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Sedimentary deposits of dust found on lake and ocean floors are here considered subaquatic dust deposits. In this chapter, a state-of-the-art overview is given of these subaquatic dust deposits and their value as archives of environmental change. Examples are given of subaquatic dust deposits that register over millions of years fluctuations in dust fluxes that can be interpreted in terms of past environmental changes in the source area(s) of the dust particles. The tools (theso-called proxies) that have been used to read these records of environmental changes are also presented and discussed. Subaquatic dust deposits are usually continuous through time, relatively easy to date; they reflect both wet and dry deposition of mineral dust particles and are not biased by the altitude at which the particles are deposited. This set of properties makes them a very valuable archive of dust as recorder of palaeo-environmental change. Finally, it is discussed in this chapter how the ocean potentially plays a role in the process of dust as a player of environmental change.

The assessment of the anthropogenic and natural contributions to PM10 concentrations is a key issue for the development of air quality policies in Europe. In areas such as the Mediterranean basin, a consistent fraction of the natural contribution to PM10 concentration is given by dust particles transported from Sahara. This study presents an estimate of the dust contribution to PM10 concentrations in years 2003–2005 at six Italian locations. The reduction (%) in the number of daily exceedances of the PM10 limit value (50μgm−3) after subtraction of the African dust contribution is also presented.The reduction varies with station between 20% and 50% in 2005 and between 5% and 25% in 2003 and 2004.

The ESA Cometary Environment Model is applied to comet 67P/Churyumov-Gerasimenko (C-G). From observed gas and dust production rates the model allows us to determine the conditions in the inner coma of a comet. Assuming a spherical nucleus and an axis symmetric surface activity, the densities and velocities of the gas and of dust particles are calculated as functions of location in the coma. The model is also used to estimate the infrared and visible radiation received by an observer inside the coma due to dust. Observational data for the activity of 67P/C–G are available mainly from the apparitions in 1982/83 and 2002/03. For an insolation-driven activity model corresponding to a homogenous surface composition, the results for 67P/C-G are compared to those obtained earlier for P/Wirtanen. In order to derive an upper limit for the local densities inside a jet, a Gaussian activity profile centred at the subsolar point is considered.

Observations of the linear polarization of light scattered by cometary dust (spatial variations, phase and wavelength dependences) provide unique clues to the physical properties of the dust particles. The polarization of 67P/Churyumov-Gerasimenko has, up to now, only been observed at its 1982/1983 return. Data suggest that the coma is rather dust poor, in agreement with the absence of any silicate feature in the infrared spectra. However, outbursts may modify for a while the properties of the dust coma. Laboratory experiments on aggregates of grains representative of cometary particles should take place on board the ISS before the Rosetta rendezvous. Their results, together with complementary remote observations, should provide a better understanding of the morphology, size distribution and porosity properties of the dust particles to be encountered by the spacecraft within the coma.

Most of the work on hydrodynamic resuspension has concentrated on the lift (and drag) forces generated by motion in the turbulent boundary layer beneath some mean flow. In the fluvial context, this hydrodynamic mechanism represents the dominant component of resuspension for most naturally occurring particle-laden flows. However, in the aeolian context, the hydrodynamic mechanism has great difficultly resus-pending fine dust particles, although may often resuspend larger ‘sand’ particles. It is then the saltating of these sand particles (which perform a series of approximately parabolic hops along the ground) that drives the ballistic mechanism of direct mechanical interaction that is capable of resuspending the finer dust. Further details may be found in the many review articles on both these processes (e.g. Willets 1998). An additional hydrodynamic mechanism, whereby the wake of a colliding particle can play a role, has explored recently by Eames & Dalziel (2000). The resuspension mechanism driven by droplets, however, turns out to be quite different.

After an introduction to molecular observations pertaining to interstellar clouds, we discuss current ideas on the chemical processes occurring in the gas phase and on the surfaces of dust particles in clouds. Various pathways to the synthesis of polyatomic molecules are then illuminated. We summarize detailed gas-phase and gas-grain models of the chemistry in the cores of dense interstellar clouds and compare their results with observations. Extensions of modelling efforts to star formation regions are mentioned. We close with a discussion of current difficulties and likely directions of future activity.

In this short paper we present a quick view of the composition of the nucleus of comet Halley deduced by the analysis of the dust particles detected by VEGA and GIOTTO spacecraft.

