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Instrumental neutron activation analysis (INAA), inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) were used for the determination of major and trace elements in sediment samples of the Bouregreg river (Morocco). The reliability of the results was checked, by using IAEA Soil-7 certified reference material. Results obtained by the three techniques were compared to control digestions efficiencies. A general good agreement was found between INAA and both ICP-MS and ICP-AES after alkaline fusion (ICPf). The ICP-MS technique used after acid attack (ICPa) was satisfactory for a few elements. A principal component analysis (PCA) has been used for analyzing the variability of concentrations, and defining the most influential sites with respect to the general variation trends. Three groups of elements could be distinguished. For these groups a normalization of concentrations to the central element concentration (that means Mn, Si or Al) is proposed.

The heavy metals bio-accumulation ability of algae was studied along the North Atlantic Morrocan coast. Instrumental neutron activation analysis was used, to determine concentrations of various elements. The k 0 standardization method was used. Some interferences corrections, particularly due to high concentrations of uranium were applied. The quality of the method was checked by using the CRM 140, a Fucus provided by IAEA. Important pollutions appear for several heavy metals from the Morrocan phosphate industry, with respect to the natural background environment.

There is a need to know, before dismantling nuclear plants, how the induced radioactivity is distributed in concrete. Computer codes are used to predict such a distribution, by applying input data like, among others, the chemical composition of the material. Biological shield concretes with particularly high boron or barium concentrations had to be analyzed. Instrumental neutron activation analysis is not able to determine all elements, thus, additional techniques are required, like ICP-MS and ICP-AES. The respective performances of these techniques are discussed. For INAA, the thermal neutron self-shielding was empirically corrected by using comparisons between thermal neutron activation (TNAA), epithermal and fast neutron activation (ENAA), ICP-AES and ICP-MS measurements.

The Moroccan phosphate industry releases large amounts of heavy metals in the Atlantic Ocean in the surroundings of two places: Safi and Jorf Lasfar. The major waste, called phosphogypsum and composed of calcium sulphate and other additional salts, is introduced into sea water in particulate form. After dissolution of the particles, heavy metal concentrations can be influenced near the release point. Two multi-element analytical techniques were used to measure 47 element concentrations in various materials involved in the study of the phosphate pollution: Inductively Coupled Plasma Mass Spectrometry (ICPMS) and instrumental neutron activation analysis (INAA). At first, phosphate and phosphogypsum were characterized in order to recognize the overall features of the heavy metal pollution source. From the yearly amount of phosphogypsum produced by the Moroccan industry and the element concentrations in phosphogypsum, it has been possible to estimate a yearly flux of heavy metals introduced in the Atlantic Ocean. Algae were used as bio-accumulator materials of heavy metals in the marine environment, in the region of Jorf Lasfar, in order to significantly reveal the signal of the heavy metal pollution. Ulva lactuca Linnaeus was selected to assess heavy metal pollution around the waste release point. Accumulation factors were determined for 47 elements in U. lactuca, by comparing mean concentrations obtained in algae collected in non-polluted sites (background sites) and an average sea water concentration given in the literature. The ratio between the concentration in U. lactuca, collected in a polluted site to the background concentration in U. lactuca, was determined, giving an estimate of the pollution factor for the same elements by the phosphate industry. The decrease of the pollution due to the dilution in the sea water was observed as far as 6 km southward of the release point. A specific variation was observed for lead and its isotopic composition, denoting that the phosphate industry is not the only pollution source in this region. Natural processes were likely involved to induce the lead concentrations variations along the littoral.

(2000). Demonstration of the determining role of dissolved methane in the consumption of dissolved oxygen in an equatorial river. SIL Proceedings, 1922-2010: Vol. 27, No. 3, pp. 1400-1405.

