Effect of the effective stress coefficient and sorption-induced strain on the evolution of coal permeability: Experimental observations

Permeability is one of the most important parameters for CO₂ injection in coal to enhance coalbed methane recovery. Laboratory characterization of coal permeability provides useful information for in situ permeability behavior of coal seams when adsorbing gases such as CO₂ are injected. In this study, a series of experiments have been conducted for coal samples using both non-adsorbing and adsorbing gases at various confining stresses and pore pressures. Our observations have showed that even under controlled stress conditions, coal permeability decreases with respect to pore pressure during the injection of adsorbing gases. In order to find out the causes of permeability decrease for adsorbing gases, a non-adsorbing gas (helium) is used to determine the effective stress coefficient. In these experiments using helium, the impact of gas sorption can be neglected and any permeability reduction is considered as due to the variation in the effective stress, which is controlled by the effective stress coefficient. The results show that the effective stress coefficient is pore pressure dependent and less than unity for the coal samples studied. The permeability reduction from helium experiments is then used to calibrate the subsequent flow-through experiments using adsorbing gases, CH₄ and CO₂. Through this calibration, the sole effect of sorption-induced strain on permeability change is obtained for these adsorbing gas flow-through experiments. In this paper, experimental results and analyses are reported including how the impact of effective stress coefficient is separated from that of the sorption-induced strain on the evolution of coal permeability.     

The European eel quality database: towards a pan-European monitoring of eel quality

The stocks of the European eel Anguilla anguilla are in decline and there is an increasing awareness that poor health status due to contaminants and/or diseases might be a key element in this decline and might be a hindrance to recovery. Many countries have started compiling data on the health status of eels in their water bodies. Objectives for these monitoring actions are diverse and there is a large amount of information collected by EU member countries. However, this information is widely scattered over Europe in agencies, institutes or universities. As there is a growing need to collect and report on data on the health status of the eel on international level, the Joint EIFAC/ICES Working Group on Eels initiated in September 2007 the set up of an European Eel Quality Database to collect recent data of contaminants and diseases over the distribution area of the eel. This paper describes the aim, the set up and future development of the database in order to give it greater publicity and to call on scientists or managers to submit data on eel health status. The database represents now the first comprehensive pan-European compilation of eel health data, including data from over 10,000 eels from approximately 1,200 sites over 14 countries. Preliminary work has indicated a number of shortcomings and future developments will be needed. Guaranteeing further development of the database, harmonisation of methods, quality assurance, and setting up harmonised eel monitoring strategies over Europe will be a great challenge and will need pan-European cooperative work.     

Direct radiative forcing of urban aerosols over Pretoria (25.75°S, 28.28°E) using AERONET Sunphotometer data: First scientific results and environmental impact

The present study uses the data collected from Cimel Sunphotometer of Aerosol Robotic Network（AERONET） for the period from January to December, 2012 over an urban site,Pretoria（PTR; 25.75°S, 28.28°E, 1449 m above sea level）, South Africa. We found that monthly mean aerosol optical depth（AOD, τa） exhibits two maxima that occurred in summer（February） and winter（August） having values of 0.36 ± 0.19 and 0.25 ± 0.14,respectively, high-to-moderate values in spring and thereafter, decreases from autumn with a minima in early winter（June） 0.12 ± 0.07. The Angstrom exponents（α440–870） likewise,have its peak in summer（January） 1.70 ± 0.21 and lowest in early winter（June） 1.38 ± 0.26,while the columnar water vapor（CWV） followed AOD pattern with high values（summer） at the beginning of the year（February, 2.10 ± 0.37 cm） and low values（winter） in the middle of the year（July, 0.66 ± 0.21 cm）. The volume size distribution（VSD） in the fine-mode is higher in the summer and spring seasons, whereas in the coarse mode the VSD is higher in the winter and lower in the summer due to the hygroscopic growth of aerosol particles.The single scattering albedo（SSA） ranged from 0.85 to 0.96 at 440 nm over PTR for the entire study period. The averaged aerosol radiative forcing（ARF） computed using SBDART model at the top of the atmosphere（TOA） was- 8.78 ± 3.1 W/m2, while at the surface it was- 25.69 ± 8.1 W/m2 leading to an atmospheric forcing of ＋ 16.91 ± 6.8 W/m2, indicating significant heating of the atmosphere with a mean of 0.47 K/day.     

