The metastability of natural and urban aerosols

Summary The principle of the sampling method of submicron aerosols with the Aerosol Spectrometer is briefly described and the analytic procedures for deriving the frequency-size distributionC _d (d) from photo-micrographic particle counts and microphotometric light scattering measurementsS _d (d) of identical areas of the particle deposit.After initial analysis the deposits were exposed to elevated temperature (80° C) for several hours and re-analyzed. Four representative aerosol types, originating from the high sea, the shore, vegetation, and metropolitan smog are analyzed in this manner for the range (0.2 d1.3 ). All show a very marked decrease, even disappearance of the smaller particles (d<0.5 ) and shrinkage of the larger particles (d<1 ). By far the largest effect is observed for the smog aerosols.This volatility appears to be caused by either evaporation of the particle substace or by the gradual oxidation of its organic components into more volatile products (CO₂, H₂O).     

Organic compounds in aerosol samples

In 1975, aerosols were collected with high-volume-samplers and impactors on the west coast of Ireland. The ether extractable organic material (EEOM) was separated into three main fractions: bases (B), acids (A), and neutral compounds (N). Each fraction is a very complex mixture of numerous species. Detailed investigations were carried out on these three main fractions. The individual species were determined quantitatively by gas chromatography. Qualitative identification was done by combined GC-MS.The concentration of total particulate matter (TPM) was in the range of 10 g/m³ (STP) air and the concentration of EEOM was 1 g/m³. The relative composition of the EEOM with regard to the main fractions A, B, and N was N>A>B — the same as in previous measurements. Particles with radii <1 m were investigated separately and showed an enrichment in organic matter.A comparison of individual species from several sample locations is now possible for then-paraffins C₁₀ to C₂₈. The concentrations of all thesen-paraffins are below 10 ng/m³, with no overall obvious preference for specific compounds and no obvious dependence on particle size above or below 1 m radius.A preliminary survey does not show any characteristic differences in the relative composition of the organic constituents of clean air aerosols from different sampling localities. The relative composition with regard to the three main fractions is rather uniform in clean air samples and in samples from polluted regions.     

A study of the attachment of radon daughter atoms to aerosol particles

Previous studies of the attachment of radon daughter atoms to aerosol particles in the atmospheric air have given varying results, a few of which did not conform to the diffusion theory developed byLassen andRau (1960). Our studies suggest that the radiolytic aerosols formed by gas-phase reactions in the presence of ionizing radiations interfere in the studies carried out with known aerosols. Radiolytic aerosols are formed spontaneously in the system, depending on the concentrations of aerosol-forming gases in the atmospheric air. It is shown that, under experimental conditions which suppressed the formation of radiolytic aerosols, the attachment rates of Ra-A atoms to aerosol particles in the range of 0.2 to 1.0 m in diameter agree with the diffusion theory developed byLassen andRau (1960). Such investigations of the interactions between atoms, molecules, ions, and aerosol particles are highly useful in atmospheric tracer studies.     

Measurements of the coefficient of combination of small ions with aerosol particles

Summary The equilibrium small ion concentration (n) was measured in aerosols for various ionization rates (q) and particle concentrations (Z). The results agree with the formulaq=bZn+n ². These experiments were carried out with different particle sizes and the results provided a series of values of the combination coefficientb. The size of the particles was determined by the diffusion box method and the diameter (d) ranged from 0.01 to 0.1 microns. The results fitted an empirical formulab=0.29d.     

The Role of Atmospheric Aerosols in the Origin Of Life

Recent results from the real time analysis of individual aerosol particles by laser mass spectrometry have revived interest in the inverted micelle structure for aerosols containing organic molecules; indeed for many aerosols the organic content is high enough, for example 50% by mass in the tropical upper troposphere, that it is likely to be the only viable structure. It is pointed out that atmospheric aerosols would have had many advantages as prebiotic chemical reactors, having the potential to address several key problems in a way arising naturally from the probable geophysical and chemical environment on the prebiotic planet. Bacterial and viral size can be predicted for these structures by an equation combining atmospheric aerodynamics and gravity, and which is therefore applicable to other astronomical objects which are candidates for supporting life. Experimental tests and mathematical modelling of the early stages of the chemical evolution of aerosols should be possible.     

On the stationary charge distribution on aerosol particles in a bipolar ionic atmosphere

Summary By the «limiting sphere» method the combination coefficients for gaseous ions and aerosol particles were calculated, allowing for the jump in ion concentration at the surface of the particles. Hence the stationary charge distribution on aerosol particles in a symmetrical bipolar ionic atmosphere was determined. The use of the Boltzmann equation for this purpose proposed by some authors is theoretically wrong asthis equation applies to equilibrium rather than to stationary states. In practice, the Boltzmann equation can be used for particles with radius 3·10^–5 cm (under atmospheric pressure). Within this range the image forces and the jump in ion concentration may be neglected. The conditions of the applicability of the steady diffusion equations to the theory of the stationary charge distribution in aerosols are discussed.     

