Structure and optical properties of soot aerosol in a moist atmosphere: 2. Influence of hydrophilicity of particles on the extinction, scattering, and absorption coefficients

The optical coefficients of soot particles are measured in a flow-through optical cell at the wavelength 635 nm in a dry atmosphere and in an atmosphere saturated with water vapor. Two types of systems modeling atmospheric soot aerosols and differing in the degree of hygroscopicity of their particles are investigated and compared. One of the systems contains hydrophobic acetylene soot, and the other contains hydrophilic soot obtained through modification of the initial soot by vapors of glutaric acid. The results show that the optical properties of hydrophobic soot depend only slightly on the conditions of moistening, whereas the optical properties of hydrophilic soot change abruptly upon its moistening because of the formation of a hydrate shell. In the atmosphere saturated with water-vapor, the monomolecular layer of a hydrophilic organic substance leads to the watering of particles and an abrupt (more than twofold) increase in the cross section of light scattering. A further growth of the hydrophilic component of soot particles initiates the formation of micron drops on them, thus resulting not only in the natural effect of light scattering enhancement but also in a noticeable light absorption increase. In particular, a light absorption enhancement by a factor of 3.5 is characteristic of particles of enriched hydrophilic soot.     

Aircraft-generated soot aerosols: Physicochemical properties and effects of emission into the atmosphere

This review describes the new results of analysis of both the physicochemical properties of soot particles emitted by commercial aircraft and subsequent variations in these properties under aircraft-contrail conditions. The results of the study of model laboratory soot samples are given for comparison. The state-of-the-art level of experimental studies of hygroscopicity of soot particles and their efficiency as crystallization centers are presented. The ability of soot aerosols to form condensation nuclei in aircraft contrails and ice nuclei in the upper troposphere is estimated. The estimates of the effects of aircraft soot emissions into the atmosphere are given.     

烟尘气溶胶对星地量子通信性能的影响

根据烟尘气溶胶的尺寸分布参数和消光系数,分析了烟尘气溶胶粒子数浓度与传输距离对链路衰减的影响。结合幅值阻尼信道对信道容量、信道保真度及信道误码率进行数值仿真。仿真结果表明,当传输距离为3 km,烟尘气溶胶粒子数浓度由2.1×10⁶ m^-3增加到3.2×10⁶ m^-3时,链路衰减由0.30 dB增加到0.46 dB,误码率由0.008 7增加到0.012 2。由此可见,烟尘气溶胶对星地量子通信的各项性能均有影响,且影响程度不一。仿真结果可为烟尘气溶胶影响下的量子信号传输提供参考。     

The hydrophobic fraction of organic matter in the Krka River Estuary

Surface active substances have been studied in the Krka River Estuary using an a.c. polarography method and various fractionation procedures. Total surface substances (SA_T) were separated into (particulate) heterodispersed and dissolved fractions by filtration. The dissolved fraction was separated into hydrophobic basic and neutral components, hydrophobic acid and hydrophilic components by sorption on to XAD-8 resin.The content and the composition of SA_T varied seasonally, depending on the biological activities taking place in the Krka River Estuary. The accumulation of SA_T, with hydrophobic properties, occurred at the fresh/saline water interface along the vertical profile. Daily changes in the form of the surface active substances along the vertical profile were observed. The formation of the heterodispersed fraction, especially observable in the upper freshwater layer and at the halocline, resulted in the change of physico-chemical properties of surface active substances. Organic matter appeared mainly in a dissolved form in the deeper saline water layer, showing negligible oscillations.The electrochemical characterization of the fractionated SA_T indicated that strong hydrophobicity of the surface active substances under natural pH conditions could be attributed to the significant contribution of the heterodispersed fraction of the organic material, which is the most reactive part of the surface active substances in the Krka River Estuary.The dissolved fraction of the surface active substances, prevailing in the deeper saline water layer, exhibited either hydrophilic or conditionally hydrophobic properties, depending on pH and ionic strength of the medium.     

