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  • Articles  (302)
  • geostatistics  (109)
  • kriging  (90)
  • ozone  (62)
  • climate change
  • kinetics
  • Springer  (302)
  • Geosciences  (301)
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  • 1
    Electronic Resource
    Electronic Resource
    Late-glacial and early-Holocene Trichoptera (Insecta) from Kråkenes Lake, western Norway (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 49-56 
    Details
    ISSN: 1573-0417
    Keywords: Trichoptera ; caddisflies ; late glacial ; Allerød ; Younger Dryas ; early Holocene ; Kråkenes ; palaeolimnology ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Fossil Trichoptera (caddisfly) remains have been identified and quantitatively recorded in the late-glacial and early-Holocene sediments from Kråkenes Lake, western Norway. The sediment sequence was deposited between 12,300 and 8850 14C BP, covering the Allerød, Younger Dryas, and early-Holocene periods. The first Trichoptera were recorded at 12,000 14C BP, and during the Allerod a diverse assemblage of Limnephilidae taxa developed in the lake. By about 11,400 14C BP the relatively thermophilous Polycentropus flavomaculatus and Limnephilus rhombicus were present, suggesting that the summer water temperature was at least 17 °C. This temperature fell by 5-8 °C at the start of the Younger Dryas, and the thermophilous taxa were replaced within 20-40 14C yrs by Apatania spp., including the arctic-alpine A. zonella, suggesting a maximum summer water temperature of 10-12 °C. The Trichoptera assemblage was impoverished in numbers and in diversity over the next 200 yrs as the severe conditions of the Younger Dryas developed. As soon as temperatures rose and glacial meltwater and silt input ended about 700 14C yrs later, the resident Apatania assemblage expanded immediately, within 10 yrs. About 130 yrs later, thermophilous taxa replaced Apatania, and a much more diverse assemblage than in the Allerod occupied the varied habitats made available by the development of the Holocene lake ecosystem. The 130 yr delay may have been caused by a gradual temperature increase crossing a critical threshold, or by the time taken for thermophilous taxa to migrate from their Younger Dryas refugia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008064831048
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  • 2
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    Electronic Resource
    Evidence for mid-Eemian cooling in continental climatic record from Lake Baikal (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 365-371 
    Details
    ISSN: 1573-0417
    Keywords: Lake Baikal ; diatoms ; biogenic silica ; Eemian ; climate change ; Siberia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The discussion on climatic instability observed in Greenland ice cores during the Eemian period (substage 5e) resulted in discovery of a pronounced mid-Eemian cooling event. We report that the mid-Eemian cooling is found for the first time in the biogenic silica climatic record and microfossil abundance record of Lake Baikal. Timing of this event in Lake Baikal correlates well with timing of the European pollen records and marine sedimentary records. The presence of the mid-Eemian cooling signal in the Lake Baikal record suggests a much closer link between Asian climate influenced by strong pressure fields over the vast land masses and the climate-controlling processes in the North Atlantic during interglacial periods, than what was generally believed. Furthermore, the Lake Baikal record suggests that after the mid-Eemian cooling, the climatic conditions returned close to the warmth of the 5e optimum and thus argues that the warm conditions of the last interglacial persisted in Siberia throughout 5e, and did not end with the mid-Eemian cooling as suggested by several published marine records.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008188100542
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  • 3
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    Holocene lake sediment records of Arctic hydrology (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 1-13 
    Details
    ISSN: 1573-0417
    Keywords: Arctic ; Holocene ; paleohydrology ; paleolimnology ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Although paleoclimatic research in the Arctic has most often focused on variations in temperature, the Arctic has also experienced changes in hydrologic balance. Changes in Arctic precipitation and evaporation rates affects soils, permafrost, lakes, wetlands, rivers, ice and vegetation. Changes in Arctic soils, permafrost, runoff, and vegetation can influence global climate by changing atmospheric methane and carbon dioxide concentrations, thermohaline circulation, and high latitude albedo. Documenting past variations in Arctic hydrological conditions is important for understanding Arctic climate and the potential response and role of the Arctic in regards to future climate change. Methods for reconstructing past changes in Arctic hydrology from the stratigraphic, isotopic, geochemical and fossil records of lake sediments are being developed, refined and applied in a number of regions. These records suggest that hydrological variations in the Arctic have been regionally asynchronous, reflecting the impacts of different forcing factors including orbitally controlled insolation changes, changes in geography related to coastal emergence, ocean currents, sea ice extent, and atmospheric circulation. Despite considerable progress, much work remains to be done on the development of paleohydrological proxies and their application to the Arctic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008100714795
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  • 4
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    Diatom transfer-functions for quantifying past air temperature, pH and total organic carbon concentration from lakes in northern Sweden (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 109-123 
    Details
    ISSN: 1573-0417
    Keywords: diatoms ; climate change ; temperature ; pH ; transfer functions ; lake sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The relationships between diatoms (Bacillariophyceae) in surface sediments of lakes and summer air temperature, pH and total organic carbon concentration (TOC) were explored along a steep climatic gradient in northern Sweden to provide a tool to infer past climate conditions from sediment cores. The study sites are in an area with low human impact and range from boreal forest to alpine tundra. Canonical correspondence analysis (CCA) constrained to mean July air temperature and pH clearly showed that diatom community composition was different between lakes situated in conifer-, mountain birch- and alpine-vegetation zones. As a consequence, diatoms and multivariate ordination methods can be used to infer past changes in treeline position and dominant forest type. Quantitative inference models were developed to estimate mean July air temperature, pH and TOC from sedimentary diatom assemblages using weighted averaging (WA) and weighted averaging partial least squares (WA-PLS) regression. Relationships between diatoms and mean July air temperature were independent of lake-water pH, TOC, alkalinity and maximum depth. The results demonstrated that diatoms in lake sediments can provide useful and independent quantitative information for estimating past changes in mean July air temperature (R2 jack = 0.62, RMSEP = 0.86 °C; R2 and root mean squared error of prediction (RMSEP) based on jack-knifing), pH (R2 jack = 0.61, RMSEP = 0.30) and TOC (R2 jack = 0.49, RMSEP = 1.33 mg l-1). The paper focuses mainly on the relationship between diatom community composition and mean July air temperature, but the relationships to pH and TOC are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008128014721
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  • 5
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    A first estimate of organic carbon storage in Holocene lake sediments in Alberta, Canada (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 395-400 
    Details
    ISSN: 1573-0417
    Keywords: carbon storage ; lake sediment ; Holocene ; Canada ; climate change ; organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract This paper reports a first estimate of the Holocene lake sediment carbon pool in Alberta, Canada. The organic matter content of lake sediment does not appear to depend strongly on lake size or other limnological parameters, allowing a simple first estimate in which we assume all Alberta lake sediment to have the same organic matter content. Alberta lake sediments sequester about 15 g C m-2 yr-1, for a provincial total of 0.23 Tg C yr-1, or 2.3 Pg C over the Holocene. Alberta lakes may represent as much as 1/1700 of total global, annual permanent carbon sequestration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008103605817
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  • 6
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    Elicited Data and Incorporation of Expert Opinion for Statistical Inference in Spatial Studies (2000)
    Springer
    Mathematical geology 32 (2000), S. 465-487 
    Details
    ISSN: 1573-8868
    Keywords: Bayesian inference ; elicited prior ; hierarchical models ; honesty parameter ; kriging ; optimal sequential sample design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Spatial data are often sparse by nature. However, in many instances, information may exist in the form of “soft” data, such as expert opinion. Scientists in the field often have a good understanding of the phenomenon under study and may be able to provide valuable information on its likely behavior. It is thus useful to have a sensible mechanism that incorporates expert opinion in inference. The Bayesian paradigm suffers from an inherent subjectivity that is unacceptable to many scientists. Aside from this philosophical problem, elicitation of prior distributions is a difficult task. Moreover, an intentionally misleading expert can have substantial influence on Bayesian inference. In our experience, eliciting data is much more natural to the experts than eliciting prior distributions on the parameters of a probability model that is a purely statistical construct. In this paper we elicit data, i.e., guess values for the realization of the process, from the experts. Utilizing a hierarchical modeling framework, we combine elicited data and actual observed data for inferential purposes. A distinguishing feature of this approach is that even an intentionally misleading expert proves to be useful. Theoretical results and simulations illustrate that incorporating expert opinion via elicited data substantially improves the estimation, prediction, and design aspects of statistical inference for spatial data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007525900030
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  • 7
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    Integrated Interpolation Methods for Geophysical Data: Applications to Mineral Exploration (2000)
    Springer
    Natural resources research 9 (2000), S. 53-64 
    Details
    ISSN: 1573-8981
    Keywords: Geophysical data integration ; geostatistics ; mineral exploration ; interpolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Geophysical data are used routinely in mineral exploration to delineate the geology of an area.Because geophysical attributes are sparsely sampled, interpolation methods are used to gridthe individual sets of data. Whereas traditional techniques interpolate constituent attributes ofinterest independently, frequently resulting in simplistic geological models, alternativetechniques interpolate by integrating secondary data sets collected in the explored area. Traditionaltechniques include minimum curvature and ordinary kriging. Alternative integrated interpolationtechniques include standardized ordinary cokriging, collocated cokriging, and kriging withexternal drift. Application of these techniques to a specific exploration area in interpolatinggravity measurements (primary data) using weakly correlated aeromagnetics (secondary data)suggests that when gravity is well sampled, all techniques generate similar results. However,when gravity is undersampled, the secondary data can contribute substantially to identifyinggeophysical anomalies. Considering the high cost of geophysical data collection, this observationcan make geophysical data collection more efficient and cost effective. The case studyshows how, in the absence of a strong correlation, cokriging varieties tend to produce mapssimilar to those generated by traditional techniques. Kriging with external drift is shown togenerate a gravity map reproducing all gravity anomalies. The technique produces excellentresults when features identified in the secondary data need to be reflected in the map of theprimary data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010161813931
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  • 8
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    Adding Local Accuracy to Direct Sequential Simulation (2000)
    Springer
    Mathematical geology 32 (2000), S. 815-850 
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    ISSN: 1573-8868
    Keywords: sequential simulation ; kriging ; local vs. global accuracy ; bootstrap ; entropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Geostatistical simulations are globally accurate in the sense that they reproduce global statistics such as variograms and histograms. Kriging is locally accurate in the minimum local error variance sense. Building on the concept of direct sequential simulation, we propose a fast simulation method that can share these opposing objectives. It is shown that the multiple-point entropy of the resulting simulation is related to the univariate entropy of the local conditional distributions used to draw simulated values. Adding local accuracy to conditional simulations does not detract much from variogram reproduction and can be used to increase multiple-point entropy. The methods developed are illustrated using a case study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007596423578
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  • 9
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    Correcting the Smoothing Effect of Estimators: A Spectral Postprocessor (2000)
    Springer
    Mathematical geology 32 (2000), S. 787-813 
    Details
    ISSN: 1573-8868
    Keywords: local accuracy ; conditional bias ; spectral amplitudes ; kriging ; stochastic simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The postprocessing algorithm introduced by Yao for imposing the spectral amplitudes of a target covariance model is shown to be efficient in correcting the smoothing effect of estimation maps, whether obtained by kriging or any other interpolation technique. As opposed to stochastic simulation, Yao's algorithm yields a unique map starting from an original, typically smooth, estimation map. Most importantly it is shown that reproduction of a covariance/semivariogram model (global accuracy) is necessarily obtained at the cost of local accuracy reduction and increase in conditional bias. When working on one location at a time, kriging remains the most accurate (in the least squared error sense) estimator. However, kriging estimates should only be listed, not mapped, since they do not reflect the correct (target) spatial autocorrelation. This mismatch in spatial autocorrelation can be corrected via stochastic simulation, or can be imposed a posteriori via Yao's algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007544406740
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  • 10
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    Gradual Deformation and Iterative Calibration of Gaussian-Related Stochastic Models (2000)
    Springer
    Mathematical geology 32 (2000), S. 87-108 
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    ISSN: 1573-8868
    Keywords: heterogeneity ; geostatistics ; optimization ; inversion ; nonlinearity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract This paper describes a new method for gradually deforming realizations of Gaussian-related stochastic models while preserving their spatial variability. This method consists in building a stochastic process whose state space is the ensemble of the realizations of a spatial stochastic model. In particular, a stochastic process, built by combining independent Gaussian random functions, is proposed to perform the gradual deformation of realizations. Then, the gradual deformation algorithm is coupled with an optimization algorithm to calibrate realizations of stochastic models to nonlinear data. The method is applied to calibrate a continuous and a discrete synthetic permeability fields to well-test pressure data. The examples illustrate the efficiency of the proposed method. Furthermore, we present some extensions of this method (multidimensional gradual deformation, gradual deformation with respect to structural parameters, and local gradual deformation) that are useful in practice. Although the method described in this paper is operational only in the Gaussian framework (e.g., lognormal model, truncated Gaussian model, etc.), the idea of gradually deforming realizations through a stochastic process remains general and therefore promising even for calibrating non-Gaussian models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007506918588
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  • 11
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    Blending-Based Stochastic Simulator (2000)
    Springer
    Mathematical geology 32 (2000), S. 367-379 
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    ISSN: 1573-8868
    Keywords: random functions ; simulation ; geostatistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract This paper presents a new method of constructing random functions whose realizations can be evaluated efficiently. The basic idea is to “blend,” both stochastically and linearly, a limited set of independent initial realizations previously generated by any chosen simulation method. The blending stochastic coefficients are determined in such a way that the new random function so generated has the same mean and covariance functions as the random function used for generating the initial realizations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007590012189
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  • 12
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    A Method to Estimate Length Distributions from Outcrop Data (2000)
    Springer
    Mathematical geology 32 (2000), S. 389-419 
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    ISSN: 1573-8868
    Keywords: shale ; geostatistics ; Bayes' theorem ; Frontier Formation ; Erlangian ; tide-influenced delta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Dimensions of shales and other geologic bodies that affect fluid flow through reservoirs and aquifers are often estimated from analogous deposits exposed in outcrops. Shale lengths observed in outcrops are biased because the finite length of outcrops truncates longer shales and long shales tend to be overrepresented in the sample. Shale length distributions can be modeled using an Erlangian probability density function based on termination frequency. Termination frequency can be calculated from outcrop observations even if the shales are incompletely exposed. Termination frequency is unbiased regardless of underlying shale length distribution and outcrop size and shape. Complex length distributions can be represented by a weighted sum of Erlangian models, each with a distinct termination frequency. The proportions and termination frequencies of the component models can be estimated using Bayes' theorem. Subsamples of the outcrop area can be analyzed to quantify spatial trends in termination frequency and thus shale length. These methods can be applied to estimate length distributions of any geologic object exposed in outcrops or other spatially limited samples. In many cases estimated termination frequency is normally distributed, and its variance can be estimated using closed-form expressions. Shale length distributions for the Frewens Sandstone were modeled using one- and two-component Erlangian probability density functions. The Frewens Sandstone is a tide-influenced deltaic sandstone body within the Cretaceous-age Frontier Formation, exposed in central Wyoming, USA. Length observations and Erlangian models agree reasonably well. Because the models correct for the effects of shale truncation in limited outcrop exposures, predicted means and proportions of long shales are substantially greater than observed values. There is a vertical trend and pronounced vertical cyclicity in termination frequency, indicating that shales become shorter upward and intervals of longer and shorter shales alternate. Along strike, termination frequency decreases away from the sandstone-body axis, reflecting greater preserved shale lengths toward sandstone-body margins. No correlation was observed between distance along dip and termination frequency. Termination frequencies and histograms of shale length for adjacent, perpendicular walls are similar, indicating that there is no anisotropy in shale length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007510615051
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  • 13
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    Mercury speciation in natural waters: Measurement of dissolved gaseous mercury with a field analyzer (2000)
    Springer
    Biogeochemistry 48 (2000), S. 237-259 
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    ISSN: 1573-515X
    Keywords: gaseous ; kinetics ; mercury ; methods ; speciation ; waters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Mercury evasion from water is commonly modeled using measurements of dissolved gaseous mercury (DGM). We developed a method using a recently available automated field-ready mercury vapor analyzer to rapidly measure the concentrations of DGM in surface waters. We summarize here results of laboratory tests of the method, field intercomparisons with a manual method, and selected data from recent sampling campaigns in Florida and Michigan. The method uses the 1.5 lpm flow of a Tekran® Model 2537A mercury analyzer to purge and analyze discrete water samples, generating near real time (5-min) data on DGM in samples and blanks. Application of the Tekran allowed for detailed analysis of DGM removal kinetics and short-term diel studies characterizing the influence of sunlight and precipitation on DGM production in surface waters. Gas removal kinetics for dozens of samples indicates a first-order rate constant, and supports a 20-min. purge time for surface water samples from Florida (40-min for Michigan samples). Blanks are measured during a second such purge. Our results indicate that DGMs determined by both automated and manual methods are generally comparable, and that DGM in Florida samples is unstable during storage (loss rate constant ∼0.1--0.2 h-1), probably due to oxidation. This suggests that rapid in-field analysis is preferred to storage with delayed analysis. Our data indicate that DGM at the Florida site is influenced by inputs of reactive Hg in rainwater, and by production of surface DGM during photoreduction of oxidized Hg in the water column.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006228612872
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  • 14
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    The Use of Fractal Geostatistics and Artificial Neural Networks for Carbonate Reservoir Characterization (2000)
    Springer
    Transport in porous media 41 (2000), S. 173-195 
    Details
    ISSN: 1573-1634
    Keywords: carbonate reservoir characterization ; geostatistics ; fractals ; artificial neural networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract In this study, a carbonate oil reservoir located in the southeast part of Turkey was characterized by the use of kriging and the fractal geometry. The three-dimensional porosity and permeability distributions were generated by both aforementioned methods by using the wireline porosity logs and core plug permeability measurements taken from six wells of the field. Since classical regression (lognormal or polynomial) and geostatistical techniques (cross variograms) fail to estimate permeability from wireline log-porosity data, the use of artificial neural networks (ANNs) is proposed in this study to generate permeability data at uncored intervals of porosity logs. For both of the methods, kriging and fractal techniques, the validation of the estimated/simulated data with known wellbore data resulted with acceptable agreements, especially for porosity. Also the comparison of both methods at unsampled locations show better agreements for porosity than permeability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006725709303
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  • 15
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    Application of kriging with external drift to estimate hydraulic conductivity from electrical-resistivity data in unconsolidated deposits near Montalto Uffugo, Italy (2000)
    Springer
    Hydrogeology journal 8 (2000), S. 356-367 
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    ISSN: 1435-0157
    Keywords: Key words hydraulic properties ; heterogeneity ; geophysical methods ; geostatistics ; Italy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé Dans le cadre de plusieurs études réalisées pour caractériser l'aquifère sur le site expérimental près de Montalto Uffugo (Italie), ce travail analyse la distribution spatiale de la conductivité hydraulique de formations non consolidées présentes dans cette région. La technique géostatistique du krigeage a été appliquée, avec une dérive externe, aux données de résistivitéélectrique et de conductivité hydraulique. La fiabilité de la méthode d'estimation a été testée en établissant un modèle, basé sur la méthode des cellules, qui simule l'écoulement souterrain, à partir des valeurs estimées de la conductivité hydraulique. Les résultats obtenus indiquent que cette méthode d'estimation présente un degré de fiabilité acceptable.