Chemistry of atmospheric aerosols

Summary A survey is given on the present status of knowledge about the chemical composition of atmospheric aerosols. Results on the size distribution and the physical structure of the nuclei provide the necessary basis for an under-standing of their chemistry. Very little is known about the chemistry of particles smaller than 0.1. For larger particles micro-analyses show the presence of sulfate, nitrate, chloride, sodium and ammonium which varies in a characteristic way with the size of the particles. The sea spray component can be isolated. Data from rain water analyses are used to obtain information on the large scale distribution of these components and their sources. Some remarks about the fraction of the particles acting as true condensation nuclei and the radioactivity will conclude the paper.The subject has been already developed in detail inAdvances of Geophysics, Vol. 4 (edited byH. E. Landsberg & J. van Miechem), Academic Press Inc., New York, 1958.     

On spectral extinction of solar radiation within a tropical atmospheric boundary layer

Helicopter measurements of solar irradiance and meteorological data within the atmospheric boundary-layer were made in Lagos during February 1979. Filter samples of aerosols were collected both during flight in February 1979 and at ground level in December 1978. Profile data on spectral aerosol optical depth were obtained and, from these, the aerosol extinction coefficient at two wavelengths (0.5 and 0.88 m) were calculated. Precipitable water was low and was contained mainly within the 750 m layer above ground, suggesting the establishment of a deep unstable boundary layer. Calculated channel energy depletions by aerosols show that, within the first 750 m of the surface, the 0·88 m might be more efficient at attenuating solar energy than 0·5 m. The lagoon (maritime) aerosol sample indicated a more monodisperse size-distribution than the dusty harmattan aerosol sample.     

Resuspension of radioactive fall-out from the soil surface and particulate contamination of vegetative cover

A method for the determination of resuspension parameters of radioactive fall-out from nuclear explosions, deposited on soil from the stratospheric reservoir, is presented. The seasonal variation ofk -¹³⁷Cs resuspension parameter, the trend ofk with time in 1963–1978, the trend over this period of time of the wind component fraction of the concentration of global¹³⁷Cs in the surface boundary layer over arable and natural soils are given. An estimate of radioactive contamination of vegetation by the effect considered is given as an example of practical use of this work.     

Preliminary Results from Paleomagnetic Records on Lake Sediments from South America

The preliminary results of paleomagnetic and radiocarbon dating of late pleistocene-holocene sediments from two lakes of south-western Argentina (41°S, 71.5°W) are presented. The magnetic susceptibility, intensity and direction of the natural remanent magnetisation were measured. The stability of the natural remanent magnetisation was investigated by alternating field demagnetisation. The magnetic parameters allowed the cores within each lake to be correlated. ¹³ C analysis, total organic content measurements and C ¹⁴ dating were carried out. A model of sedimentation is suggested. Using this model and the correlation, curves of variations of magnetic inclination and declination in time are shown.     

Evaluation of crystallization temperatures of mineral paragenesis in consolidated crust and uppermost mantle from explosion seismology data

In terms of the general endogeneous evolution of the lithosphere, the continental crystalline crust and the uppermost mantle, formed by regional metamorphic and magmatic processes, show mineral paragenesis stratification, expressed by a regular mineral sequence. The continuous macrolayering of mineral paragenesis through lithospheric depth profile is caused by phase transformations and variations in composition of complex natural systems, and affects the vertical distribution of seismic velocities,V _p,V _s, and other physical parameters.To evaluate palaeotemperatures (crystallization temperatures of mineral paragenesis), consistentV _pandV _s (Z) velocity models for the consolidated crust of two regionally separated areas of different geological structures — Precambrian shield (Voronezh Massif) and a young fold-mountain structure in the central part of the Transasian orogeneous belt (Himalaya) — are used as starting data.The velocity models are recalculated into (Z) and (Z) profiles (Z) being the seismic parameter. (Z) the Debye temperature). These, according to Debye theory, allow the determination of variations in entropy, thermodynamic and temperature gradients at the time of crustal generation.For the two regions chosen, palaeotemperature distributions are eventually calculated for the depth intervals given by velocity profiles. Crystallization temperatures calculated from seismic data show good agrrement with the values obtained from mineralogical thermobarometry.     