Modeling aerosol dynamics during forest fires

A hydrodynamic model is used to reproduce the atmospheric circulation during forest fires. The dynamics is simulated with an improved model of free convection with allowance for heat flux emission from the fire area. Against the background of the atmospheric circulation patterns obtained, the problem of aerosol evolution and size distribution due to the forest’s combustible materials from the fire area was solved. The evolution of soot particles is described by solving the kinetic equations of condensation and coagulation. The results of numerical experiments to develop a process that considers water-vapor condensation in a moist atmosphere are presented.     

Acute ecological risk associated with soot deposition: a Persian Gulf case study

Many studies have been carried out in the past to provide solutions to the threat of chemicals to the ecosystem. However, the basic scientific capability to predict the risk of adverse effects on the ecological system has not kept pace with society's increasing demand for uses of chemicals. As a scientific methodology for quantifying the risk to the environment associated with exposure to chemicals, ecological risk assessment is increasingly important in environmental problem solving. The purpose of this paper is to present a methodology for conducting ecological risk assessment using deterministic and probabilistic approaches. A systematic discussion on elements of ecological risk assessment is presented. A framework of ecological risk assessment is explained with the help of the Persian Gulf environmental problem as a case study. The study was based on the output of a long-range transport model of soot deposition in the Gulf. Results of the assessment using the deterministic and probabilistic approaches are discussed.     

Effect of coagulation on a model planktonic food web

Observations have shown that aggregates (“marine snow”) are an important fraction of the organic matter vertical flux in the ocean. There has been a separation in biological models describing this flux, with coagulation models focused on phytoplankton blooms for which particle concentrations are high and grazing is low and neglectable and with plankton models focused on food web interactions neglecting coagulation dynamics. This separation has partly resulted from the difficulty in describing the interactions among the multiple particle sources using a coagulation model for a food web. New approaches for describing particle dynamics now make it possible to do so. The present study examines the effect of combining the food web model of Fasham et al. (1990. Journal of Marine Research 34, 591–639) with a coagulation dynamics model and applying the combined model to describe the annual cycle of an oligotrophic plankton system. As part of the model formulation, the coagulation kernels had to be altered to include both the case of fractal particles interacting and the case of smaller particles being faster settling. Results show that coagulation can have an important effect on particle flux even in the low particle concentration oligotrophic environment by increasing average particle settling speed and by increasing the ratio of maximum to minimum daily vertical flux over the course of a yearly cycle. As part of this, coagulation forms large, rapidly sinking particles. Grazing and the accompanying formation of fecal pellets can compete with coagulation for particles, but the fecal pellets can also participate in the formation of large aggregates. Among the variables that can influence export rates are phytoplankton size and concentration as well as depth of the surface mixed layer. The results provide evidence for the importance of coagulation processes in enhancing particle export even in central ocean regions.     

Carbonaceous aerosols of aviation and shipping emissions

This is a study of the physical and chemical properties of carbonaceous aerosols emitted by transport systems (namely, by aircraft gas turbine engines and large ship diesel engines) into the atmosphere. A comparative analysis of the morphology, size, elemental composition, and surface chemistry between aviation and diesel soot particles reveals the general and characteristic features of emissions from each source. The high pollution rate of diesel soot particles, considerable fraction of metal admixtures, and availability of char particles characterize the specific features of the formation of particles of this type. The main characteristics characterizing the interaction between aviation and shipping emission aerosols in the moist atmosphere (the composition of organic and water-soluble fractions at the surface) have been obtained. Due to high hygroscopicity, the microparticles can generate cloud condensation nuclei and initiate contrails and additional tropospheric cloudiness.     

Amphiphilic sodium alginate-vinyl acetate microparticles for drug delivery

To overcome the fast or burst release of hydrophilic drugs from hydrophilic alginate-based carriers,hydrophobic molecule(vinyl acetate,VAc)was grafted on alginate(Alg),which was further used to prepare drug carriers.Amphiphilic Alg-g-PVAc hydrogel beads were firstly prepared by emulsification/internal gelation technique for the loading of bovine serum albumin(BSA).Then,chitosan was coated on the surface of beads to form novel amphiphilic Alg-g-PVAc/chitosan(Alg-g-PVAc/CS)microcapsules.The BSA-loading amphiphilic Alg-g-PVAc/chitosan(Alg-g-PVAc/CS)microcapsules display similar morphology and size to the hydrophilic alginate/chitosan(AC)microcapsules.However,the drug loading and loading efficiency of BSA in Alg-g-PVAc/CS microcapsules are higher,and the release rate of BSA from Alg-g-PVAc/CS microcapsules is slower.The results demonstrate that the introduction of hydrophobic PVAc on alginate can effectively help retard the release of BSA,and the higher degree of substitution is,the slower the release rate is.In addition,the complex membrane can also be adjusted to delay the release of BSA.As a whole,amphiphilic sodium alginate-vinyl acetate/CS microparticles could be developed for macromolecular drug delivery.     

