Showing papers on "Particle published in 2003"
TL;DR: In this paper, the free energy of formation of emulsion drops covered with close-packed monolayers of monodisperse spherical particles was investigated and the possibility of preparing novel solid materials by evaporating solid-stabilised emulsions is also proposed.
2,114 citations
TL;DR: In this article, the authors investigate the coupling between pairs of elliptical metal particles by simulations and experiments and demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling.
Abstract: The collaborative oscillation of conductive electrons in metal nanoparticles results in a surface plasmon resonance that makes them useful for various applications including biolabeling. We investigate the coupling between pairs of elliptical metal particles by simulations and experiments. The results demonstrate that the resonant wavelength peak of two interacting particles is red-shifted from that of a single particle because of near-field coupling. It is also found that the shift decays approximately exponentially with increasing particle spacing and become negligible when the gap between the two particles exceeds about 2.5 times the particle short-axis length.
1,492 citations
TL;DR: In this paper, a hypothesis for the bonding of particles in cold gas spraying, by making use of numerical modelling of the deformation during particle impact, is presented, with the results of modelling assessed with respect to the experimentally evaluated critical velocities, impact morphologies and strengths of coatings.
1,366 citations
TL;DR: In this paper, a detailed study of static and dynamic magnetic behavior of Fe3O4 nanoparticles with average particle sizes ranging from 5 to 150 nm is presented, and the existence of surface spin disorder can be inferred from the decrease of saturation magnetization MS at low temperatures, as the average particle size is reduced.
Abstract: We present a detailed study of static and dynamic magnetic behavior of Fe3O4 nanoparticles with average particle sizes 〈d〉 ranging from 5 to 150 nm. Bulk-like properties such as saturation magnetization, hyperfine parameters, coercive field, and Verwey transition are observed in 150 nm particles. For decreasing particle size, the Verwey temperature, TV, shifts down to ∼20 K for 〈d〉=50 nm and is no longer observable for smaller particles. The smallest particles (〈d〉=5 nm) display superparamagnetic behavior at room temperature, with transition to a blocked state at TB∼45 K, which depends on the applied field. The existence of surface spin disorder can be inferred from the decrease of saturation magnetization MS at low temperatures, as the average particle size is reduced. This disordered surface did not show effects of exchange coupling to the particle core, as observed from hysteresis loops after field cooling in a 7 T magnetic field. For particles with 〈d〉=5 nm, dynamic ac susceptibility measurements show...
1,265 citations
TL;DR: These controls of the size and shape of inorganic nanomaterials are discussed and it is shown that nanoparticles can be considered to be efficient nanoreactors.
Abstract: In the past decade, colloidal solutions have been assumed to be very efficient templates for controlling particle size and shape A large number of groups have used reverse micelles to control the size of spherical nanoparticles This makes it possible to determine the various parameters involved in such processes, and demonstrates that nanoparticles can be considered to be efficient nanoreactors However, some discrepancies arise There are few reports concerning the control of particle shape, and it is still rather difficult to determine the key parameters, such as the adsorption of salts and other molecules, and the synthesis procedure Here, we discuss these controls of the size and shape of inorganic nanomaterials
1,032 citations
TL;DR: In this article, the response of two different aethalometers (AE10 with white light and AE30 with multi-wavelength capability) to several types of soot was investigated, including diesel soot, spark-generated carbon particles, and mixtures of these soot particles with ammonium sulfate and oxidation products of �pinene.
991 citations
TL;DR: A photoinduced transformation is described in which nanoparticles, initially soluble only in toluene, were transported across an interface into water and were dispersed in the water phase, providing a direct probe of their spatial distribution.
Abstract: The self-assembly of particles at fluid interfaces, driven by the reduction in interfacial energy, is well established. However, for nanoscopic particles, thermal fluctuations compete with interfacial energy and give rise to a particle-size-dependent self-assembly. Ligand-stabilized nanoparticles assembled into three-dimensional constructs at fluid-fluid interfaces, where the properties unique to the nanoparticles were preserved. The small size of the nanoparticles led to a weak confinement of the nanoparticles at the fluid interface that opens avenues to size-selective particle assembly, two-dimensional phase behavior, and functionalization. Fluid interfaces afford a rapid approach to equilibrium and easy access to nanoparticles for subsequent modification. A photoinduced transformation is described in which nanoparticles, initially soluble only in toluene, were transported across an interface into water and were dispersed in the water phase. The characteristic fluorescence emission of the nanoparticles provided a direct probe of their spatial distribution.