A Method for Spatially Explicit Representation of Sub-watershed Sediment Yield,Southern California,USA

We present here a method to integrate geologic, topographic, and land-cover data in a geographic information system to provide a fine-scale, spatially explicit prediction of sediment yield to support management applications. The method is fundamentally qualitative but can be quantified using preexisting sediment-yield data, where available, to verify predictions using other independent data sets. In the 674-km² Sespe Creek watershed of southern California, 30 unique “geomorphic landscape units” (GLUs, defined by relatively homogenous areas of geology, hillslope gradient, and land cover) provide a framework for discriminating relative rates of sediment yield across this landscape. Field observations define three broad groupings of GLUs that are well-associated with types, relative magnitudes, and rates of erosion processes. These relative rates were then quantified using sediment-removal data from nearby debris basins, which allow relatively low-precision but robust calculations of both local and whole-watershed sediment yields, based on the key assumption that minimal sediment storage throughout most of the watershed supports near-equivalency of long-term rates of hillslope sediment production and watershed sediment yield. The accuracy of these calculations can be independently assessed using geologically inferred uplift rates and integrated suspended sediment measurements from mainstem Sespe Creek, which indicate watershed-averaged erosion rates between about 0.6–1.0 mm year^?1 and corresponding sediment yields of about 2 × 10³ t km^?2 year^?1. A spatially explicit representation of sediment production is particularly useful in a region where wildfires, rapid urban development, and the downstream delivery of upstream sediment loads are critical drivers of both geomorphic processes and land-use management.     

Estimation of terrestrial chemical spill risk factors using a modified Delphi approach

The large number of chemical spills each year in the United States presents a potentially significant risk to human health and the environment. In an effort to manage this risk, the authors are developing a screening tool to assess the immediate threat to human and environmental receptors from land-based chemical spills. As part of this development effort, a modified Delphi survey was employed to determine the most important factors governing this risk and the relative importance of these factors. Results of the survey indicate that accounting for the attributes of the spilled chemical as well as the characteristics of the surrounding environment is imperative in making informed decisions regarding spill planning and mitigation. Survey results further indicate the greatest concern during spill events to be the risk to human health, which must be considered directly as well as factored into decisions concerning the protection of environmental receptors.     

Water-based condensation particle counters for environmental monitoring of ultrafine particles

TSI Inc. (Shoreview, MN) has introduced three new water-based condensation particle counters (WCPCS) that were designed to detect airborne particles larger than 2.5 nm (model 3786), 5 nm (model 3785), and either 10 or 20 nm (model 3782). These WCPCs are well suited for real-time, environmental monitoring of number concentration of airborne ultrafine particles. Their unique design incorporates the use of water as the working fluid instead of alcohol. Water is odor free, readily available, and eliminates the problem of water condensation and absorption into alcohol working fluids during operation in humid environments. In this study, the performance of three TSI WCPCs was characterized for several aerosol compositions, including sucrose, salt (NaCl), dioctyl sebacate (DOS), dioctyl phthalate (DOP), emery oil (poly-alpha-olefin), silver, impurity residue particles, and ambient aerosol particles. All particles were size selected using a nano differential mobility analyzer (nano-DMA; model 3085, TSI Inc.) to create monodisperse challenge aerosols. The challenge aerosol was mixed uniformly with clean makeup flow and split into a WCPC and a reference instrument to determine the counting efficiency of the WCPC. For the model 3785 WCPC, the D50 (i.e., the particle diameter with 50% counting efficiency) was determined to be 3.1 nm for salt particles, 4.7 nm for sucrose and ambient particles, 5.6 nm for silver particles, and >50 nm for ultrapure oil particles. The sensitivity to oil droplets increased dramatically (D50 < 10 nm) when the oil was slightly contaminated. The D50 of model 3786 ultrafine water-based CPC (UWCPC) was 2.4 nm for impurity residue particles. The D50 of the model 3782 WCPC was 10.8 (with a nominal setting of 10 nm) or 19.8 nm (with a nominal setting of 20 nm) for sucrose particles. All three WCPCs have response times of less than 2 or 3 sec and are therefore able to detect fast-changing events.