Suspended Dust Particles Research Articles

The Global Transport of Dust

dirt is carried aloft. Drifting with the sus pended dust particles are soil pollutants such as herbicides and pesticides and a significant number of microorganisms? bacteria, viruses and fungi. We can gain some appreciation of how much micro bial life is actually floating in our atmos phere by perfonning a quick calculation. There are typically about one million bacteria per gram of soil, but lef s be con servative and suppose there are only 10,000 bacteria per gram of airborne sed iment. Assuming a modest one billion metric tons of sediment in the atmos phere, these numbers translate into a quintillion (1018) sediment-borne bacte ria moving around the planet each year?enough to form a microbial bridge between Earth and Jupiter.

Critical Conditions of Spark Ignition of a Mixture of Gases (Oxidizer and Fuel) and Reactive Particles

The problem of spark ignition of a gas suspension including a fuel, an oxidizer, and reactive particles is considered using a two-temperature thermodiffusion model of combustion. Dependences of the minimum ignition energy on disperse-phase parameters are obtained. It is shown that the presence of exothermically reacting disperse-phase particles has an ambiguous effect on the minimum spark energy leading to ignition of the gas suspension. The values of the lower and upper concentration limits for ignition of a methane–air mixture with suspended coal dust particles are in good agreement with experimental data. Key words: hybrid gas suspension, spark ignition, critical conditions, concentration limits.

Spectral Content of Solar Radiation on Martian Surface Based on Mars Pathfinder

Photovoltaicarrayswereused successfully to power thevarious instrumentsfortheMars Pathe nder.To identify the type of the solar cell most suitable for Mars surface missions in the future, the spectral content of Mars’ s solar radiation must e rst be determined. The response of photovoltaic cells depends on the solar cell type and the wavelengths of the incident light. The suspended dust particles of Mars’ s atmosphere affect the intensity and spectralcontent of the solarradiation reaching theplanet’ s surface. ThePathe nderemployed fourbandpasse lters formeasuring theatmosphericoptical depth during the courseof themission that lasted for about80 sols (Martian days). Thecentral wavelengths of thesee lterswere 450, 670, 883, and 989 nm. This paper deals with theanalysis of theopticaldepthoftheMartian atmospherebased ontheMarsPathe ndermeasurementsand includes1 ) variation of the monochromatic optical depth with the time of the day, 2 ) variation of the monochromatic optical depth with sol for the duration of the mission, 3 ) variation of the optical depth with wavelength, 4 ) transmittance of the direct beam with wavelength, and 5 ) solar cell response on the Martian surface of the direct beam irradiance.

The charged dust in processing plasma sheath

For small and dense dusts, using the fluid model, the distribution and suspension of dust particles under the action of electrostatic, gravitational and ion-drag forces are investigated in the plasma sheath. It is shown that competition among the forces results in spatial oscillations of the particle distribution. However, for large and rare dusts using the isolated particle model the suspension of the particles is studied under the action of forces mentioned above. It is shown that particle traps can exist only for negatively charged particles and the size of trapped particles is of upper and lower critical values. In addition, the effects of the rate of density between dust and ion, the beam electrons emitted from the electrode, and the ion loss charging to the dusts on the dust distribution and the dust charge is discussed.

Airborne bacteria and fungal spores in the indoor environment. A case study in Singapore

AbstractThe concentration of airborne fungal spores and bacteria as related to room temperature, humidity and occupancy levels within a library building in Singapore was determined. Measurement of indoor air quality with respect to microorganisms is of particular importance in tropical environments due to the extensive use of air‐conditioning systems and the potential implications for human health. This study has revealed a number of interesting relationships between the concentrations of fungal spores and bacteria in relation to both environmental and human factors. The levels of fungal spores measured in the indoor environment were approximately fifty times lower than those measured outside, probably because of the lowered humidity caused by air‐conditioning in the indoor environment. The variation in fungal spore concentration in the outdoor environment is likely to be due to the diurnal periodicity of spore release and the response to environmental factors such as light temperature and humidity. The indoor concentration of fungal spores in air was not clearly correlated to concentrations measured in air outside of the library building and remained relatively constant, unaffected by the difference in the numbers of occupants in the library. In contrast, the indoor concentrations of bacteria in air were approximately ten times higher than those measured outdoors, indicating a signficant internal source of bacteria. The elevated levels of indoor bacteria were primarily attributed to the number of library occupants. Increased human shedding of skin cells, ejection of microorganisms and particulates from the respiratory tract, and the transport of bacteria on suspended dust particles from floor surfaces probably accounts for the strong positive correlation between occupancy levels and the concentration of bacteria in internal air.

