Small Dust Particles Research Articles

Method for computing the coefficient of particle capture by a drop moving in a dust-laden gas

A method for calculating the coefficient of capture of small (dust) particles by a drop that allows one to take into account the influence of the surface tension and the hydrodynamic resistance of a particle being immersed in a drop is proposed. The dependence of the critical particle velocity necessary to overcome the surface tension forces and the pressure resistance on the governing parameters is found. The existence of a critical Stokes number limiting the region of particle capture is demonstrated. The calculated dependences of the coefficient of capture on the Stokes number are compared with the experimental data. It is found that in comparison with the conventional method, the relation obtained using the proposed method is in better agreement with the experimental data.

Dust Storm Fallout: Tiniest Travelers Pose Greatest Infection Threat

Vol. 116, No. 3 EnvironewsOpen AccessDust Storm Fallout: Tiniest Travelers Pose Greatest Infection Threat Angela Spivey Angela Spivey Search for more papers by this author Published:1 March 2008https://doi.org/10.1289/ehp.116-a128bAboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Dust isn’t just a nuisance—its ability to clog human airways and carry pathogens poses a human health problem. In the sub-Saharan region of Africa, the World Health Organization pinpointed dust storms exacerbated by the dry season and drought as a cause of outbreaks of meningococcal meningitis. Dust from Saharan storms can reach as far away as Florida, with particles smaller than 2.5 μm traveling the greatest distances. Studies have shown that human exposure to these tiny particles is associated with human mortality, and new research now shows that such particles are also more likely to carry health-threatening bacteria [EHP 116:292–296; Polymenakou et al.].During a strong Saharan dust storm in 2006, researchers collected air samples in Heraklion, Crete, an area that often feels the effects of such storms. Particles from the samples were separated according to size (> 7.9 μm, 3.3–7.9 μm, 1.6–3.3 μm, 1.0–1.6 μm, 0.55–1.0 μm, or <0.55 μm) using a machine called a high-volume cascade impactor. The researchers characterized the bacteria traveling on particles of various sizes by taking samples from the machine’s filters, then cloning and sequencing a strand of DNA commonly used to identify bacteria. This process created an inventory of the bacterial gene sequences present in each of the six particle-size ranges. The creation of large clone libraries allows investigators to detect bacteria that are missed using culture methods, as some bacteria are difficult to grow.The researchers identified clones that were genetically related to pathogens linked to human diseases such as pneumonia, meningitis, and bacteremia, or to pathogens suspected of inducing infections such as endocarditis. Of the sequenced clones related to bacteria that are dangerous to humans, almost half (43%) were found at particle sizes less than 3.3 μm. Spore-forming bacteria such as Firmicutes dominated the particle sizes larger than 3.3 μm. Most of these bacteria are nonpathogenic.The authors conclude that the prevalence of breathable bacteria on small dust particles may pose a significant, widespread health risk to humans, given that dust, especially the smallest particles, is known to travel across continents. To determine just how much of a threat these tiny travelers pose, long-term studies are needed to further investigate how pathogens are distributed across dust particle size, and the distances these pathogens can travel and still survive.The dust storm that provided samples for Polymenakou et al. obscures the eastern Mediterranean Sea, 25 February 2006FiguresReferencesRelatedDetails Vol. 116, No. 3 March 2008Metrics About Article Metrics Publication History Originally published1 March 2008Published in print1 March 2008 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Warm Dust in the Terrestrial Planet Zone of a Sun‐like Pleiades Star: Collisions between Planetary Embryos?

Only a few solar-type main-sequence stars are known to be orbited by warm dust particles; the most extreme is the G0 field star BD +20 307 that emits ~4% of its energy at mid-infrared wavelengths. We report the identification of a similarly dusty star HD 23514, an F6-type member of the Pleiades. A strong mid-IR silicate emission feature indicates the presence of small warm dust particles, but with the primary flux density peak at the nonstandard wavelength of ~9 μm. The existence of so much dust within an AU or so of these stars is not easily accounted for given the very brief lifetime in orbit of small particles. The apparent absence of very hot (≳1000 K) dust at both stars suggests the possible presence of a planet closer to the stars than the dust. The observed frequency of the BD +20 307/HD 23514 phenomenon indicates that the mass equivalent of Earth's Moon must be converted, via collisions of massive bodies, to tiny dust particles that find their way to the terrestrial planet zone during the first few hundred million years of the life of many (most?) Sun-like stars. Identification of these two dusty systems among youthful nearby solar-type stars suggests that terrestrial planet formation is common.