935 citations
TL;DR: In this article, an apparently paradoxical behaviour of heat transfer deterioration was observed in nano-fluid and its dependence on parameters such as particle concentration, material of the particles and geometry of the containing cavity have been investigated.
Abstract: Fluids with nano size solid particles suspended in them have been given the name nano-fluid which in recent studies have shown tremendous promise as heat transfer fluids. However, before suggesting such fluids for applications a thorough knowledge of physical mechanism of heat transfer in such fluids is wanted. The present study deals with one such aspect of natural convection of nano fluids inside horizontal cylinder heated from one end and cooled from the other. An apparently paradoxical behaviour of heat transfer deterioration was observed in the experimental study. Nature of this deterioration and its dependence on parameters such as particle concentration, material of the particles and geometry of the containing cavity have been investigated. The fluid shows characters distinct from that of common slurries.
906 citations
TL;DR: The Aerodyne Aerosol Mass Spectrometer (AMS) as mentioned in this paper was designed to measure size-resolved mass distributions and total mass loadings of volatile and semivolatile chemical species in/on submicron particles.
Abstract: The Aerodyne Aerosol Mass Spectrometer (AMS) has been designed to measure size-resolved mass distributions and total mass loadings of volatile and semivolatile chemical species in/on submicron particles. This paper describes the application of this instrument to ambient aerosol sampling. The AMS uses an aerodynamic lens to focus the particles into a narrow beam, a roughened cartridge heater to vaporize them under high vacuum, and a quadrupole mass spectrometer to analyze the vaporized molecules. Particle size is measured via particle time-of-flight. The AMS is operated in two modes: (1) a continuous mass spectrum mode without size information; and (2) a size distribution measurement mode for selected m/z settings of the quadrupole. Single particles can also be detected and sized if they have enough mass of a chemical component. The AMS was deployed at a ground sampling site near downtown Atlanta during August 1999, as part of the Environmental Protection Agency/Southern Oxidant Study Particulate Matter “Supersite” experiment, and at a suburban location in the Boston area during September 1999. The major observed components of the aerosol at both sites were sulfate and organics with a minor fraction of nitrate, consistent with prior studies and colocated instruments. Different aerosol chemical components often had different size distributions and time evolutions. More than half of the sulfate mass was contained in 2% of the ambient particles in one of the sampling periods. Trends in mass concentrations of sulfate and nitrate measured with the AMS in Atlanta compare well with those measured with ion chromatography-based instruments. A marked diurnal cycle was observed for aerosol nitrate in Atlanta. A simple model fit is used to illustrate the integration of data from several chemical components measured by the AMS together with data from other particle instruments into a coherent representation of the ambient aerosol.
852 citations
TL;DR: In this paper, a series of new mesoporous silica materials with MCM-41 type of structure containing a homogeneous layer of organic functional groups inside the pores was prepared using a co-condensation method under low surfactant concentration condition.
Abstract: A series of new mesoporous silica materials with MCM-41 type of structure containing a homogeneous layer of organic functional groups inside the pores was prepared using a co-condensation method under low surfactant concentration condition. This reproducible synthetic approach resulted in high surface coverage with several functional groups such as a primary amine, secondary amine, urea, isocyanate, vinyl, and nitrile. In addition, the presence of organoalkoxysilane precursors during the base catalyzed condensation greatly influenced the final particle shape. By changing the precursor or its concentration, the particle morphology was tuned to various shapes, including spheres, tubes, and rods of various dimensions. The synthetic procedures that gave rise to the specific particle morphologies were investigated and the mechanism responsible for shape control was postulated. The structure and functionality of these materials were characterized by field-emission scanning electron microscopy, transmission elec...
749 citations
TL;DR: In this article, the movement and behaviour of particles suspended in aqueous solutions subjected to non-uniform ac electric fields is examined and the relative influence of each type of force is described.
Abstract: The movement and behaviour of particles suspended in aqueous solutions subjected to non-uniform ac electric fields is examined. The ac electric fields induce movement of polarizable particles, a phenomenon known as dielectrophoresis. The high strength electric fields that are often used in separation systems can give rise to fluid motion, which in turn results in a viscous drag on the particle. The electric field generates heat, leading to volume forces in the liquid. Gradients in conductivity and permittivity give rise to electrothermal forces and gradients in mass density to buoyancy. In addition, non-uniform ac electric fields produce forces on the induced charges in the diffuse double layer on the electrodes. This causes a steady fluid motion termed ac electro-osmosis. The effects of Brownian motion are also discussed in this context. The orders of magnitude of the various forces experienced by a particle in a model microelectrode system are estimated. The results are discussed in relation to experiments and the relative influence of each type of force is described.