A scintillator purification system for a large scale solar neutrino experiment

An on-line purification system for a large-scale low-background liquid scintillation detector has been tested with the 5-ton liquid scintillation detector, the Counting Test Facility at Gran Sasso. Counter-current water extraction removes polar and charged impurities such as ions and metal salts. Vacuum distillation of the entire scintillator has been applied to remove both radioactive impurities and chemical impurities that affect the optical properties of the scintillator. Filtration with a 0.05 μm particulate filter removed suspended dust particles that may contain U, Th and K. Nitrogen stripping was employed to remove dissolved water and noble gases (e.g. 85Kr) from the scintillator. The system has effectively reduced the internal back in the 5 ton liquid scintillation detector from 470±90 events/d to the detection limit of the detector (±45 events/d) in the energy window 250<E<800 keV.

A scintillator purification system for a large scale solar neutrino experiment

An on-line purification system for a large-scale low-background liquid scintillation detector has been tested with the 5 t liquid scintillation detector, the Counting Test Facility at Gran Sasso. Counter-current water extraction removes polar and charged impurities such as ions and metal salts. Vacuum distillation of the entire scintillator has been applied to remove both radioactive impurities and chemical impurities that affect the optical properties of the scintillator. Filtration with a 0.05 μm particulate filter removed suspended dust particles that may contain U, Th and K. Nitrogen stripping was employed to remove dissolved water and noble gases (e.g. 85Kr) from the scintillator. The system has effectively reduced the internal back in the 5 t liquid scintillation detector from 470±90 events/d to the detection limit of the detector (±45 events/d) in the energy window 250< E<800 keV.

Effects of various forces on the distribution of particles at the boundary of a dusty plasma

The distribution and suspension of dust particles under the action of electrostatic, gravitational, ion-drag and neutral collision forces are investigated near the boundary of a dusty plasma. It is shown that the competition among the forces results in spatial oscillations (multi-layer) of the particle distribution. For sub-micron grains the ion-drag has a significant effect on the grain dynamics while for micrometer sized grains the gravity quickly dominates over other forces. The effect of the neutral gas flux is to enhance or diminish that of the gravity while the effect of the neutral viscosity is to shift the profile toward the wall. Under the force balance, the particles are suspended in a narrow region with sharp boundaries within the sheath.

A Boundary-Layer Model for Mars: Comparison with Viking Lander and Entry Data

A 1D boundary-layer model of Mars based on a momentum equation that describes friction, pressure gradient, and Coriolis forces is presented. Frictional forces and convective heating are computed using the level-2 turbulence closure theory of Mellor and Yamada (1974). The model takes into account the radiative effects of CO2 gas and suspended dust particles. Both radiation and convection depend on surface temperatures which are computed from a surface heat budget. Model predictions are compared with available observations from Viking landers. It is concluded that, in general, the model reproduces the basic features of the temperature data. The agreement is particularly good at entry time for the V L-2 site, where the model and observations are within several degrees at all levels for which data are available.

Assessment of the African airborne dust mass over the western Mediterranean Sea using Meteosat data

The mass of African dust present over the western Mediterranean during a transport episode from northwestern Africa, which occurred in early July 1985, is estimated using a desert aerosol model, an Earth‐atmosphere radiative transfer model and Meteosat visible channel data from 4 days running. Dust pixels are selected from Meteosat images, and their aerosol optical thickness is retrieved. A proportionality factor between aerosol optical thickness and atmospheric columnar aerosol loading is computed and applied to the dust pixels. The total mass of atmospheric particles over the basin is obtained by interpolation and spatial integration. The maximum aerosol optical thickness is 1.8. The maximum aerosol columnar loading is evaluated to be 2.3 g m−2. The integrated mass of particles present at a given time is estimated to raise up to about 0.6 × 1012 g at the maximum and the total mass of dust exported from Africa to be of the order of 1012 g. The method is carefully evaluated and uncertainties are discussed, with particular emphasis on the relationship between atmospheric dust mass and aerosol optical depth. The overall uncertainty on the total mass is roughly a factor ±3. In the absence of clouds it appears that the major uncertainty results from the lack of knowledge of the actual mass‐size distribution of suspended dust particles, pointing out the lack of relevant data on particles larger than 10 μm in diameter. A simple calculation based on results from both computations and simultaneous field measurements yields a net transfer velocity of particles from the dust layer of approximately 1 cm s−1.