First observation of the overshoot effect for polar mesosphere winter echoes during radiowave electron temperature modulation

Polar mesosphere winter echoes (PMWE), observed with the EISCAT VHF radar located near Tromsø, Norway on October 24, 2006, were modulated using the EISCAT Heating facility. The heater was turned on for 20 s and then off for 160 s. The experiment confirmed previous results that when the heater was switched on, the PMWE power dropped significantly compared to the undisturbed level measured before heating. The experiment showed for the first time that, after the heater was switched off, the PMWE strength overshot the value that it had before heating. By using data from 6 heating cycles we find that the overshoot effect is about 50% of the pre‐heating value, which is rather weak compared to 3–5 times for PMSE. No, or little recovery of PMWE strength during heating periods was observed. This may indicate the presence of very small dust particles, such as meteoric smoke particles.

Effect of collisions on dust particle charging via particle-in-cell Monte-Carlo collision

In this paper, the effect of collisions on the charging and shielding of a single dust particle immersed in an infinite plasma is studied. A Monte-Carlo collision (MCC) algorithm is implemented in the particle-in-cell DEMOCRITUS code to account for the collisional phenomena which are typical of dusty plasmas in plasma processing, namely, electron-neutral elastic scattering, ion-neutral elastic scattering, and ion-neutral charge exchange. Both small and large dust particle radii, as compared to the characteristic Debye lengths, are considered. The trends of the steady-state dust particle potential at increasing collisionality are presented and discussed. The ions and electron energy distributions at various locations and at increasing collisionality in the case of large particle radius are shown and compared to their local Maxwellians. The ion-neutral charge-exchange collision is found to be by far the most important collisional phenomenon. For small particle radius, collisional effects are found to be important also at low level of collisionality, as more ions are collected by the dust particle due to the destruction of trapped ion orbits. For large particle radius, the major collisional effect is observed to take place in proximity of the presheath. Finally, the species energy distribution functions are found to approach their local Maxwellians at increasing collisionality.

Analysis of the emission of very small dust particles from Spitzer spectro-imagery data using blind signal separation methods

This work was conducted as part of the SPECPDR program, dedicated to the study of very small particles and astrochemistry, in Photo-Dissociation Regions (PDRs). We present the analysis of the mid-IR spectro-imagery observations of Ced 201, NCG 7023 East and North-West and rho-Ophiuchi West filament. Using the data from all four modules of the InfraRed Spectrograph onboard the Spitzer Space Telescope, we produced a spectral cube ranging from 5 to 35 um for each one of the observed PDRs. The resulting cubes were analysed using Blind Signal Separation methods (NMF and FastICA). For Ced 201, rho-Ophiuchi West filament and NGC 7023 East, we find that two signals can be extracted from the original data cubes, which are 5 to 35 um spectra. The main features of the first spectrum are a strong continuum emission at long wavelengths, and a broad 7.8 um band. On the contrary, the second spectrum exhibits the classical Aromatic Infrared Bands (AIBs) and no continuum. The reconstructed spatial distribution maps show that the latter spectrum is mainly present at the cloud surface, close to the star whereas the first one is located slightly deeper inside the PDR. The study of the spectral energy distribution of Ced 201 up to 100 um suggests that, in cool PDRs, the 5-25 um continuum is carried by Very Small Grains (VSGs). The AIB spectra in the observed objects can be interpreted as the contribution of neutral and positively-charged Polycyclic Aromatic Hydrocarbons (PAHs). We extracted the 5 to 25 um emission spectrum of VSGs in cool PDRs, these grains being most likely carbonaceous. We show that the variations of the mid-IR (5-35 um) spectra of PDRs can be explained by the photo-chemical processing of these VSGs and PAHs, VSGs being the progenitors of free PAH.

Monte Carlo studies of surface chemistry and nonthermal desorption involving interstellar grains.

Although still poorly understood, the chemistry that occurs on the surfaces of interstellar dust particles profoundly affects the growth of molecules in the interstellar medium. The most important surface reaction is the conversion of atomic to molecular hydrogen, which is a precursor for all subsequent molecular development and which occurs both in diffuse and dense interstellar clouds. Another set of surface reactions produces icy mantles of many monolayers in cold and dense regions of the interstellar medium. The monolayers are dominated by water ice but also contain CO, CO(2), and occasionally methanol. In this work, we first review both our stochastic approach to the surface chemistry that can occur on small dust particles and how it has been applied to the problem of the formation of molecular hydrogen. This latter problem is strongly affected by the pulsed heating of smaller grains by photons. Photons are not the only source of pulsed heating; cosmic rays also can heat interstellar grains in a pulsed manner. Here, we calculate the heating by cosmic rays for different grain sizes and cosmic ray components. It is then shown that this mechanism is an important one for desorption of ice mantles.

