Atmospheric Dust Particles Research Articles

Frequency of cleaning the surface of photovoltaic cells in the environment of Riyadh City, Saudi Arabia

SYNOPSIS The effect of accumulation of atmospheric dust particles onto the surface of photovoltaic cells has been examined, and the permissible reduction in the power output was determined along with the associated dust deposition density. The annual patterns of dustfall over six different districts in the City of Riyadh which were previously measured by the author have been used to determine dustfall dependence for three groups of months over the year. A method for determining the frequency of cleaning the surface of photovoltaic cells is presented and used to determine the periods between cleaning during each group of months. The determination of such periods is based on the dust deposition density which would result in the maximum allowable power output reduction and the rate of dustfall during each group of months.

Martian global dust storms: Zonally symmetric numerical simulations including size‐dependent particle transport

The size‐dependent transport of dust particles in the Martian atmosphere away from a specified surface source is numerically investigated employing a coupled system of a zonally symmetric primitive equation grid point model of the Martian atmosphere and an aerosol transport/microphysical model. The coupled model accounts for diabatic heating due to a radiatively active evolving dust field but neglects feedbacks between atmosphere‐surface interactions and surface dust lifting, which is prescribed. The differing suspension lifetimes of various sized dust particles (radius = 1–80 μm) in conjunction with spatially varying atmospheric dynamics results in latitudinal differences in several measurements of the column integrated particle concentration. The latitudinal extent of dust (opacity) transport away from a southern subtropical source is enhanced by the presence in suspension of smaller dust particles (r < 1 μm) when compared to the presence of only a single dust particle size (2.5 μm). The input particle size distribution, that inferred by Toon et al. (1977) from Mariner 9 IRIS measurements, is not preserved in suspension at subsolar latitudes for spherical particles (r = 1–10 μm), counter to Toon et al.'s interpretation of IRIS spectra. Visible to 9‐μm dust opacity ratios, which provide an indication of the relative number of large particles, are generally smaller (<1.7) than values (2–2.5) inferred from both Mariner 9 and Viking measurements. The invocation of slower falling nonspherical (disk) shaped particles results in an improved maintenance in suspension of the input particle size distribution at subtropical latitudes and visible to‐9 μm opacity ratios in better agreement with inferred values. Calculated visible opacity values at the Viking lander latitudes increase less abruptly than was observed at the onsets of the two 1977 dust storms, which has implications for both source locations and magnitudes. This work indicates the importance of considering the full range of particle sizes (and shapes) of the suspended dust during Martian global dust storms and their impact upon the spatial extent and wavelength‐dependent radiative influence of such storms.

Study of continental material transported through the atmosphere to the oeean

I am deeply honored to have been selected as a recipient of the 1987 Okada Prize by the Oceanographical Society of Japan. The present paper reviews my work and recent studies of other investigators concerning mineral aerosol (dust) particles in the marine atmosphere over the Pacific Ocean. I would like to emphasize the importance of atmospheric deposition of continental substances to the ocean environment.

Forced release of sodium from upper atmospheric dust particles

The almost explosive growth of narrow sodium layers at altitudes near 95 km was observed by ground‐based LIDAR located at 69°N, 16°E. Starting from typical conditions at these altitudes (sodium density approximately 1 to 2× 10³ cm−3) the density is observed to increase by large factors within a few minutes in a narrow layer, the half height of which is typically 1 km only. One of the more spectacular cases involved an increase by a factor 25 within 5 min and a layer width of 0.8 km (full width at half maximum). We propose that the sodium forming these sudden layers is released from upper atmospheric dust by energetic auroral particles. Prior to the auroral bombardment the dust particles were concentrated into a narrow layer by appropriate meteorological processes. Our observations thus imply that considerable amounts of sodium are stored on the surface of upper atmospheric dust.

Movement of atmospheric dust in a point-grid corona discharge

It is shown that the trajectories of atmospheric dust particles in the electric wind of a point-grid corona discharge are perpendicular to the grid and that there are few dust particles on the discharge axis. A laser anemometry system is used to measure the velocity component of the particles in the discharge region. A repulsive field method is used to estimate the mean mobility of charged dust particles outside the discharge. The motion of the electric wind is discussed.

Low Vitamin D Levels in Saudi Arabians

ABSTRACT Circulating 25-hydroxycholecalciferol (25-OHD) levels were measured in 134 adults; 82 Saudi Arabian patients, 43 normal Saudi Arabians, and nine Western employees of the King Faisal Specia...

Sources and sediment associations of heavy metals in polluted coastal regions

Vertical profiles and lateral distribution patterns of heavy metals in Recent sediments are increasingly employed in the assessment of the major sources of pollution in coastal regions, including estuaries and marginal seas. After a general review of studies from typical locations, examples from New Bedford Harbor, Mass./U.S.A., and from the southern German Bight in the North Sea are described in more detail. Chemical extraction procedures are used to evaluate different forms of metal associations in aquatic sediments: (i) heavy metals are transported and deposited as major, minor and trace constituents in the natural rock detritus, mostly in inert positions; (ii) slight alkalinity in sea water results in the formation and precipitation of hydroxides, carbonates, sulphides and phosphates of heavy metals; (iii) sorption and cation exchanges takes place in particular on fine-grained substances with large surface areas, e.g. on manganese dioxide, humic acids, hydrous iron oxides and clay minerals; (iv) organic substances play an important role in the transfer of metals between dissoved and solid phases, particularly by the process of flocculation; (v) under oxidizing conditions, the redox-sensitive Fe- and Mn-hydroxides and -oxides are significant “sinks” of heavy metals in aquatic systems. The characteristic rise in the residual content of lead, copper and cadmium in the polluted samples points toward the strong influence of atmospheric dust particles. Heavy metals immobilized in the bottom sediment constitute a potential hazard to water quality and aquatic life since they may be released as a result of chemical changes. In relation to the marine environment, the following mechanisms should be taken into account: (i) increased salinities at the inflow of rivers into the sea water will affect the partial exchange of metal cations sorbed onto the surface of suspended particles; (ii) oxygen deficiency in the bottom sediments may lead to the dissolution of hydrous iron and manganese oxides and to a release of co-precipitated heavy metals; (iii) complexing substances of both natural and synthetic origin increases the solubilization of metals; (iv) microbial activities can convert inorganic metal compounds to organic molecules and may thereby increase toxicity, as exemplified in organo-mercurial transformations.