Generating electric-discharge layers in mesoscale convective systems

A system of quasi-hydrodynamic equations for the electric field, charges, and concentrations of cloud particles and light aeroions in stratified regions of mesoscale convective systems is proposed and analyzed numerically in a one-dimensional approximation. The important role of Debye-charge layers, which are caused by light ions, is established. It is shown that, under certain aerodynamic conditions, both noninductive and inductive melting-related charging of particles may cause a narrow intense positive-charge layer to form near the zero-temperature isotherm; the altitude at which the vertical velocity component changes sign with respect to the height of the zero-temperature isotherm is of particular importance. When consideration is taken for an inductive charging mechanism and the real structure of the rising flow’s velocity, the distributions of charges and field strength (with a peak of about 100 kV/m), which describe the profiles observed in experiments, form in about 30 min. Taking into account the polarization of melting aggregates and water drops in an electric field when aeroions attach to them causes the rate of generating electric-charge layers to reduce. Thus, the solutions obtained in this study describe the structure and dynamics of spatially separated regions of electric charges in the stratified region and offer a satisfactory explanation for the experimental data. The results are important for explaining the abnormally high lightning activity of mesoscale convective systems, their role in initiating charges in the middle atmosphere, and maintaining the quasi-stationary state of the global electric circuit.     

Numerical simulation of the action on a warm convective cloud by hygroscopic particles

A one-dimensional numerical model of a warm convective cloud is presented. This model is used to study the effectiveness of the action on the cloud by hygroscopic particles with the aim of intensifying precipitation. The numerical simulation takes into account the processes of condensation, coagulation, and sedimentation of cloud droplets and makes it possible to obtain spatiotemporal characteristics of cloud development. A system of differential equations describing time variations in the temperature, pressure, and watervapor supersaturation during the adiabatic rise of a continuous air flow is solved. The evolution of the size distribution of cloud droplets is described by a kinetic equation. A continuous acting source of droplets with the size distribution calculated with consideration for condensation properties and dispersion characteristics of condensation nuclei (natural and additionally introduced during the action) is specified at the cloud-base level. The cloud top is formed owing to the evaporation of droplets in the barrier atmospheric layer over the cloud. The influence of changes in the barrier-layer height on the structure of cloud parameters and precipitation-formation processes is analyzed. The introduction of additional hygroscopic particles into a cloud is shown to act as a trigger mechanism initiating the processes of coagulation and sedimentation in the cloud medium. In this case, a positive effect of action by fine particles can be achieved if a certain reserve of sufficiently large droplets is present in the cloud. The results of calculating the dependence of the action effect on the height of the barrier layer, restricting cloud development, are presented.     

The role of organic matter in the sorption capacity of marine sediments

Past studies have suggested that desiccation enhances hydrophobicity of salt marsh sediment, and that drying and rewetting sediment can be used to investigate sorption mechanisms of amino acids and other organic compounds [Liu, Z., Lee, C., 2006. Drying effects on sorption capacity of coastal sediment: The importance of architecture and polarity of organic matter. Geochim. Cosmochim. Acta 70, 3313–3324]. Here we further develop this technique to study sorption of hydrophobic and hydrophilic organic compounds in a wide range of marine sediments. Our results show that hydrophilic compounds sorb strongly to wet coastal sediments; in dried sediments, sorption of hydrophilic compounds decreases, while sorption of hydrophobic compounds is greatly enhanced. Small compounds with aromatic rings sorb more in dried than wet coastal sediments, suggesting that aromatic groups have a stronger effect on sorption than polar groups like amino and carboxyl moieties. Sorption of lysine, glutamic acid and putrescine decreases greatly when sediment is pretreated with KCl, indicating the importance of cation ion exchange. However, α-amino acids sorb much more than corresponding β- or γ-amino acids, and l-alanine sorbs more than d-alanine, suggesting that amino group location and chiral selectivity play an important role in sorption. Comparison of lysine and tyrosine sorption in different sediments indicates that source and diagenetic state of organic matter are important factors determining sorption capacity. Lysine sorbs much more to organic detritus from salt marsh sediment than to fresh Spartina root materials, marine particles, lignin or humic acids, indicating the importance of structural integrity in sorption. Desorption hysteresis of glutamic acid, putrescine and lysine (in dried sediment) suggests the presence of enzyme-type sorption sites of high sorption energy or multiple binding mechanisms. Taken together, these findings suggest that organic matter plays the major role in amino acid sorption in organic-rich sediments.     