    Abstract: Resumen Dentro del marco de los estudios destinados a la caracterización del acuífero del campo experimental de aguas subterráneas cercano a Montalto Uffugo (Italia), el presente trabajo estima la distribución espacial de la conductividad hidráulica de los depósitos no consolidados subyacentes. El estudio se ha llevado a cabo mediante la técnica geoestadística del krigeado con deriva externa de los datos de resistividad eléctrica y de conductividad hidráulica. Se ha verificado la fiabilidad de la estimación mediante un modelo de simulación del flujo de aguas subterráneas, basado en el método de las celdas, que utiliza los valores estimados de la conductividad hidráulica. Los resultados obtenidos indican que el método de estimación empleado posee un grado de fiabilidad aceptable.
    Notes: Abstract  In the framework of various studies to characterize the aquifer at the groundwater experimental field near Montalto Uffugo, Italy, the present work estimates the spatial distribution of hydraulic conductivity of the unconsolidated deposits that underlie the area, by applying the geostatistical technique of kriging with external drift to electrical-resistivity and hydraulic-conductivity data. The reliability of the estimation method was tested by implementing a model, based on the method of cells, that simulates groundwater flow, with the estimated values of hydraulic conductivity. The results obtained indicate that the estimation method used has an acceptable degree of reliability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100400000083
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  • 16
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    Single Particle Analysis of Aerosols, Observed in the Marine Boundary Layer during the Monterey Area Ship Tracks Experiment (MAST), with Respect to Cloud Droplet Formation (2000)
    Springer
    Journal of atmospheric chemistry 37 (2000), S. 299-329 
    Details
    ISSN: 1573-0662
    Keywords: aerosols ; cloud formation ; microanalysis ; ship tracks ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The chemical composition of individual particles 〉0.2 μm sampled duringthe MAST-experiment wereanalysed by SEM-EDX, in combination with multivariatetechniques. The objective of this experiment was toidentify the mechanisms responsible for themodification of marine stratocumulus clouds byemissions from ships and in a wider sense to provideinformation on the global processes involved inatmospheric modification of cloud albedo. Aerosolswere examined under different MBL pollution levels(clean, intermediately polluted and moderatelypolluted) in five different reservoirs: backgroundbelow-cloud and above-cloud aerosol; background clouddroplet residual particles; below-cloud ship plumeaerosol and ship track cloud droplet residualparticles.In this study a relation was provided between theaerosol emitted from the ship's stack to an effect incloud. Additionally, a large fraction of the ambientaerosol was found to be composed of organic materialor other compounds, consisting of low Z-elements,associated with chlorine. Their number fraction waslargest in clean marine boundary layers, and decreasedwith increasing pollution levels. The fraction of`transformed sea salt' (Na, Cl, S), on the other hand,increased with the pollution level in the MBL. Only20% of the particles fell within the detectable rangeof the analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006416600722
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  • 17
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    NOx or VOC Limitation in East German Ozone Plumes? (2000)
    Springer
    Journal of atmospheric chemistry 35 (2000), S. 1-18 
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    ISSN: 1573-0662
    Keywords: ozone ; nitrogen oxides ; VOC ; ozone formation ; air pollution ; urban emissions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The ozone forming potential of VOCs and NOx for plumes observed from several cities and a power plant in eastern Germany was investigated. A closed box model with a gas phase photochemical reaction mechanism was employed to simulate several scenarios based upon aircraft observations. In several of the scenarios, the initial concentrations of NOx, VOCs, and SO2, were reduced to study the factors limiting the O3 production. Ozone production was limited by the initial VOC concentrations for all of the simulated plumes. Higher O3 concentrations were produced with reduced initial NOx. In one sample with high SO2 mixing ratios (〉100 ppb), SO2 was also identified as a significant contributor to the production of O3.
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    URL: http://dx.doi.org/10.1023/A:1006237921920
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  • 18
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    Boundary Layer Ozone in the Tropical America Northern Hemisphere Region (2000)
    Springer
    Journal of atmospheric chemistry 35 (2000), S. 249-272 
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    ISSN: 1573-0662
    Keywords: ozone ; tropical atmosphere ; boundary layer ozone ; biomass burning ; Venezuelan savannah
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In recent field campaigns, boundary layer ozone concentrations were measuredat different sites in the Orinoco river basin (mainly savannahs) and nearbylocations (cloud forest and coastal sites), during dry and wet seasons. Theresults provide a comprehensive description of boundary layer ozone in atropical region north of the equator where scarce information is available.Ozone measurements were made using photometric ozone analyzers. In thesavannah region, ozone profiles (up to 1000 m) were also obtained usingelectrochemical concentration cell sondes, launched in a tethered balloon.The results, in comparison with other parts of the world, confirm the lowvalues for the concentration of ozone in the boundary layer of the studyregion. Throughout the entire region (marine, coastal, and continental areas),higher concentrations were produced during the dry season (20–30 ppbv)than during the wet season (13–17 ppbv), likely due to the photochemicalproduction of ozone from biomass burning emissions. This seasonal variationobserved in the boundary layer contrasts with satellite data, that show highertotal tropospheric ozone columns during the wet season in the 0–15°Nregion; this means that the ozone annual cycles in the boundary layer and freetroposphere are out of phase.At the most pristine continental sites in the southern part of Venezuela,quite a `peculiar' diurnal variation was observed, with maximum concentrationsin the morning and a steady decrease of ∼0.6 ppbv hr-1 duringthe hours of high solar irradiation. Although dynamic aspects cannot be ruledout, the daytime ozone decrease, which cannot be explained by thewell-established `classical' continental O3 sinks, suggests thatin this region part of the ozone consumption is caused byHO x cycles at low NO x levels. Futurestudies to elucidate the causes of the daytime ozone decrease at thesecontinental sites should be undertaken.
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    URL: http://dx.doi.org/10.1023/A:1006270911796
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    Is the Arctic Surface Layer a Source and Sink of NOx in Winter/Spring? (2000)
    Springer
    Journal of atmospheric chemistry 36 (2000), S. 1-22 
    Details
    ISSN: 1573-0662
    Keywords: active nitrogen ; ozone ; radicals ; snow chemistry ; Arctic ; surface layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of ≤10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be ∼1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006301029874
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    Impact of Non-Methane Hydrocarbons on Tropospheric Chemistry and the Oxidizing Power of the Global Troposphere: 3-Dimensional Modelling Results (2000)
    Springer
    Journal of atmospheric chemistry 36 (2000), S. 157-230 
    Details
    ISSN: 1573-0662
    Keywords: non-methane hydrocarbons ; ozone ; HO x ; CO ; NO x ; tropospheric chemistry ; global ; 3-d modeling ; upper troposphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The impact of natural and anthropogenicnon-methane hydrocarbons (NMHC) on troposphericchemistry is investigated with the global,three-dimensional chemistry-transport model MOGUNTIA.This meteorologically simplified model allows theinclusion of a rather detailed scheme to describeNMHC oxidation chemistry. Comparing model resultscalculated with and without NMHC oxidation chemistryindicates that NMHC oxidation adds 40–60% to surfacecarbon monoxide (CO) levels over the continents andslightly less over the oceans. Free tropospheric COlevels increase by 30–60%. The overall yield of COfrom the NMHC mixture considered is calculated to beabout 0.4 CO per C atom. Organic nitrate formationduring NMHC oxidation, and their transport anddecomposition affect the global distribution of NO x and thereby O3 production. The impact of theshort-lived NMHC extends over the entire tropospheredue to the formation of longer-lived intermediateslike CO, and various carbonyl and carboxyl compounds.NMHC oxidation almost doubles the net photochemicalproduction of O3 in the troposphere and leads to20–80% higher O3 concentration inNO x -rich boundarylayers, with highest increases over and downwind ofthe industrial and biomass burning regions. Anincrease by 20–30% is calculated for the remotemarine atmosphere. At higher altitudes, smaller, butstill significant increases, in O3 concentrationsbetween 10 and 60% are calculated, maximizing in thetropics. NO from lightning also enhances the netchemical production of O3 by about 30%, leading to asimilar increase in the global mean OH radicalconcentration. NMHC oxidation decreases the OH radicalconcentrations in the continental boundary layer withlarge NMHC emissions by up to 20–60%. In the marineboundary layer (MBL) OH levels can increase in someregions by 10–20% depending on season and NO x levels.However, in most of the MBL OH will decrease by10–20% due to the increase in CO levels by NMHCoxidation chemistry. The large decreases especiallyover the continents strongly reduce the markedcontrasts in OHconcentrations between land and oceanwhich are calculated when only the backgroundchemistry is considered. In the middle troposphere, OHconcentrations are reduced by about 15%, although dueto the growth in CO. The overall effect of thesechanges on the tropospheric lifetime of CH4 is a 15%increase from 6.5 to 7.4 years. Biogenic hydrocarbonsdominate the impact of NMHC on global troposphericchemistry. Convection of hydrocarbon oxidationproducts: hydrogen peroxides and carbonyl compounds,especially acetone, is the main source of HO x in theupper troposphere. Convective transport and additionof NO from lightning are important for the O3 budgetin the free troposphere.
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    URL: http://dx.doi.org/10.1023/A:1006300616544
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    Kinetic Studies of OH and O3 Reactions with Allyl and Isopropenyl Acetate (2000)
    Springer
    Journal of atmospheric chemistry 37 (2000), S. 161-172 
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    ISSN: 1573-0662
    Keywords: OH radicals ; ozone ; rate coefficients ; allyl acetate ; isopropenyl acetate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Rate coefficients have been measured for the gas phasereactions of hydroxyl (OH) radicals and ozone with twounsaturated esters, allyl acetate(CH3C(O)OCH2CH=CH2) and isopropenylacetate (CH3C(O)OC(CH3)=CH2). The OHexperiments were carried out using the pulsed laserphotolysis – laser induced fluorescence technique overthe temperature range 243–372 K and the kinetic dataused to derive the following Arrhenius expressions (inunits of cm3 molecule-1 s-1): allylacetate, k 1 = (2.33 ± 0.27) ×10-12 exp[(732 ± 34)/T]; and isopropenyl acetate,k 2 = (4.52 ± 0.62) × 10-12exp[(809 ± 39)/T]. At 298 K, the rate coefficients obtained (inunits of 10-12 cm3 molecule-1 s-1)are: k 1 = (27.1 ± 3.0) and k 2= (69.6± 9.4). The relative rate technique has been usedto determine rate coefficients for the reaction ofozone with the acetates. Using methyl vinyl ketone asthe reference compound and a value of4.8 × 10-18 cm3 molecule-1s-1 asthe rate coefficient for its reaction with O3,the following rate coefficients were derived at 298 ± 4 K (in units of10-18 cm3molecule-1 s-1): allyl acetate, (2.4 ± 0.7) andisopropenyl acetate (0.7 ± 0.2). Theresults are discussed in terms of structure-activityrelationships and used to derive atmospheric lifetimesfor the acetates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006499008759
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    Contemporary carbon stocks of mineral forest soils in the Swiss Alps (2000)
    Springer
    Biogeochemistry 50 (2000), S. 111-136 
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    ISSN: 1573-515X
    Keywords: carbon sequestration ; geostatistics ; mountain forest soils ; national assessment ; soil organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Soil organic carbon (SOC) has been identified as the main globalterrestrial carbon reservoir, but considerable uncertainty remains as toregional SOC variability and the distribution of C between vegetationand soil. We used gridded forest soil data (8–km × 8–km)representative of Swiss forests in terms of climate and forest typedistribution to analyse spatial patterns of mineral SOC stocks alonggradients in the European Alps for the year 1993. At stand level, meanSOC stocks of 98 t C ha−1 (N = 168,coefficient of variation: 70%) were obtained for the entiremineral soil profile, 76 t C ha−1 (N =137, CV: 50%) in 0–30 cm topsoil, and 62 t Cha−1 (N = 156, CV: 46%) in0–20 cm topsoil. Extrapolating to national scale, we calculatedcontemporary SOC stocks of 110 Tg C (entire mineral soil, standarderror: 6 Tg C), 87 Tg C (0–30 cm topsoil, standarderror: 3.5 Tg C) and 70 Tg C (0–20 cm topsoil, standarderror: 2.5 Tg C) for mineral soils of accessible Swiss forests(1.1399 Mha). According to our estimate, the 0–20 cm layers ofmineral forest soils in Switzerland store about half of the Csequestered by forest trees (136 Tg C) and more than five times morethan organic horizons (13.2 Tg C). At stand level, regression analyses on the entire data set yielded nostrong climatic or topographic signature for forest SOC stocks in top(0–20 cm) and entire mineral soils across the Alps, despite thewide range of values of site parameters. Similarly, geostatisticalanalyses revealed no clear spatial trends for SOC in Switzerland at thescale of sampling. Using subsets, biotic, abiotic controls andcategorial variables (forest type, region) explained nearly 60%of the SOC variability in topsoil mineral layers (0–20 cm) forbroadleaf stands (N = 56), but only little of thevariability in needleleaf stands (N = 91,R 2 = 0.23 for topsoil layers). Considerable uncertainties remain in assessments of SOC stocks, due tounquantified errors in soil density and rock fraction, lack of data onwithin-site SOC variability and missing or poorly quantifiedenvironmental control parameters. Considering further spatial SOCvariability, replicate pointwise soil sampling at 8–km × 8–kmresolution without organic horizons will thus hardly allow to detectchanges in SOC stocks in strongly heterogeneous mountain landscapes.
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    URL: http://dx.doi.org/10.1023/A:1006320129112
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    Heat Waves in the South Moravian Region During the Period 1961-1995 (2000)
    Springer
    Studia geophysica et geodaetica 44 (2000), S. 57-72 
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    ISSN: 1573-1626
    Keywords: extreme events ; heat wave ; tropical day ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Heat waves (periods of extremely hot summer weather) in the region of south Moravia are in the focus of this study. The introduced definition consists of three requirements imposed on the period that is considered a heat wave: at least three days with T MAX ≥30.0°C must be observed; the mean T MAX over the whole period is at least 30.0°C; and T MAX must not drop below 25.0°C. To compare the severity of the individual heat waves, various characteristics (duration, number of tropical days, peak temperature, cumulative temperature excess, precipitation amount) are examined. The heat wave index HWI is defined to express the severity of heat waves in the most comprehensive way. An extraordinary heat wave occurred in July and August 1994; it lasted more than a month at several stations, while the duration of a typical heat wave is only 4 - 7 days. The extremely long unbroken period of tropical days, and even of days with T MAX ≥32.0°C, represents the most distinct feature of the severe 1994 heat wave. With regard to heat wave characteristics, the summer temperature exceptionality of the early 1990s is indubitable.
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    URL: http://dx.doi.org/10.1023/A:1022009924435
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    Mineral magnetic and geochemical records of late Glacial climatic change from two northwest European carbonate lakes (1999)
    Springer
    Journal of paleolimnology 22 (1999), S. 97-107 
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    ISSN: 1573-0417
    Keywords: environmental magnetism ; lacustrine marl ; late Glacial ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We present the results of mineral magnetic measurements and geochemical analyses of late Glacial sediments from two marl-precipitating lakes in the Northwest of England. Mineral magnetic assemblages dominated by detrital and/or authigenic ferrimagnetic minerals, and enhanced delivery of metal elements, characterise a lower (Oldest Dryas) and an upper (Younger Dryas) phase of catchment instability, with detrital clay and silt sedimentation. Magnetic mineral assemblages with lower concentrations of finer ferrimagnetic grains characterise the authigenic carbonate sediments (marls). The marls indicate both enhanced lake productivity and catchment stability in response to prevailing warm conditions during the Bølling - Allerød Interstadial. The Bølling - Allerød marl phase contains two short-term, low amplitude shifts characterised by changes in the concentration and the size of ferrimagnetic grains. These shifts may represent the Older Dryas and the Amphi-Atlantic Oscillation, short-lived Northern hemisphere climatic deteriorations. Overall, the results suggest that marl lakes are sensitive indicators of Lateglacial climatic change, and that these changes are readily identifiable through the use of mineral magnetic measurements.
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    URL: http://dx.doi.org/10.1023/A:1008097518004
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    Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater (1999)
    Springer
    Journal of paleolimnology 21 (1999), S. 409-422 
    Details
    ISSN: 1573-0417
    Keywords: Africa ; climate change ; conductivity ; diatoms ; Ethiopia ; Holocene ; lake levels ; palaeolimnology ; Rift Valley
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A 6,500-year diatom stratigraphy has been used to infer hydrochemical changes in Lake Awassa, a topographically closed oligosaline lake in the Ethiopian Rift Valley. Conductivity was high from ~6400-6200 BP, and from 5200-4000 BP, with two brief episodes of lower conductivity during the latter period. Although the timing of the conductivity changes is similar to the timing of lake-level change in the nearby Zwai-Shalla basin, their directions are the reverse of that expected from a climatic cause. Dissolution of the tephras which precede both phases of high conductivity cannot explain the increases in salinity, because rhyolitic tephras are only sparingly soluble. Instead, the pulsed input of groundwater made saline by the reaction of silicate minerals and volcanic glass with carbonic acid, formed from the solution of carbon dioxide degassed from magma under the Awassa Caldera, is suggested as a plausible mechanism for the observed change in lake chemistry. Diatom-inferred hydrochemistry cannot therefore be used to reconstruct climate change in Lake Awassa.