Various crystalline forms of manganese oxides were synthesized by redox reaction between alkali metal permanganates and manganese sulphate. The structure of samples precipitated from0 KMnO4, RbMnO4 and NH4MnO4 were similar to those reported for α-crystalline form of MnO2 and exhibited a high selectivity for the cations whose ionic radii are included in the range 135-155 pm i.e. K+, NH4 +. Rb+, Ba2+ and Ra2+. The samples precipitated from NaMnO4 were more similar to the γ-form of MnO2 and exhibit much lower affinity for the Ra2+ cations. High selective α-type MnO2 samples can also be obtained in strong acidic solutions. The obtained α-MnO2 samples can be used for the determination of 226,228Ra in natural water at a very low level of radioactivity.

In order to investigate the seasonal and geographical distribution of snow concentrations anddeposition fluxes of environmentally relevant ionic species in the Alps, the international programSNOSP was initiated. In the framework of this program, intercomparisons of snow samplingtechniques and analytical methods to determine the ionic species C1-, NO 3 - ,SO 4 2- , K+, Na+, NH4 +, Mg2+, and Ca2+, as well as the pH and the specificconductivity were performed. The concentrations of these species in the snow samples collectedin the SNOSP program varied by orders of magnitude with, e.g., concentrations of NO 3 - , SO 4 2- , and NH4 + ranging from 0.2-60, 0.2-90, and 0.1-60 µeq L-1,respectively. The intercomparisons revealed a reasonable agreement of the determinations of thespecies Cl-, NO 3 - , SO 4 2- , Na+, and NH4 + in snow. Results were less satisfactory for K+, Mg2+, Ca2+,and H+, mainly due to the very low concentrations. In conclusion, recommendations areformulated for the reliable derivation of chemical inventories from snow packs.

Theko-standardization method has been extensively used in the Pierre Sue laboratory during the last few years. We had developed two different new programs which both used parts of a commercial package (Canberra or Nuclear Data), for example: isotope parameter editor, automatic peak search, nuclide identification. However, further adaptation of these packages is not easy, due to the specific data handling of the two programs. In order to overcome these constraints, we decided to write a completely new program, Ko-LABSUE, which is as independent of the manufacturer specifications as possible. All of the different steps of theko-quantification (automatic peak search, nuclide identification, calculation of elemental concentration etc.) are processed by modules written in TURBO-PASCAL. Only two “unit” modules have to be re-written to process manufacturer data files of different formats: the modules used to read the spectrum data and the detector efficiency curve. This program runs on an IBM-PC and is currently on “β-test” in our laboratory.

Biomass burning, in a broad sense, encompasses different burning practices, including open and confined burnings, and different types of vegetation. Emission factors of gaseous or particulate trace compounds are directly dependent both on the fuel type and the combustion process. Emission factors are generally calculated by stoichiometric considerations using the carbon mass balance method, applied either to combustion chamber experiments or to field experiments based on ground-level measurements or aircraft sampling in smoke plumes. There have been a number of experimental studies in the last 10 years to investigate wildfires in tropical, temperate, or boreal regions. This article presents an overview of measurement methods and experimental data on emission factors of reactive or radiatively active trace compounds, including trace gases and particles. It focuses on fires in tropical regions, that is, forest and savanna fires, agricultural burns, charcoal production, use of fuelwood, and charcoal combustion.

Since the nineties, atmospheric measurement systems have been deployed at Reunion Island, mainly for monitoring the atmospheric composition in the framework of NDSC/NDACC (Network for the Detection of Stratospheric Change/Network for the Detection of Atmospheric Composition Change). The location of Reunion Island presents a great interest because there are very few multi-instrumented stations in the tropics and particularly in the Southern Hemisphere. In 2012, a new observatory was commissioned in Maïdo at 2200 m a.s.l.: it hosts various instruments for atmospheric measurements, including LiDAR systems, spectro-radiometers and in situ gases and aerosols measurements. This new high-altitude Maïdo station allows: 1. To improve the performance of the optical instruments above the marine boundary layer, and to open new perspectives on upper troposphere and lower stratosphere studies. 2. To develop in-situ measurements of the atmospheric composition for climate change survey, in a reference site in the tropical/subtropical region of the Southern Hemisphere. 3. To offer trans-national access to host experiments or measurement campaigns for focused process studies.