Mapping and Mass Measurement of the Cold Dust in NGC 205 withSpitzer

We present observations at 3.6, 4.5, 5.8, 8, 24, 70 & 160um of NGC 205, the dwarf elliptical companion of M31, obtained with the Spitzer Space Telescope. The point sources subtracted images at 8 and 24um display a complex and fragmented infrared emission coming from both very small dust particles and larger grains. The extended dust emission is spatially concentrated in three main emission regions, seen at all wavelengths from 8 to 160um. These regions lie approximately along NGC 205's semi-major axis and range from ~100 to 300 pc in size. Based on our mid-to-far infrared flux density measurements alone, we derive a total dust mass estimate of the order of 3.2e4 solar masses, mainly at a temperature of ~20K. The gas mass associated with this component matches the predicted mass returned by the dying stars from the last burst of star formation in NGC 205 (~0.5 Gyr ago). Analysis of the Spitzer data combined with previous 1.1mm observations over a small central region or Core'' (18 diameter), suggest the presence of very cold (~12K) dust and a dust mass about sixteen times higher than is estimated from the Spitzer measurements alone. Assuming a gas to dust mass ratio of 100, these two datasets, i.e.with and without the millimeter observations, suggest a total gas mass range of 3.2e6 to 5e7 solar masses.

Dust evolution in the star forming turbulent interstellar medium

AbstractUnderstanding interstellar dust evolution is a major challenge underlying the interpretation of Spitzer observations of interstellar clouds, star forming regions and galaxies. I illustrate on-going work along two directions. I outline the potential impact of interstellar turbulence on the abundance of small dust particles in the diffuse interstellar medium and translucent sections of molecular clouds. I present results from an analysis of ISO and Spitzer observations of the central part of 30 Doradus, looking for dust evolution related to the radiative and dynamical impact of the R136 super star cluster on its parent molecular cloud.

Temperature-influenced dynamics of small dust particles

The motion of spherical dust particles under the action of gravity, electromagnetic radiation force and Lorentz force (LF) is studied theoretically for materials with temperature-dependent dielectric functions in the visible (VIS) spectral range. Even a weak variation of the optical constants with heliocentric distance may influence predominately a long-term dynamical behaviour of submicron-sized and small micron-sized dust grains. It is shown that the lifetime of carbonaceous or Si particles may change by several tens of per cent because of the temperature dependence of particle refractive indices. The orbital inclination is the most evident difference between the evolution of a dust particle with temperature-dependent optical properties and one without. While carbonaceous 2-μm-sized particles with optical constants independent of temperature may evolve in orbits with inclinations greater than an initial value, grains of the same size with variable refractive indices will be spread along orbits characterized with inclinations lower than the initial one. Here the temperature works as a separation factor for particles having slightly different temperature dependences of the optical constants.

Dust settling in local simulations of turbulent protoplanetary disks

Aims. In this paper, we study the effect of MHD turbulence on the dynamics of dust particles in protoplanetary disks. We vary the size of the particles and relate the dust evolution to the turbulent velocity fluctuations. Methods. We performed numerical simulations using two Eulerian MHD codes, both based on finite difference techniques: ZEUS-3D and NIRVANA. These were local shearing box simulations incorporating vertical stratification. Both ideal and non ideal MHD simulations with midplane dead zones were carried out. The codes were extended to incorporate different models for the dust as an additional fluid component. Good agreement between results obtained using the different approaches was obtained. Results. The simulations show that a thin layer of very small dust particles is diffusively spread over the full vertical extent of the disk. We show that a simple description obtained using the diffusion equation with a diffusion coefficient simply expressed in terms of the velocity correlations accurately matches the results. Dust settling starts to become apparent for particle sizes of the order of 1 to 10 centimeters for which the gas begins to decouple in a standard solar nebula model at 5.2 AU. However, for particles which are 10 centimeters in size, complete settling toward a very thin midplane layer is prevented by turbulent motions within the disk, even in the presence of a midplane dead zone of significant size. Conclusions. These results indicate that, when present, MHD turbulence affects dust dynamics in protoplanetary disks. We find that the evolution and settling of the dust can be accurately modelled using an advection diffusion equation that incorporates vertical settling. The value of the diffusion coefficient can be calculated from the turbulent velocity field when that is known for a time of several local orbits.