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    URL: http://dx.doi.org/10.1023/A:1008092823410
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    An Experimental Comparison of Ordinary and Universal Kriging and Inverse Distance Weighting (1999)
    Springer
    Mathematical geology 31 (1999), S. 375-390 
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    ISSN: 1573-8868
    Keywords: geostatistics ; spatial interpolation ; spatial pattern ; surface-fitting algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A factorial, computational experiment was conducted to compare the spatial interpolation accuracy of ordinary and universal kriging and two types of inverse squared-distance weighting. The experiment considered, in addition to these four interpolation methods, the effects of four data and sampling characteristics: surface type, sampling pattern, noise level, and strength of small-scale spatial correlation. Interpolation accuracy was measured by the natural logarithm of the mean squared interpolation error. Main effects of all five factors, all two-factor interactions, and several three-factor interactions were highly statistically significant. Among numerous findings, the most striking was that the two kriging methods were substantially superior to the inverse distance weighting methods over all levels of surface type, sampling pattern, noise, and correlation.
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    URL: http://dx.doi.org/10.1023/A:1007586507433
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    Simulation of Non-Gaussian Transmissivity Fields Honoring Piezometric Data and Integrating Soft and Secondary Information (1999)
    Springer
    Mathematical geology 31 (1999), S. 907-927 
    Details
    ISSN: 1573-8868
    Keywords: conditional probabilities method ; self-calibrated method ; stochastic inversion ; probabilistic assessment ; geostatistics ; stochastic hydrology ; probability fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The conditional probabilities (CP) method implements a new procedure for the generation of transmissivity fields conditional to piezometric head data capable to sample nonmulti-Gaussian random functions and to integrate soft and secondary information. The CP method combines the advantages of the self-calibrated (SC) method with probability fields to circumvent some of the drawbacks of the SC method—namely, its difficulty to integrate soft and secondary information or to generate non-Gaussian fields. The SC method is based on the perturbation of a seed transmissivity field already conditional to transmissivity and secondary data, with the perturbation being function of the transmissivity variogram. The CP method is also based on the perturbation of a seed field; however, the perturbation is made function of the full transmissivity bivariate distribution and of the correlation to the secondary data. The two methods are applied to a sample of an exhaustive non-Gaussian data set of natural origin to demonstrate the interest of using a simulation method that is capable to model the spatial patterns of transmissivity variability beyond the variogram. A comparison of the probabilistic predictions of convective transport derived from a Monte Carlo exercise using both methods demonstrates the superiority of the CP method when the underlying spatial variability is non-Gaussian.
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    URL: http://dx.doi.org/10.1023/A:1007580902175
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    Long-Term Variations of Potential Temperature and Dissolved Oxygen of the Japan Sea Proper Water (1999)
    Springer
    Journal of oceanography 55 (1999), S. 197-205 
    Details
    ISSN: 1573-868X
    Keywords: Japan Sea ; Japan Sea Proper Water ; climate change ; long-term variation ; one-dimensional model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Observed potential temperatures and concentrations of dissolved oxygen are analyzed to elucidate their variations during the period from 1958 to 1996 at Stn. P (37°43′ N, 134°43′ E) and from 1965 to 1996 at Stn. H (40°30′ N, 137°40′ E) in the Japan Sea. At Stn. P, increases of the potential temperature for the period are found below 800 m depth with the largest value of 0.16 ± 0.09°C per century at 800 m depth. At Stn. H, the potential temperature increased below 500 m depth. The increase rate has the largest value of 0.50 ± 0.18°C per century at 500 m depth and it is 0.30 ± 0.09°C per century at 800 m depth. The concentrations of dissolved oxygen increased around 800 m depth at Stn. P. At Stn. H, they increased above 800 m depth. On the other hand, they decreased below 1200 m depth at both stations. The layer of the dissolved oxygen minimum has deepened in these decades. These features appearing in the distributions of temperature and dissolved oxygen are successively simulated by a vertical one-dimensional advection-diffusion model including consumption of dissolved oxygen and termination of the deep water supply. These results suggest that the supply of the Japan Sea Proper Water into the deep layer, which is cold and rich in dissolved oxygen, has been decreasing for the last four decades.
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    URL: http://dx.doi.org/10.1023/A:1007889929187
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    Bayesian Inference of Spatial Covariance Parameters (1999)
    Springer
    Mathematical geology 31 (1999), S. 47-65 
    Details
    ISSN: 1573-8868
    Keywords: geostatistics ; prior distribution ; likelihood function ; posterior distribution ; variogram ; covariance ; range
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract This paper shows the application of the Bayesian inference approach in estimating spatial covariance parameters. This methodology is particularly valuable where the number of experimental data is small, as occurs frequently in modeling reservoirs in petroleum engineering or when dealing with hydrodynamic variables in groundwater hydrology. There are two main advantages of Bayesian estimation: firstly that the complete distribution of the parameters is estimated and, from this distribution, it is a straightforward procedure to obtain point estimates, confidence regions, and interval estimates; secondly, all the prior information about the parameters (information available before the data are collected) is included in the inference procedure through their prior distribution. The results obtained from simulation studies are discussed.
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    URL: http://dx.doi.org/10.1023/A:1007541330206
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    Geostatistical Space–Time Models: A Review (1999)
    Springer
    Mathematical geology 31 (1999), S. 651-684 
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    ISSN: 1573-8868
    Keywords: space–time models ; geostatistics ; time series ; trend models ; stochastic simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Geostatistical space–time models are used increasingly for addressing environmental problems, such as monitoring acid deposition or global warming, and forecasting precipitation or stream flow. Each discipline approaches the problem of joint space–time modeling from its own perspective, a fact leading to a significant amount of overlapping models and, possibly, confusion. This paper attempts an annotated survey of models proposed in the literature, stating contributions and pinpointing shortcomings. Stochastic models that extend spatial statistics (geostatistics) to include the additional time dimension are presented with a common notation to facilitate comparison. Two conceptual viewpoints are distinguished: (1) approaches involving a single spatiotemporal random function model, and (2) approaches involving vectors of space random functions or vectors of time series. Links between these two viewpoints are then revealed; advantages and shortcomings are highlighted. Inference from space–time data is revisited, and assessment of joint space–time uncertainty via stochastic imaging is suggested.
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    URL: http://dx.doi.org/10.1023/A:1007528426688
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    Analyzing Censored Spatial Data (1999)
    Springer
    Mathematical geology 31 (1999), S. 551-561 
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    ISSN: 1573-8868
    Keywords: reliability ; kriging ; Expectation-Maximization (EM) algorithm ; spatial linear model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Spatial data that are incomplete because of observations arising below or above a detection limit occur in many settings, for example, in mining, hydrology, and pollution monitoring. These observations are referred to as censored observations. For example, in a life test, censoring may occur at random times because of accident or breakdown of equipment. Also, censoring may occur when failures are discovered only at periodic inspections. Because the informational content of censored observations is less than that of uncensored ones, censored data create difficulties in an analysis, particularly when such data are spatially dependent. Traditional methodology applicable for uncensored data needs to be adapted to deal with censorship. In this paper we propose an adaptation of the traditional methodology using the so-called Expectation-Maximization (EM) algorithm. This approach permits estimation of the drift coefficients of a spatial linear model when censoring is present. As a by-product, predictions of unobservable values of the response variable are possible. Some aspects of the spatial structure of the data related to the implicit correlation also are discussed. We illustrate the results with an example on uranium concentrations at various depths.
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    URL: http://dx.doi.org/10.1023/A:1007516023962
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    Lunar Influences On Climate (1999)
    Springer
    Earth, moon and planets 85-86 (1999), S. 99-113 
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    ISSN: 1573-0794
    Keywords: Astronomic influence ; climate change ; Moon ; solar cycles ; weather
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Popular beliefs on the effects of the Moon on the weather probably go back to when ancient civilisations followed a lunar calendar, and the Moon went from being a purely temporal reference to becoming a causal reference. The incoming heat flow on the Earth may vary slightly after solar activity. to and generate considerable effects. The light reflected from the Moon has also been hypothesised as a cause, but the associated energy is too small. The anomalistic period of the Moon (i.e., 27.5 days) coincides substantially with that of the sunspots found on the 17–18th parallel of the heliocentric latitude. Climatic modulation which lasts for around 27.5 days should be related to solar activity, which supplies energy with an amount of two orders of magnitude greater than the lunar-reflected energy. Another mechanism responsible for climatic variations is the redistribution of heat on the Earth. The Moon with the tides induces movement of the water masses of the oceans and with this there is a transport of heat. Semidiurnal lunar tides have been identified, although with modest impact, in the atmospheric pressure, the wind field and the precipitation. On a monthly time scale, variation of daily precipitation data shows that gravitational tides do indeed affect heavy rainfalls more than mean precipitation values. On the longer time scale, several authors have identified the 18.6-yr nutation cycle, which is clearly visible in several data analyses, but often it cannot be easily distinguished from the 19.9 Saturn–Jupiter cycle and the quasi-regular 22-yr double sunspot cycle which at times may be dominant. In the time scale of centuries, covering a number of periods with minimum solar activity, an analysis of meteorological data has demonstrated that only the Spörer Minimum (A.D. 1416–1534) was characterised by climatic anomalies., whereas the other periods had no singularities, or else the weak climate forcing was covered or masked by other factors, leaving the question still open. In practice, lunar and solar influences can be found and have been demonstrated with more or less the same level of confidence. Both have the same order of magnitude, and are generally weak, interacting, and being often masked by local effects.
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    URL: http://dx.doi.org/10.1023/A:1017099427908
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    Assessment of the Uncertainties in the NO2 and O3 Measurements by Visible Spectrometers (1999)
    Springer
    Journal of atmospheric chemistry 32 (1999), S. 121-145 
    Details
    ISSN: 1573-0662
    Keywords: nitrogen dioxide ; ozone ; visible spectrometer ; NDSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The column amounts of nitrogen dioxide (NO2) and ozone (O3) were measured using a visible spectrometer based on the twilight zenith-sky technique at two observatories located at similar latitudes in the northern part of Japan separated by a distance of 150 km. The measurements began in April 1991 at the Moshiri Observatory (44.4°N, 142.3°E) and in April 1994 at the Rikubetsu Observatory (43.5°N, 143.8°E). Since weather conditions and the possible influence from tropospheric pollution were not always identical at these two observatories, the overall accuracy of the measurements was studied comparing these data sets. The first year data obtained at a solar zenith angle of 90 degrees indicated that the NO2 slant column values at sunrise and sunset agreed within 0.36 and 0.54 × 1016 cm-2, respectively, corresponding to 5 % (June) and to 12 % (December) of the columns. The O3 values agreed within 0.76 × 1019 cm-2, corresponding to 4 % (March) ∼6 % (August) of the columns, although a part of the difference was systematic. The O3 column amounts were also compared to those obtained by the Dobson spectrometer at Sapporo (43.5°N, 143.8°E), whose latitude is similar to these observatories. When an air mass factor of 17.5 was used, the two-year Moshiri vertical column values agreed with the Dobson direct sun values to within 15 Dobson Units, or 3 ∼ 6 % of the column. The difference between the two values was found to be due partly to the change in the air mass factor caused by seasonal and day-to-day changes in the shape of the O3 vertical profiles. These results confirm the reliability of the NO2 and O3 measurements by visible spectrometers at these sites for the Network for the Detection of Stratospheric Change (NDSC).
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    URL: http://dx.doi.org/10.1023/A:1006184628196
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    Influence of Continental Sources on Oceanic Air Composition at the Eastern Edge of the North Atlantic Ocean, TOR 1992–1995 (1999)
    Springer
    Journal of atmospheric chemistry 32 (1999), S. 233-280 
    Details
    ISSN: 1573-0662
    Keywords: hydrocarbons ; ozone ; PAN ; long-range transport ; oceanic air
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The atmospheric concentrations of O3, NMHCs, PAN and NOx were measured at the TOR station in Porspoder (Brittany, France) from 1992 to 1995. The results from April 1992 to December 1994 are reported here. In order to study the behaviour of trace gases in the air masses coming from the Atlantic Ocean, the origin of these air masses was characterised by the analysis of the five-day back-trajectories reaching 950 mbar at Porspoder. Three kinds of oceanic air masses are considered, depending on their origin: North Atlantic northern and southern latitudes and North American continent. It appears that the oceanic high-latitude troposphere was strongly influenced by continental emissions, which in turn impacted the median latitude troposphere during polar outflow events. A greater accumulation of anthropogenic compounds in the Arctic sector was calculated and may be at the origin of the high oxidant levels measured in spring in this same sector. The influence of north American emissions on the European coast was also studied and seems to reach a maximum in spring. Long-range transport of long- lived species was observed throughout the year, but evidence for winter transport of more reactive species, such as ethene, is also shown. Meteorological parameters and local photochemistry appear to play an important role in the distribution of the pollutants over the North Atlantic Ocean throughout the year. Further investigations are needed to give more complete information about the origin, formation and destruction of the secondary pollutants.
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    The Reaction of Unsaturated Aliphatic Oxygenates with Ozone (1999)
    Springer
    Journal of atmospheric chemistry 32 (1999), S. 205-232 
    Details
    ISSN: 1573-0662
    Keywords: ozone ; biogenic hydrocarbons ; reaction products and mechanisms ; reaction rate constants ; unsaturated esters ; unsaturated ethers ; unsaturated carbonyls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The reaction of ozone with unsaturated aliphatic oxygenates has been studied at ambient T (287–297 K) and p = 1 atm. of air (RH = 55 ± 10%) with sufficient cyclohexane added to scavenge the hydroxyl radical. Reaction rate constants, in units of 10-18 cm3 molecule-1 s-1, are 10.7 ± 1.4 for methyl trans-3-methoxy acrylate, 63.7 ± 9.9 for 4-hexen-3-one (predominantly the trans isomer), 125 ± 17 for trans-4-methoxy-3-buten-2-one, ≥148 ± 13 for cis-4-heptenal, ≥439 ± 37 for 3- methyl-2-buten-1-ol and ≥585 ± 132 for (cis + trans)-ethyl 1-propenyl ether. The influence of the oxygen-containing substituents on reactivity toward ozone is examined. Unsaturated ethers react with ozone faster than their alkene structural homologues; the reverse is observed for unsaturated esters and unsaturated carbonyls. Major reaction products have been identified by liquid chromatography with ultraviolet detection (LC-UV), particle beam-mass spectrometry (PB- MS) and gas chromatography-mass spectrometry (GC-MS) and are methyl formate and methyl glyoxylate from methyl trans-3-methoxy acrylate, acetaldehyde and 2-oxobutanal from 4-hexen-3-one, propanal and succinic dialdehyde from cis-4-heptenal, hydroxyacetaldehyde and acetone from 3-methyl-2-buten-1-ol, and ethyl formate and acetaldehyde from (cis + trans)-ethyl 1-propenyl ether. PB-MS and GC- MS were also employed to identify new reaction products and to confirm the structure of products tentatively identified in a previous study of the reaction of ozone with five unsaturated oxygenates (Grosjean and Grosjean, 1997a): formic acid and methyl glyoxylate from methyl acrylate, formic acid and formic acetic anhydride from vinyl acetate, 2-oxoethyl acetate and 3-oxopropyl acetate from cis-3-hexenyl acetate, ethyl formate and formic acid from ethyl vinyl ether, and methyl formate from trans-4-methoxy-3- buten-2-one. The nature and formation yields of the reaction products are consistent with (and supportive of) the reaction mechanism: O3 + R1R2C=CR3X → α(R1COR2 + R3C(X)OO) + (1 - α)(R3COX + R1C(R2)OO), where R1, R2 and R3 = H or alkyl, X is the oxygen-containing substituent, R1COR2 and R3COX are the primary products and R1C(R2)OO and R3C(X)OO are the carbonyl oxide biradicals. The variations of the coefficient α, which ranges from 0.25 to 0.61, are discussed in terms of the number and nature of alkyl and oxygen-containing substituents. Subsequent reactions of the alkyl-substituted biradicals R1C(R2)OO and of the biradicals R3C(X)OO that bear the oxygen-containing substituent are discussed. For the biradical CH3CHOO, the ratio ka/kb for the competing pathways of rearrangement to acetic acid (CH3CHOO → CH3C(O)OH, reaction (a) and formation of an unsaturated hydroperoxide (CH3CHOO → CH2=CH(OOH), reaction (b) is 〈0.25 for ethyl 1-propenyl ether and 〈0.27 for 4-hexen-3-one. Concentrations measured in co- located samples, one downstream of a water impinger and the other without water impinger, show the uptake in water impingers to be high (from 83.2 to 〉99.9%) and comparable to that for formaldehyde (98.4%) for formic acetic anhydride and for difunctional oxygenated compounds. Uptake in water impingers was lower (19–78%) for monofunctional aldehydes and ketones.
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    Slant Column Measurements of O3 and NO2 During the NDSC Intercomparison of Zenith-Sky UV-Visible Spectrometers in June 1996 (1999)
    Springer
    Journal of atmospheric chemistry 32 (1999), S. 281-314 
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    ISSN: 1573-0662
    Keywords: ozone ; NO2 ; UV visible
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In June 1996, 16 UV-visible sensors from 11 institutes measured spectra of the zenith sky for more than 10 days. Spectra were analysed in real-time to determine slant column amounts of O3 and NO2. Spectra of Hg lamps and lasers were measured, and the amount of NO2 in a cell was determined by each spectrometer. Some spectra were re-analysed after obvious errors were found. Slant columns were compared in two ways: by examining regression analyses against comparison instruments over the whole range of solar zenith angles; and by taking fractional differences from a comparison instrument at solar zenith angles between 85° and 91°. Regression identified which pairs of instruments were most consistent, and so which could be used as universal comparison instruments. For O3, regression slopes for the whole campaign agreed within 5% for most instruments despite the use of different cross-sections and wavelength intervals, whereas similar agreement was only achieved for NO2 when the same cross-sections and wavelength intervals were used and only one half-day's data was analysed. Mean fractional differences in NO2 from a comparison instrument fall within ±7% (1-sigma) for most instruments, with standard deviations of the mean differences averaging 4.5%. Mean differences in O3 fall within ±2.5% (1- sigma) for most instruments, with standard deviations of the mean differences averaging 2%. Measurements of NO2 in the cell had similar agreement to measurements of NO2 in the atmosphere, but for some instruments measurements with cell and atmosphere relative to a comparison instrument disagreed by more than the error bars.