Model Driven Engineering practitioners already bene¦t from many well established veri¦cation tools, for Object Constraint Language (OCL), for instance. Recently, constraint satisfaction techniques have been brought to Model-Driven Engineering (MDE) and have shown promising results on model veri¦cation tasks. With all these tools, it becomes possible to provide users with formal support from early model design phases to model instantiation phases. In this paper, a selection of such tools and methods is presented, and an attempt is made to de¦ne a veri¦cation and validation process for model design and instance creation centered on UML (Uni¦ed Modeling Language) class diagrams and declarative constraints, and involving the selected tools. The suggested process is illustrated with a simple example.

Human-induced change in the composition of the atmosphere seriously threatens the global climate. In an effort to address this threat, 161 nations signed the United Nations Framework Convention on Climate Change at the Earth Summit in Rio de Janeiro in June 1992. The ultimate objective of this international agreement is to achieve stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. As of the first session of the Conference of the Parties (March/April 1995), 128 nations had ratified the Convention. Parties to the Convention commit to numerous obligations, including commitments to: develop national inventories of anthropogenic emissions using agreed, comparable methodologies’, and to formulate and implement national programs containing measures to mitigate, and to facilitate adaptation to, climate change. Several bilateral and multilateral programs, including the United States Country Studies Program (U.S. CSP) and the United Nations Environment Programme/Global Environment Facility Country Case Studies Project (UNEP), have been established to provide technical and financial assistance to developing countries and countries with economies in transition in meeting their commitments under the Convention.

A 13 m fimcore was recovered in April 1991 at Col du Dome (4250 m.a.s.l.), located below the Mont Blanc summit (Northern French Alps). The core spans a complete sequence of 3.5 years of high alpine precipitation, as indicated by the stratigraphic and the isotopic profiles. Subsamples were analysed for Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3− and SO42− using ion chromatography, and for H+ or HCO3− using a titration technique. In absence of alkaline Saharan dust, the snow is slightly acid (2–20 μ Eq l −1. All analysed ions show a sharply pronounced seasonal pattern, with concentrations, extremely low in winter, increasing in spring and reaching a maximum in summer. This picture supports the idea that in winter the high alpine sites are generally not affected by polluted air masses from lower altitudes, whereas during spring and summer, vertical convective transport significantly affects the highest sites located well above 4000 m a.s.l. The lowest impurity levels of alpine winter snow are comparable with central Greenland values, suggesting that at this time, and just in opposite to what occurs in the Arctic, the highest alpine regions are representative of the continental free troposphere. Annual and seasonal deposition fluxes are calculated. In order to assess the spatial representativeness of these results, a comparison is made with similar records obtained from a 10m firncore recovered in summer 1991, at the low accumulation site Colle Gnifetti (4450 m.a.s.l.) located in the Swiss Alps, 80 km east of Col du Dome. An excellent agreement is found between the overall mean isotopic and chemical composition of the two firncores, suggesting that, since clean winter snow is well preserved at Col du Dome, this site is presumably more influenced by precipitation during summer. Finally, the attractive perspectives for deep drilling in the Mont Blanc area are assessed, and the merits of making use of both sites, where comparable and complementary information can be obtained, are outlined.

Measurements of anthropogenic 129 I and 41 Ca in two Greenland firn cores spanning the years 1935 to 1989 have been performed by accelerator mass spectrometry. The two sets of data points measured for 129 I show a discrepancy and prevent definitive conclusions. One of the sets indicates no large increase of 129 I concentrations in contrast to precipitation at lower latitudes. Data on the 41 Ca profile are preliminary and show a few points markedly above background. The feasibility of detection of 90 Sr in the environment by accelerator mass spectrometry is studied and first results are reported.