Global distribution of gaseous mercury in the troposphere

Atmospheric mercury concentrations were measured during a nautical expedition on the Atlantic Ocean between Hamburg (54°N, 10°E) and Santo Domingo (20°N, 67°W). In addition, samples were taken during flights on a commerical aircraft in the upper and middle troposphere between 60°N and 55°S, mostly over the Pacific Ocean. The data obtained in the lower troposphere over the Northern Atlantic show considerable variation in the Hg concentrations, with values ranging between 1 and 11 ng/m³; the average concentration was found to be 2.8 ng/m³. The upper tropospheric data show an interhemispheric difference with average values of 1.45 ng/m³ and 1.08 ng/m³ in the Northern and Southern Hemisphere, respectively. This suggests that mercury production occurs predominantly over the continents both by natural and anthropogenic processes. The mercury content in aerosols was found to be 0.3 ng/m³, or one-tenth of the atmospheric concentration. The data indicate a mean residence time of mercury in the atmosphere of a few months to one year.     

Generalized thermoelastic longitudinal waves in unbounded medium

Summary In this paper the generalized thermoelastic longitudinal waves and the temperature field set up due to coupling of the displacement and the temperature fields, with heat wave travelling with certain finite velocity, in an unbounded medium are studied. The thermoelastic displacement potential and the temperature field at any point are obtained in terms of the surface integrals involving the potential, the temperature and their normal derivatives.Notation x _i the cartesian coordinate system,i=1,2,3 - n (u _i) the displacement vector - (/x _i) the del operator - _t /t the derivative with respect to time - T _o the temperature corresponding to the natural stat of zero stress and strain - T Absolute temperature - c _e the specific heat - , Lamé's constants - ₀ the density - coefficient of linear thermal expansion - K thermal conductivity coefficient - _kk u - ₀ the relaxation time     

Towards realistic flow modelling. Creation and evaluation of two-dimensional simulated porous media: An image analysis approach

This work is part of an attempt to quantify the relationship between the permeability tensor (K) and the micro-structure of natural porous media. A brief account is first provided of popular theories used to relate the micro-structure toK. Reasons for the lack of predictive power and restricted generality of current models are discussed. An alternative is an empirically based implicit model whereinK is expressed as a consequence of a few pore-types arising from the dynamics of depositional processes. The analytical form of that implicit model arises from evidence of universal association between pore-type and throat size in sandstones and carbonates. An explicit model, relying on the local change of scale technique is then addressed. That explicit model allows, from knowledge of the three-dimensional micro-geometry to calculateK explicitly without having recourse to any constitutive assumptions. The predictive and general character of the explicit model is underlined. The relevance of the change of scale technique is recalled to be contingent on the availability of rock-like three-dimensional synthetic media. A random stationary ergodic process is developed, that allows us to generate three-dimensional synthetic media from a two-dimensional autocorrelation functionr( _x , _y ) and associated probability density function measured on a single binary image. The focus of this work is to ensure the rock-like character of those synthetic media. This is done first through a direct approach:n two-dimensional synthetic media, derived from single set ( ,r( _x , _y )) yieldn permeability tensorsK _i-1,n ⁱ (calculated by the local change of scale) of the same order. This is a necessary condition to ensure thatr( _x , _y ) and carry all structural information relevant toK. The limits of this direct approach, in terms of required Central Process Unit time and Memory is underlined, raising the need for an alternative. This is done by comparing the pore-type content of a sandstone sample andn synthetic media derived fromr( _x , _y ) and measured on that sandstone-sample. Achievement of a good match ensures that the synthetic media comprise the fundamental structural level of all natural sandstones, that is a domainal structure of well-packed clusters of grains bounded by loose-packed pores.     

On estimating frequency-magnitude relations from heterogeneous catalogs

The paper studies the effect of magnitude errors on heterogeneous catalogs, by applying the apparent magnitude theory (seeTinti andMulargia, 1985a), which proves to be the most natural and rigorous approach to the problem. Heterogeneities in seismic catalogs are due to a number of various sources and affect both instrumental as well as noninstrumental earthquake compilations.The most frequent basis of heterogeneity is certainly that the recent instrumental records are to be combined with the historic and prehistoric event listings to secure a time coverage, considerably longer than the recurrence time of the major earthquakes. Therefore the case which attracts the greatest attention in the present analysis is that of a catalog consisting of a subset of higher quality data, generallyS ₁, spanning the interval T ₁ (the instrumental catalog), and of a second subset of more uncertain magnitude determination, generallyS ₂, covering a vastly longer interval T ₂ (the historic and/or the geologic catalog). The magnitude threshold of the subcatalogS ₁ is supposedly smaller than that ofS ₂, which, as we will see, is one of the major causes of discrepancy between the apparent magnitude and the true magnitude distributions. We will further suppose that true magnitude occurrences conform to theGutenberg-Richter (GR) law, because the assumption simplified the analysis without reducing the relevancy of our findings.The main results are: 1) the apparent occurrence rate exceeds the true occurrence rate from a certain magnitude onward, saym _GR; 2) the apparent occurrence rate shows two distinct GR regimes separated by an intermediate transition region. The offset between the two regimes is the essential outcome ofS ₁ being heterogeneous with respect toS ₂. The most important consequences of this study are that: 1) it provides a basis to infer the parameters of the true magnitude distribution, by correcting the bias deriving from heterogeneous magnitude errors; 2) it demonstrates that the double GR decay, that several authors have taken as the incontestable proof of the failure of the GR law and of the experimental evidence of the characteristic earthquake theory, is instead perfectly consistent with a GR-type seismicity.     