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    The Radiative-Dynamical Effects of High Cloud on Global Ozone Distribution (1999)
    Springer
    Journal of atmospheric chemistry 33 (1999), S. 1-22 
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    ISSN: 1573-0662
    Keywords: high cloud ; ozone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Previous studies (e.g., Dessler et al., 1996; Haigh, 1984) have discussed the effect of cloud on modelled ozone distribution through changes in the radiative heating in the lower stratosphere. Here the relationship is investigated using an interactive chemical-radiative- transport 2D model. It is shown that, while similar cooling in the lower stratosphere due to high cloud is found, the effect on ozone is not as previously expected. The inclusion of high cloud is found to bring about a warming of the troposphere, resulting in a net heating in the lower stratosphere. This strengthens the circulation, leading to a decrease in total tropical ozone. Importantly, the effect of the cloud-induced temperature changes on heating rates does not combine linearly with the direct radiative effect of cloud changes. The possibility of a link between the high cloud increases and total ozone decreases observed in some regions during strong El Niño episodes is investigated. The possible impact on ozone of a global trend in high cloud cover is also discussed.
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    Partitioning of Semivolatile Organic Compounds in the Presence of a Secondary Organic Aerosol in a Controlled Atmosphere (1999)
    Springer
    Journal of atmospheric chemistry 33 (1999), S. 241-264 
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    ISSN: 1573-0662
    Keywords: gas-particle partitioning ; secondary organic aerosol ; α-pinene ; ozone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid α-pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.
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    URL: http://dx.doi.org/10.1023/A:1006108430033
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    Absolute Rate Coefficients for the Gas-Phase Reactions of NO3 Radical with a Series of Monoterpenes at T = 298 to 433 K (1999)
    Springer
    Journal of atmospheric chemistry 33 (1999), S. 265-282 
    Details
    ISSN: 1573-0662
    Keywords: atmosphere ; kinetics ; nitrate radical ; monoterpenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The aim of this work is to study the reactivity of some naturally emitted terpenes, 2-carene, sabinene, myrcene, α-phellandrene, d-limonene, terpinolene and γ-terpinene, towards NO3 radical to evaluate the importance of these reactions in the atmosphere and their atmospheric impact. The experiments with these monoterpenes have been carried out under second-order kinetic conditions over the range of temperature 298–433 K, using a discharge flow system and monitoring the NO3 radical by Laser Induced Fluorescence (LIF). This work is the first temperature dependence study for the reactions of the nitrate radical with the above-mentioned monoterpenes. The measured rate constants at 298 K for the reaction of NO3 with such terpenes are as follows: 2-carene, 16.6 ± 1.8, sabinene 10.7 ± 1.6, myrcene 12.8 ± 1.1, α-phellandrene 42 ± 10, d-limonene 9.4 ± 0.9, terpinolene 52 ± 9 and γ-terpinene 24 ± 7, in units of 10-12 cm3 molecule-1 s-1. The proposed Arrhenius expressions, for the reactions of NO3 with 2-carene, sabinene, myrcene and α-phellandrene are, respectively k1 = (1.4 ± 0.7) × 10-12 exp[(741 ± 190/T)] (cm3 molecule-1 s-1), k2=(2.3 ± 1.3) × 10-10 exp[−(940 ± 200/T)] (cm3 molecule-1 s-1), k3 = (2.2 ± 0.2) × 10-12 exp[(523 ± 35/T)] (cm3 molecule1 s-1) and k4 = (1.9 ± 1.3) × 10-9 exp[−(1158 ± 270/T)] (cm3 molecule-1 s-1). A decrease in the rate constants when raising the temperature has also been found for the reaction of d-limonene with NO3 while an increase in the rate constant with temperature has been observed for the reactions of terpinolene and γ-terpinene with NO3. Tropospheric half-lives for these terpenes have been calculated at night and during the day for typical NO3 and OH concentrations showing that both radicals provide an effective tropospheric sink for these compounds and that the night-time reaction with NO3 radical can be an important, if not dominant, loss process for these naturally emitted organics and for NO3 radicals.
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    URL: http://dx.doi.org/10.1023/A:1006178530211
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    Laboratory Kinetic Studies of the Reactions of Cl Atoms with Species of Biogenic Origin: δ3-Carene, Isoprene, Methacrolein and Methyl Vinyl Ketone (1999)
    Springer
    Journal of atmospheric chemistry 34 (1999), S. 163-170 
    Details
    ISSN: 1573-0662
    Keywords: δ3-carene ; chlorine atoms ; isoprene ; kinetics ; methacrolein and methyl vinyl ketone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The rate coefficients for the reaction between atomic chlorine and a number of naturally occurring species have been measured at ambient temperature and atmospheric pressure using the relative rate technique. The values obtained were (4.0 ± 0.8) × 10-10, (2.1 ± 0.5) × 10-10, (3.2 ± 0.5) × 10-10, and (4.9 ± 0.5) × 10-10 cm3 molecule-1 s-1, for reactions with isoprene, methyl vinyl ketone, methacrolein and δ3-carene, respectively. The value obtained for isoprene compares favourably with previously reported values. No values have been reported to date for the rate constants of the other reactions.
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    Ozone Dry Deposition and Resistances onto Green Grassland in Summer in Central Spain (1999)
    Springer
    Journal of atmospheric chemistry 34 (1999), S. 321-338 
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    ISSN: 1573-0662
    Keywords: ozone ; dry deposition ; green grassland ; resistances ; parameterization model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of ozone concentrations, and meteorological and surface parameters were carried out over a flat green grassland in northwest Spain, in July 1995. Turbulent parameters and sensible and latent heat fluxes were calculated using the gradient technique. Fluxes and deposition velocity and resistances were evaluated assuming that the diffusivity for heat fluxes was equal to pollutant diffusivity. The daily average value of dry deposition velocity was 6 mm s-1 but it was influenced by wind velocity and atmospheric stability. Resistances have been calculated according to a simple resistance model and a comparison between theoretical and measured values has been made.
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    Interpretation of Mid-Stratospheric Arctic Ozone Measurements Using a Photochemical Box-Model (1999)
    Springer
    Journal of atmospheric chemistry 34 (1999), S. 281-290 
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    ISSN: 1573-0662
    Keywords: ozone ; photochemical balance ; catalytic ozone destruction ; oxygene photolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In this study measurements of mid-stratospheric Arctic ozone are compared with model simulations. The measurements obtained at Spitsbergen (79°N, 12°E) by ground based millimeter-wave radiometry exhibit large day to day variabilities as well as periods with low ozone. To interpret these measurements, calculations were made using the new photochemical box-trajectory model BRAPHO, with air parcel trajectories calculated from analyzed wind fields. Using a relatively simple approach, the model reproduces the observed ozone variability well, including inter-annual variations. The explanation for the observed ozone behavior is that at these altitudes ozone is determined by what we call ‘dynamically controlled photochemistry’. This means that the photochemical evolution of the ozone volume mixing ratio is mainly controlled by the atmospheric dynamics, in particular the solar zenith angle the air parcel has experienced.
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    URL: http://dx.doi.org/10.1023/A:1006198414518
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    Measurements of Trace Substances in the Arctic Troposphere as Potential Precursors and Constituents of Arctic Haze (1999)
    Springer
    Journal of atmospheric chemistry 34 (1999), S. 291-319 
    Details
    ISSN: 1573-0662
    Keywords: arctic air pollution ; precursor substances ; vertical profiles ; ozone ; PAN ; SO2 ; gaseous HNO3 ; particulate nitrate ; sulfate ; ammonium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract During two measuring campaigns in early spring 1994 and 1995 (March/April) and one campaign in summer 1994, measurements of ozone, PAN, sulfur dioxide, nitric acid, and particulate nitrate, sulfate, and ammonium (only 1995) were recorded in the Arctic. Observations were made by aircraft at various sites in the eastern and western Arctic. Ozone concentrations showed a steady increase with altitude both in spring and summer. During five flights in springtime, low ozone events (LOEs) could be observed near the surface and up to altitudes of 2000 m. SO2 background concentrations, ranging from detection limit (0.5 nmol/m3) to 5 nmol/m3, were observed during both spring and summer. Distinct maxima up to 55 nmol/m3 in lower altitudes were only obtained in springtime. Concentrations of the organic nitrate PAN were within a similar range as those of the inorganic nitrate HNO3 during spring campaigns. In contrast, concentrations of particulate nitrate were one half an order of magnitude lower. HNO3 concentrations increased significantly with altitude. Evidently, HNO3 was intruded from the stratosphere into the troposphere. Sulfate concentrations ranged between 5 and 30 nmol/m3; ammonium concentrations were obtained within a range from 10 to 50 nmol/m3.
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    Nitrous oxide emissions from a gully mire in mid-Wales, UK, under simulated summer drought (1999)
    Springer
    Biogeochemistry 44 (1999), S. 151-162 
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    ISSN: 1573-515X
    Keywords: ammonium ; climate change ; drought ; groundwater table ; nitrate ; nitrous oxide ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Certain general circulation models predict that a doubling of atmospheric carbon dioxide concentrations will increase the frequency of summer drought in northern wetlands due to hotter, drier summers. There is currently much uncertainty as to how drought will affect emissions of the greenhouse gas, nitrous oxide, from wetlands. We have demonstrated that an eight centimetre drawdown of the water table in a gully mire does not significantly affect nitrous oxide emissions from this site. However, under a more extreme drought scenario carried out on peat monoliths, nitrous oxide emissions increased exponentially with a linear decrease in water table height. Drought caused a significant increase in nitrous oxide production below the water table but most of the total increase could be attributed to increased emissions above the water table. Results from an acetylene block experiment suggested that increased emissions were caused by increased nitrous oxide production from denitrification, rather than by increased production from nitrification. In the laboratory study, drought severity had no effect on peatwater nitrate concentrations below the water table, however, increasing drought severity decreased ammonium concentrations.
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    Nitrous oxide emissions from a gully mire in mid-Wales, UK, under simulated summer drought (1999)
    Springer
    Biogeochemistry 44 (1999), S. 151-162 
    Details
    ISSN: 1573-515X
    Keywords: ammonium ; climate change ; drought ; groundwater table ; nitrate ; nitrous oxide ; wetland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Certain general circulation models predict that a doubling of atmospheric carbon dioxide concentrations will increase the frequency of summer drought in northern wetlands due to hotter, drier summers. There is currently much uncertainty as to how drought will affect emissions of the greenhouse gas, nitrous oxide, from wetlands. We have demonstrated that an eight centimetre drawdown of the water table in a gully mire does not significantly affect nitrous oxide emissions from this site. However, under a more extreme drought scenario carried out on peat monoliths, nitrous oxide emissions increased exponentially with a linear decrease in water table height. Drought caused a significant increase in nitrous oxide productionbelow the water table but most of the total increase could be attributed to increased emissionsabove the water table. Results from an acetylene block experiment suggested that increased emissions were caused by increased nitrous oxide production from denitrification, rather than by increased production from nitrification. In the laboratory study, drought severity had no effect on peatwater nitrate concentrations below the water table, however, increasing drought severity decreased ammonium concentrations.
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    URL: http://dx.doi.org/10.1007/BF00992976
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    Climate Change Projections Based on GCM-Simulated Daily Data (1999)
    Springer
    Studia geophysica et geodaetica 43 (1999), S. 201-222 
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    ISSN: 1573-1626
    Keywords: climate change ; GCM-based scenarios ; daily series of extreme and mean temperatures ; global radiation ; precipitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Three-dimensional general circulation models (GCMs) are 'state-of-the-art' tools for projecting possible changes in climate. Scenarios constructed for the Czech Republic are based on daily outputs of the ECHAM-GCM in the central European region. Essential findings, derived from validating, procedures are summarized and changes in variables between the control and perturbed experiments are examined. The resulting findings have been used in selecting the most proper methods of generating climate change projections for assessing possible hydrological and agricultural impacts of climate change in selected exposure units. The following weather variables have been studied: Daily extreme temperatures, daily mean temperature, daily sum of global solar radiation, and daily precipitation amounts. Due to some discrepancies revealed, the temperature series for changed climate conditions (2×CO 2 ) have been created with the help of temperature differences between the control and perturbed runs, and the precipitation series have been derived from an incremental scenario based on an intercomparison of the GCMs' precipitation performance in the region. Solar radiation simulated by the ECHAM was not available and, therefore, it was generated using regression techniques relating monthly means of daily extreme temperatures and global radiation sums. The scenarios published in the paper consist of monthly means of all temperatures, their standard deviations, and monthly means of solar radiation and precipitation amounts. Daily weather series, the necessary input to impact models, are created (i) by the additive or multiplicative modification of observed weather daily series or (ii) by generating synthetic time series with the help of a weather generator whose parameters have been modified in accord with the suggested climate change scenarios.
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    Molecular structure of trans-[Co(NH3)4(NH2CH3)Cl](ClO4)2 (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 69-72 
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    ISSN: 1572-8854
    Keywords: Co(III) complex ; crystal structure ; kinetics ; steric effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the orthorhombic space group Pnma, with a = 7.9209(5), b = 9.818(1), c = 16.867(2) Å, and Z = 4. The structure was solved employing 1864 independent x-ray reflections with I〉2σ(I) by Patterson and difference Fourier techniques and refined by full-matrix least-squares to R = 0.036. The trans-[CO(NH3)4(NH2CH3)Cl](ClO4)2 molecule is on a crystallographic mirror plane. The cobalt ion is in an elongated octahedral coordination with four equatorial ammonia ligands [average Co–N distance equal to 1.966(2) Å], an axial methylamine [Co–N=1.965(3)Å], and an axial chlorine ion [Co–Cl=2.2771(9)Å]. Kinetic steric effects of the complex are interpreted in terms of structural results.
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    A weighted-averaging regression and calibration model for inferring lakewater salinity from fossil diatom assemblages in saline lakes of the Vestfold Hills: a new tool for interpreting Holocene lake histories in Antarctica (1998)
    Springer
    Journal of paleolimnology 19 (1998), S. 99-113 
    Details
    ISSN: 1573-0417
    Keywords: Antarctica ; saline lakes ; weightedaveraging ; transfer function ; diatom analysis ; palaeolimnology ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The relationship between surface sediment diatom assemblages and measured limnological variables in thirty-three coastal Antarctic lakes from the Vestfold Hills was examined by constructing a diatom-water chemistry dataset. Previous analysis of this dataset by canonical correspondence analysis revealed that salinity accounted for a significant amount of the variation in the distribution of the diatom assemblages. Weighted-averaging regression and calibration of this diatom-salinity relationship was used to establish a transfer function for the reconstruction of past lakewater salinity from fossil diatom assemblages. Weighted-averaging regression and calibration with classical deshrinking provided the best model for salinity reconstructions and this was applied to the fossil diatom assemblages from one of the saline lakes in the Vestfold Hills in order to assess its potential for palaeosalinity and palaeoclimate reconstruction.
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    Late Quaternary diatom response to vegetation and climate change in a subalpine lake in Banff National Park, Alberta (1998)
    Springer
    Journal of paleolimnology 20 (1998), S. 253-265 
    Details
    ISSN: 1573-0417
    Keywords: Late Quaternary ; diatoms ; climate change ; vegetation change ; shallow ; subalpine ; Crowfoot Lake ; Alberta ; paleolimnology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The late Quaternary diatom record from subalpine Crowfoot Lake, Banff National Park, Alberta (lat. 51° 61′N; long. 116° 31′W) has been analyzed. Results are related to independently inferred vegetation and climate changes. No diatoms were found in the basal diamict that predates 11330 14C yr BP. Very few occur until ca. 10 10014 C yr BP probably due to the short time between de-glaciation and an advance of the Crowfoot Glacier during the ‘Younger Dryas Chron’. Initial pioneering species were characteristic of alkaline water and calcareous organic sediments. They appeared as sediments became organic and laminated suggesting increasing water clarity, and as the Pinus-dominated forest expanded and the climate warmed. After ca. 9060 14C yr BP diatom numbers increased rapidly, reaching a maximum prior to the Mazama tephra; they remained high until ca. 3500 14C yr BP. The period between ca. 9060 and 3500 14C yr saw timberline elevation increase and the dominance of xerophytic taxa. These are consistent with early to mid-Holocene warmth and aridity. Diatom productivity reflects the warm climate and presumably longer ice-free season, a stable catchment and transparent water. Decreases in diatom productivity coincide with a vegetation change with reduction of xerophytic taxa and the appearance of a closed Picea-Abies forest, hence a cooler, wetter climate at ca. 4100 to 3500 14C yr BP. The diatom numbers during the Neoglacial were of the same magnitude as prior to ca. 9060 14C yr BP. Small species of Fragilaria (overwhelmingly Fragilaria construens v. venter) became extremely dominant during the period of high diatom productivity, and remained so thereafter. Recovery of the lake appears to have been rapid after deposition of the Mazama tephra. Maximum occurrence of Cyclotella radiosa occurred ca. 8000 14C yr BP during the warm early Holocene and may reflect this warmer climate, a longer ice-free season than presently, perhaps less turbid water, or it may reflect a subtly higher nutrient status of the lake water. The diatom record of Crowfoot Lake has responded with sensitivity, particularly in terms of productivity, to the Holocene vegetation and climate changes.