The present paper summarizes the results of SNOSP, a snow sampling program carried out in the Alps in the years from 1991 to 1993 in order to study the chemical composition of the high alpine snow pack. The paper briefly describes the sampling sites and the procedures used, focussing then on the geographical, seasonal and year to year variation of the mean concentration and total deposition of eight major ions, viz., chloride, nitrate, sulfate, ammonium, sodium, potassium, magnesium and calcium. NH 4 + , NO 3 − and SO 4 = concentrations in spring snow are higher by a factor of two to three than in winter snow since the lower tropospheric convection is confined to the valleys in winter and extends beyond glacier altitudes in spring. This underlines the importance of local and regional versus long range transport of contamination to the high elevated sites. The Ca ++ deposition occurs in single events (e.g., dust input from the Sahara) with a slightly higher incidence in spring that is consistent with the annual course of atmospheric circulation patterns. Most ionic species display a west to east increase of concentration by about one third. The prevailing precipitation patterns have opposite gradients so that total ionic load of the respective snowpack has no regional preference. The seasonal contrast as expressed by ratios of spring to winter concentrations of NH 4 + , NO 3 − and SO 4 2− is stronger in the west than in the east, and the east to west contrast is greater in winter than in spring. DOI: 10.1034/j.1600-0889.49.issue1.4.x

Une etude des sources naturelles de soufre a ete faite dans une zone peu polluee et favorable aux degagements naturels de gaz soufres: la foret equatoriale humide de Cote d'Ivoire. On a mesure pour cela, entre Novembre 1974 et Aout 1975, la variation de la fraction soluble des sulfates dans l'air dans deux stations differentes. Adiopodoume et Lamto respectivement a 10 et 100 kilometres de la mer. L'estimation des sources directes de sulfates (oceanique et terrigene) au moyen d'elements representatifs (Cl et Ca) montre que celles-ci ne representent que 30% des sulfates solubles presents dans l'air. La difference (70%) serait due a l'oxydation dans l'air de composes soufres gazeux, comme le confirment les mesures de SO 2 effectuees entre decembre 1975 et mars 1976. En effet, on observe une variation annuelle de la concentration en sulfates avec de fortes valeurs (3 µg m -3 ) en Janvier et Juillet et de faibles valeurs (0,5 µg m -3 ) en fin de saison seche (Mai). D'autre part, les concentrations en sulfates et SO 2 decroissent en allant de la zone forestiere vers la savane. En l'absence de sources locales de pollution, ces degagements naturels s'expliquent par la decomposition de la matiere organique dans la foret et la lagune Ebrie. L'apport oceanique de SO 2 parait peu important a partir des donnees obtenues au cours de deux campagnes dans le Golfe de Guinee. The natural sources of sulphur in the moist equatorial forest of the Ivory Coast have been studied. From November 1974 to August 1975, the variation of the soluble fraction of atmospheric sulphates in two different stations, Adiopodoume and Lamto, 10 and 100 km from the seaside respectively, has been considered. The estimating of the direct sources of sulphates (oceanic and terrigenous) by means of representative elements (Cl and Ca) shows that these sources account for only 30% of the atmospheric soluble sulphates. The difference (70%) might be due to the oxidation of gaseous sulphur compounds in the air as confirmed by SO 2 measurements made from December 1975 to March 1976. As a matter of fact, an annual variation of the concentrations of sulphates with high values (3 µg m -3 ) in January and July and with low values (0.5 µg m -3 ) at the end of the dry season (May) has been observed. Moreover, the concentrations of sulphates and of SO 2 decrease when comparing the forest belt with the savannah. As there are no local sources of pollution, these natural emissions are explained by the decomposition of organic matter in the forest and in the Ebrie Lagoon. From the data obtained during two campaigns in the Gulf of Guinea, the oceanic flux of SO 2 is thought to be unimportant. DOI: 10.1111/j.2153-3490.1978.tb00829.x

The use of a radiotracer shows that the magnetic field induces no detectable modification of the exchange current at the Cu{sup 2+}/Cu interface. This paper reports that the variations of the exchange current obtained by electrochemical methods are due to modifications of the surface state of the deposit.