Perihelion motion of small irregular dust particles due to radiation forces

Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Klačka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1–61]: (i) perihelion motion is of the order v ⇒ 2 / c 2 ( v ⇒ is heliocentric velocity of the meteoroid and c is the speed of light in vacuum), if a component of electromagnetic radiation acceleration is considered as a part of central acceleration; (ii) perihelion motion is of the first order in v ⇒ / c if the total electromagnetic radiation force is considered as a disturbing force. The new facts presented in this paper concern irregular dust particles. Detailed numerical calculations were performed for the grains ejected at aphelion of comet Encke. Perihelion motion for irregular interplanetary dust particles exists already in the first order in v ⇒ / c for both cases of central accelerations. Moreover, perihelion motion of irregular particles exhibits both positive and negative directions during the particle orbital motion. Irregularity of the grains causes not only perihelion motion, but also dispersion of the dust in various directions, also normal to the orbital plane of the parent body.

Microwave Emission from Spinning Dust in Circumstellar Disks

In the high-density environments of circumstellar disks dust grains are expected to grow to large sizes by coagulation. Somewhat unexpectedly, recent near-IR observations of PAH features from disks around Herbig Ae/Be stars demonstrate that a substantial amount of dust mass in the surface layers of these disks (up to several tens of percent of the local carbon content) can be locked up in small nanometer-sized particles. We investigate the possibility of detecting the electric dipole emission produced by these nanoparticles (sizes ~1 nm) as they spin at thermal rates (tens of GHz) in cold gas. We show that such emission peaks in the microwave range and dominates over the thermal disk emission at ν 50 GHz typically by a factor of several if 5% of the total carbon abundance is locked up in nanoparticles. We test the sensitivity of this prediction to various stellar and disk parameters and show that if the potential contamination of the spinning dust component by the free-free and/or synchrotron emission can be removed, then the best chances of detecting this emission would be in disks with small opacities, having SEDs with steep submillimeter slopes (which minimize thermal disk emission at GHz frequencies). Detection of the spinning dust emission would provide important evidence for the existence, properties, and origin of the population of small dust particles in protoplanetary disks, with possible ramifications for planet formation.

Properties of Dust Particles Sampled from Windboxes of an Iron Ore Sintering Plant: Surface Structures of Unburned Carbon

Aiming to understand the formation mechanism of dioxins in the iron ore sintering process, dust samples obtained from some windboxes of a commercial iron ore sintering plant have been characterized with a powder X-ray diffraction (XRD), by the transmission electron microscope (TEM) equipped with an electron energy loss spectroscopy (EELS), and by the temperature-programmed desorption (TPD) and temperature- programmed oxidation (TPO) techniques. The elemental and XRD analyses reveal that the content of the Cl present in the samples ranges from 0.075 mass%-dry to 5.1 mass%-dry and tends to be higher at smaller dust particles, and that some of the Cl exists as KCl with the average crystalline size between 40 nm and 50 nm. Dust samples also contain a significant amount of unburned carbon, and the smallest dust particles, <500 μm, show the highest C contents in many cases and consist partly of C, K, and Cl elements. The TPD and TPO experiments exhibit that the dust samples have several types of oxygen functional forms on the carbon surface, and the proportion of carboxyl and lactone/acid anhydride groups, which can be partly decomposed into CO2 and carbon active sites at 150 to 500°C, tends to be larger at smaller dust particles. On the basis of the above results, the formation mechanism of chlorinated organic compounds including dioxins is discussed in term of interactions among HCl (and/or Cl2), metallic chlorides, and carbon active sites.

Collection of Small Dust Particles with Electrified Packed Bed

Collection of Small Dust Particles with Electrified Packed Bed

Concentration and sorting of chondrules and CAIs in the late Solar Nebula

The high concentration and sorting of chondrules, sub-mm sized spherules found in undifferentiated meteorites, is one of the great unsolved mysteries in planetology. Here we present a unifying explanation for these phenomena based on the assumption that chondrules were present when the Solar Nebula was optically thin but had a significant amount of gas. An immediate consequence is that chondrules feel a force known as photophoresis. Photophoresis is based on a temperature gradient over the surface of a particle resulting from absorption of radiation and non-uniform interaction with its gaseous environment. In comparison to well-known forces originating from starlight, i.e. radiation pressure, Poynting–Robertson drag, or the Yarkovski effect, photophoresis can be stronger by many orders of magnitude in gaseous environments. In the application discussed here photophoresis concentrates chondrules and CAIs, which are both found in chondrites, in the region of the asteroid belt. Chondrules from any place in the Solar Nebula will be dragged to the asteroid belt region, while smaller dust particles and their aggregates will be removed from this region at the same time. This leads to a high relative concentration of chondrules, sorted with respect to their thermal conductivity, density, and size, for building chondrite parent bodies. Furthermore, photophoresis prevents CAIs from being lost to the Sun.