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    URL: http://dx.doi.org/10.1023/A:1007978730349
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    Recent diatom assemblage changes in subarctic Lake Saanajärvi, NW Finnish Lapland, and their paleoenvironmental implications (1998)
    Springer
    Journal of paleolimnology 20 (1998), S. 205-215 
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    ISSN: 1573-0417
    Keywords: subarctic lakes ; diatoms ; paleolimnology ; climate change ; Cyclotella ; Finnish Lapland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatoms were analysed from a 30-cm long sediment core obtained from remote subarctic Lake Saanaärvi (69°03′N, 20°52′E) in order to trace possible changes in the lake. Diatom assemblages were relatively constant throughout the core, except in the top 4–5 cm (approx 1850 A.D.) where relative frequencies of Aulacoseira italica subsp. subarctica, A. lirata var. biseriata, Cyclotella comensis and C. glomerata increased markedly. No significant trends were observed in the weighted averaging (WA) reconstructed pH values. Several hypotheses, including (i) airborne pollution, (ii) climatic change, and (iii) catchment disturbances have been put forth to explain the recent changes in diatom assemblages. The diatom change coincides with a marked increase in mean annual temperature that has been documented in the area since the termination of the Little Ice Age. Our evidence favours climate change as the main causative mechanism for the observed diatom compositional changes, although other explanations cannot be ruled out.
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    URL: http://dx.doi.org/10.1023/A:1007953515620
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    Gas Production from an Ombrotrophic Bog-Effect of Climate Change on Microbial Ecology (1998)
    Springer
    Climatic change 40 (1998), S. 277-284 
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    ISSN: 1573-1480
    Keywords: ombrotrophic bogs ; microbial ecology ; methane ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Gases are produced from wetlands when plant biomass is degraded by microbial consortia, producing carbon dioxide aerobically and methane when oxygen is lacking. In anaerobic waterlogged situations, such as the catotelm of ombrotrophic bogs, this methane forms minute gas bubbles that severely reduce the hydraulic conductivity and hence the degradation of biomass due to the lack of nutrients. The bogs thus become carbon sinks, formed from the partially degraded biomass that accumulates as peat. The results of an investigation of an ombrotrophic bog, Mer Bleue, Ontario, Canada are summarized here, and the effects that climate change may have on such bogs are discussed. Any change of the water table in wetlands will have a substantial effect upon their ecology. If the water table should fall allowing bogs to become aerobic, most of the accumulated biomass carbon could be returned to the atmosphere by degradation to carbon dioxide, and as well, methane entrapped within the matrix would be released directly to the atmosphere. If on the other hand, the bogs are flooded, then the entrapped bubbles will coalesce allowing the gas to escape to the atmosphere, while at the same time the degradation of the peat will be enhanced.
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    Analysis and Estimation of Natural Processes with Nonhomogeneous Spatial Variation Using Secondary Information (1998)
    Springer
    Mathematical geology 30 (1998), S. 57-76 
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    ISSN: 1573-8868
    Keywords: vector random fields ; generalized covariances ; permissibility criteria ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Natural processes encountered in mining, hydrogeologic, environmental, etc. applications usually are poorly known because of scarcity of data over the area of interest. Therefore, stochastic estimation techniques are the tool of choice for a careful accounting of the heterogeneity and uncertainty involved. Within such a framework, a better utilization of all available data concerning the process of interest and all other natural processes related to it, is of primary importance. Because many natural processes show complicated spatial trends, the hypothesis of spatial homogeneity cannot be invoked always, and the more general theory of intrinsic spatial random fields should be employed. Efficient use of secondary information in terms of the intrinsic model requires that suitable permissibility criteria for the generalized covariances and cross-covariances are satisfied. A set of permissibility criteria are presented for the situation of two intrinsic random fields. These criteria are more general and comprehensive than the ones currently available in the geostatistical literature. A constrained least-square technique is implemented for the inference of the generalized covariance and cross-covariance parameters, and a synthetic example is used to illustrate the methodology. The numerical results show that the use of secondary information can lead to significant reductions in the estimation errors.
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    Geological Controls of Variograms in a Complex Carbonate Reservoir, Eastern Province, Saudi Arabia (1998)
    Springer
    Mathematical geology 30 (1998), S. 309-322 
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    ISSN: 1573-8868
    Keywords: variograms ; geostatistics ; geological controls ; reservoir characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract To derive meaningful results from a geostatistical study, it is extremely important to establish the relationship between geology and variograms. However, it is not always easy to establish such a relationship, mainly because of the inadequacy of quantitative or qualitative information. Large amounts of reliable well-log porosity data and the detailed geological information from a complex carbonate reservoir located in the Eastern Province of Saudi Arabia provided an ideal case study of the relationships between geology and variograms. The reservoir under consideration is in the form of a gently dipping, elongated anticline and consists of three productive zones which have been subdivided into several lithologically distinct layers. Results, which indicate an excellent match between geology and porosity variograms, are summarized as follows: (1) use of stratigraphic distances resulted in considerable improvement in the behavior of variograms, (2) structurally controlled geometrical anisotropy is the most obvious feature of variograms, and (3) layers consisting of more complex lithologic framework provided variograms with relatively greater nugget variances and shorter ranges. These results provide further insight into geology and form a meaningful basis for estimation and simulation of the reservoir. They also could be used as a general guide in the geostatistical study of similar carbonate reservoirs.
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    An Improved Perturbation Mechanism for Simulated Annealing Simulation (1998)
    Springer
    Mathematical geology 30 (1998), S. 801-816 
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    ISSN: 1573-8868
    Keywords: geostatistics ; stochastic simulation ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Simulated annealing (SA) is being increasingly used for the generation of stochastic models of spatial phenomena because of its flexibility to integrate data of diverse types and scales. The major shortcoming of SA is the extensive CPU requirements. We present a perturbation mechanism that significantly improves the CPU speed. Two conventional perturbation mechanisms are to (1) randomly select two locations and swap their attribute values, or (2) visit a randomly selected location and draw a new value from the global histogram. The proposed perturbation mechanism is a modification of option 2: each candidate value is drawn from a local conditional distribution built with a template of kriging weights rather than from the global distribution. This results in accepting more perturbations and in perturbations that improve the variogram reproduction for short scale lags. We document the new method, the increased convergence speed, and the improved variogram reproduction. Implementation details of the method such as the size of the local neighborhood are considered.
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    Maximum Likelihood Estimation of Spatial Covariance Parameters (1998)
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    Mathematical geology 30 (1998), S. 95-108 
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    ISSN: 1573-8868
    Keywords: geostatistics ; maximum likelihood estimation ; spatial covariance ; sampling distribution ; mean square error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract In this paper, the maximum likelihood method for inferring the parameters of spatial covariances is examined. The advantages of the maximum likelihood estimation are discussed and it is shown that this method, derived assuming a multivariate Gaussian distribution for the data, gives a sound criterion of fitting covariance models irrespective of the multivariate distribution of the data. However, this distribution is impossible to verify in practice when only one realization of the random function is available. Then, the maximum entropy method is the only sound criterion of assigning probabilities in absence of information. Because the multivariate Gaussian distribution has the maximum entropy property for a fixed vector of means and covariance matrix, the multinormal distribution is the most logical choice as a default distribution for the experimental data. Nevertheless, it should be clear that the assumption of a multivariate Gaussian distribution is maintained only for the inference of spatial covariance parameters and not necessarily for other operations such as spatial interpolation, simulation or estimation of spatial distributions. Various results from simulations are presented to support the claim that the simultaneous use of maximum likelihood method and the classical nonparametric method of moments can considerably improve results in the estimation of geostatistical parameters.
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    URL: http://dx.doi.org/10.1023/A:1021765405952
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    An Alternative to Cokriging for Situations with Small Sample Sizes (1998)
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    Mathematical geology 30 (1998), S. 259-274 
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    ISSN: 1573-8868
    Keywords: cokriging ; small sample size ; pedotransfer functions ; geostatistics ; parameter uncertainty ; measurement error
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Lack of large datasets in soil protection studies and environmental engineering applications may deprive these fields of achieving accurate spatial estimates as derived with geostatistical techniques. A new estimation procedure, with the acronym Co_Est, is presented for situations involving primary and secondary datasets of sizes generally considered too small for geostatistical applications. For these situations, we suggest the transformation of the secondary dataset into the primary one using pedotransfer functions. The transformation will generate a larger set of the primary data which subsequently can be used in geostatistical analyses. The Co_Est procedure has provisions for handling measurement errors in the primary data, estimation errors in the converted secondary data, and uncertainty in the geostatistical parameters. Two different examples were used to demonstrate the applicability of Co_Est. The first example involves estimation of hydraulic conductivity random fields using 42 measured data and 258 values estimated from borehole profile descriptions. The second example consists of estimating chromium concentrations from 50 measured chromium data and 150 values estimated from a relationship between chromium and copper concentrations. The examples indicate that in situations where the size of the primary data is small, Co_Est can produce estimates which are comparable to cokriging estimates.
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    URL: http://dx.doi.org/10.1023/A:1021724830427
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    Conditional Spectral Simulation with Phase Identification (1998)
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    Mathematical geology 30 (1998), S. 285-308 
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    ISSN: 1573-8868
    Keywords: conditional simulation ; kriging ; spectral simulation ; Fast Fourier Transform ; Fourier coefficient ; phase identification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Spectral simulation is used widely in electrical engineering to generate random fields with a given covariance spectrum. The algorithms used are fast particularly when based on Fast Fourier Transform (FFT). However, because of lack of phase identification, spectral simulation only generates unconditional realizations. Local data conditioning is obtained typically by adding a simulated kriging residual. This conditioning process requires an additional kriging at each simulated node thus forfeiting the speed advantage of FFT. A new algorithm for conditioning is proposed whereby the phase values are determined iteratively to ensure approximative data reproduction while reproducing the frequency spectrum, that is, the covariance model. A case study is presented to demonstrate the algorithm.
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    A Comparison of the Sequential Gaussian and Markov-Bayes Simulation Methods for Small Samples (1998)
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    Mathematical geology 30 (1998), S. 1011-1032 
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    ISSN: 1573-8868
    Keywords: spatial statistics ; stochastic simulation ; kriging ; GSLIB
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract We compared the performance of sequential Gaussian simulation (sGs) and Markov-Bayes simulation (MBs) using relatively small samples taken from synthetic datasets. A moderate correlation (approximately r = 0.70) existed between a continuous primary variable and a continuous secondary variable. Given the small sample sizes, our objective was to determine whether MBs, with its ability to incorporate the secondary information, would prove superior to SgS. A split-split-plot computer experiment was conducted to compare the two simulation methods over a variety of primary and secondary sample sizes as well as spatial correlations. Using average mean square prediction error as a measure of local performance, sGs and MBs were roughly equivalent for random fields with short ranges (2 m). As range increased (15 m) the average mean square prediction error for sGs was less than or equal to that for MBs, even when number of noncollocated secondary observations was twice the number of collocated observations. Median variance within nonoverlapping subregions was used as a measure of the local heterogeneity or surface texture of the image. In most situations sGs images more faithfully reflected the true local heterogeneity, while MBs was more erratic, sometimes oversmoothing and sometimes undersmoothing.
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    Plant-soil Interactions in Deserts (1998)
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    Biogeochemistry 42 (1998), S. 169-187 
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    ISSN: 1573-515X
    Keywords: aridisols ; desertification ; erosion ; geostatistics ; Larrea tridentata ; nitrogen ; phosphorus ; Prosopis glandulosa ; soil heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Geostatistical analyses show that the distribution of soil N, P and K is strongly associated with the presence of shrubs in desert habitats. Shrubs concentrate the biogeochemical cycle of these elements in ‘islands of fertility’ that are localized beneath their canopies, while adjacent barren, intershrub spaces are comparatively devoid of biotic activity. Both physical and biological processes are involved in the formation of shrub islands. Losses of semiarid grassland in favor of invading shrubs initiate these changes in the distribution of soil nutrients, which may promote the further invasion and persistence of shrubs and cause potential feedbacks between desertification and the Earth's climate system.
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    URL: http://dx.doi.org/10.1023/A:1005939924434
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    Potential Effects of Global Warming on Waterfowl Populations Breeding in the Northern Great Plains (1998)
    Springer
    Climatic change 40 (1998), S. 343-369 
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    ISSN: 1573-1480
    Keywords: effects of global warming ; drought ; climate change ; Prairie Pothole Region ; waterfowl ; waterfowl breeding ecology ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Prairie Pothole Region (PPR) of the Northern Great Plains is the most important breeding area for waterfowl in North America. Historically, the size of breeding duck populations in the PPR has been highly correlated with spring wetland conditions. We show that one indicator of climate conditions, the Palmer Drought Severity Index (PDSI), is strongly correlated with annual counts (from 1955 to 1996) of both May ponds (R2 = 0.72, p 〈 0.0001) and breeding duck populations (R2 = 0.69, p 〈 0.0001) in the Northcentral U.S., suggesting the utility of PDSI as an index for climatic factors important to wetlands and ducks. We then use this relationship to project future pond and duck numbers based on PDSI values generated from sensitivity analyses and two general circulation model (GCM) scenarios. We investigate the sensitivity of PDSI to fixed changes in temperature of 0°C, +1.5°C, +2.5°C, and +4.0°C in combination with fixed changes in precipitation of -10%, +0%, +7%, and +15%, changes spanning the range of typically-projected values for this region from human-induced climatic change. Most (11 of 12) increased temperature scenarios tested result in increased drought (due to greater evapotranspiration under warmer temperatures) and declining numbers of both wetlands and ducks. Assuming a doubling of CO2 by 2060, both the equilibrium and transient GCM scenarios we use suggest a major increase in drought conditions. Under these scenarios, Northcentral U.S. breeding duck populations would fluctuate around means of 2.1 or 2.7 million ducks based on the two GCMs, respectively, instead of the present long-term mean of 5.0 million. May pond numbers would fluctuate around means of 0.6 or 0.8 million ponds instead of the present mean of 1.3 million. The results suggest that the ecologically and economically important PPR could be significantly damaged by climate changes typically projected. We make several recommendations for policy and research to help mitigate potential effects.
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    Potential Impacts of Climate Change on Fire Regimes in the Tropics Based on Magicc and a GISS GCM-Derived Lightning Model (1998)
    Springer
    Climatic change 39 (1998), S. 273-296 
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    ISSN: 1573-1480
    Keywords: Fire regime ; fire scenarios ; climate change ; tropical vegetation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Investigations of the ecological, atmospheric chemical, and climatic impacts of contemporary fires in tropical vegetation have received increasing attention during the last 10 years. Little is known, however, about the impacts of climate changes on tropical vegetation and wildland fires. This paper summarizes the main known interactions of fire, vegetation, and atmosphere. Examples of predictive models on the impacts of climate change on the boreal and temperate zones are given in order to highlight the possible impacts on the tropical forest and savanna biomes and to demonstrate parameters that need to be involved in this process. Response of tropical vegetation to fire is characterized by degradation towards xerophytic and pyrophytic plant communities dominated by grasses and fire-tolerant tree and bush invaders. The potential impacts of climate change on tropical fire regimes are investigated using a GISS GCM-based lightning and fire model and the Model for the Assessment of Greenhouse Gas-Induced Climate Change (MAGICC).
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    Conditional LAS stochastic simulation of regionalized variables in random fields (1998)
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    Computational geosciences 2 (1998), S. 37-45 
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    ISSN: 1573-1499
    Keywords: conditional simulation ; regionalized variables ; local average subdivision ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Computer Science
    Notes: Abstract Ore reserves forecasts are required to aid in investment decisions, mine design and valuation, short and long term production plans and proper and efficient mill design. In random multivariable fields with limited data and high levels of uncertainty, the kriged block estimates produce a smoothing effect resulting in underestimating high values and overestimating low values. The modified conditional simulation (MCS) methodology solves these problems by simulating the random field to preserve its mean and the variance structure. The simulation model is conditioned to reproduce the data at known sample points to minimize the variability between the simulated data and the true field data. In this study, the authors develop the MCS methodology to simulate ore reserve grades using the best linear unbiased estimation (BLUE) and the local average subdivision (LAS) techniques. The MCS methodology is applied to simulate block grades in a section of the Sabi Gold Project in Zimbabwe. The results are compared with the kriged estimates for this section. Analysis of the results shows that the MCS methodology reproduces the known sample grades with minimum estimation error of 0.001 while the estimation error associated with the kriged estimates is 1.104, a 100% efficiency of the MCS method over the kriging technique.
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    Depth of the base of the Jackson aquifer, based on geophysical exploration, southern Jackson Hole, Wyoming, USA (1998)
    Springer
    Hydrogeology journal 6 (1998), S. 374-382 
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    ISSN: 1435-0157
    Keywords: Key words geophysical methods ; groundwater exploration ; geostatistics ; unconsolidated sediments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé Une campagne géophysique a été entreprise pour préciser la profondeur du mur de l'aquifère dans le secteur sud de Jackson Hole (Wyoming, États-Unis). Des mesures audio-magnétotelluriques (audio MT) sur 77 sites de ce secteur ont fourni des logs de résistivitéélectrique du sous-sol ; les variations de la lithologie en fonction de la profondeur en ont été déduites. Un niveau géoélectrique à 100–600 ohm.m, dénommé "aquifère de Jackson", a servi à définir des dépôts superficiels quaternaires saturés en eau et non consolidés. La profondeur médiane de la base de l'aquifère de Jackson est de l'ordre de 61 m, à partir des 62 sites ayant fourni suffisamment de données de résistivité. Les valeurs audio MT mesurées ont été krigées afin d'estimer la profondeur de la base de la formation aquifère dans la partie sud de Jackson Hole. Les cartes d'isovaleurs d'estimation krigées indiquent que la profondeur de la base de la formation aquifère de Jackson est faible dans la partie centrale de la zone d'étude à l'est et à l'ouest des monts Gros Ventre, plus grande dans le secteur ouest près de la zone faillée de Teton, et faible sur la bordure sud de Jackson Hole. Les profondeurs estimées vont de 30 m au sud, près des confluences des rivières Spring et Flat avec la rivière Snake, à 210 m à l'ouest près de la ville de Wilson (Wyoming).