An automatic wet-only precipitation collector and a fogwater collector were operated in the coastal forest of equatorial Congo (Dimonika), for a complete seasonal cycle (November 1986–September 1987). Inorganic (Na + , K + , NH 4 + , Ca 2+ , NO 3 − , Cl − , SO 4 2− ) and organic (HCOO − , CH 3 COO − ) ions were determined in 33 stratiform rain events and nine fog events. With the raindrop size distributions, measured over a 1 year period (June 1988–June 1989) at the site of Enyele in the Equatorial forest of Congo, were established the relationship between the liquid water content ( LWC in gm −3 ) and the rate of rainfall ( R in mm h −1 ) for the stratiform rains: LWC = 0.055 × R 0.871 with a correlation coefficient of 0.98. Taking into account the dilution effect due to LWC , ionic concentrations of fogwater and stratiform precipitation are enriched during the dry season. In particular, K + , NO 3 − , SO 4 2− and Ca 2+ are considerably enriched indicating the seasonal influence of the biomass burning due to savanna fires and terrigenous source from deserts of the Southern Hemisphere. Comparison of the chemical contents of fogwater—which mainly represents the local emission of the forest—and stratiform precipitation—which represent the air chemical content of the planetary boundary layer—during the dry season enabled us to show the following. Fog and rain with comparable chemical contents in mineral elements indicate a generalized contamination of the boundary layer by marine (Na + , Cl − ), terrigenous (Ca 2+ ) and above all by biomass burning (K + , NO 3 − , SO 4 2− ) sources. The organic content (HCOO − , CH 3 COO − ) higher for the fogs than for rains, unexplainable by the dilution effect, has its source at a local level in the forest ecosystem. The estimation, from the organic content of fog and rain, of the gaseous concentrations of formic and acetic acids confirm the production of carboxylic acids measured in Amazonia during ABLE (for HCOOH : 510 ppt at canopy level and 170 ppt in free troposphere and for CH 3 COOH : 410 ppt and 210 ppt, respectively).

On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a V = 7.2 , K0 III star). This was the first-ever observed occultation by this satellite, a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or professionals, to monitor this unique event, providing fifty-seven occultations chords over three continents, all reported here. Selecting the best 27 occultation chords, and assuming a circular limb, we derive Titania's radius: R T = 788.4 ± 0.6 km ( 1 - σ error bar). This implies a density of ρ = 1.711 ± 0.005 g cm −3 using the value G M = ( 2.343 ± 0.006 ) × 10 11 m 3 s −2 derived by Taylor [Taylor, D.B., 1998. Astron. Astrophys. 330, 362–374]. We do not detect any significant difference between equatorial and polar radii, in the limit r eq − r po = − 1.3 ± 2.1 km , in agreement with Voyager limb image retrieval during the 1986 flyby. Titania's offset with respect to the DE405 + URA027 (based on GUST86 theory) ephemeris is derived: Δ α T cos ( δ T ) = − 108 ± 13 mas and Δ δ T = − 62 ± 7 mas (ICRF J2000.0 system). Most of this offset is attributable to a Uranus' barycentric offset with respect to DE405, that we estimate to be: Δ α U cos ( δ U ) = − 100 ± 25 mas and Δ δ U = − 85 ± 25 mas at the moment of occultation. This offset is confirmed by another Titania stellar occultation observed on August 1st, 2003, which provides an offset of Δ α T cos ( δ T ) = − 127 ± 20 mas and Δ δ T = − 97 ± 13 mas for the satellite. The combined ingress and egress data do not show any significant hint for atmospheric refraction, allowing us to set surface pressure limits at the level of 10–20 nbar. More specifically, we find an upper limit of 13 nbar ( 1 - σ level) at 70 K and 17 nbar at 80 K, for a putative isothermal CO2 atmosphere. We also provide an upper limit of 8 nbar for a possible CH4 atmosphere, and 22 nbar for pure N2, again at the 1 - σ level. We finally constrain the stellar size using the time-resolved star disappearance and reappearance at ingress and egress. We find an angular diameter of 0.54 ± 0.03 mas (corresponding to 7.5 ± 0.4 km projected at Titania). With a distance of 170 ± 25 parsecs, this corresponds to a radius of 9.8 ± 0.2 solar radii for HIP 106829, typical of a K0 III giant.