Internal mechanism of metastable liquid water crystallization and its effects on intracloud processes

Specific features of an internal freezing (crystallization) mechanism for both ordinary supercooled water and amorphous water (A-water) are considered. Amorphous water plays the role of an intermediate phase in condensation ice formation and is capable of metastable existence in the form of cloud drops. It is demonstrated that, after passing the crystallization front, the ice phase takes the liquid-phase volume and the excessive water mass is detached from the front in the form of free molecules, which escape through the liquid into the gaseous medium. The released energy of the phase transition is removed with these molecules, so that the formed ice retains the initial temperature of the liquid. A high-rate vapor outflow from the freezing drop generates (around the drop) a zone of microscale turbulence, which accelerates the mass exchange between cloud particle and vapor. Since the freezing frequency of drops in a cloud increases with their size, the effects of their freezing develop initially in time. At the same time, these effects initiate such processes that end in a complete evaporation of supercooled water drops and in a sharp enlargement of A-water and ice particles, i.e., in cloud transition to such a phase-mixed state where the liquid disperse phase consists of A-water drops. A reduction in the duration of the initial (fine-dispersed) stage of the evolution of clouds with their temperature lowering can be explained only by the development of microscale disturbances as a result of the freezing of drops.     

Surface Oscillations of a Free-Falling Droplet of an Ideal Fluid

According to observations, drops freely falling in the air under the action of gravity are deformed and oscillate in a wide range of frequencies and scales. A technique for calculating surface axisymmetric oscillations of a deformed droplet in the linear approximation under the assumption that the amplitude and wavelength are small when compared to the droplet diameter is proposed. The basic form of an axisymmetric droplet is chosen from observations. The calculation results for surface oscillations agree with recorded data on the varying shape of water droplets falling in the air.     

The Kuroshio Extension System: Its Large-Scale Variability and Role in the Midlatitude Ocean-Atmosphere Interaction

The Kuroshio Extension and its recirculation gyre form an interconnected dynamic system. The system is located at a crossroads where the meso-scale and large-scale oceanic variability are highest, and where the ocean-atmosphere interaction is most active in the Pacific Ocean outside of the tropics. Following a brief review of the mean flow and meso-scale eddy variability, this study describes in detail the large-scale structural change (an oscillation between an elongated and a contracted state) observed in the Kuroshio Extension system. Causes for this structural change are explored next, and it is argued that the basin-wide external wind forcing and the nonlinear dynamics associated with the inertial recirculation gyre are both important factors. Data analysis results are reviewed and presented, emphasizing that the surface Kuroshio Extension is not simply a well-mixed layer passively responding to heat flux anomalies imposed by the atmosphere. It is argued that large-scale changes in the Kuroshio Extension system influence the surface ocean heat balance and generate wintertime sea surface temperature (SST) anomalies through both horizontal geostrophic heat advection and re-emergence to the surface mixed layer of sequestered mode water temperature anomalies. This revised version was published online in August 2006 with corrections to the Cover Date.     

微平面接触分离中弯月面力的计算

微平面间黏着力对微机电系统(MEMS)非常重要,常是决定其能量损耗乃至寿命长短的最主要因素.MEMS中的黏着力主要来源之一就是介于两互相接触平面间的弯月面力.弯月面力主要取决于相互接触的两平面间形成的弯月面形状.本文通过分析两微小平面在分离过程中弯月面形状的变化,得到在不同表面亲水/疏水性能、初始液面高度、分离距离等条件下的弯月面形状,计算得出在不同初始条件下断裂高度和弯月面力的数值以及随之变化的规律,为MEMS的性能分析和寿命计算提供依据.     

