significantly different from that of constant property flow. The variation trend of drag of coarse graining particle is consistent with that of isolated particle. The physical properties lead to significant differences in the values of drag. In this paper, the dominance of the effects of physical properties in a variety of cases is confirmed. Finally, a physical properties effect model is developed accordingly.     

蒙特卡洛方法数值研究大气颗粒物动力学效应和辐射传输性质

爆发性增强的雾天,空气污染严重能见度低,这与大气边界层湍流性质、悬浮颗粒的动力学及散射性质密切相关.文中基于颗粒群平衡方程和Mie理论,采取加权蒙特卡洛方法,自行开发了Fortran程序.文中计算所得的颗粒尺度分布函数、颗粒散射性质与实验值、理论解一致,验证了数值模型和方法的正确性.此外,数值研究了雾爆发性增强阶段雾滴谱拓宽、能见度降低的机理,讨论湍流输运和颗粒局部聚集效应下颗粒间的碰并过程,并耦合颗粒散射性质,数值分析雾发展中湍流耗散率对颗粒对径向相对速度、系统透过率的影响;以及颗粒对径向相对速度与系统透过率、颗粒尺度的关系.研究结果表明:随着湍流耗散率的增大,颗粒的径向相对速度呈现先缓慢而后快速增大的变化趋势.1000s时刻,湍流的耗散率为1.0×10-2m2/s3,颗粒径向相对速度(无量纲)为0.0969;对于0.6μm的可见光,雾环境颗粒系统的透过率为0.47.此外,雾发展中雾滴易与气溶胶碰并,系统的散射性质与水组成的雾滴系统不同,天气的能见度明显降低.      

SPATIAL AND SEASONAL DISTRIBUTIONS OF ATMOSPHERIC CARBONACEOUS AEROSOLS IN PEARL RIVER DELTA REGION, CHINA

Concentrations and spatial distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of Pearl River Delta Region (PRDR), China during 2001 winter period and 2002 summer period. PM2.5 (particie diameter smaller than 2.5 um) and PM10 (particie diameter smaller than 10 um) samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed using thermal optical reflectance (TOR) method. The average PM2.5and PM10 Ievel were 60.1 and 93.1 μg·m-3, respectively, with PM2.5 constituting 65.3% of the PM10 mass. The average OC and EC concentrations in PM2.5 were 12.0 and 5.1 μg·m-3, respectively, while those in PM10 were 16.0 and 6.5 μg·m-3, respectively. The carbo-naceous aerosol accounted for 37.2% of the PM2.5 and 32.8% of the PM10. The highest concentrations of OC and EC were observed at Guangzhou city in both vvinter and summer seasons. The average OC/EC ratios were 2.     

粗粒土离散元非球趋真颗粒模型

颗粒形状对粗粒土的物理力学特性有着显著的影响。离散元法广泛应用于粗粒土宏观物理力学特性的细观机理研究。为了考虑颗粒形状的影响,亟待发展计算高效的离散元非球趋真颗粒模型。本文基于X射线CT扫描技术并结合数字图像处理技术,对光滑和棱角性两类典型粗粒土(鹅卵石与碎石)进行三维重构,并提出了两类趋真颗粒模型,分别采用扩展超椭球模型和球多面体模型进行趋真逼近;开展了两类颗粒试样的3D打印和单轴压缩试验,分析了配位数和局部孔隙率分布等细观特性;基于离散元开源程序SudoDEM开展了两类试样的离散元模拟,并将模拟细观分析结果与物理试验进行了对比。结果表明,提出的两类趋真颗粒模型能够较好地对粗粒土颗粒进行离散元建模。     

PIV- and LDV-measurements of baroclinic wave interactions in a thermally driven rotating annulus

Already in the 1950s, an elegant laboratory experiment had been designed to understand how the atmospheric circulation transports heat from equatorial to polar latitudes. It consists of a cooled inner and heated outer cylinder mounted on a rotating platform, mimicking the heated tropical and cooled polar regions of the earth’s atmosphere. Depending on the strength of the heating and the rate of rotation, different flow regimes had been identified: wave-regimes that can be classified by pro-grade propagating waves of different wavenumbers and quasi-chaotic regimes where waves and small-scale vortices coexist. In the present paper, we will use multivariate statistical techniques to understand better the variability of the heated rotating flow (i) in the transition region between regular waves with zonal wave number 3 and 4 and (ii) in the transition region to the quasi-chaotic regime. The former regime is studied by applying the complex empirical orthogonal function (CEOF) method to particle image velocimetry data, the latter by applying the multichannel singular spectrum analysis (M-SSA) to laser Doppler velocimetry (LDV) data. In the annulus, interactions between the dominant mode and the so-called weaker modes, explaining less variance than the dominant mode, can lead to low-frequency amplitude and wave structure vacillations. The CEOF analysis reveals the coexistence of a dominant and a weak mode in the 3-4 wave transition region. This finding confirms earlier ideas on wave dispersion in transition regions between regular waves. Increasing the annulus’ rotation leads to a growth of the weak mode until this mode becomes the dominant one. No coexistence of modes could be found for the regular 4-wave regime but a slight structural vacillation was present. The M-SSA was applied to LDV data corresponding with much faster annulus rotation for which the flow becomes more irregular. The analysis reveals a coexistence of a dominant 4 mode and a much weaker 5 mode for this regime. Our results complement previous observations recovered primarily by thermocouple arrangements.     