In previous work, we defined a component oriented framework dedicated to the specification of embedded systems in the aeronautics domain. A component is defined as a formal entity with three internal layers together with a collection of models defined in domain-oriented views. A categorical frame- work has been proposed to provide a unified representation of the component calculus as well as the various formal models used for the analysis of the system. In this paper, we present an implementation of this categorical framework using the EXPRESS data modelling language. EXPRESS is used to give an operational representation of the formalization, which is quite different from classical implementations of category theory based approaches.

This paper presents a component oriented framework dedicated to the specification of embedded systems in the aeronautics domain. A component is an entity with three internal layers (hardware, operating functions and applicative functions) together with a collection of models in different domain-oriented views. A composition operation allows the expression of composition scenarios, yielding a component calculus for representing composite systems. An institutional framework supports this component calculus, allowing the expression of coherence criteria between heterogeneous views. This framework can be seen as a formal documentation of a system development and analysis, supporting heterogeneous modeling and compositional verification. The approach is illustrated on a non trivial case study.

Describes a new technique for segmentation of infrared sea surface images applied to detection of bi-dimensional oceanic structures. The method is based on a multiscale analysis of isotherms curvature and a characterization through phase portraits technique. The main interest of the method is that the isotherm curvature can be related to ocean dynamic, particularly to detect and describe such phenomena as mesoscale eddies with spiral patterns. The other appealing side of this approach is that the algorithm only needs information on the characteristic sizes of the structures to be observed. The authors used this method for the analysis of several images of the Bay of Biscay. >

Presents some new developments of a technique for automatic detection of oceanic eddies on satellites infrared sea surface images. This technique relies on an algorithm using multiscale analysis of isotherm curvature and characterization of eddies through the phase portraits method. The main interest of the method is that isotherm curvature can be related to ocean dynamic, particularly to detect and describe such phenomena as mesoscale eddies with spiral patterns. The aim of this work is to obtain a much efficient method both in term of calculation time and stability in the characterization step. This algorithm has been then tested on several thermal infrared images of Bay of Biscay issued from AVHRR radiometer. The results on some typical images are given and statistics on the whole set are briefly described and discussed.

Direct removal of both As(III) and As(V) from strongly acidic industrial liquid wastes is possible using several oxides. We have studied hydrated antimony pentoxide (HAP) and manganese dioxide (MDO) in detail. The kinetics and capacity of the As sorption were determined radiochemically, the exchange balance of the elements in solution by ICP/AES and quantitative analysis of the As species in the solutions using capillary zone electrophoresis (CZE). Sb or Mn release was low and not related to the As sorption, except for As(III) on MDO. Manganese dioxide rapidly oxidised As(III) to As(V) and Mn(II) was simultaneously released into solution. HAP had the highest capacity and selectivity for As(III). A single layer of As oxycomplexes could be formed on the surface of both solids.

The potential impact on aquatic ecosystems of supplementing the diets of beef cattle with selenium (Se) was studied on 4 northern California ranches. All study sites included an area of concentrated use by cattle that had diets supplemented with Se. In each case, a stream flowed through the site and provided a control sampling area upstream and a treated sampling area downstream. Specimens of water, sediment, algae, aquatic plants, aquatic invertebrates, and fish were analyzed fluorometrically for total Se content. Significant differences in Se concentration were not found between specimens from upstream control areas and those from downstream areas subjected to use by Se-treated cattle. Evidence was not found that Se supplementation in cattle at maximal permitted concentrations caused Se accumulation in associated aquatic ecosystems.

Le système étudié est un réacteur rotatif à source plasma axiale pour la fusion de matériaux réfractaires. Le diagnostic thermique en transitoire de la première phase de fonctionnement (régime monophasique) est réalisé l'aide d'un dispositif de télémesure embarqué. Ce système a permis en particulier de mesurer l'évolution du champ des température à l'intérieur du réacteur (profils axial et radial de températures). Le domaine exploré est compris entre 500 K et 1640 K.

The DECAFE (Dynamique Et Chimie Atmospherique en Foret Equatoriale) project was set up to study meteorological and chemical processes in and above the rain forest of equatorial Africa. This project makes use of a combination of aircraft, balloon, and ground measurements of chemical and physical parameters at several sites in equatorial Africa. The DECAFE-88 experiment was carried out near Impfondo in the rain forest region of the northern Congo during February 1988.