Patent•
01 Apr 2003TL;DR: In this paper, the authors present a system for microfluidic manipulation and analysis of particles, such as cells, viruses, organelles, beads, and vesicles.
Abstract: The invention provides systems, including apparatus, methods, and kits, for the microfluidic manipulation and/or detection of particles, such as cells and/or beads. The invention provides systems, including apparatus, methods, and kits, for the microfluidic manipulation and/or analysis of particles, such as cells, viruses, organelles, beads, and/or vesicles. The invention also provides microfluidic mechanisms for carrying out these manipulations and analyses. These mechanisms may enable controlled input, movement/positioning, retention/localization, treatment, measurement, release, and/or output of particles. Furthermore, these mechanisms may be combined in any suitable order and/or employed for any suitable number of times within a system. Accordingly, these combinations may allow particles to be sorted, cultured, mixed, treated, and/or assayed, among others, as single particles, mixed groups of particles, arrays of particles, heterogeneous particle sets, and/or homogeneous particle sets, among others, in series and/or in parallel. In addition, these combinations may enable microfluidic systems to be reused. Furthermore, these combinations may allow the response of particles to treatment to be measured on a shorter time scale than was previously possible. Therefore, systems of the invention may allow a broad range of cell and particle assays, such as drug screens, cell characterizations, research studies, and/or clinical analyses, among others, to be scaled down to microfluidic size. Such scaled-down assays may use less sample and reagent, may be less labor intensive, and/or may be more informative than comparable macrofluidic assays.
TL;DR: In this paper, a twin screw extruder with a particle content of 0.07-1.9 µm and surface treatment of the particles (with and without stearic acid) on the toughening properties were studied.
TL;DR: It is found that in the most common experimental circumstances, using micron-sized polystyrene or silica beads, absorption of the laser light in the solvent around the trapped particle, not in the particle itself, is the most important contribution to heating.
TL;DR: In this article, the electrochemical reaction of lithium with crystallized -Fe2O3 (hematite) has been studied by means of in situ X-ray diffraction, and it is shown that a careful control of the texture/particle size of electrochemically active oxide particles is likely an important variable that has been largely disregarded for such properties.
Abstract: The electrochemical reaction of lithium with crystallized -Fe2O3 (hematite) has been studied by means of in situ X-ray diffraction. When reacting large particles (~0.5 µm), we observed the well-known transformation of the close-packed anionic array from hexagonal (hc) to cubic (ccp) stacking. At the early stage of the reduction, a very small amount of lithium (xc<0.1 Li/Fe2O3) can be inserted before this structural transformation occurs. Nanosize -Fe2O3 made of fine monolithic particles (200 A) behaves very different, since up to one Li per formula unit (-Li1Fe2O3,xc = 1) can be inserted in the corundum structure without phase transformation. To our knowledge, this is the first time this phase is maintained for such large xc values. This cationic insertion was found to come with a small cell volume expansion evaluated to 1%. Unsuccessful attempts to increase the xc values on large particles by decreasing the applied discharge current density suggest that the particle size is the only parameter involved. The better structural reversibility of this monophasic process compared to the biphasic one was confirmed by electrochemical cycling tests conducted with hematite samples of various particle sizes. Therefore, by using nanosize particles, we can drastically increase the critical Li concentration required to observe the hcccp transition. This work demonstrates that a careful control of the texture/particle size of electrochemically active oxide particles is likely an important variable that has been largely disregarded for such properties. ©2002 The Electrochemical Society. All rights reserved.
TL;DR: In this article, a three-phase model was developed to calculate the modulus of the nanocomposite as a function of various parameters, including the exfoliation ratio, clay layer and cluster aspect ratios, d-spacing, intragallery modulus, matrix modulus and matrix Poisson's ratio.
TL;DR: It was found that the intraparticle diffusion model could be used to well describe the adsorption of two basic dyes on modified peat-resin particle and the kinetics experiment indicated that initial dye concentrations, particle dose and particle size could affect the adsOrption processes ofbasic dyes.
TL;DR: In this article, a mixed solution of acetonitrile and water using various kinds of titanium dioxide (TiO 2 ) powders as photocatalysts and molecular oxygen as the electron acceptor was investigated.