Comet Hale—Bopp was the largest comet by almost any definition, observed at least since the advent of modern observing techniques. In a more typical comet both the chemical and dynamical influences of collisional processes are limited by the short time a parcel of gas sublimated from the nucleus remains in the dense part of the coma. The resulting large size of the collisional coma in comet Hale—Bopp had important consequences on the dynamics of the coma, which in turn has important consequences on how observations are interpreted with standard models. Measured velocities of typical gas species (mostly the observed radicals) as well as dust were larger than normal comets. Conversely, velocities of superthermal atomic hydrogen were smaller than normal because of the same collisional processes. Furthermore, as a consequence, dust particles, which are dragged by the outflowing gas, were also accelerated to larger velocities. Such larger velocities are not simply an interesting curiosity in their own right, because nearly all observations of dust and gas are interpreted with models of the coma that depend directly on some measurement or assumption with regard to velocity. In this presentation both observations and theory regarding the dynamical conditions in the coma of comet Hale—Bopp are summarized.

Comet C/1999 S4 (LINEAR) showed a very special behaviour between 28 June and 1 July 2000. Optical observations of the dust coma in two distinct continuum bands revealed that it changed morphologically as well as in colour. The two-dimensional coma morphology indicates a splitting of the nucleus which probably occurred shortly before the observations of 28 June 2000. The distribution of the dust particles in sun and tail direction reflected by the slopes of the radial profiles indicate the presence of a considerable amount of disintegrating dust particles in the sunward hemisphere and an overabundance of dust, reflecting at 440 nm, within the first 18,000 km of the dust tail. The spatial profiles of the (BC—RC) colour index in sun direction are distinctly different on 28 June and 1 July, indicating the production of a large amount of particles observable in blue continuum after 28 June.

Individual cosmic dust particles come in very complex shapes but there are a variety of environments where dust particles are aggregates of smaller grains. These aggregates often can be characterized by a fractal particle structure. Within this fractal framework, morphologically averaged particle properties depend only on a few parameters. Despite the complexity of the individual particles, fractal dimension, aggregate size, and building-block size are sufficient parameters for many applications. This paper reviews the process of aggregation to generate fractal aggregates with focus on some general features of those aggregates (mass to surface ratios, aspect ratios). Some implications for aerodynamical and optical properties (gas- grain coupling times, polarization, extinction) are discussed.

It is found that velocity shear enables the extraction of kinetic energy from the background flow by Dust-Acoustic waves. It is also shown that the velocity shear leads to the appearance of a new mode of the dust particles collective behaviour, called shear dust vortices.

Ulysses measurements yield reliable in-situ detection of large dust particles which stem from the interstellar medium (ISM) and which are not observed in interstellar extinction data. Both current models of large grains in the ISM: core-mantle grains as well as composite grains, are in agreement with dust properties implied by the Ulysses results. However, the size of particles detected by Ulysses still exceeds the size of the large grains that are predicted for the ISM.

The outer part of the saturnian system, comprising four saturnian satellites — Phoebe, Iapetus, Hyperion, and Titan — is believed to excel in intricate mechanisms of production, evolution, and transport of dust between the involved moons. This paper is focused on the delivery of the dust material to Titan, with the neighboring Hyperion being the most effective dust supplier. Hypervelocity impacts of dust particles coming from Phoebe, as well as bombardments by interplanetary micrometeoroids should eject the surface material of Hyperion to the planetocentric space. We discuss the complex dynamics of the Hyperion ejecta, resulting from the interplay between the resonant gravity of Titan, solar radiation pressure, and plasma drag force. It is shown that unlike Hyperion, the motion of which is stabilized by a strong 4:3 mean motion resonance with Titan, a significant part of the Hyperion debris either is free of resonance initially or is liberated from the resonance during the subsequent dynamical evolution. These particles get in unstable orbits and experience multiple close approaches to Titan. Most of the grains larger than several μm in size finally collide with Titan. We show that the dust influx to Titan from Hyperion may exceed markedly the direct influx of interplanetary grains. It is argued that the influx of water-containing particles from Hyperion may play an important role in the chemistry of Titan’s atmosphere, making a significant contribution to the budget of the oxygen-bearing compounds.