The determination of Ir and Pt in rhodium neutron monitors was investigated via192Ir and199Au after neutron activation, via191Pt and194Au−196Au after proton activation. Ir was determined by instrumental NAA. A chemical separation of gold, with a yield measurement method by a radioactive tracer, was developed for platinum determination after neutron or proton irradiation.

Surface effects in the determination of sulfur by neutron activation analysis Thermal neutron activation analysis leads to overestimated sulfur contents in some metals. This phenomenon was studied for samples of iron. It is attributed to ineffective chemical etching arising from dissolution of the metal through a surface layer which retains impurities, especially sulfur-35. Significant amounts of this isotope are produced at the surface through the 35 Cl(n, γ) 35 S reaction. Experimental modifications which lead to the correct sulfur concentration are proposed.

In this study, we report sulfate content measurements of eighty snow samples collected in East Antarctica. Stringent contamination free techniques were used both for sampling and analysis (ionometric titration with a lead selective electrode after preconcentration). Sulfate concentrations (range: 50–100.10−9 g g−1, accuracy ±10%) do not show large variations along a 1100 km coast interior axis, if we except a narrow coastal area. The analysis of well dated snow samples (time range: 1950–1975) collected at South Pole Station and Dome C (124°E, 75°S) suggest a main marine contribution for the sulfate content, to which are added sporadic stratospheric injections linked with major volcanic events, such as Mt. Agung (1963), whose eruption is clearly recorded. There is no evident anthropogenic contribution to the measured values.

The biosphere-atmosphere exchanges of sulphur and nitrogen compounds are studied in the two main ecosystems of west Africa: the tropical forests and savannahs. The forested zones appear as important natural sources of gaseous compounds of these two elements, mainly H 2 S, NO, NH 3 . The emissions are due to the decomposition of organic matter and biological transformation in soils. The study of dry and wet depositions of gaseous and particulate compounds of the two elements shows that in this ecosystem the budget of the exchange with the atmosphere is in equilibrium. In the savannahs, the sources of sulphur and nitrogen compounds are essentially the bush fires which lead to a loss of these compounds for the ecosystem. This loss is counterbalanced, in totality for sulphur, in part for nitrogen, by the contributions of particulate matters created over the forested zones and carried over the savannahs by advection of air masses.

On expose une methode de titration potentiometrique permettant de mesurer jusqu'a 0,25μg de sulfate dans 0,25 ml echantillon liquide. Le sulfate est precipite par du perchlorate de plomb en milieu eaudioxanne. L'exces de plomb est determine a l'aide d'une electrode specifique par la methode des ajouts doses et utilisation de papier de Gran.

A simplified calculation model of the recoil and irradiation enhanced diffusion which occur in neutron activation analysis of metals is proposed. Under usual irradiation conditions, the recoil does not exceed 0.01 μm for n, γ reactions and 2 μm for other reactions; the diffusion does not exceed 1 μm. Examples, in which deep impurity diffusion leading to important analytical errors was put forward, are discussed through this calculation model. In most cases, the observed phenomena are not related to diffusion but to other causes such as unefficient etching of the sample surface.

The measurement of gases enclosed in polar ice cores provides valuable Information concerning the history of the ice sheets and their environment. The extraction of gases from ice is a critical step in the experimental procedure. We found that the most efficient methods of gas extraction for 20 to 50 g samples were ice melting and controlled refreezing of the melt water for the total gas content and ice crushing far the CO2 content. These two experimental methods are described in detail.It is shown, in particular, that ice is easily contaminated by carbonate dust during sample preparation. This contamination introduces an excess of CO2 when gases are extracted using a procedure involving ice melting.

A method is given for calculating the absorption coefficient spectra k ( v ) from experimental data in a real atmosphere for narrow spectral intervals centered in a CO 2 absorption band (λ = 740 cm −1 ). The results have been compared with radiometric data and are useful for calculating emission and absorption in the atmosphere.