Design and characterization of GRC-1: A soil for lunar terramechanics testing in Earth-ambient conditions

Earth experiments must be carried out on terrain that deforms similarly to the lunar terrain to assess the tractive performances of lunar vehicles. Most notably, terrain compaction and shear response underneath the lunar vehicle wheels must represent that of the Moon. This paper discusses the development of a new lunar soil simulant, Glenn Research Center lunar soil simulant #1 (GRC-1), which meets this need. A semi-empirical design approach was followed in which the soil was created by mixing readily available manufactured sands to a particle size distribution similar to the coarse fraction of lunar soil. By varying terrain density, a broad range of in situ cone penetration measurements collected by the Apollo mission astronauts can be replicated. An extensive set of characterization data is provided in this article to facilitate the use of this material. For reference, the index and geotechnical properties of GRC-1 are compared to the lunar soil and existing lunar soil simulants.     

粗骨料粒径对混凝土动态压缩行为的影响研究

粗骨料作为混凝土材料组成最主要的部分,对混凝土力学性能和破坏模式有着很重要的影响。为了研究粗骨料平均粒径对混凝土动态力学性能的影响规律,针对不同平均粗骨料平均粒径（6、12、24 mm）的混凝土和砂浆材料进行了一系列SHPB试验,得到了不同应变率下各试件的应力-应变曲线,并对每种材料的动态增长因子（dynamic increase factor,DIF）与应变率的对数进行了线性拟合。结果表明:砂浆和混凝土材料的抗压强度具有明显的应变率效应,其动态抗压强度随着应变率的增加而逐渐增大,应力-应变曲线呈现相似的变化趋势;在相同的动态应变率条件下,平均粗骨料粒径为12 mm的混凝土的动态抗压强度最大,这与准静态条件下砂浆抗压强度最大截然不同;不同粗骨料粒径混凝土材料的应变率强化系数均大于砂浆材料,且随着粗骨料无量纲尺寸的增大,混凝土材料的应变率强化因子呈现先增大后减小的趋势。     

Ground-based skidder traffic changes chemical soil properties in a mountainous Oriental beech (Fagus orientalis Lipsky) forest in Iran

Increased soil compaction following harvest traffic is an inroad for adverse changes in soil biological properties and processes, soil microbial activity, bacterial communities, and growth and development of plant roots. This study investigated the impacts of three levels of traffic intensity (3–6, 7–14, and 15+ passes) of a Timberjack 450C skidder on changes in several chemical soil properties at two levels of skid trail slope gradients (gentle =<20% and steep >20% inclination) in the Hyrcanian forest. Skidding increased soil bulk density between 19% and 39% and, averaged over both slope gradients, reduced amounts of soil organic carbon (33–67%), concentrations of nitrogen (51–80%), phosphorous (0–17%), potassium (11–36%), and hydrogen ions (78–98%) compared to undisturbed areas. Most soil damage occurred after a few skidder passes, particularly on steep slopes that generally experienced the highest level of soil deterioration. The primary mechanism that induced immediate chemical soil changes was an uplift and exposure of deeper soil layers in response to compression and displacement of the former soil surface. Skidding can jeopardize the sustainability of forest ecosystems by creating unfavorable changes in soil characteristics and nutrient status.     

Atmospheric temperature dependence of the aerosol backscattering coefficient

In extracting vertical profiles of aerosol backscattering coefficient from lidar signals, the effects of atmospheric temperature are usually ignored. In this study, these effects are analyzed using a rotational Raman–Mie lidar system, which is capable of simultaneously measuring atmospheric temperature and vertical profiles of aerosols. A method is presented to correct the aerosol backscattering coefficient using atmospheric temperature profiles, obtained from Raman scattering signals. The differences in the extracted aerosol backscattering coefficient with and without considering temperature effects are further discussed. The backscattering coefficients for scattering off clouds are shown to be more sensitive to temperature than that of aerosols and atmosphere molecules; the aerosol backscattering coefficient is more sensitive to temperature in summer due to higher atmospheric temperatures.     