Dynamics of dust in a plasma sheath and injection of dust into the plasma sheath above Moon and asteroidal surfaces

We have examined single dust particle dynamics in a plasma sheath near the surface of solid bodies in space, considering conditions which resemble those of planetary system bodies, when photoelectric effect can be neglected. The forces on the dust particles are assumed to be from the electric field in the sheath and from gravitation only. As the dust particles will charge negatively in the sheath, these forces will act in opposite directions and may balance. The charge delay of a moving dust particle is responsible for many of the interesting dynamical properties, and we show that for a stationary plasma, dust motion is unstable to about one Debye length out from the surface of the solid body. This part of the sheath will therefore be devoid of dust particles as they will either fall down, escape completely from the solid body or collect and make damped oscillations at stable positions in the outer part of the sheath. With increasing plasma bulk speed towards the surface, the inner unstable part of the sheath will decrease in thickness. The sources for the dust in the sheath are assumed to be mainly ejecta from meteorites and micrometeorites, but may also, for the smallest solid bodies, be from electrostatic levitation of very small dust particles. We have for different sizes of solid bodies calculated the sizes of ejecta that can be ‘floated’ in the sheath. For the solar wind plasma, the suspended dust particles range from less than 1 Μm for the Moon to about 80 Μm for an asteroid with radius 1 km. These particles create a ‘dust atmosphere’. The results in this paper hold when the dust particle density is so low that the charges on the dust particles do not contribute significantly to the total space charge; a higher density will lead to a modification of the sheath. Our calculations show that ejecta below a certain size will be accelerated in the sheath and totally escape from the body even if they have near zero initial vertical velocity, while ejecta above this size will need a much larger velocity to escape. This is especially significant for the small solid bodies (radius of order km and less) which will therefore act as important sources of micronsized dust. This could be of significance for the dust production and the size distribution of dust in planetary ring systems.

Linear flow induced in fluid particle suspension by an infinite differentially rotating disk

The steady, axisymmetric laminar flow of a homogeneous incompressible fluid with suspended particles occupying the half-infinite space over a differentially rotating rigid plane boundary is analyzed in this paper. The effect of suspended particles is described by two parametersf and τ. The mass concentration parameterf is a measure of the concentration of suspended dust particles. The interaction parameter τ is a measure of the rate at which the velocity of dust particles adjusts to changes in the fluid velocity and depends upon the size of the individual particles. Due to Ekman suction, the particle density remains no longer a constant in the boundary layer but varies with the axial coordinate ξ. Flow characteristics and density variations are studied as functions off, τ and ξ. Possible limiting cases for τ≪1 and τ≫1 which correspond to the case of fine dust and coarse dust respectively are derived and discussed.

Studies on pollution in the atmosphere near the aluminium reduction plant at Nagi Hammady/Egypt

Suspended dust was sampled at four sites weekly for 8 mo in the atmosphere near the Aluminium Reduction Plant at Nagi Hammady. The samples were analyzed with respect to the concentration of suspended dust particles, their size, shape and size distribution. Also the concentrations of: Fe, Mg, Pb, Cu, Zn and fluoride (the main waste products of an Aluminium Reduction Plant) have been measured. The effect of meteorology and topography on the distribution of the suspended dust and elements is discussed. Results show that the average concentrations of both dust and elements are larger than those obtained in urban localities but do not exceed the concentrations in industrial localities. These concentrations were much smaller than the allowable values in Egypt.

Sudies on the size distribution of the suspended dust particles in the atmosphere of Qena, Egypt

Studies on particular size, shape and distribution for the dust particles suspended In !he atmosphere of Qena (upper Egypt) have been carried out. The results show that the concentration of these particles decreases with Increasing Size according to lunge power law size distribution n (dp) = In 10 C ( dp )--(a+1). The values of exponent a range from 1.3 to 2. The largest number of particles have sizes less than 2 pm with irregular shape. Effective mean diameters were calculated.