The role of organic coatings in the enrichment of marine particles with selenium. The fixation of selenite on an adsorbed amino acid

The enrichment of marine particles with selenium cannot be explained as that with metals present in cationic form by complexation with anionic functional groups of adsorbed organic matter. Physicochemical data obtained using a model system are reported. The surface of the particles is modelized by a mercury electrode whose surface charge density can be easily changed, covered by a layer of adsorbed polymers. Studies with different kinds of macromolecules and salts show a specific interaction between adsorbed polyalanine and selenite. The results can be explained by the concordance of the distances between two oxygen atoms in this oxyanion and between two amine groups of the adsorbed polypeptide. A similar mechanism could occur in marine aggregates whatever their nature, as long as they contain amine groups at their surface which result in this concordance. Some prospects derived from the results are discussed.     

Speciation of dissolved metals associated with organic matter in coastal seawaters

By combined use of chloroform extraction and Amberlite XAD-2 resin chromatography, metal-organic compounds dissolved in coastal seawaters of Harima Sound, the Seto Inland Sea, were separated into three groups: hydrophobic, hydrophilic neutral and basic, and hydrophilic acidic. The hydrophobic metal-organic compounds, which are associated with organic matter with molecular weight less than 300, accounted for only a small fraction of the metal-organic compounds; 6 % for Cu and an insignificant fraction for Fe, Mn and Zn. The hydrophilic metal-organic compounds with molecular weights between 100 and 1,500 were major components of the metal-organic compounds. The metals associated with the organic matter on average accounted for 12 % of the Fe, 11 % of the Mn, 7 % of the Zn and 23 % of the Cu of the reactive dissolved metals.     

粘土-MMH体系对赤潮生物的絮凝作用机制研究

根据粘土表面改性对其絮凝作用影响的理论模型,提出在粘土中引入ＭＭＨ（混合金属层状氢氧化物正电胶体）的改性方法,考察了ＭＭＨ浓度及ｐＨ值对絮凝作用的影响。结果表明,粘土中引和ＭＭＨ后,显著提高了对赤潮异弯藻（Ｈｅｔｅｒｏｓｉｇｍａａｋａｓｈｉｖｏ）和新月菱形藻（Ｎｉｔｚｃｈｉａｃｌｏｓｔｅｒｉｕｍ）的去除效率,二者的适宜配比为ＭＭＨ;粘土＝０．１ｇ：１ｇ,在此基础上,进一步研究了ＭＭＨ促进粘土絮凝作     

The chemical changes of DOM from black waters to coastal marine waters by HPLC combined with ultrahigh resolution mass spectrometry

How dissolved organic matter (DOM) undergoes chemical changes during its transit from river to ocean remains a challenge due to its complex structure. In this study, DOM along a river transect from black waters to marine waters is characterized using an offline combination of reversed-phase high performance liquid chromatography (RP-HPLC) coupled to electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS), as well as tandem ESI-FTICR-MS. In addition, a water extract from degraded wood that mainly consists of lignins is used for comparison to the DOM from this transect. The HPLC chromatograms of all DOM samples and the wood extract show two major well-separated components; one is hydrophilic and the other is hydrophobic, based on their elution order from the C₁₈ column. From the FTICR-MS analysis of the HPLC fractions, the hydrophilic components mainly contain low molecular weight compounds (less than 400 Da), while the hydrophobic fractions contain the vast majority of compounds of the bulk C₁₈ extracted DOM. The wood extract and the DOM samples from the transect of black waters to coastal marine waters show strikingly similar HPLC chromatograms, and the FTICR-MS analysis further indicates that a large fraction of molecular formulas from these samples are the same, existing as lignin-like compounds. Tandem mass spectrometry experiments show that several representative molecules from the lignin-like compounds have similar functional group losses and fragmentation patterns, consistent with modified lignin structural entities in the wood extract and these DOM samples. Taken together, these data suggest that lignin-derived compounds may survive the transit from the river to the coastal ocean and can accumulate there because of their refractory nature.