Abstract: Photocatalytic oxidation of naphthalene was investigated in a mixed solution of acetonitrile and water using various kinds of titanium dioxide (TiO 2 ) powders as the photocatalysts and molecular oxygen as the electron acceptor. The main product from naphthalene is 2-formylcinnamaldehyde. For this reaction, anatase small TiO 2 particles, which are commonly used as photocatalyst, are inactive, probably because band bending is necessary for the oxidation of naphthalene. If the particles are not extremely small, pure rutile and pure anatase powders show fairly high activity, and those containing both anatase and rutile phases show the highest activity. When a pure anatase powder is partly (about 90%) converted to the rutile form by heat treatment, the activity is largely enhanced. The activity of pure rutile particles is also enhanced by physically mixing them with a small amount of small-sized anatase particles, which are inactive for this reaction. These results can be explained by the synergism between rutile and anatase particles. We consider that electrons are transferred from rutile particles to anatase particles, i.e. naphthalene is mainly oxidized on rutile particles and oxygen is mainly reduced on anatase particles. This electron transfer process is supported by electrochemical properties of TiO 2 electrodes for reduction of oxygen.
TL;DR: In this article, the authors studied oil-in-water emulsions stabilized by monodisperse, fluorescent silica colloids presenting either a smooth or a rough surface.
Abstract: We have studied oil-in-water emulsions stabilized by monodisperse, fluorescent silica colloids presenting either a smooth or a rough surface. The presence of the fluorescent core allows for direct visualization of the colloids on the surface of the emulsion droplets. Droplet interfacial tension, measured by micropipet tensiometry, is not modified by particle adsorption at the interface, suggesting a purely steric stabilization mechanism. Surface roughness is shown to considerably lessen the ability of particles to stabilize droplets. At variance with what is commonly assumed, no straightforward relation exists between the extent of particle interfacial adsorption and emulsion macroscopic stability; stable emulsions can be obtained even with very low droplet surface coverage. Finally, we directly monitor the Brownian motion of the adsorbed particles, showing that their surface diffusion coefficient is very close to the bulk value. Evidence of a possible role of particle surface dynamics on the stabilizatio...
TL;DR: The results indicate that the derivatised particles induce alterations in cell behaviour and morphology distinct from the plain particles, suggesting that cell response can be directed via specifically engineered particle surfaces.
TL;DR: The phenomenology is independent of the mixing type and of the droplet volume fraction allowing the fabrication of both direct and inverse emulsion with average droplet sizes ranging from micron to millimetre.
Abstract: We produce direct and inverse emulsions stabilized by solid mineral particles. If the total amount of particles is initially insufficient to fully cover the oil-water interfaces, the emulsion droplets coalesce such that the total interfacial area between oil and water is progressively reduced. Since it is likely that the particles are irreversibly adsorbed, the degree of surface coverage by them increases until coalescence is halted. We follow the rate of droplet coalescence from the initial fragmented state to the saturated situation. Unlike surfactant-stabilized emulsions, the coalescence frequency depends on time and particle concentration. Both the transient and final droplet size distributions are relatively narrow and we obtain a linear relation between the inverse average droplet diameter and the total amount of solid particles, with a slope that depends on the mixing intensity. The phenomenology is independent of the mixing type and of the droplet volume fraction allowing the fabrication of both direct and inverse emulsion with average droplet sizes ranging from micron to millimetre.
TL;DR: In this article, a nanometer-scale Au or Ag core is functionalized with Raman active molecules and encapsulated in a glass shell, and the scattering from the Raman tag is amplified through surface enhanced Raman scattering.
Abstract: Glass-coated, analyte-tagged nanoparticles (GANs) are core−shell particles where a nanometer-scale Au or Ag core is functionalized with Raman active molecules and encapsulated in a glass shell. The glass shell provides the particle with mechanical and chemical stability. Specifically, the glass coating renders the particle amenable to use in many solvents without altering the Raman spectral response and makes agglomeration a nonfactor. The density and thickness of the glass shell are controllable through synthetic conditions; thus, the rate of diffusion through the silica network can be tuned and the metal cores kept sequestered from any exterior reaction. This will allow for the attachment of biomolecules to the glass shell without altering the Raman response. GANs can be identified by the Raman spectrum of the attached Raman tag, and two differently labeled samples are unambiguously identified. The scattering from the Raman tag is amplified through surface-enhanced Raman scattering. The narrow bandwidth...
TL;DR: In ternary systems consisting of block copolymer and two different-sized nanocrystal species, the distinct morphological types are conserved, resulting in autonomous size-selective separation and organization of the respective nanocrystals within alternating arrays and sheets.
