Eulerian derivation of the fractional advection-dispersion equation

A fractional advection-dispersion equation (ADE) is a generalization of the classical ADE in which the second-order derivative is replaced with a fractional-order derivative. In contrast to the classical ADE, the fractional ADE has solutions that resemble the highly skewed and heavy-tailed breakthrough curves observed in field and laboratory studies. These solutions, known as alpha-stable distributions, are the result of a generalized central limit theorem which describes the behavior of sums of finite or infinite-variance random variables. We use this limit theorem in a model which sums the length of particle jumps during their random walk through a heterogeneous porous medium. If the length of solute particle jumps is not constrained to a representative elementary volume (REV), dispersive flux is proportional to a fractional derivative. The nature of fractional derivatives is readily visualized and their parameters are based on physical properties that are measurable. When a fractional Fick's law replaces the classical Fick's law in an Eulerian evaluation of solute transport in a porous medium, the result is a fractional ADE. Fractional ADEs are ergodic equations since they occur when a generalized central limit theorem is employed.     

Formulation of a soil-pesticide transport model based on a compartmental approach

A semianalytical soil-pesticide transport model is formulated based on a compartmental approach to determine spatial and temporal variations of pesticide residues across a soil profile. The compartmental model is implemented by drawing an analogy between a series of continuous-flow stirred tank reactors and a soil horizon that consists of multiple perfectly mixed compartments. The analogy is strengthened by exploiting a relation between the compartment series and the conventional convective-dispersive equation (CDE) for vertical transport in the soil. Consequently, the number of compartments in the model formulation is not free, but dictated as a function of transport parameters. The model formulation allows consideration of arbitrary boundary value specifications and also, for some cases, spatially varying initial concentration profiles. Sorption kinetics is represented via a two-site model that involves a linear sorption isotherm and a first-order irreversible sorption or a radial diffusive penetrating model. For these three cases, analysis of the compartmental model allows the resultant concentration profiles to be expressed in terms of the Poisson distribution. When a nonlinear kinetic sorption model is used to simulate the sorption processes, an analytical solution is not found and a numerical approach is required.     

On the influence of the urban roughness sublayer on turbulence and dispersion

The concept of the urban roughness sublayer is discussed and this lowest atmospheric layer over a rough surface is shown to have a non-negligible vertical extension over typical urban surfaces. The existing knowledge on the turbulence and flow structure within an urban roughness sublayer is reviewed, focusing on the height dependence of turbulent fluxes and a scaling approach for turbulence statistics, such as velocity variances, in the above-roof part of the roughness sublayer. Finally, the implication of this turbulence and flow structure upon dispersion characteristics is investigated. The most prominent difference of explicitly taking into account the roughness sublayer in a dispersion simulation (as compared to assuming a `constant flux layer') is a clearly enhanced ground level concentration far downwind from the source. For the example of a tracer release experiment over a (sub) urban surface (Copenhagen) it is shown that introducing the roughness sublayer clearly improves the model performance.     

Noncatalytic Auto Exhaust Combustor

Present methods for the determination of carbon monoxide are discussed including indicator tubes, the iodine pentoxide reaction and measurement by gas chromatography. In the gas chromatographic method an air sample is separated on a gas-solid chromatogra-phic column and the separated CO is converted to methane by hydrogenation at elevated temperature. The separated CO, in the form of methane, is passed into a hydrogen flame detector and measured. The conversion from CO to methane allows the use of a sensitive ionization detector in place of the thermal conductivity cell which is insufficiently sensitive for the measurement of trace amounts of CO. The optimum operating conditions are discussed. It is possible to determine one ppm CO in air. The iodine pentoxide reaction with CO has been combined with electrometric measurement. The iodine liberated is passed into a Ditte cell and the current generated is measured by an electrometerrecorder combination. This method is continuously direct reading with a permanent record. It is suitable for the continuous routine analysis of one ppm CO.     

Economic insight into municipal solid waste management in Mumbai: a critical analysis

Mumbai generates 6256 tonnes of waste every day, of which 17.20% is recyclable, but only a fraction of this is retrieved by rag-pickers. The economic value of the retrieved material is not considered by the Municipal Corporation of Greater Mumbai in valuing the waste management system as there is no retrieval mechanism except the informal rag-picking activity. Moreover, the cost of land used for the dumping of waste is also not accounted for. In the present paper, a comprehensive cost-benefit analysis for the present system of municipal solid waste management in Mumbai is carried out, with due consideration for implicit or hidden costs and benefits. Accounting for the implicit costs and benefits showed a difference of $6 per every tonne of waste disposal. This could show a considerable difference in policy development at the municipality level. Demand supply analysis proved that the present system of waste management would not yield a feasible market solution without private sector participation. With the increasing demand for improved waste management, private sector participation is essential and a Pigouvian tax is a necessary tool to make the private sector participation in solid waste management a success.     

Colloid migration in symmetrical non-uniform fractures: particle tracking in three dimensions

A three-dimensional model for the migration of colloids in a saturated fracture is presented, which considers the motion of colloids as a result of advection and diffusion, as well as colloid-surface interactions at the fracture walls. This model is successfully incorporated into a three-dimensional particle tracking algorithm that tracks particles within a continuum and allows consideration of the migration of colloids in symmetrical, three-dimensional, non-uniform fractures. The framework is general enough to incorporate non-local interactions that provide colloid motion relative to the fluid. The algorithm is verified against classical Taylor dispersion, and its generalization to a sorbing phase, in a uniform fracture and shows excellent agreement with theory. A simple, non-uniform fracture that has an analytically tractable velocity field is also considered, and both quantitative and qualitative comparisons are made with the uniform fracture case. The modelling of more complex fracture geometries is also discussed and a particular case is implemented within the particle tracking framework.     