Characterization of the Frequency of Extreme Earthquake Events by the Generalized Pareto Distribution

Recent results in extreme value theory suggest a new technique for statistical estimation of distribution tails (Embrechts et al., 1997), based on a limit theorem known as the Gnedenko-Pickands-Balkema-de Haan theorem. This theorem gives a natural limit law for peak-over-threshold values in the form of the Generalized Pareto Distribution (GPD), which is a family of distributions with two parameters. The GPD has been successfully applied in a number of statistical problems related to finance, insurance, hydrology, and other domains. Here, we apply the GPD approach to the well-known seismological problem of earthquake energy distribution described by the Gutenberg-Richter seismic moment-frequency law. We analyze shallow earthquakes (depth h<70 km) in the Harvard catalog over the period 1977–2000 in 12 seismic zones. The GPD is found to approximate the tails of the seismic moment distributions quite well over the lower threshold approximately M 10²⁴ dyne-cm, or somewhat above (i.e., moment-magnitudes larger than m _W =5.3). We confirm that the b-value is very different (b=2.06 ± 0.30) in mid-ocean ridges compared to other zones (b=1.00 ± 0.04) with a very high statistical confidence and propose a physical mechanism contrasting crack-type rupture with dislocation-type behavior. The GPD can as well be applied in many problems of seismic hazard assessment on a regional scale. However, in certain cases, deviations from the GPD at the very end of the tail may occur, in particular for large samples signaling a novel regime.     

Interaction of trace metals with natural particle surfaces: Comparison between adsorption experiments and field measurements

The distribution of the metal ions Zn and Pb between particulate and dissolved phase in river Glatt was studied by field measurements and compared with calculated simulations, using parameters obtained by adsorption experiments with natural suspended particulate material. Differences in distribution coefficients obtained from field data are observed in function of the sampling locations and of the composition of the particulate matter.Experiments in which metal ion solutions are titrated with a suspension of natural particles and analyzed by anodic stripping voltammetry, are interpreted in terms of binding capacities and conditional stability constants of Zn and Pb with the surface sites. Binding constants of a particular metal ion varied very little for all samples. We obtained mean values for the conditional average complex formation constants at pH 8 of: log^cond K _Pb = 9.44 ± 0.18 and log^cond K _Zn = 8.17 ± 0.20. At this pH, binding capacities of 5 10^–3 – 1.7 10^–2 mol/kg of particles were obtained for samples collected at different locations and times; organic material, iron and manganese oxides are considered to be the main components that control the adsorption to the particles.Distribution coefficients are calculated from the experimentally obtained binding capacities and conditional stability constants. Calculated distribution coefficients for Zn agree with those obtained from the field data and are not very sensitive to changes in the composition of the solution. Good agreement was obtained for lead as well; for some samples it was important to take two types of sites with different affinity into consideration.     

Chemical aspects of iron oxide coagulation in water: Laboratory studies and implications for natural systems

Initial coagulation rates of colloidal hematite (-Fe₂O₃) particles (diameter less than 0.1 µm) were measured experimentally in well-defined laboratory systems at constant temperature. The relative stability ratio,W, was obtained at various ionic strengths in NaCl medium and at pH values in the range from 3 to 12. ExperimentalW values ranged from 1 to 10⁴ in various systems. The results delineate the roles ofspecific andgeneralized coagulation mechanisms for iron oxides. Among the specifically-interacting species (G _ads ⁰ >G _coul ⁰ ) studied were phosphate, monomeric organic acids of various structures, and polymeric organic acids. The critical coagulation-restabilization concentrations of specifically-interacting anions (from 10^–7 to 10^–4 molar) can be compared with the general effects of non-specific electrolyte coagulants (10^–3 to 10^–1 molar). The laboratory results are interpreted with the help of a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) which describes variations of interfacial charge and potential resulting from variations of coagulating species in solution. Comparison of these laboratory experiments with observations on iron behavior in estuarine and lake waters aids in understanding iron removal mechanisms and coagulation time scales in natural systems.