相变颗粒改性聚酰胺的高速摩擦学行为

采用填充聚合法制备了相变颗粒改性聚酰胺复合材料.在摩擦速率为6~24 m/s条件下的测试结果表明:相比纯聚酰胺,所得聚酰胺复合材料具有明显更低的摩擦系数和磨损率,并且对摩擦速率呈现一定的自适应性.当复合材料中相变颗粒含量较少时(质量分数5%),复合材料对摩擦速率的自适应能力较弱,而当复合材料中相变颗粒含量较多时(质量分数10%),复合材料的自适应能力较强.纯聚酰胺的磨损模式为严重的黏着磨损;5%相变颗粒改性聚酰胺复合材料呈现典型的磨粒磨损和轻微的黏着磨损,而10%相变颗粒改性聚酰胺复合材料以轻微的磨粒磨损和轻微的疲劳磨损共存.     

基于CE/SE方法模拟空气中RDX-Al悬浮粉尘的两相爆轰

通过CE/SE方法模拟了空气中炸药-铝粉尘的两相爆轰过程, 研究了双粉尘爆轰过程中粒子不同密度对爆轰波速度、压力的影响, 得到密度与波速、爆压间的线性关系。模拟得到悬浮粉尘在复杂通道中的爆轰波传播过程, 研究了双粉尘爆轰的流场演化过程, 选取流场中的一些点对该处流场的压力及温度随时间的变化进行重点研究, 对比了单铝粉尘在同种条件下的爆轰过程, 发现双粉尘爆轰明显提高了爆轰波波速和流场的压力及温度。模拟结果表明CE/SE方法可以成功模拟双粉尘的爆轰过程, 可为多粉尘爆轰的研究提供参考。     

NUMERICAL SIMULATION WITH A COMPREHENSIVE CHEMICAL TRANSPORT MODEL OF NITRATE, SULFATE, AND AMMONIUM AEROSOL DISTRIBUTIONS OVER EAST ASIA

The transport and chemical production processes of nitrate, sulfate, and ammonium aerosols over East Asia were investigated by use of the Models-3 Community Multi-scale Air Quality （CMAQ） modeling system coupled with the Regional Atmospheric Modeling System （RAMS）. For the evaluation of the model＇s ability in depicting their 3-dimensional concentration distributions and temporal variations, modeled concentrations of nitrate, sulfate, and ammonium aerosols are compared with the observations obtained at a ground station in Japan in March 2001 and onboard of an aircraft DC-8 on 18 and 21 March 2001 during the Transport and Chemical Evolution over the Pacific （TRACE-P） field campaign. Comparison shows that simulated values of nitrate, sulfate, and ammonium aerosols are generally in good agreement with their observed data, and the model captures most important observed features, and reproduces temporal and spatial variations of nitrate, sulfate, and ammonium aerosol concentrations reasonably well, e.g., the timing and locations of the concentration spikes of nitrate, sulfate, and ammonium aerosols are well reproduced, but large discrepancies between observed and simulated values are also clearly seen at some points and some times due to the coarse grid resolution and uncertainties of the emissions used in this study. This comparison results indicate that CMAQ is able to simulate the distributions of nitrate, sulfate, and ammonium aerosols and their related species in the troposphere over East Asia reasonably well.     

SOURCE PROFILES AND FINGERPRINTS OF FINE AND COARSE SANDS RESUSPENDED FROM SOILS SAMPLED IN CENTRAL INNER MONGOLIA

Fingerprints and source profiles of fine and coarse sands that originate from Central Inner Mongolia during Asian continental sandstorms （ACS） can be used to identify the odgin of Asian sands and to trace them as they travel downwind. Soil samples collected at various land surfaces in Central Inner Mongolia were resuspended using a dry powder atomizer in an enclosure chamber. The resuspended sands were then sampled by two dichotomous samplers situated at the bottom of the enclosure chamber for fine （PM2 5） and coarse （PM2.5-10） sands, respectively. The chemical composition of sands, including water-soluble ionic species, metallic contents, and carbonaceous contents, were further analyzed. Results from resuspension tests indicated that the soils contained considerably more coarse particles than fine Moreover, Mg, K, Al, and Fe in coarse sand had strong correlations with each other. The ratio of Mg, K. Fe （or Al） to Al （or Fe） and OC/EC in the coarse sands can be used as the fingerprints of Asian sands originating from Central Inner Mongolia.