Abstract: Dependent on the relative particle core size, two distinct types of particle topologies in block copolymer/nanocrystal blends have been identified, that is, the localization of particles along the intermaterial dividing surface or at the center of the respective polymer domain. In ternary systems consisting of block copolymer and two different-sized nanocrystal species, the distinct morphological types are conserved, resulting in autonomous size-selective separation and organization of the respective nanocrystals within alternating arrays and sheets.
TL;DR: In situ linear dipolar structures in ferrofluids in zero field are shown, visualized on the particle level by electron cryo-microscopy on thin, vitrified films of organic dispersions of monodisperse metallic iron particles, showing that the experimental model used is well suited to study the structural properties of dipolar particle systems.
Abstract: A key issue in research on ferrofluids (dispersions of magnetic colloids) is the effect of dipolar interactions on their structure and phase behaviour1,2, which is not only important for practical applications3 but gives fundamental insight in dipolar fluids in general. In 1970, de Gennes and Pincus4 predicted a Van der Waals-like phase diagram and the presence of linear chains of particles in ferrofluids in zero magnetic field. Despite many experimental studies5,6,7, no direct evidence of the existence of linear chains of dipoles has been reported in the absence of magnetic field, although simulations8,9,10,11 clearly show the presence of chain-like structures. Here, we show in situ linear dipolar structures in ferrofluids in zero field, visualized on the particle level by electron cryo-microscopy on thin, vitrified films of organic dispersions of monodisperse metallic iron particles. On systematically increasing the particle size, we find an abrupt transition from separate particles to randomly oriented linear aggregates and branched chains or networks. When vitrified in a permanent magnetic field, these chains align and form thick elongated structures, indicating lateral attraction between parallel dipole chains. These findings show that the experimental model used is well suited to study the structural properties of dipolar particle systems.
TL;DR: In this paper, the cold-gas dynamic-spray process is analyzed by numerical modeling of the impact between a single spherical feed-powder particle and a semi-infinite substrate and the results obtained indicate that the two main factors contributing to the observed higher deposition efficiency in the case of copper deposition on aluminum are larger particle/substrate interfacial area and higher contact pressures.
TL;DR: The models and methods presented in this review are sufficiently general to be of use in a broad range of applications for biological dielectrophoresis and particle electrokinetics and may be extended further to the case of nonspherical particles, where alignment torques can be considered.
Abstract: This article presents a concise, unifying treatment of the electromechanics of small particles under the influence of electroquasistatic fields and offers a set of models useful in calculating electrical forces and torques on biological particles in the size range from /spl sim/1 to /spl sim/100 /spl mu/m. The theory is used to consider DEP trapping, electrorotation, traveling-wave induced motion, and orientational effects. The effective dipole method, and its generalization to effective multipoles, makes it possible to treat multilayered concentric shells and particles exhibiting ohmic and dielectric loss. This method may be extended further to the case of nonspherical particles, where alignment torques can be considered. These capabilities are well suited to modeling DEP behavior of biological particles including cells. The models and methods presented in this review are sufficiently general to be of use in a broad range of applications for biological dielectrophoresis and particle electrokinetics. The range of validity can be stated confidently to cover particles having diameters approximately 1/spl mu/m and larger.
TL;DR: A nanoparticle system that undergoes structural changes in response to changes in the surface environment rather than particle size is described, implying that the structure and reactivity of nanoparticles at planetary surfaces, in interplanetary dust and in the biosphere, will depend on both particle size and the nature of the surrounding molecules.
Abstract: The thermodynamic behaviour of small particles differs from that of the bulk material by the free energy term γA—the product of the surface (or interfacial) free energy and the surface (or interfacial) area. When the surfaces of polymorphs of the same material possess different interfacial free energies, a change in phase stability can occur with decreasing particle size1,2. Here we describe a nanoparticle system that undergoes structural changes in response to changes in the surface environment rather than particle size. ZnS nanoparticles (average diameter 3 nm) were synthesized in methanol and found to exhibit a reversible structural transformation accompanying methanol desorption, indicating that the particles readily adopt minimum energy structural configurations3,4. The binding of water to the as-formed particles at room temperature leads to a dramatic structural modification, significantly reducing distortions of the surface and interior to generate a structure close to that of sphalerite (tetrahedrally coordinated cubic ZnS). These findings suggest a route for post-synthesis control of nanoparticle structure and the potential use of the nanoparticle structural state as an environmental sensor. Furthermore, the results imply that the structure and reactivity of nanoparticles at planetary surfaces, in interplanetary dust5 and in the biosphere6,7, will depend on both particle size and the nature of the surrounding molecules.