Measurements of the filtration efficiencies of selected filter types

The filtration efficiencies of selected filter types including polytetrafluoroethylene membranes have been measured by a simple method using ambient dust particles. Pressurized room air is passed through the filter and the particles penetrating the filter are detected with a condensation nuclei counter. Lower limits ranging from 99.0 to 99.9% were established for the efficiencies of Gelman GA-1 cellulose acetate, Gelman Spectrograde glass fiber, Gelman A glass fiber, MSA glass fiber and EPA glass fiber filters. Nuclepore (0.8 μm pore) and Whatman 41 filters were found to have much lower efficiencies. Of the polytetrafluoroethylene membrane filters, Ghia 1–3 μm pore, Ghia 2–4 μm pore and Fluoropore 1 μm pore, have efficiencies > 99.9% Ghia 3–5 μm pore and Fluoropore 3 μm pore show a small amount of penetration, generally less than 1%. Pressure drops across the polytetrafluoroethylene membrane filters are presented for several flow rates. At high flow rates, the pressure drop across 1 μm pore size Fluoropore has been found to increase with time, even with clean air.

Dust Particle Trajectories in Aircraft Radial Turbines

This paper presents the results of analytical and experimental studies of the trajectories that atmospheric dust particles follow as they move through a radial turbine. A dimensionless parameter is derived which can be used during preliminary design analysis to indicate the sizes of particles that will be most damaging to the turbine. The study reveals several internal surfaces that will be more severely eroded because most particles entering the turbine will strike them. A moderate amount of erosion can be expected near the end of the scroll and on the last few nozzle passages near the end of the scroll. All particles greater that 42/t will strike these surfaces. A severe erosion problem occurs on the nozzle trailing edges, because particles greater than 2-3fi will not penetrate the rotor. These particles are pushed outward by centrifugal forces where they bounce off the nozzle trailing edges. Particles greater than 1\\i have enough inertia to overcome the centrifugal force and these particles enter the rotor. After striking the rotor with a perpendicular impact, they also travel outward to the nozzle trailing edges.

Martian cratering III: Theory of crater obliteration

This paper discusses a theoretical basis for interpretation of Martian crater obliteration. Strong evidence is found that Martian craters are being degraded and obliterated at a rate much faster than on the Moon, but much slower than on Earth. Evidence includes (1) morphology of craters (shallow flat floors, flat rims, lack of “Copernican” ray craters), (2) obliteration theory, which successfully predicts the form of the Martian crater curve and the lifetimes of terrestrial craters against obliteration, and (3) laboratory experiments. The theory obviates the need to interpret the diameter distribution in terms of two classes of impacting bodies, as has been done elsewhere. It is suggested that obliteration is caused by filling of the craters, probably by deposition of dust. Evidence is found in (1) theoretically-demonstrated mobility of Martian dust, (2) shallow depths of craters, (3) observed aerial transport of dust on Mars by dust storms, (4) measurements indicating suspension of micron-sized dust particles in the normal Martian atmosphere, (5) depletion of small craters as predicted by theory, (6) patchy light markings preferentially on the northern half of crater floors in and near Meridiani Sinus, suggesting dust deposits, (7) “resurgence” of dark surfaces suggesting periodic covering and uncovering by aeolian dust, and (8) obliteration of features in the basin Hellas.

Studies on protein-like products from radiofrequency plasmas of CO, N 2 and H 2

Solid protein-like products have been produced from “cold” plasmas of the inorganic gases CO, N 2, and H 2 reacting under specific discharge conditions. The excitation of gases under electrodeless radiofrequency (13.56 MHz) conditions produced polymers whose chemical composition was tailorable as a function of gas flow rates. The polymers on hydrolysis showed the presence of alanine, glutamic acid, glycine, serine, and tyrosine as the most common hydrolysate amino acids. Many other compounds of unknown structure are shown to be separable by two-dimensional thin-layer chromatography. These compounds can be quite complex, and may be polymeric, or heterocyclic in nature. Presence of aromatic systems has been unequivocally established for sym. trimethylpyridine and strongly indicated for tyrosine. Possible reaction mechanisms leading to the synthesis of the glycyl unit are proposed, and the role of surfaces or other nucleation sites for condensation of products is discussed. A suggestion is presented whereby reactions between CO, N 2, and H 2 induced in primordial times by ultraviolet energy could have led to condensation of organic products on upper atmospheric dust particles.

Sodium in the upper atmosphere: meteoric origin

Recent observations of the distribution of atomic sodium have shown that the scale height on the topside of the sodium layer can be much smaller than the atmospheric scale height. These observations have been interpreted in terms of release of atomic sodium from dust particles in the upper atmosphere; it is suggested here that an alternate explanation may be obtained from consideration of ablation from meteors.

The Sources of Nitrogen in Vegetation

THE discrepancy between the results obtained in the experiments on plants grown in free air instead of closed vessels appears to be general, as stated in NATURE (p. 333). Some years ago I ventured to suggest an explanation of this, based on an observation made in the course of some investigations of atmospheric dust particles.