    Abstract: Resumen Se llevó a cabo una campaña geofísica para determinar la profundidad del basamento de un acuífero libre en la zona sur de Jackson Hole, Wyoming, EEUU. USA. Medidas audio-magnetotelúricas (ATM) en 77 lugares de la zona de estudio dieron lugar a registros de resistividad eléctrica del subsuelo, que se usaron para inferir los cambios litológicos con la profundidad. Los depósitos superficiales, saturados y no consolidados de edad cuaternaria, el acuífero de Jackson, forman una capa de resistencia geoeléctrica entre 100–600 ohm-m. La profundidad media de la base del acuífero de Jackson se estima en unos 61 m (200 pies), a partir de 62 registros con medidas suficientes. Los valores ATM fueron krigeados para obtener una medida de la profundidad del basamento del acuífero en la zona sur de Jackson Hole. Los mapas de isoprofundidades obtenidos por krigeado indican que el acuífero es poco profundo en la parte central de la zona de estudio, cerca de los Gros Ventre Buttes orientales y occidentales, más profundo al oeste, cerca del sistema de fallas de Teton, y menos profundo en el borde sur de Jackson Hole. Las profundidades van desde 30 m (100 pies) en el sur, en la confluencia entre los desfiladeros Spring y Flat con el Río Snake, hasta 210 m (700 pies) al oeste, cerca de la ciudad de Wilson, Wyoming.
    Notes: Abstract  A geophysical survey was conducted to determine the depth of the base of the water-table aquifer in the southern part of Jackson Hole, Wyoming, USA. Audio-magnetotellurics (AMT) measurements at 77 sites in the study area yielded electrical-resistivity logs of the subsurface, and these were used to infer lithologic changes with depth. A 100–600 ohm-m geoelectric layer, designated the Jackson aquifer, was used to represent surficial saturated, unconsolidated deposits of Quaternary age. The median depth of the base of the Jackson aquifer is estimated to be 200 ft (61 m), based on 62 sites that had sufficient resistivity data. AMT-measured values were kriged to predict the depth to the base of the aquifer throughout the southern part of Jackson Hole. Contour maps of the kriging predictions indicate that the depth of the base of the Jackson aquifer is shallow in the central part of the study area near the East and West Gros Ventre Buttes, deeper in the west near the Teton fault system, and shallow at the southern edge of Jackson Hole. Predicted, contoured depths range from 100 ft (30 m) in the south, near the confluences of Spring Creek and Flat Creek with the Snake River, to 700 ft (210 m) in the west, near the town of Wilson, Wyoming.
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    Trace Gas Measurements Between Moscow and Vladivostok Using the Trans-Siberian Railroad (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 179-194 
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    ISSN: 1573-0662
    Keywords: tropospheric chemistry ; ozone ; Russia ; trans-Siberian railroad ; Siberia ; carbon monoxide ; methane ; nitrogen oxides ; trace gases ; atmospheric composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a laboratory wagon traveling along the Trans-Siberian railroad, O3, NO, NO2, CO, CH4, SF6 and black carbon aerosol have been measured during the summer of 1996. The expedition from Niznij Novgorod (500 km east of Moscow) to Vladivostok (and back to Moscow) has shown the great potential of the train method; here the first results are presented and discussed. A wealth of boundary layer air data was obtained during the over 18000 km travel without serious contamination problems from the electric train itself. The diurnal O3 cycle peaked generally below 50 nmole/mole, showed the effects of changes in J(NO2), and often dropped to a few nmole/mole at night time during inversions. Over the vast Siberian lowlands situated between the Ural mountains and the river Yenisey, CH4 levels were consistently elevated at around 1.95 µmole/mole, which we mainly attribute to wetland emissions. Over eastern Siberia, however, CH4 levels were generally lower at 1.85 µmole/mole. In contrast, over the west Siberian lowlands, CO levels were relatively low, often reaching values of only 110 nmole/mole, whereas over eastern Siberia CO levels were higher. Very high CO levels were detected over a 2000 km section east of Chita, along the river Amur, which represented an enormous polluted air mass. 14C analysis performed on several CO samples confirms that the origin was biomass burning. SF6, which was measured as a general conserved tracer, showed an eastward attenuation from 4.0 to 3.9 pmole/mole, with peaks in a number of places due to local Russian emissions.
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    Peroxy Radical Kinetics Resulting from the OH-Initiated Oxidation of 1,3-Butadiene, 2,3-Dimethyl-1,3-Butadiene and Isoprene (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 267-298 
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    ISSN: 1573-0662
    Keywords: peroxy radicals ; kinetics ; conjugateddienes ; biogenic VOC ; degradation mechanisms ; tropospheric ozone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The laser flash photolysis/UV absorption spectrometry technique has been used to investigate the kinetics of the peroxy radical permutation reactions (i.e. self and cross reactions) arising from the OH-initiated oxidation of isoprene (2-methyl-1,3-butadiene), and of the simpler, but related conjugated dienes, 1,3-butadiene and 2,3-dimethyl-1,3-butadiene. The results of the two simpler systems are analysed to provide values of the rate coefficients for the 6 peroxy radical permutation reactions of the three types of isomeric peroxy radical produced in each system (T = 298 K, P = 760 Torr). The rate coefficients are all significantly larger than values estimated previously by extrapolation of structure-reactivity relationships based on the kinetics of a limited dataset of simpler radicals containing similar structural features. The results are discussed in terms of trends in self and cross reaction reactivity of primary, secondary and tertiary peroxy radicals containing combinations of allyl, β-hydroxy and δ-hydroxy functionalities. Since the peroxy radicals formed in these systems are structurally very similar to those formed in the isoprene system, the kinetic parameters derived from the results of the simpler systems are used to assist the assignment of kinetic parameters to the 21 permutation reactions of the six types of isomeric peroxy radical generated in the isoprene system. Kinetic models describing the OH-initiated degradation of all three conjugated dienes to first generation products in the absence of NOx are recommended, which are also consistent with available end product studies. The model for isoprene is considered to be a further improvement on that suggested previously for its OH-initiated oxidation in the absence of NOx. The mechanism is further extended to include chemistry applicable to ‘NOx-present’ conditions, and calculated product yields are compared with those reported in the literature.
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    URL: http://dx.doi.org/10.1023/A:1005940332441
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    Upper Limit of Iodine Oxide in the Lower Stratosphere (1998)
    Springer
    Journal of atmospheric chemistry 30 (1998), S. 173-185 
    Details
    ISSN: 1573-0662
    Keywords: stratosphere ; ozone ; iodine ; visible spectroscopy ; balloon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract It has been suggested that iodine oxides, IOx, could play a significant role in the ozone destruction in the lower stratosphere. To investigate this suggestion, spectra from nine SAOZ uv-visible spectrometer balloon flights were examined for the IO absorption signature between 405 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0.2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km at the 95% confidence level (2σ), was derived from the best measurements at 90° SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at that time, it is concluded that unless iodine chemistry is different from that assumed at the moment, the role of iodine in stratospheric ozone depletion is small.
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    Gaseous and Particulate Oxidized and Reduced Nitrogen Species in the Atmospheric Boundary Layer in Scandinavia in Spring (1998)
    Springer
    Journal of atmospheric chemistry 30 (1998), S. 241-271 
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    ISSN: 1573-0662
    Keywords: total nitrate ; total ammonium ; ozone ; filter pack ; denuder ; numerical modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Observations of the concentration of several nitrogen containing compounds at five rural Scandinavian sites during March–June 1993 are reported. Total nitrate (NO 3 - + HNO3) and total ammonium (NH 4 + + NH3) were measured by denuder and filter pack. In general the methods agree well. At all sites the particulate fraction dominated, with the largest fraction of NO 3 - and the lowest of NH 4 + at the sites which were closest to the emission sources. The fraction of NO 3 - of total nitrate increased with increasing NO2 concentrations, indicating that the nighttime conversion of NO2 to NO 3 - is an important route of formation for NO 3 - . A positive correlation was found between HNO3 and O3 in June at all sites, while no correlation was found early in the spring. Model calculations were made with a lagrangian boundary layer photooxidant model for the whole period, and compared to the measured concentrations. The calculated ratio between mean observed and modelled daily maximum concentrations of ozone over the measurement period were within +/−10% at all sites. The models ability to describe the daily ozone maximum concentration was satisfactory with an average deviation of 19–22% from the observed concentrations. HNO3 was underestimated by over 50% at all sites except the one closest to the emission sources. The correlation between modelled and observed concentrations was generally best for the sites with shortest transport distance from the sources of emission.
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    Absorption Spectra Measurements for the Ozone Molecule in the 350–830 nm Region (1998)
    Springer
    Journal of atmospheric chemistry 30 (1998), S. 291-299 
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    ISSN: 1573-0662
    Keywords: ozone ; absorption cross-sections ; Chappuis bands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Absolute absorption cross-sections of ozone have been measured at ambient (295 K) and low temperature (218 K) in the visible region corresponding to the Chappuis bands. The temperature effect has been studied and found to be very small. The minimum of the absorption between the Hartley and the Chappuis bands is observed for the first time at 377,5 nm.
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    Kinetics of the Gas-Phase Reactions of OH and NO3 Radicals and O3 with the Monoterpene Reaction Products Pinonaldehyde, Caronaldehyde, and Sabinaketone (1998)
    Springer
    Journal of atmospheric chemistry 31 (1998), S. 281-297 
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    ISSN: 1573-0662
    Keywords: hydroxyl radical ; nitrate radical ; ozone ; pinonaldehyde ; caronaldehyde ; sabinaketone ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Using a relative rate method, rate constants have been measured for the gas-phase reactions of OH and NO3 radicals with pinonaldehyde, caronaldehyde and sabinaketone at 296 ± 2 K. The OH radical reaction rate constants obtained are (in units of 10−12 cm3 molecule−1 s−1): pinonaldehyde, 48 ± 8; caronaldehyde, 48 ± 8; and sabinaketone, 5.1 ± 1.4, and the NO3 radical reaction rate constants are (in units of 10−14 cm3 molecule−1 s−1): pinonaldehyde, 2.0 ± 0.9; caronaldehyde, 2.5 ± 1.1; and sabinaketone, 0.036 ± 0.023, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. Upper limits to the O3 reaction rate constants were also obtained, of 〈2 × 10−20 cm3 molecule−1 s−1 for pinonaldehyde and caronaldehyde, and 〈5 × 10−20 cm3 molecule−1 s−1 for sabinaketone. These reaction rate constants are combined with estimated ambient tropospheric concentrations of OH radicals, NO3 radicals and O3 to calculate tropospheric lifetimes and dominant transformation process(es) of these and other monoterpene reaction products.
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    Nonlinear Dynamics in Atmospheric Chemistry Rate Equations (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 1-16 
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    ISSN: 1573-0662
    Keywords: bifurcation ; oscillation ; autocatalysis ; ozone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nonlinear terms in the gas-phase rate equations of atmospheric trace constituents give rise to unexpected oscillations in the concentrations. For a simplified chemical scheme of the troposphere that contains only the generic reaction paths, the underlying dynamical structure is investigated. It is shown that the source strengths of CO and NO are the controlling parameters of the system. A linear stability analysis reveals that the steady state solutions lose stability due to the occurrence of two Hopf bifurcations. Furthermore, it appears that the dynamical behaviour of the oscillatory solutions is dominated by O3 and CO. Based on the two-variable system (CO–O3) it is shown that the oscillatory solution involves an autocatalytic ozone production phase which is followed by a phase in which CO is oxidised quickly. A simple expression is presented from which the period of the oscillation can be obtained. The implications for the present troposphere are unclear, since other hydrocarbons are present and transport is taking place. Nevertheless, the system nicely shows the general nonlinear mechanisms that operate in the tropospheric chemistry equations.
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    Validation of Ground-Based Visible Measurements of Total Ozone by Comparison with Dobson and Brewer Spectrophotometers (1998)
    Springer
    Journal of atmospheric chemistry 29 (1998), S. 55-83 
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    ISSN: 1573-0662
    Keywords: stratosphere ; ozone ; validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Comparisons of total column ozone measurements from Dobson, Brewer and SAOZ instruments are presented for the period 1990 to 1995 at seven stations covering the mid- and the high northern latitudes, as well as the Antarctic region. The main purpose of these comparisons is to assess, by reference to the well established Dobson network, the accuracy of the zenith-sky visible spectroscopy for the measurement of total ozone. The strengths and present limitations of this latter technique are investigated. As a general result, the different instruments are found to agree within a few percent at all stations, the best agreement being obtained at mid-latitudes. On average, for the mid-latitudes, SAOZ O3 measurements are approximately 2% higher than Dobson ones, with a scatter of about 5%. At higher latitudes, both scatter and systematic deviation tend to increase. In all cases, the relative differences between SAOZ and Dobson or Brewer column ozone are characterised by a significant seasonal signal, the amplitude of which increases from about 2.5% at mid-latitude to a maximum of 7.5% at Faraday, Antarctica. Although it introduces a significant contribution to the seasonality at high latitude, the temperature sensitivity of the O3 absorption coefficients of the Dobson and Brewer instruments is shown to be too small to account for the observed SAOZ/Dobson differences. Except for Faraday, these differences can however be largely reduced if SAOZ AMFs are calculated with realistic climatological profiles of ozone, pressure and temperature. Other sources of uncertainties that might affect the comparison are investigated. Evidence is found that the differences in the air masses sampled by the SAOZ and the other instruments contribute significantly to the scatter, and the impact of the tropospheric clouds on SAOZ measurements is displayed.
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    URL: http://dx.doi.org/10.1023/A:1005815902581
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    Response of tundra CH4 and CO2 flux tomanipulation of temperature and vegetation (1998)
    Springer
    Biogeochemistry 41 (1998), S. 215-235 
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    ISSN: 1573-515X
    Keywords: arctic ; carbon dioxide ; climate change ; methane ; plant transport ; species composition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We conducted plant species removals, air temperaturemanipulations, and vegetation and soil transplants inAlaskan wet-meadow and tussock tundra communities todetermine the relative importance of vegetation typeand environmental variables in controlling ecosystemmethane (CH4) and carbon dioxide (CO2) flux. Plastic greenhouses placed over wet-meadow tundraincreased air temperature, soil temperature, and soilmoisture, but did not affect CH4 or CO2 flux(measured in the dark). By contrast, removal ofsedges in the wet meadow significantly decreased fluxof CH4, while moss removal tended to increaseCH4 emissions. At 15 cm depth, pore-waterCH4 concentrations were higher in sedge-removalthan in control plots, suggesting that sedgescontribute to CH4 emissions by transportingCH4 from anaerobic soil to the atmosphere, ratherthan by promoting methanogenesis. Inreciprocal-ecosystem transplants between thewet-meadow and tussock tundra communities, CH4and CO2 emissions were higher overall in thewet-meadow site, but were unrelated to transplantorigin. Methane flux was correlated with localvariation in soil temperature, thaw depth, andwater-table depth, but the relative importance ofthese factors varied through the season. Our resultssuggest that future changes in CH4 and CO2flux in response to climatic change will be morestrongly mediated by large-scale changes in vegetationand soil parameters than by direct temperature effects.
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    URL: http://dx.doi.org/10.1023/A:1005984701775
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    The sedimentary record of recent (last 500 years) environmental changes in the Seixal Bay marsh, Tagus estuary, Portugal (1998)
    Springer
    Netherlands journal of geosciences 77 (1998), S. 283-293 
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    ISSN: 1573-9708
    Keywords: climate change ; estuary ; foraminifera ; geochemistry ; human impact ; salt marshes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The inner Tagus estuary is essentially a sedimentation basin that receives cohesive sediment from terrestrial, marine, biological and anthropogenic sources. Three short cores from one site in a marsh area of this estuary (Seixal Bay) were analysed for sedimentary, geochemical and micropalaeontological contents (benthic foraminifera and nannoplankton). The length of the cores represents about half a millennium of sedimentation. Textural analysis suggests a highly uniform mud sedimentation for most of the cores but geochemical, mineralogical and micropaleontological results indicate climatic and environmental changes and anthropogenic disturbance. Three Foraminifera zones were identified. The lower part of the lower zone indicates sedimentation in an open channel or a lower domain of an exposed high-energy sandflat. Sediments of the upper part of the lower zone and of the middle zone were deposited in a lower-energy environment, probably associated with a sheltered, vertically aggrading mudflat located within the Seixal Bay. Biological and mineralogical indicators suggest that periods of total or partial closure of this bay occurred. Clay minerals indicate that drier and colder conditions prevailed in the lower half of this zone evolving gradually to a wetter and warmer environment towards the top. The upper zone indicates persistence of low-energy sedimentation and evolution towards the present salt-marsh conditions. Anthropogenic pollution is clear in geochemical proxies at the top of the sedimentary column and was used for dating purposes.
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    Simulation of normal distributed smooth fields by Karhunen-Loéve expansion in combination with kriging (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 459-482 
    Details
    ISSN: 1436-3259
    Keywords: Karhunen-Loéve expansion ; Empirical Orthogonal Functions ; stochastic simulation ; gaussian fields ; analytical covariance functions ; eigenfunctions ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function. This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the 2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the predefined covariance functions are evaluated.
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    URL: http://dx.doi.org/10.1007/BF02428429
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    A preliminary investigation of siliceous microfossil succession in late Quaternary sediments from Lake Baikal, Siberia (1997)
    Springer
    Journal of paleolimnology 18 (1997), S. 189-206 
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    ISSN: 1573-0417
    Keywords: Lake Baikal ; Russia ; paleolimnology ; diatoms ; chrysophyte cysts ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Siliceous microfossil assemblage succession was analyzed in a 100 m sediment core from Lake Baikal, Siberia. The core was recovered from the lake's central basin at a water depth of 365 m. Microfossil abundance varied greatly within the intervals sampled, ranging from samples devoid of siliceous microfossils to samples with up to 3.49 × 1011 microfossils g-1 sediment. Fluctuations in abundance appear to reflect trends in the marine δ18O record, with peak microfossil levels generally representing climate optima. Microfossil taxa present in sampled intervals changed considerably with core depth. Within each sample a small number of endemic diatom species dominated the assemblage. Changes in dominant endemic taxa between sampled intervals ranged from extirpation of some taxa, to shifts in quantitative abundance. Differences in microfossil composition and the association of variations in abundance with climate fluctuations suggest rapid speciation in response to major climatic excursions.