Our ideas on the interstellar medium (ISM) have changed radically during the past two decades with the rapid advancement of our knowledge of space astrophysics. Originally the interstellar medium was thought to be a simple, quiescent medium; but now it is well known that the ISM is a complex and dynamical medium and plays a key role in the cycle of birth to death of stars. Out of this medium new stars are born and it is being continuously replenished by the mass loss from stars. The ISM is a dynamic medium which is continuously being blown by stellar winds, supernova explosions and the expanding envelopes of supernova remnants. The interstellar medium has four main constituents: (a) Gas in all phases,-molecular, atomic and ionized gases, (b) Dust particles, which obscures several regions from visible and UV radiations, (c) High energy cosmic ray particles (which were discussed in detail in Chapter 7), and (d) the Galactic magnetic field. Here we shall discuss the basic features of the first two aspects.

X-ray fluxes observed from comet C/1996 B2 (Hyakutake) are readily explained in terms of scattering by carbonaceous particles with radii of several tens of Angstroms. A few tenths of a megatonne of such particles appear to have been present in the cometary coma on March 26-28, 1996.

Analysis of the polarization of light scattered by cometary particles reveals similarities amongst the phase curves, together with some clear differences: i) comets with a strong silicate emission feature present a high maximum in polarization, ii) the polarization is always slightly lower than the average in inner comae and stronger in jet-like structures. These results are in excellent agreement with the Greenberg model of dust particles built up of fluffy aggregates of much smaller grains. Also, they suggest the existence of different regions of formation, and of different stages of evolution for the scattering particles inside a given cometary coma.

The sodium emissions have been observed in several new and long-period comets, but only for comet Mrkos 1957d (Nguyen-Huu-Doan, 1960) was a sodium tail detected on a Schmidt plate obtained with a objective prism. Comet Hale-Bopp 1995 O1 offered the first great opportunity to get an image of a long sodium tail. It was more than 3 × 107 km long, defined as a third type of tail, as it was composed only of neutral atoms (Cremonese, 1997a). After the discovery of the sodium tail another team announced it had observed it (Wilson et al., 1998), but it was soon realized they had seen a different sodium tail. The image of Wilson et al. (1998) showed a very diffuse sodium tail superimposed on the dust tail, most likely due to the release of sodium atoms from dust particles. It was different from the narrow tail found in the image obtained by the European Hale-Bopp Team and its position angle was 15–20 degrees lower. Spectroscopic observations have been performed on the dust tail, at different beta values, and along the narrow sodium tail showing that the sodium emissions had very different line profiles. The analysis of these profiles will yield important insights into the sources in the inner coma and in the dust tail. This work will report on preliminary analysis of both sodium tails and emphasize the high-resolution spectroscopy performed on the dust tail.

Dusty plasmas have recently acquired a lot of attention. The subject was initiated by the semiconductor industry. With the arrival of VLSI and ULSI (very/ultra large scale integration) plasma etching and plasma deposition techniques have become indispensible. With the decreasing feature sizes on the devices the tolerance for dust particles becomes smaller. Now that feature sizes are below 0.25 micron, very small dust particles with a diameter of only a few tenths of a micron can kill the device. Therefore about 5 years ago substantial research efforts were started in order to investigate the trapping and transport of dust particles in processing plasmas.

The concentrations of environmentally relevant compounds in soils, stream sediments and air dust particles are controlled by various sources and by the mechanisms of transport, transformation and retention, for example, the heavy metal contents of soils depend on geological background concentrations, various contamination sources, the immission rates of the elements and hydrological and weathering conditions. Analytical scatter and sampling homogeneity also contribute to the variation of the data.

Over the last two decades observations of dust emission in the infrared have played an important role in the development of research on the interstellar medium. The study of the spectral energy distribution has led to the discovery of small dust particles including the large aromatic molecules (PAHs). Infrared sky images have been used to study the structure of interstellar matter, the evolution of dust within the interstellar medium and the star formation efficiency of interstellar clouds.

Analysis of the composition of aerosol particles in the Eastern Mediterranean shows that dust particles are often coated with soluble sulphate. The role of these types of particles in the formation of clouds and rain is discussed. Numerical cloud model simulations suggest that the presence of such large particles in the atmosphere could substantially increase rain amounts from convective clouds.

The major population of particles in diffuse interstellar clouds consists of elongated grains with a silicate core and an “organic refractory” mantle (Hage and Greenberg, 1990). When a diffuse cloud contracts, gases condense on the core-mantle dust particles and an outer mantle of volatile ices forms.

