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1.
H. E. Scheel H. Areskoug H. Geiss B. Gomiscek K. Granby L. Haszpra L. Klasinc D. Kley T. Laurila A. Lindskog M. Roemer R. Schmitt P. Simmonds S. Solberg G. Toupance 《Journal of Atmospheric Chemistry》1997,28(1-3):11-28
Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O3 concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO3 ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO3 values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O3 mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O3 levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O3 and Ox(= O3 + NO2)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere. 相似文献
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This study integrated surface and subsurface stratigraphic data with geophysical logs and hydrogeologic data in order to
characterize the hydraulic properties of the Silurian dolomite in northeastern Wisconsin. Silurian stratigraphy consists of
predictable alternations of characteristic facies associations. A vertical profile of hydraulic conductivity, obtained from
short-interval packer tests in a core hole that penetrates a majority of the Silurian section, indicates that hydraulic conductivity
ranges over five orders of magnitude (10–1 to 10–6 cm/s). Matrix conductivity is generally low and varies with texture; the finer-grained restricted-marine and transitional
facies being less permeable than the coarser-grained open-marine facies. High-conductivity values are generally associated
with bedding-plane fractures, and fracture frequency is greater in the restricted-marine facies.
High-flow features in 16 wells were identified using fluid-temperature/resistivity and heat-pulse flowmeter logs. Natural-gamma
logs were used to identify the stratigraphic position of flow features in each well and to correlate flow features to specific
stratigraphic horizons. By combining stratigraphic, geophysical, and hydrogeologic data, 14 high-permeability zones within
the Silurian aquifer have been identified and correlated in wells more than 16 km apart. These zones parallel bedding, appear
most pronounced at contacts between contrasting lithologies, and are most abundant in restricted-marine lithologies.
Electronic Publication 相似文献
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Field-based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 microg/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid-phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 microg/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic-bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole. 相似文献
5.
Aspects of the Fine-Scale Climatology Over Lake Tanganyika as Resolved by a Mesoscale Model 总被引：1，自引：0，他引：1
Summary An hourly averaged climatology at 0.05 ° horizontal resolution over the Lake Tanganyika region was created by making simulations
with a mesoscale model (HIRLAM) using a high resolution physiography to represent the surface. Initial and boundary values
were interpolated from ECMWF analyses. Climatologies for a typical dry season month (July 1994) and wet season month (March
1994) were created by 7-day segmenting. Model results were validated by utilizing a special coastal observation network. A
number of experiments were made with changes to the physiography (mountains/no mountains, lake/no lake).
The results reveal local channelling and blocking effects of the near-surface southeasterly trade winds by the high mountain
chains in the region of the East African rift. Furthermore, surface winds display regular diurnal cycles in many places, due
to slope winds over hills and lake-land-type breezes near the coast. The diurnal coastal winds (defined by the observation
network) are reasonably well simulated. Precipitation patterns display the semi-annual march of the ITCZ across the area,
plus considerable topographic effects. There is high evaporation from lakes and wetlands during the windy dry season, while
evaporation from the moist land surface dominates the rainy season.
Received October 15, 1998/Revised September 2, 1999 相似文献
6.
Large-eddy Simulation of the Dispersion of Solid Particles in a Turbulent Boundary Layer 总被引：2，自引：2，他引：2
Ivana Vinkovic Cesar Aguirre Michel Ayrault Serge Simoëns 《Boundary-Layer Meteorology》2006,121(2):283-311
A large-eddy simulation (LES) with the dynamic Smagorinsky-Germano subgrid-scale (SGS) model is used to study the dispersion of solid particles in a turbulent boundary layer. Solid particles are tracked in a Lagrangian way. The instantaneous velocity of the surrounding fluid is considered to have a large-scale part (directly computed by the LES) and a small-scale part. The SGS velocity of the surrounding fluid is given by a three-dimensional Langevin model written in terms of SGS statistics at a mesh level. An appropriate Lagrangian correlation time scale is considered in order to include the influences of gravity and inertia of the solid particle. Inter-particle collisions and the influence of particles on the mean flow are also taken into account. The results of the LES are compared with the wind-tunnel experiments of Nalpanis et al. (1993 J Fluid Mech 251: 661–685) and of Tanière et al. (1997 Exp in Fluids 23:463–471) on sand particles in saltation and in modified saltation, respectively. 相似文献
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Stratigraphic and geochemical controls on naturally occurring arsenic in groundwater,eastern Wisconsin,USA 总被引：5，自引：0，他引：5
High arsenic concentrations (up to 12,000 7g/L) have been measured in groundwater from a confined sandstone aquifer in eastern Wisconsin. The main arsenic source is a sulfide-bearing secondary cement horizon (SCH) that has variable thickness, morphology, and arsenic concentrations. Arsenic occurs in pyrite and marcasite as well as in iron oxyhydroxides but not as a separate arsenopyrite phase. Nearly identical sulfur isotopic signatures in pyrite and dissolved sulfate and the correlation between dissolved sulfate, iron, and arsenic concentrations suggest that sulfide oxidation is the dominant process controlling arsenic release to groundwater. However, arsenic-bearing oxyhydroxides can potentially provide another arsenic source if reducing conditions develop or if they are transported as colloids in the aquifer. Analysis of well data indicates that the intersection of the SCH with static water levels measured in residential wells is strongly correlated with high concentrations of arsenic in groundwater. Field and laboratory data suggest that the most severe arsenic contamination is caused by