Removing Interfering Contaminations from Gelatin Lifters

Gelatin lifter is widely used for recovering shoeprints from crime scenes. Dusty shoeprints removed from paper with loose fibers, cloth or plasterboard, might be concealed by the detached fibers. A novel technique to clean the gelatin lifter from the interfering contaminations, using adhesive lifters, was developed. The adhesive lifter is applied directly on the surface of the gelatin lifter, and is removed instantly. The adhesive lifter removes the upper layer of the attached material on the gelatin lifter. After removing the concealing material from the hidden imprint, the quality of the visualized imprint is improved. The cleaning process can be applied as many times as needed and the optimum number is different for each substrate. The small dust particles comprising the shoeprint remained attached to the sticky side of the gelatin lifter even though the adhesion force applied by the adhesive lifter is great. Repeating the procedure too many times could harm the quality of the print severely, yet the advantages of this method are greater than the risks of relocation of image quality reduction.

Spitzer Space TelescopeObservations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

Fluxes and upper limits in the wavelength range from 3.6 to 70 μm from the Spitzer Space Telescope are provided for 20 solar-mass Pleiades members. One of these stars shows a probable mid-IR excess, and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS (Multiband Imaging Photometer for Spitzer) wavelengths, HII 1101, we derive log(Ldust/L*) ∼ -3.8 and an estimated debris disk mass of 4.2 × 10-5 M for an assumed uniform dust grain size of 10 μm. If the stars with detected excesses are interpreted as stars with relatively recent, large collisional events producing a transient excess of small dust particles, the frequency of such disk transients is ∼10% for our ∼100 Myr, Pleiades G dwarf sample. For the stars without detected 24–70 μm excesses, the upper limits to their fluxes correspond to approximate 3 σ upper limits to their disk masses of 6 × 10-6 M using the MIPS 24 μm upper limit or 2 × 10-4 M using the MIPS 70 μm limit. These upper limit disk masses (for "warm" and "cold" dust, respectively) are roughly consistent with, but somewhat lower than, predictions of a heuristic model for the evolution of an "average" solar-mass star's debris disk based on extrapolation backward in time from current properties of the Sun's Kuiper Belt.

A cold globule with a Class 0/I embedded source

Infrared observations of the dark cloud DC 303.8-14.2 and the embedded point source IRAS 13036-7644 have been made with the ISOPHOT instrument aboard ISO at 7.7 μm, 60 μm, 100 μm and 200 μm. We have compared the properties of dust in DC 303.8-14.2 and the Thumbprint Nebula (TPN), a morphologically similar globule but without star formation. The dust temperature at the center of DC 303.8-14.2 has a minimum of 14.6 ± 1 K, similar to that in the TPN. A comparison of far-infrared radial optical depth distributions between these clouds at angular scales of ∼1.5'-3' shows no difference. The observations suggest that there is a bright rim of 7,7 μm emission that peaks just outside the,optical bright rim of the cloud, indicating a halo of very small dust particles or PAHs around the cloud. The bolometric luminosity of the IRAS source is estimated to be about 1.0 L ○. . The heating of the cloud by the IRAS source is negligible; the thermal structure of the cloud is dominated by external heating. We have studied the evolutionary status of the IRAS source and find it to be located between Class 0 and Class I, at a late accretion phase. The source was detected at 7.7 μm and we suggest that this emission is due to the 7.7 μm UIR band. We also give a compilation of small molecular clouds whose extended FIR emission has been mapped with ISO.

Possible method for diagnosing waves in dusty plasmas with magnetized charged dust particulates

We discuss theoretically a possible method for diagnosing some features of dust wave behavior in a magnetized plasma containing small (tens of nm) charged dust grains whose motion is magnetized. It is easier to magnetize a small dust particle because its charge-to-mass ratio increases as its size decreases. However, it is more difficult to use the backscattering of light from the dust as a diagnostic as the dust size decreases below the diffraction limit. The idea proposed here is to measure the reduction in transmitted UV or optical light intensity due to enhanced extinction by small metal dust particles that have surface plasmon resonances at those wavelengths. Such measurements could indicate the spatial location of the dust density compressions or rarefactions, which may yield information on the dust wave behavior, or perhaps even charged dust transport. Parameters that may be relevant to possible laboratory dusty plasma experiments are discussed.