I review progress in interpreting the opposition effect and negative linear polarization observed for solar system dust particles. The so-called coherent backscattering mechanism has recently been introduced to explain the observations. However, fundamental difficulties in theoretical modeling still prevent quantitative interpretation. I also review some of the key observations that questioned the hitherto widely accepted mutual-shadowing explanation for the opposition effect. I summarize previous theoretical and experimental work on the opposition effect and negative polarization.

The natural atmosphere that we breathe contains not only its gaseous constituents but also large numbers of liquid and solid particles. These are known by the generic name aerosols. They arise from a combination of natural and industrial sources including condensation, smokes, volcanic activity, soils and sands, and microflora. Most of the particles are small enough to be invisible to the naked eye. Dust is the term we use in reference to the solid particles. The physiologies of air-breathing creatures have evolved to be able to deal efficiently with most of the aerosols that occur naturally. However, within closed industrial environments, concentrations of airborne particulates may reach levels that exceed the ability of the human respiratory system to expel them in a timely manner. In particular, mineral dusts are formed whenever rock is broken by impact, abrasion, crushing, cutting, grinding or explosives. The fragments that are formed are usually irregular in shape. The large total surface area of dust particles may render them more active physically, chemically and biologically than the parent material. This has an important bearing on the ability of certain dusts to produce lung diseases.

Experimental laboratory work on simulation of the electrostatic fragmentation was started with loosely bound A12O3 particles of 1 to 10 micrometers size. These particles were suspended in an electrodynamic quadrupole inside a vacuum chamber and electrically charged by ion beams of energies up to 5 keV. The electrostatic fragmentation was observed and derived tensile strengths of the particles range from 103 to 105 Pa what is compatible with theoretical estimates. A dependence of the tensile strength on the size of particles has been found. This dependence can be well fitted by inverse square power law.

The diazotrophic metabolism that allows Trichodesmium to thrive in nitrogen-poor oligotrophic oceans relies on many iron-containing enzymes and proteins. The iron dependent processes in Trichodesmium and the theoretical amount of iron required for these processes are comparable to the measured iron content of colonies from the open ocean. The high iron requirement of these species is problematic in light of the limited iron delivery to open ocean systems. Trichodesmium can take up soluble forms of iron and has unique mechanisms that may allow it to use iron contained in dust particles. Their ability to add new nitrogen through nitrogen fixation and their potential for increasing the amount of biologically available iron make Trichodesmium crucial organisms in the geochemistry of tropical and sub-tropical oceans.

The sanitary production of foods as outlined in the federal code for good manufacturing practice includes restrictions that prevent contamination by physical or nonliving objects or chemicals. The physical objects range from dust particles to hammers, and the chemicals range from toxic lubricants to juices of another variety. Most of these objects and chemicals are necessary for the operation of a citrus processing plant. However, regardless of their value, they all have the potential for misuse and can damage the quality of the plant’s products. Such misuse can range from accidental or careless contamination to intentional adulteration, and, unlike the contamination discussed in previous chapters, can be lethal to product consumers. For this reason, prevention of such contamination should be a vital part of any sanitation or quality control system in citrus processing plants.

The unique morphology of the synchronic band in the cometary dust tail is explained by finite-lifetime fragment model (Nishioka and Watanabe, 1990). However, this model needs a severe restriction on the lifetime of the dust fragments;25–70 days (r = 1 A.U.). This implies that detailed analysis of the synchronic band may reveal physical properties of the cometary dust particles. In this paper, we suggest that the fragments in the synchronie band are relatively pure ice if they are not organic grains.

After briefly evaluating the observations of the Zodiacal Light and F-corona, we review the laboratory results on the light scattering by dust particles and the various theories which have been recently proposed. We then discuss the optical properties of the dust with emphasis on the phase function, the polarization, the color, the albedo and the local enhancement in the Gegenschein.

The Munich Dust Counter (MDC) is a scientific experiment on board the MUSES-A mission of Japan measuring cosmic dust. The satellite HITEN of this mission has been launched on January 24th, 1990 from Kago-shima Space Center. Here the present status of the MDC experiment is summarized. The number of dust particles measured so far is presented together with first and preliminary results of flux calculations and spatial as well as directional distributions of cosmic dust particles measured until July 25, 1990. A clear evidence of particles coming from the inner solar system (beta-meteoroids) already has been found. These are compared to particles coming from the apex direction.