localized borehole interactions of air, water, and sulfides. Although arsenic contamination is caused by oxidation of naturally occurring sulfides, it is influenced by water-level fluctuations caused by municipal well pumping or climate changes, which can shift geographic areas in which contamination occurs. Résumé De fortes concentrations en arsenic, jusqu'à 12000 7g/L, ont été mesurées dans l'eau souterraine d'un aquifère gréseux captif, dans l'est du Wisconsin. La principale source d'arsenic est un horizon à cimentation secondaire (SCH) comportant des sulfures, dont l'épaisseur, la morphologie et les concentrations en arsenic sont variables. L'arsenic est présent dans la pyrite et dans la marcassite, de même que dans des oxy-hydroxydes de fer, mais non pas dans une phase séparée d'arsénopyrite. Les signatures isotopiques du soufre presque identiques dans la pyrite et dans les sulfates dissous et la corrélation entre les concentrations en sulfates, en fer et en arsenic dissous laissent penser que l'oxydation des sulfures est le processus dominant contrôlant la libération de l'arsenic dans les eaux souterraines. Cependant, les oxy-hydroxydes contenant de l'arsenic sont susceptibles d'être une autre source d'arsenic si des conditions réductrices apparaissent ou s'ils sont transportés dans l'aquifère sous forme de colloïdes. L'analyse des données provenant de puits montre que l'intersection entre le SCH et les niveaux statiques des puits domestiques est fortement corrélée à de fortes concentrations en arsenic dans les eaux souterraines. Des données de terrain et de laboratoire conduisent à penser que la contamination en arsenic la plus forte est causée par l'interaction localisée aux forages entre l'air, l'eau et les sulfures. Bien que la contamination en arsenic soit causée par l'oxydation de sulfures présents naturellement, elle est influencée par les fluctuations du niveau piézométrique causées par les pompages du captage municipal ou par les variations climatiques, ce qui peut conduire au déplacement des zones géographiques où se produisent les contaminations. Resumen Se han medido concentraciones de arsénico muy altas (de hasta 12000 7g/L) en las aguas subterráneas de un acuífero confinado, en areniscas, localizado en la parte oriental de Wisconsin (EEUU). La fuente principal de arsénico es un horizonte de cementación secundaria (SCH) con un alto contenido en sulfuros, y con una gran variabilidad en espesor, morfología y concentraciones de As. El arsénico aparece en piritas y marcasitas, además de en oxihidróxidos de hierro, pero no como una fase independiente de arsenopiritas. El hecho que la marca isotópica de piritas y sulfatos disueltos sea muy similar, y que exista una gran correlación entre las concentraciones de sulfato disuelto, hierro y arsénico sugiere que la oxidación de sulfuros es el proceso que controla la aportación de arsénico al agua subterránea. Sin embargo, los oxihidróxidos con alto contenido en arsénico podrían suponer otra fuente de arsénico si se llegaran a desarrollar condiciones reductoras o si se transportaran como coloides por el acuífero. De los datos procedentes de pozos, se ve una fuerte correlación entre la presencia de altas concentraciones de As en el agua y que el nivel freático intersecte el SCH. Los datos de campo y de laboratorio indican que los puntos con mayor contaminación de arsénico son debidos a interacciones de carácter local y en los propios pozos entre aire, agua y sulfuros. Aunque la contaminación por As está causada por la oxidación de sulfuros presentes de manera natural, también está muy influenciada por las fluctuaciones en los niveles freáticos causadas por bombeos o cambios climáticos. 相似文献
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“Honest broker” refers to scientists facilitating complex political decisions from a neutral position, aiming to expand the scope of choice available instead of advocating a certain policy. This article reflects on the experiences of three scientists acting as honest brokers while carrying out a multicriteria evaluation to help politicians choose the water supply option for the city of Oulu, Finland. The process was considered successful and many politicians said that they have never before been that well informed when making a decision. The case primarily shows that besides the common knowledge brokerage roles targeting knowledge exchange, the honest brokerage approach relates more to managing social relationships and balancing political games and rapidly evolving discussions. Trustful relationships increased the perceived credibility of the brokers and ensured two-way communication. On the other hand, the brokers faced ethical dilemmas and difficulties of staying impartial while finding out confidential information related to political strategies. 相似文献
10.
The aim of this study is to date by the archaeomagnetic method the last heatingcooling cycle of one Roman and two Medieval tile kilns, discovered in Belgium. The investigation demonstrates the limitations when well-documented local directional secular variation curves of the geomagnetic field in the past are used for dating and the difficulties when trying to determine field intensities from “in situ” baked clays from the kilns. The three kilns yielded very well defined ancient field directions but two possible dating solutions for each of them when no a priori time constraints are taken into account, due to field direction recurrence. As an increase of the dating accuracy and reduction of the number of dating solutions can be expected using the full field vector information, also field intensity determinations on burnt clays from the kilns were attempted. Field intensities from samples of the Roman and of one of the Medieval kilns are quite scattered. On the other hand, results obtained applying the Thellier-Thellier method and the modified method developed by Dekkers and Böhnel on sister samples from the Roman kiln agree fairly well. Rock magnetic properties reveal high variance in the kilns that point to varying spatial heating and cooling conditions in the kilns. Even well burnt material from the kilns shows irreversible changes when heated in air in the laboratory. Reliable field intensities on “in situ” baked materials from kilns themselves can therefore only be obtained when measuring sufficient number of samples from different parts of the kiln, taking into account the spatial-temporal conditions during kiln operation and cooling history. More reference intensity data is needed in our regions in order to improve dating based on directional reference data only. 相似文献