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    The significance of storms for the concentration and export of dissolved organic carbon from two Precambrian Shield catchments (1997)
    Springer
    Biogeochemistry 36 (1997), S. 67-88 
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    ISSN: 1573-515X
    Keywords: climate change ; dissolved organic carbon (DOC) ; forested catchments ; nutrient export ; Precambrian Shield streams ; storm runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Dissolved organic carbon (DOC) concentrations and DOC export arestudied during storms to examine the relationship between DOCconcentration and stream discharge and to assess the importance of stormson DOC export. Storms were monitored in seven subcatchments within twosmall watersheds (Harp 4--21 and Harp 3A) on the Precambrian Shield inCentral Ontario, Canada. Stream DOC concentrations increase during stormsby as much as 100% and 410% in Harp3A and Harp 4--21 respectively. The seasonal regression between DOC andstream discharge is significant in subcatchments without wetlands(r2 〉 0.7) but is not significant in thetwo subcatchments with small wetland areas (r2 〈0.06). On average, regressions based on weekly data yield accurate estimatesof DOC export but the variation in regressions among individual storms andthe small number of high DOC samples result in uncertainties of more than30% in DOC export. The period-weighted calculation ofDOC export from weekly data underestimates export by 14%and 22% in Harp 3A and Harp 4--21 respectively. Stormswere responsible for 57% to 68% of theDOC export in the autumn and 29% to 40%of the DOC export in the spring. A single large storm accounted for31% of the autumn DOC export in Harp 3A. The importanceof individual storms for DOC export and the variation in the relationshipbetween DOC and stream discharge among storms make it difficult to predictthe effects of climate change on DOC export and DOC concentrations.
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    Tropospheric Ozone in a Global-Scale Three-Dimensional Lagrangian Model and Its Response to NOX Emission Controls (1997)
    Springer
    Journal of atmospheric chemistry 26 (1997), S. 223-274 
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    ISSN: 1573-0662
    Keywords: global model ; three-dimensional ; Lagrangian tropospheric chemistry ; ozone ; NOX ; emission controls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A three-dimensional Lagrangian tropospheric chemistry modelis used toinvestigate the impact of human activities on the tropospheric distributionofozone and hydroxyl radicals. The model describes the behaviour of 50 speciesincluding methane, carbon monoxide, oxides of nitrogen, sulphur dioxide andnineorganic compounds emitted from human activities and a range of other sources.Thechemical mechanism involves about 100 chemical reactions of which 16 arephotochemical reactions whose diurnal dependence is treated in full. The modelutilises a five minute chemistry time step and a three hour advection timestepfor the 50,000 air parcels. Meteorological data for the winds, temperatures,clouds and so on are taken from the UK Meteorological Office global model for1994 onwards. The impacts of a 50% reduction in European NOXemissions onglobal ozone concentrations are assessed. Surface ozoneconcentrations decrease in summertime and rise in wintertime, but to differentextents.
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    On the Budget of OH Radicals and Ozone in an Urban Plume from the Decay of C5–C8 Hydrocarbons and NOx (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 263-282 
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    ISSN: 1573-0662
    Keywords: ozone ; hydrocarbons ; NOx ; photochemistry ; OH-radicals ; budget
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Simultaneous measurements of ozone and ozoneprecursors were made during a field campaign atSchauinsland in the Black Forest and in the valleynorth of Schauinsland that channels the flow ofpolluted air from the city of Freiburg to the site.From the decay of hydrocarbons and NOx between the twomeasuring sites and the known rate coefficients, theconcentration of OH radicals was calculated. From abudget analysis of OH and HOx it is concluded that therelatively high OH concentrations (5–8 ×106cm-3) in the presence of high NO2concentrations cannot be explained by the knownprimary sources. The budget can be closed if efficientrecycling of OH via HO2 is assumed to occur andthat, based on the measured hydrocarbons, 2 HO2molecules are formed for each OH radical that reactswith a hydrocarbon molecule. This assumption is inaccordance with the budget of Ox obtained from ourmeasurements and with results from earliermeasurements of alkylnitrates and peroxy radicals atSchauinsland. A possible conclusion is that the decayof precursors and production of photooxidants in urbanplumes proceeds at a faster rate than is currentlyassumed. The potential role of biogenichydrocarbons for the radical budget is alsodiscussed.
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    Tropospheric Ozone at the Swedish Mountain Site Åreskutan: Budget and Trends (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 61-76 
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    ISSN: 1573-0662
    Keywords: ozone ; beryllium-7 ; annual cycle ; spring maximum ; stratosphere-troposphere exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Ozone measurements, performed since 1987, at the Swedish TOR/EUROTRACstation Åreskutan (lat. 63.4° N, long. 13.1° E, 1250 m abovesea level) are analyzed. The annual average ozone concentration at the sitehas increased by about 0.4 ppbv (∼1%) per year during the period1987–1994. The corresponding trends for individual months show adecrease during April–September and an increase during the rest of theyear. The ozone budget at Åreskutan has been investigated using backtrajectories of the air parcels, and the cosmogenic radionuclide7Be as a tracer of stratospheric air. From a simple diagnosticmodel, it is estimated that the contribution of stratospheric ozone to theconcentrations measured at Åreskutan is 5 ppbv (or 14% of themeasured values) on average, reaching a maximum of 23 ppbv (50%),during the episodes of direct stratospheric influence. In spring, thestratospheric contribution to ozone budget at Åreskutan is at itsmaximum, and approximately equal to the net photochemical ozone productionin the air mass affecting the site, whereas in winter, it is compensated byozone chemical sink during the transport of air masses from pollutedEuropean regions, to Scandinavia.
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    Climatology of Ozone, PAN, CO, and NMHC in the Free Troposphere Over the Southern North Atlantic (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 245-262 
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    ISSN: 1573-0662
    Keywords: free troposphere ; ozone ; non methane hydrocarbons ; peroxyacetylnitrate ; carbon monoxide ; photo chemistry ; North Atlantic ; seasonal cycle ; long range transport ; back-trajectories ; photochemical age
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18′N, 16°30′W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.
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    Climate Change, Extreme Events and the Canadian Insurance Industry (1997)
    Springer
    Natural hazards 16 (1997), S. 135-163 
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    ISSN: 1573-0840
    Keywords: climate change ; extreme events ; insurance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract At the same time that a scientific consensus has arisen that the world will most likely experience a changing climate in the near future, with more frequent extreme events of some weather hazards, the insurance industry, worldwide, has been hit with rapidly escalating costs from weather-related disasters. This conjunction of scientific belief and economic impact has raised the questions as to (1) whether more frequent extreme events have contributed to the rising insurance costs and (2) how will future climate change affect the industry? Based upon historical data, it is difficult to support the hypothesis that the recent run of disasters both world-wide and in Canada are caused by climate change; more likely other factors such as increased wealth, urbanization, and population migration to vulnerable areas are of significance. It seems likely, though, that in the future some extreme events such as convective storms (causing heavy downpours, hail and tornadoes), drought and heat waves will result in increased costs to the industry, should the climate change as anticipated.
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    Photochemical Effects in the Heterogeneous Reaction of Soot with Ozone at Low Concentrations (1997)
    Springer
    Journal of atmospheric chemistry 26 (1997), S. 77-91 
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    ISSN: 1573-0662
    Keywords: ozone ; soot ; solar radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The soot-ozone reaction at low concentrations (ppm O3) hasbeen examined todetermine any influence of solar radiation on its products and kinetics. Theeffect of simulatedsolar radiation is to change the product distribution towardsCO2(g), CO (g) and H2O(g) at theexpense of soot surface functional groups formation. Little effect on theextent or rate ofdiminution of O3 through this rapid reaction is observed. Theinitial rate laws for formation ofall products remain the same under simulated solar radiation, with changes inthe rate constants(and thus in the relative importance of mechanistic pathways) responsible forthe differingproduct distributions. Decarboxylation of soot surface functionalities hasbeen shown to be onepossible mechanism underlying these effects. Atmospheric soot, particularlythat emitted nearthe tropopause by increasing numbers of subsonic and supersonic aircraft, mayplay a role inozone depletion; the rapid diminution of ozone in soot's presence isunaffected by solarradiation.
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    Formation of Organic Aerosols from the Oxidation of Biogenic Hydrocarbons (1997)
    Springer
    Journal of atmospheric chemistry 26 (1997), S. 189-222 
    Details
    ISSN: 1573-0662
    Keywords: biogenic hydrocarbons ; ozone ; nitrate radicals ; aerosol formation ; gas/particle partitioning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of aerosol formation during thephotooxidation of α-pinene, β-pinene,d-3-carene, d-limonene, ocimene, linalool, terpinene-4-ol, andtrans-caryophyllene were conducted in anoutdoor smog chamber. Daylight experiments in thepresence of $${\text{NO}}_x $$ and dark experiments withelevated ozone concentrations were performed. Theevolution of the aerosol was simulated by theapplication of a gas/particle absorption model inconnection with a chemical reaction mechanism. Thefractional aerosol yield is shown to be a function ofthe organic aerosol mass concentration andtemperature. Ozone and, for selected hydrocarbons, theNO3 reaction of the compounds were found torepresent efficient routes to the formation ofcondensable products. For initial hydrocarbon mixingratios of about 100 ppb, the fractional aerosol yieldsfrom daylight runs have been estimated to be ∼5%for open-chain hydrocarbons, such as ocimene andlinalool, 5–25% for monounsaturated cyclicmonoterpenes, such as α-pinene, d-3-carene, orterpinene-4-ol, and ∼40% for a cyclic monoterpenewith two double bonds like d-limonene. For the onlysesquiterpene investigated, trans-caryophyllene, afractional aerosol yield of close to 100% wasobserved. The majority of the compounds studied showedan even higher aerosol yield during dark experimentsin the presence of ozone.
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    Variability of Near-Ground Ozone Concentrations During Cold Front Passages – a Possible Effect of Tropopause Folding Events (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 77-95 
    Details
    ISSN: 1573-0662
    Keywords: ozone ; tropopause folding ; stratospheric ozone intrusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The analysis of surface ozone variability requires besides chemicalstudies the consideration of meteorological conditions and dynamicprocesses. Our research focuses on the mechanisms in connection with coldfront passages. A statistical study and case studies of cold front passageswere carried out at six German ground-based sites during the year 1990.After the passage of cold fronts three typical developments of thenear-ground ozone concentrations could be identified. Usually the ozoneconcentrations decrease due to advection of clean air masses or due toenhanced cloudiness preventing the photochemical production of ozone,chemical destruction by nitrogenoxides, and heterogeneous chemistry. In somecases the concentrations increased by reason of downward mixing of ozoneenriched air intruded from the stratosphere into the troposphere bytropopause foldings. For a few cases no modification set in. The decreasewas mostly twice as strong as the increase. The latter was between 4 and 8ppb on the average. Special emphasis is given to the transport ofstratospheric ozone down to the ground. There is no direct evidence forstratospheric ozone at ground level, because it can‘t be distinguished fromthe tropospheric one, but from case studies circumstantial evidence is foundin favour of it. As an example of increasing ozone behind the passage ofcold fronts one case study typical of all other case studies is presented.It shows the characteristic properties of the corresponding fronts, whichare fast movement, a vertical split structure and strong convection.
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    Atmospheric Effects of the Emerging Mainland Chinese Transportation System at and Beyond the Regional Scale (1997)
    Springer
    Journal of atmospheric chemistry 27 (1997), S. 31-70 
    Details
    ISSN: 1573-0662
    Keywords: Chine vehicles ; ozone ; aerosols ; carbon dioxide ; alternative fuels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Local surface travel needs in the People‘s Republic of China (mainlandChina) have traditionally been met largely by nonpolluting bicycles. A majorautomobile manufacturing/importing effort has begun in the country over thelast decade, and planning documents indicate that the Chinese may strive toacquire more than 100 million vehicles early in the next century. By analogywith large automotive fleets already existing in the western world, bothregional and global scale pollution effects are to be expected from theincrease. The present work adopts the latest projections of Chinese automobilemanufacture and performs some quantitative assessments of the extent ofpollution generation.Focus for the investigation is placed upon the oxidant ozone. Emissions of theprecursor species nitrogen oxides and volatile organics are constructed basedon data for the current automotive sector in the eastern portion of the UnitedStates. Ozone production is first estimated from measured values forcontinental/oceanic scale yields relative to precursor oxidation. Theestimates are then corroborated through idealized two dimensional modeling ofthe photochemistry taking place in springtime air flow off the Asian land massand toward the Pacific Ocean. The projected fleet sizes could increase coastaland remote oceanic ozone concentrations by tens of parts per billion (ppb)in the lower troposphere. Influences on the tropospheric aerosol system andon the major greenhouse gas carbon dioxide are treated peripherally. Nitrogenoxides created during the vehicular internal combustion process willcontribute to nitrate pollution levels measured in the open Pacific. Thepotential for soot and fugitive dust increases should be considered as theautomotive infrastructure develops. Since the emerging Chinese automotivetransportation system will represent a substantial addition to the globalfleet and all the carbon in gasoline is eventually oxidized completely, asignificant rise in global carbon dioxide inputs will ensue as well.Some policy issues are treated preliminary. The assumption is made thatalterations to regional oxidant/aerosol systems and to terrestrial climate areconceivable. The likelihood that the Chinese can achieve the latest vehiclefleet goals is discussed, from the points of view of new production, positivepollution feedbacks from a growing automobile industry, and known petroleumreserves. Vehicular fuel and maintenance options lying before the Chinese areoutlines and compared. To provide some perspective on the magnitude of theenvironmental changes associated with an Asian automotive buildup, recentestimates of the effects of future air traffic over the Pacific Rim aredescribed.
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    URL: http://dx.doi.org/10.1023/A:1005726818613
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    High-Latitude Springtime Photochemistry. Part I: NOx, PAN and Ozone Relationships (1997)
    Springer
    Journal of atmospheric chemistry 27 (1997), S. 127-153 
    Details
    ISSN: 1573-0662
    Keywords: PAN ; ozone ; troposphere ; photochemistry ; Alaska
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Springtime measurements of NOx, ozone, PAN,J(NO2), and other compounds were made near Ny-Ålesund,Svalbard (78°54′N, 11°53′E), in 1994 and Poker Flat,Alaska (65°08′N, 147°29′W), in 1995. At Svalbard medianmixing ratios for PAN and NOx of 237 and 23.7 pptv,respectively, were observed. The median mixing ratios at Poker Flat for PANand NOx were 79.5 and 85.9 pptv, respectively. These data areused to estimate thermal PAN decomposition using several differentapproaches. At Svalbard PAN decomposition was very small, while at PokerFlat up to 30 pptv/h PAN decomposed. At both sites the NOx/PANratio increased with temperature between –10 and 20°C implyingthat PAN decomposition is an important NOx source. In-situozone production was calculated from the measured NO, NO2,O3, J(NO2), and temperature data, using thesteady state assumption Median ozone production was 605 pptv/h at PokerFlat, and one order of magnitude smaller at Svalbard during the daytime.Only at Poker Flat could a direct influence on the diurnal ozone cycle beobserved from in-situ production. These results imply that PAN decompositionis a major source of NOx in the high latitude troposphere, andthat this contributes to the observed spring maximum in surface ozone.
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    URL: http://dx.doi.org/10.1023/A:1005869900567
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    First-Order Chemistry in the Surface-Flux Layer (1997)
    Springer
    Journal of atmospheric chemistry 27 (1997), S. 249-269 
    Details
    ISSN: 1573-0662
    Keywords: atmospheric surface layer ; constant-flux layer ; ozone ; nitric oxide ; radon ; thoron ; thoron exhalation ; Damköhler ratio ; eddy diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We have discussed the behavior of a non-conserved scalar in the stationary, horizontally homogeneous, neutral surface-flux layer and, on the basis of conventional second-order closure, derived analytic expressions for flux and for mean concentration of a gas, subjected to a first-order removal process. The analytic flux solution showed a clear deviation from the constant flux, characterizing a conserved scalar in the surface-flux layer. It decreases with height and is reduced by an order of magnitude of the surface flux at a height equal to about the typical mean distance a molecule can travel before destruction. The predicted mean concentration profile, however, shows only a small deviation from the logarithmic behavior of a conserved scalar. The solution is consistent with assuming a flux-gradient relationship with a turbulent diffusivity corrected by the Damköhler ratio, the ratio of a characteristic turbulent time scale and the scalar mean lifetime. We show that if we use only first-order closure and neglect the effect of the Damköhler ratio on the turbulent diffusivity we obtain another analytic solution for the profiles of the flux and the mean concentration which, from an experimental point of view, is indistinguishable from the first analytic solution. We have discussed two cases where the model should apply, namely NO which, by night, is irreversibly destroyed by interaction with mainly O3 and the radioactive 220Rn. Only in the last case was it possible to find data to shed light on the validity of our predictions. The agreement seemed such that a falsification of our model was impossible. It is shown how the model can be used to predict the surface flux of 220Rn from measured concentration profiles.
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    URL: http://dx.doi.org/10.1023/A:1005800416423
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    Transformation of Irradiance Measurements into Spectral Actinic Flux for Photolysis Rates Determination (1997)
    Springer
    Journal of atmospheric chemistry 26 (1997), S. 1-28 
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    ISSN: 1573-0662
    Keywords: actinic flux ; irradiance ; photodissociation rate ; spectroradiometer ; ozone ; nitrogen oxides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The actinic flux is the only radiometric quantity suitable for photolysisfrequency determination. It is derived from solar spectral irradiancemeasurements performed by a portable spectroradiometer in the 300–850nm wavelength range. The spectral irradiance is first divided into a directpart and a diffuse part, according to the atmospheric conditions, and thenconverted into the corresponding actinic flux quantity. As an intermediary,the ratio $$r_{dd} $$ of diffuse actinic flux to diffuseirradiance is calculated by the spherical harmonics radiative code withrespect to wavelength, solar zenith angle, surface albedo, and aerosolproperties.The results of extensive sensitivity studies of $$r_{dd} $$ asa function of the main atmospheric parameters are discussed and lead to theconclusion that aerosol optical depth is the major critical value for aprecise $$r_{dd} $$ determination. The global algorithm totransform spectral irradiance into actinic flux is finally applied forphotodissociation rate calculations by convolution of the obtained actinicflux spectra with the absorption cross-sections and quantum yields of themolecule studied. Photolysis rates of different atmospheric photooxidants havebeen measured with this spectroradiometric method during the summers of 1993and 1994 in Brittany and in Portugal. The ozone and nitrogen dioxidephotodissociation rates obtained present a good agreement with thej(O3) and j(NO2) actinometerresults, for the same experimental conditions in Brittany.