Dust particles originating from comets are an important constituent of the interplanetary dust regime. In order to study the ejection mechanisms from the cometary nucleus surface simulation experiments in the laboratory have been performed. Samples consisting of water ice, carbon dioxide ice and dust grains have been studied when they are irradiated by artificial sunlight within a cooled vacuum system. It has been shown that particle emission is extremely dependent on the initial composition of the samples. For samples with a distinct amount of non-volatile, mineral particles the formation of a dust mantle and, as a consequence, rapid decrease of particle ejection has been observed.

Radio observations of comets complement studies at other wavelengths as well as providing certain kinds of unique information. Studies of continuum emission may probe the thermal emission of the nucleus and large-size dust particles. Spectroscopic observations of gas in the coma allow searches for parent molecular species that have no signatures in the optical spectral range. The 18-cm wavelength spectral lines of the OH radical now are relatively easy to detect, and observations of them permit long-term and short-term monitoring of the cometary gaseous output. Moreover, with the unique spectral resolution of radio techniques, aspects of the kinematics of the coma may be also studied, such as the gas expansion velocity and the anisotropy of gas production from the nucleus. In this review, we present recent results of cometary radio observations, and discuss what may be learned from such studies in the future.

The survey of elemental composition of P/Halley dust component according to the data acquired by the PUMA-2 instrument installed on the board of the VEGA-2 spacecraft is presented. Possible mineralogical composition of dust particles is considered. Some reasons for possible presence in comet’s dust particles of virgin organic compounds are presented.

This is a shortened and slightly adapted version of a paper by Chini, Krugel and Kreysa to appear in Astronomy and Astrophysics. It reports the detection of four nearby main-sequence stars at mm/submm wavelengths and its interpretation that this emission is due to dust particles which are, at least, a hundred times larger than interstellar grains. If one assumes that their size distribution follows a power law of the form n(a) ∝ a−3.5 then there is no limit on the upper boundary of the grain size and much larger bodies cannot be excluded observationally.

In-vivo kinetic studies of inhaled bacteria has been carried out in order to determine if the retention of deposited viable bacteria as an example for biologically active particles in comparison to inert dust particles is due to different short-term clearance mechanisms in the respiratory and gastrointestinal (GI) tract. An exposition model has been developed to study the elimination rates of Erysipelothrix rhusiopathiae and of inhaled polystyrene latex (PSL) microspheres in rats after inhalation compared with intratracheally application.

Analytical approximations used often in the literature for calculating energy rates emitted by dust grains in infrared are discussed. Comparisons with correct complete formulations are made for three grain models: (1) pure graphite, (2) ice mantle-graphite core, (3) silicates. λ-1 and λ-1 dependences for the average effective emissivity of such grains are used. We find that for silicate and graphite grains the simplified approximations are valid only when accuracies between 10% and 50% are required and only for grain temperatures higher than 80 K. At lower temperatures the validity of the approximations fails for the graphite particle while it is variable for the silicate dust grain. The ice core mantle particles can instead be treated with approximated formulae without introducing appreciable errors.

From a fundamental point of view there is not much reason to distinguish between the various parts of outer stellar envelopes, such as chromospheres, coronae, dust shells, etc. Such a distinction might easily leave the reader with the false impression that these layers are separate physical entities. The contrary is true: the complicated interplay between the mechanical, magnetic, radiative and conductive fluxes, in addition to stellar winds in outer atmospheric regions can lead to the formation of extended envelopes, with a complicated temperature and density distribution. Conventionally, different names are assigned to the various temperature regions — cf. Section 1.8. In the extreme parts of these envelopes where the gas has low temperatures, molecules and even dust particles may form. In other cases youngly formed stars may still partly be embedded in the gas and dust cloud out of which they originated.

Local, proximal and distal dusts are mainly distinguished by their grain-size distributions in relation to the distance from their desert sources. The coarse particles have an inherited micromorphology derived from the incipient eolian mobilization in the source area. This is shown by SEM examination, image analysis and correspondence factor analyses. Yet, mineralogical identification may be difficult for the finest dust particles. In the presently deposited dusts or trapped dusts in the rock cracks, the grain-size and micromorphological characters, inherited from the previous eolian phase, are well-preserved.