01 Jan 2003
TL;DR: In this paper, the size and shape effects in surface plasmon resonance have been studied and a growth mechanism was proposed for Ag particle growth from adsorbed Ag silver ions in the presence of citrate.
Abstract: The photoreduction of silver ions by citrate, catalyzed on silver seeds, is used to synthesize disk-shaped silver nanoparticles in solution. The reaction is characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), optical absorption spectroscopy, and by measuring the silver ion concentration during the reaction. The irradiation wavelength determines the final shape of these particles due to the shape dependence of the Ag plasmon spectrum. The quantum yield of this reaction has been calculated, and a growth mechanism is outlined. Introduction. Silver particles provide an ideal system for study of size and shape effects in the surface plasmon resonance; indeed, this sensitivity is a tool to monitor the shape of the particles during their synthesis via the optical extinction spectrum. Plasmon resonances concentrate an incident electromagnetic field via near-field enhancement; this antenna effect is the source of surface enhanced Raman scattering (SERS). The intense Ag resonance allows single molecule observation in SERS, 1-5 enables coupled Ag particles to form a subwavelength waveguide, 6 and enables sensitive colorimetric DNA screening. 7,8 Henglein 9,10 has shown that the physical and chemical properties of finely divided, nm-sized Ag particles are strongly modified by the adsorption of nucleophilic species and that Ag particles catalyze thermal and optical electro- chemical reactions. For example, core/shell metallic particles can be grown. 11 Indeed, adsorption of chemical species modifies the Fermi level of both the metal and the reactant, like a polarized nanoelectrode. Combining these effects, we now report controlled pho- tochemical Ag particle growth from adsorbed Ag silver ions in the presence of citrate. If different shapes and sizes are present in a seed colloid, the particle with the largest plasmon absorption cross-section at the laser wavelength initially grows fastest. The reaction accelerates for those shapes whose plasmons move into resonance with the photochemical wavelength as growth occurs. This effect allows control of shape in the dominant photoproduct by choice of photo- chemical wavelength. There have been previous observations of reduced silver formation by irradiation of citrate and Ag ion, however, without control of shape or size. 12,13
TL;DR: In this article, the authors revised the microemulsion technique with special emphasis in the mechanisms of control of particle size, namely the proper microemulsions and the control by the surfactant adsorption (capping).
Abstract: The evolution of the microemulsion technique in the last years is revised with special emphasis in the mechanisms of control of particle size, namely the control by the proper microemulsions and the control by the surfactant adsorption (capping). The kinetics of the particle formation; the possibility of the preparation of coatings, core-shell and ‘onion-like’ structures with a very precise size control; the use of microemulsions to produce fine ceramics and finally their use in the preparation of superlattices is addressed.
TL;DR: In this article, individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging.
Abstract: [1] Individual aerosol particles in smoke plumes from biomass fires and in regional hazes in southern Africa were studied using analytical transmission electron microscopy (TEM), which allowed detailed characterization of carbonaceous particle types in smoke and determination of changes in particle properties and concentrations during smoke aging. Based on composition, morphology, and microstructure, three distinct types of carbonaceous particles were present in the smoke: organic particles with inorganic (K-salt) inclusions, ‘‘tar ball’’ particles, and soot. The relative number concentrations of organic particles were largest in young smoke, whereas tar balls were dominant in a slightly aged (1 hour) smoke from a smoldering fire. Flaming fires emitted relatively more soot particles than smoldering fires, but soot was a minor constituent of all studied plumes. Further aging caused the accumulation of sulfate on organic and soot particles, as indicated by the large number of internally mixed organic/sulfate and soot/sulfate particles in the regional haze. Externally mixed ammonium sulfate particles dominated in the boundary layer hazes, whereas organic/sulfate particles were the most abundant type in the upper hazes. Apparently, elevated haze layers were more strongly affected by biomass smoke than those within the boundary layer. Based on size distributions and the observed patterns of internal mixing, we hypothesize that organic and soot particles are the cloudnucleating constituents of biomass smoke aerosols. Sea-salt particles dominated in the samples taken in stratus clouds over the Atlantic Ocean, off the coast of Namibia, whereas a distinct haze layer above the clouds consisted of aged biomass smoke particles. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; KEYWORDS: biomass burning, carbonaceous aerosol, individual particles, TEM