Studies of the number concentration and size distribution of the suspended dust particles in the atmosphere of Qena/Egypt

Studies of particle number concentration, size, shape and distribution of the dust particles suspended in the atmosphere of Qena (upper Egypt) have been conducted. The results show that the concentration of these particles decreases with increasing size according to the Junge power law size distribution: n(dp) = C/ln10 (dp)−(α+1. The values of the exponent α range from 1.3 to 2. The largest number of particles have sizes less than 2 μm with irregular shape. The effect of some weather conditions on the total number of particles was considered. The total number of particles and effective mean diameters were calculated.

Properties and toxicity of airborne wood dust in woodworking establishments

The total suspended dust levels, particle shape and size distributions and metal concentrations (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) of wood dust in the breathing zone of 3 small woodworking establishments were monitored. In vitro culture assay indicated that the mortality of alveolar macrophage was related to the metal content of dust collected from these 3 workplaces.

ANALYSIS OF MOUNT ST. HELENS ASH FROM OPTICAL PHOTOELECTRIC PHOTOMETRY

ABSTRACT The optical properties of suspended dust particles from the eruption of Mt. St. Helens on July 23, 1980 are investigated using photoelectric observations of standard stars obtained on the 0.76-m telescope at the University of Washington 48 hours after the eruption. Measurements were made with five broad-band filters centered at 3910, 5085, 5480, 6330, and 8050 A on stars of varying color and over a wide range of air masses. Anomalous extinction effects due to the volcanic ash were detected, and a significant change in the wavelength-dependent extinction parameter during the course of the observations was established by statistical analysis. Mean particle size (a) and column density (N) are estimated using the Mie theory, assuming a log-normal particle-size distribution: a = 0.18 micron throughout; N = 1.02 x 10 to the 9th/sq cm before 7:00 UT and 2.33 x 10 to the 9th/sq cm after 8:30 UT on July 25, 1980. The extinction is attributed to low-level, slowly migrating ash, possibly combined with products of gas-to-particle conversion and coagulation.

Properties of dust in the martian atmosphere and its effect on temperature structure

Data from the Viking lander imaging experiment and the IRIS experiment on board the Mariner 9 Orbiter are used to develop a one-dimensional radiative-convective model to describe the Mars temperature profile. Photography was employed to determine the optical depth, mean size, shape, visible absorption coefficient, and vertical distribution of aerosols in the Mars atmosphere. The calculation procedures are outlined, particularly for the particle size distribution function, which indicated a cross-sectional average particle radius of 2.5 microns. Dust-free conditions in the atmosphere near the equator and at lower altitudes permit full surface absorption of sunlight and subsequent adiabatic lapse rates. Difficulties were encountered in accurately modeling temperature profiles to fit Viking lander data, and resultant variations are attributed to effects of both suspended dust particles and large scale circulation.

Characterization of suspended dust particles in the Jerusalem air

Continuous measurements of particle mass concentration, particle size distribution, and other environmental measurements were conducted at a monitoring station in Jerusalem, Israel, during the 1978/79 winter season in order to characterize the processes which occur in suspended dust particles in the metropolitan area. Most of the man-made aerosol mass is initially emitted to the air in the form of small particles (submicron), but, as a result of atmospheric processes, larger particles are evolved. The rate constant which is characterized in this coagulation process (2.7 x 10 /sup -8/ cm/sup 3//S) was estimated from the field measurements. This rate constant indicated that urban particles coagulate on almost every collision and that the speed of the process is the main mechanism responsible for the sharp decrease in particle number density shortly after midnight. The influence of climatic factors (duststorms and precipitation) on suspended dust particles in Jerusalem air is also discussed.

Leaded gasoline — A cause of cancer

In the course of earlier tests the authors had found that the cancer mortality among 231 adult persons living adjacent to an automobile road was much higher than among persons living in a traffic-free section of the same town. Fifty-nine of the above individuals residing adjacent to the automobile road had been treated with calcium EDTA to eliminate lead. Only one of these later died of cancer. Of the persons who were not treated with calcium EDTA, on the other hand, 30 died of cancer, or ten times more percentage-wise. The existence of small lead deposits as well as the health-impairing effect of lead were demonstrated by measurements of lead and delta-aminolaevulinic acid in urine. After treatment with calcium EDTA, the lead content, as well as the amount of delta-aminolaevulinic acid, became normal. The concentrations of lead were found to be greater in suspended dust particles and in sediment dust along the automobile artery than elsewhere in the town. These findings, together with many other reports in the medical literature lead to the suspicion that lead in automobile gasoline, combined with other carcinogenic substances in automotive exhaust gases, increases the incidence of cancer.