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    High-Latitude Springtime Photochemistry. Part Ii: Sensitivity Studies of Ozone Production (1997)
    Springer
    Journal of atmospheric chemistry 27 (1997), S. 155-178 
    Details
    ISSN: 1573-0662
    Keywords: PAN ; ozone ; troposphere ; photochemistry ; Alaska
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A seven-year record of surface ozone measurements from Denali NationalPark, Alaska shows a persistent spring maximum. These data, combined withmeasurements of NOx, hydrocarbons, O3, and PANfrom a continental site in Alaska during the spring of 1995 are used as thebasis for a sensitivity study to explore tropospheric photochemistry in thisregion. Because of the relatively high concentrations of NOx(mean of 116, median of 91 pptv), the net tendency was for photochemicalozone production. The range of net O3 production for averageconditions measured at this site during spring is between 0.96–3.9ppbv/day depending on the assumptions used; in any case, this productionmust contribute to the observed springtime maximum in O3.Model calculations showed that of the anthropogenic ozone precursors, onlyNOx had a strong effect on the rate of ozone production; themeasured concentrations of anthropogenic hydrocarbons did not significantlyaffect the ozone budget. Naturally produced biogenic hydrocarbons, such asisoprene, may also have a significant effect on ozone production, even atconcentrations of a few 10's of pptv. An observed temperature-isoprenerelationship from a boreal site in Canada indicates that isoprene may bepresent during the Alaskan spring. Measurements of isoprene taken duringthe spring of 1996 suggest that reactive biogenic hydrocarbon emissionsbegin before the emergence of leaves on deciduous trees and that theconcentrations were sufficient to accelerate ozone production.
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    The Gas Phase Reaction of Unsaturated Oxygenates with Ozone: Carbonyl Products and Comparison with the Alkene-Ozone Reaction (1997)
    Springer
    Journal of atmospheric chemistry 27 (1997), S. 271-289 
    Details
    ISSN: 1573-0662
    Keywords: unsaturated esters ; unsaturated carbonyls ; alkenes ; ozone ; biogenic compounds ; carbonyl products ; reaction mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Carbonyl products have been identified and their formation yields measured in the gas phase reaction of ozone with unsaturated oxygenates in experiments carried out at ambient T, p = 1 atm. of purified humid air (RH = 50%) and with sufficient cyclohexane added to scavenge the hydroxyl radical. The compounds studied are the esters methyl acrylate, vinyl acetate and cis-3-hexenyl acetate, the carbonyl crotonaldehyde, the hydroxy-substituted diene linalool, the ether ethylvinyl ether and the keto-ether trans-4-methoxy-3-buten-2-one. The alkene 1-pentene was included for comparison. The nature and formation yields of the carbonyl products from this study and those measured in earlier work under the same conditions are compared to those of alkenes and are supportive of a reaction mechanism that is similar to that for the reaction of ozone with alkenes, i.e. O3 + R1R2C=CR3X → α(R1COR2 + R3XCOO) + (1 − α)(R3COX + R1R2COO), where Ri are the alkyl substituents, X is the oxygen-containing substituent (–CHO for aldehydes; –C(O)R for ketones; –C(O)OR and –OC(O)R for esters; –OH and hydroxyalkyl for alcohols; and –OR for ethers), R1COR2 is the primary carbonyl, R3COX is the other primary product and R1R2COO and R3XCOO are the carbonyl oxide biradicals. The biradicals lead to carbonyls in reactions that are also analogous to those involved in carbonyl formation from biradicals in the ozone-alkene reaction. These features make it possible to predict the nature and formation yields of the major carbonyl products of the reaction of ozone with unsaturated oxygenates that may be components of biogenic emissions.
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    URL: http://dx.doi.org/10.1023/A:1005868119515
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    Convective Redistribution of Ozone and Oxides of Nitrogen in the Troposphere over Europe in Summer and Fall (1997)
    Springer
    Journal of atmospheric chemistry 28 (1997), S. 319-337 
    Details
    ISSN: 1573-0662
    Keywords: convection ; free troposphere ; ozone ; oxides of nitrogen ; three-dimensional model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The fluxes of ozone and NOx out of the atmospheric boundary layer (ABL) over Europe are calculated in a mesoscale chemical transport model (MCT) and compared with the net chemical production or destruction of ozone and the emissions of precursors within the ABL for two 10 days' periods which had quite different synoptic situations and levels of photochemical activity (1–10 July 1991 (JUL91) and 26 October–4 November 1994 (ON94)). Over the European continent, about 8% of the NOx emissions were brought from the ABL to the free troposphere as NOx, while about 15% of the NOx emissions were brought to the free troposphere as NOy–NOx, i.e. as PAN or HNO3. The convection dominates over the synoptic scale vertical advection as a transport mechanism both for NOx and NOy out of the boundary layer in the summertime high pressure situation (JUL91), while in the fall situation (ON94) the convective part was calculated to be the smallest. NOx was almost completely transformed to NOy–NOx or removed within the ABL. Also for NOy the major part of the atmospheric cycle is confined to the ABL both for JUL91 and ON94. The vertical transport time out of the ABL is of the order of 100h both for the total model domain and over the European continent. The net convective exchange of ozone from the ABL is not a dominant process for the amount of ozone in the ABL averaged over 10 days and the whole domain, but convection reduces the maximum ozone concentration in episodes significantly. The ozone producing efficiency of NOx is calculated to increase with height to typically 15–20 in the upper half of the troposphere from around 5 in the ABL, but in the middle free troposphere the concentration of NOx is often too low to cause net chemical formation of ozone there.
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    Carbon storage in forest soil of Finland. 1. Effect of thermoclimate (1997)
    Springer
    Biogeochemistry 36 (1997), S. 239-260 
    Details
    ISSN: 1573-515X
    Keywords: boreal forests ; carbon balance ; climate change ; climatic warming ; podzols ; soil carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A total of 30 coniferous forest sites representing two productivityclasses, forest types, were investigated on a temperature gradient(effective temperature sum using +5°C threshold 800–1300degree-days and annual mean temperature –0.6–+3.9°C) inFinland for studying the effect of thermoclimate on the soil C storage.Other soil forming factors were standardized within the forest types sothat the variation in the soil C density could be related to temperature.According to the applied regression model, the C density of the 0–1 mmineral soil layer increased 0.266 kg m–2 for every 100 degree-dayincrease in the temperature sum, and the layer contained 57% and28% more C under the warmest conditions of the gradient comparedto the coolest in the less and more productive forest type, respectively.Accordingly, this soil layer was estimated to contain 23 more C ina new equilibrium with a 4°C higher annual meantemperature in Finland. The C density of the organic layer was notassociated with temperature. Both soil layers contained more C at thesites of the more productive forest type, and the forest type explained36% and 70% of the variation in the C density of the organic and 0–1m layers, respectively. Within the forest types, the temperature sumaccounted for 33–41% of the variation in the 0–1 m layer. Theseresults suggest that site productivity is a cause for the large variation inthe soil C density within the boreal zone, and relating the soil C densityto site productivity and temperature would help to estimate the soil Creserves more accurately in the boreal zone.
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    Enhanced CH4 emission from a wetland soil exposed to Elevated CO2 (1997)
    Springer
    Biogeochemistry 37 (1997), S. 77-88 
    Details
    ISSN: 1573-515X
    Keywords: climate change ; elevated carbon dioxide ; hydrology ; methane ; transpiration ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane emissions from wetland soils are generally a positive function ofplant size and primary productivity, and may be expected to increase dueto enhanced rates of plant growth in a future atmosphere of elevatedCO2. We performed two experiments with Orontium aquaticum, acommon emergent aquatic macrophyte in temperate and sub-tropical wetlands, todetermine if enhanced rates of photosynthesis in elevated CO2atmospheres would increase CH4 emissions from wetland soils.O. aquaticum was grown from seed in soil cores under ambient and elevated(ca. 2-times ambient) concentrations of CO2 in an initialglasshouse study lasting 3 months and then a growth chamber study lasting 6months. Photosynthetic rates were 54 to 71% higher underelevated CO2 than ambient CO2, but plantbiomass was not significantly different at the end of the experiment. Ineach case, CH4 emissions were higher under elevated thanambient CO2 levels after 2 to 4 months of treatment, suggestinga close coupling between photosynthesis and methanogenesis in our plant-soilsystem. Methane emissions in the growth chamber study increased by 136%. We observed a significant decrease in transpirationrates under elevated CO2 in the growth chamber study, andspeculate that elevated CO2 may also stimulate CH4 emissions by increasing the extent and duration offlooding in some wetland ecosystems. Elevated CO2 maydramatically increase CH4 emissions from wetlands, a sourcethat currently accounts for 40% of global emissions.
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    Carbon storage in forest soil of Finland. 2. Size and regional pattern (1997)
    Springer
    Biogeochemistry 36 (1997), S. 261-274 
    Details
    ISSN: 1573-515X
    Keywords: boreal forests ; carbon balance ; geostatistics ; GIS ; soil carbon ; spatial variability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract For confidently estimating the amount of carbon stored in boreal forestsoil, better knowledge of smaller regions is needed. In order to estimatethe amount of soil C in forests on mineral soil in Finland, i.e. excludingpeatland forests, and illustrate the regional patterns of the storage,statistical models were first made for the C densities of the organic and0–1 m mineral soil layers. A forest type, which indicated siteproductivity, and the effective temperature sum were used asexplanatory variables of the models. In addition, a constant C densitywas applied for the soil layer below the depth of 1 m on sortedsediments. Using these models the C densities were calculated for atotal of 46673 sites of the National Forest Inventory (NFI). The amountof the soil C was then calculated in two ways: 1) weighting the Cdensities of the NFI sites by the land area represented by these sites and2) interpolating the C densities of the NFI sites for 4 ha blocks to coverthe whole land area of Finland and summing up the blocks on forestedmineral soil. The soil C storage totalled 1109 Tg and 1315 Tg, whencalculated by the areal weighting and the interpolated blocks,respectively. Of that storage, 28% was in the organic layer, 68% inthe 0–1 m mineral soil layer and 4% in the layer below 1 m. The totalsoil C equals more than two times the amount of C in tree biomass and20% of the amount of C in peat in Finland. Soil C maps made usingthe interpolated blocks indicated that the largest soil C reserves arelocated in central parts of southern Finland. The C storage of theorganic layer was assessed to be overestimated at largest by 13% andthat of the 0–1 m mineral soil layer by 29%. The largest error in theorganic layer estimate is associated with the effects of forest harvestingand in the mineral soil estimate with the stone content of the soil.
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    Climate Change in the Urals, Russia, Inferred from Borehole Temperature Data (1997)
    Springer
    Studia geophysica et geodaetica 41 (1997), S. 225-246 
    Details
    ISSN: 1573-1626
    Keywords: climate change ; borehole temperature ; ground and air temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Borehole temperatures in the central and south Urals were analysed for the past ground surface temperature (GST) signal. 31 highquality temperature logs were selected for this purpose and inverted with algorithms based on the generalised least squares theory. The signal to noise ratio was improved by averaging the results of individual borehole inversions. No distinct regional trends were found in the studied region except for some indications of more pronounced warming in the south. The mean GST history (GSTH) was characterised by cooling down to −0.6 °C in the 18th century and subsequent warming to 0.5 °C above the longterm mean at the beginning of this century, and to 1 – 1.5 °C by 1980. The stability of the mean GSTH was tested in dependence on the number of holes used for the averaging. It showed that any subset of 15 holes yielded a GSTH similar to that obtained from the whole set. A surface air temperature (SAT) time series comprising the period 1832 – 1989 was combined from 17 meteorological records. Its least squares warming rate of 1.1 °C per 100 years is somewhat higher than that of the GST (0.7 – 0.8°C/100 years) in the same period.
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    Analytical expressions of conditional mean, covariance, and sample functions in geostatistics (1996)
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 279-294 
    Details
    ISSN: 1436-3259
    Keywords: Linear estimation ; interpolation ; kriging ; splines ; conditional
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This work presents analytical expressions for the best estimate, conditional covariance function, and conditional realizations of a function from sparse observations. In contrast to the prevalent approach in kriging where the best estimates at every point are determined from the solution of a system of linear equations, the best-estimate function can be represented analytically in terms of basis functions, whose number depends on the observations. This approach is computationally superior when graphing a function estimate and is also valuable in understanding what the solution should look like. For example, one can immediately see that all “singularities” in the best-estimate function are at observation points.
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    URL: http://dx.doi.org/10.1007/BF01581870
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    Inference of ground surface temperature history from subsurface temperature data: Interpreting ensembles of borehole logs (1996)
    Springer
    Pure and applied geophysics 147 (1996), S. 537-550 
    Details
    ISSN: 1420-9136
    Keywords: Borehole temperature ; climate change ; inversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Ground surface temperature histories (GSTHs) inferred from borehole temperaturedepth (T-z) data are often degraded, to a various extent, by random or systematic noise in theT-z data and in the measurements of thermophysical properties of the earth. To minimize the effects of noise, and hence improve the fidelity of the inferred GSTH, a plausible approach is to perform a simultaneous inversion, of theT-z logs in a region, or alternatively, to invert the individualT-z logs and then average the resulting GSTHs. Averaging and simultaneous inversion are conceptually different: whereas an averaging can always be peformed, a simultaneous inversion is predicated on the assumption of a common transient component of the GSTH in all theT-z logs. In this work we examine and compare the two approaches, using a time domain inverse formulation based on the method of least squares. We consider a set of scenarios: (a) multipleT-z logs from a single borehole, (b) multiple boreholes from a single site, (c) multiple boreholes in similar climatological settings, and (d) multiple boreholes in different climatological settings. We show that for (a), (b) and (c), averaging and simultaneous inversion yield nearly identical results. For boreholes in different settings, the assumption of a common transient GSTH may be invalid and averaging and simultaneous inversion give divergent results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878843
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  • 98
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    Late Holocene climate change and human disturbance on Andros Island, Bahamas (1996)
    Springer
    Journal of paleolimnology 15 (1996), S. 133-145 
    Details
    ISSN: 1573-0417
    Keywords: Bahamas ; Holocene ; fire history ; climate change ; human disturbance ; charcoal stratigraphy ; pollen analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A 2 m sediment core from Church's Blue Hole on Andros Island, Bahamas provides the first paleoecological record from the Bahama Archipelago. The timing of events in the lower portion of the core is uncertain due to inconsistencies in the radiocarbon chronology, but there is evidence that a late Holocene dry period altered the limnology of Church's Blue Hole and supported only dry shrubland around the site. The dry period on Andros may correlate with a widespread dry period in the Caribbean from 3200 to 1500 yr BP. After the dry period ended, a more mesic climate supported tropical hardwood thicket around Church's Blue Hole. At c. 740 radiocarbon yr BP there is a sudden rise in charcoal concentration and a rapid transition to pinewoods vegetation, while at c. 430 radiocarbon yr BP charcoal concentration drops, but is higher again near the top of the core. Although climatic shifts could have caused these changes in vegetation and charcoal concentration, the changes post-date human colonization of the Bahamas and may reflect human arrival, followed by the removal of humans c. 1530 AD and the recolonization of Andros Island c. 200 years later.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196777
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  • 99
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    Electronic Resource
    Invariant kinetic approach to the description of a rock fracture process and induced seismic events (1996)
    Springer
    Pure and applied geophysics 147 (1996), S. 367-375 
    Details
    ISSN: 1420-9136
    Keywords: Induced seismicity ; kinetics ; rock fracture ; rockburst ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Powerful seismic events, such as earthquakes and rockbursts, are caused by the accumulation of energy in rocks and loss of rock mass stability. Usually methods of their forecasting are based on the registration of anomalous behavior of geophysical fields. However an efficiency of this approach is low. The present paper proposes a kinetic approach to the description of rock fracture process, which can be used for the forecasting of seismic events and an investigation of structure and energy distributions in rock. 3-D and 1-D kinetic equations describing a process of cluster formation in rock were obtained. The equations are invariant to deformation conditions and to the scale level of events. They showed a good agreement with the results of field observations and laboratory experiments. It was also shown that these equations well describe the processes of earthquake, rockburst and rock sample failure preparation. Catalogues of rockbursts in mines were analyzed with the use of the kinetic equations to find out evidence of induced seismic events. The proposed approach makes it possible to reveal trends in rock behavior and thus predict the rock failure at different scale levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00877489
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  • 100
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    Electronic Resource
    Challenges in reservoir forecasting (1996)
    Springer
    Mathematical geology 28 (1996), S. 829-842 
    Details
    ISSN: 1573-8868
    Keywords: geostatistics ; flow simulation ; streamtubes ; scale up ; gridding ; accuracy and precision ; modeling uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The combination of geostatistics-based numerical geological models and finite difference flow simulation has improved our ability to predict reservoir performance. The main contribution of geostatistical modeling has been more realistic representations of reservoir heterogeneity. Our understanding of the physics of fluid flow in porous media is reasonably captured by flow simulators in common usage. Notwithstanding the increasing application and success of geostatistics and flow simulation there remain many important challenges in reservoir forecasting. This application has alerted geoscientists and physicists that geostatistical/flow models in many respects, are, engineering approximations to thereal spatial distribution andreal flow processes. This paper reviews current research directions and presents some new ideas of where reserach could be focused to improve our ability to model geological features, model flow processes, and, ultimately, improve reservoir performance predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02066003
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