Therapeutic potential of dopamine agonists in the treatment of type 2 diabetes mellitus

Environmental Science and Pollution Research - Diabetes is a global health concern that has affected almost 415 million people globally. Bromocriptine is a dopamine D2 agonist, which is a Food and...     

Urban CO Concentrations and Vehicle Emissions

The effect of the general growth of CO vehicular emissions in urban areas on the CAMP station measurements in downtown areas, where vehicular traffic is saturated is considered. With the assumption that the street-level CO concentration is derived from the sum of an urban background term and a local street-effect term, the urban background CO concentration is computed with a diffusion model by introducing a simple area source distribution. The local street-effect term is taken to be constant at a saturation emission level corresponding to a saturation traffic density when the emission per vehicle-mile and meteorological conditions are fixed. The present analysis indicates that the local street-effect term, AC, has a major role in determining street-level concentrations for pollutants, such as CO, whose air quality standard is based on maximum concentrations with averaging times of 1 hour and 8 hours. The relevance of this analysis to the abatement requirements of the Clean Air Amendments and to the driving cycle adopted is discussed.     

Evaluation of a simplified top-down model for the spatial assessment of hot traffic emissions in mid-sized cities

Traffic emission estimation in developing countries is a key-issue for air pollution management. In most cases, comprehensive bottom-up methodologies cannot be applied in mid-sized cities because of the resource cost related to their application. In this paper, a simplified emission estimation model (SEEM) is evaluated. The model is based on a top-down approach and gives annual global hot emission. Particular attention is paid to the quality of the input traffic data. The quality of results is assessed by application of the SEEM model in the Chilean Gran Concepción urban area and by comparison with a bottom-up approach that has been led for the year 2000. The SEEM model estimates emissions with an accuracy of about $20\%$ and is related to important resource savings. The results of the SEEM model are then distributed in space with a disaggregation approach and using GIS techniques. The relevancy of the disaggregation approach is evaluated among several possibilities through statistical methods. A spatial disaggregation using principal roads density gives the best results in terms of emissions repartition and gives a globally accurate image of the distribution of hot emissions in a mid-sized city.     

Citizen participation for integrated assessment: new pathways in complex systems

Citizen or community participation is a guiding principle for environmental decision-making, but in practice it is often compromised and contradictory. Two themes in participation can be defined. One is in the 'product' or outcome of decision-making, and aims for more effective and appropriate evaluations and decisions. The other is participation in the 'process', where devolved decision-making itself can serve wider social and economic goals. Although both strands are crucial for the practice of 'integrated assessment' in environmental governance, a clearer view is needed of the scope and limits of such participation. This paper explores such scope and limits by applying a conceptual 'integrated assessment' framework. This is drawn from a major case study on sustainable development for a city-region in the north of the UK. Such a framework helps to identify the many roles of citizen participation from a complex systems perspective. Selected examples of current practice highlight the problems and opportunities for citizen participation in environmental governance.     

Photochemistry and environment IV- Photochemical behaviour of monochlorophenols in dilute aqueous solution

The photochemical behaviour of chlorophenols is different to that of non-halogenated phenols. In the former, the first step is a C-Cl bond scission, which is not influenced by oxygen. Chlorine is converted into hydrochloric acid. For monochlorophenols, the position of the chlorine on the ring strongly influences the transformation. In the molecular form, 2-chlorophenol is converted into pyrocatechol. In the anionic form however, it is reduced in a cyclopentadienic acid which dimerizes according to a Diels-Alder reaction. The irradiation of 3-chlorophenol leads to resorcinol whatever the pH. This would appear to suggest a photohydrolysis mechanism. With 4-chlorophenol, the photochemical conversion is not so specific. Hydroquinone is formed (mainly in aerated solution), along with polyphenolic oligomers. A radical mechanism is proposed.     

A fast and efficient modified sectional method for simulating multicomponent collisional kinetics

A fast and efficient method for simulating the evolution of internally mixed multicomponent particle size distributions for aerosol coagulation and droplet coalescence is developed. The technique is based upon a bin-wise sectionalization of the particle mass domain and by imposing the condition of mass conservation for each component. The distribution of each species as a function of the total particle mass is represented in each mass bin as a two-parameter exponential function. Particles of a given mass are assumed to be internally homogeneously mixed. The method is shown to be numerically stable for a wide range of time steps. The numerical solution is compared with both analytical results and results from other well-accepted numerical schemes. This comparison reveals that the proposed technique offers the advantage of being fast and accurate, even for coarse spectral resolution. The method is computationally attractive and easily allows the treatment of ten or more different chemical species in a collisionally evolving particle size distribution. The applicability of the method is demonstrated with several examples: Coalescence growth of multicomponent cloud droplet spectra, coagulation of measured multi-species aerosol particle size distributions, and the simulation of the accumulation mode due to a source of small aerosol particles. The technique is ideally suited for modelling the interaction of microphysics and chemistry in a size-bin resolving aerosol or cloud model.     

Dynamics of sulfur dioxide absorption in a raindrop falling at terminal velocity

Sulfur dioxide absorption dynamics in a raindrop are studied numerically by means of a fully numerical simulation method (FNSM) in which a composite orthogonal grid system consisting of both gas- and liquid-phase is adopted. When a raindrop with fixed radius falls in association with terminal velocity, a recirculation bubble always accompanies the gas-phase flow field in the aft region of the drop. With regard to the drop internal flow structure it has a drastic variation with drop size. When the drop radius is small (e.g. r_s=200 μm), only a single vortex motion is seen inside the drop. Under such a situation, sulfur dioxide absorbed from the interface is mainly transported from the area in front of the aft stagnation point. In contrast, as the drop is relatively large, say, r_s=500 μm, it is of interest to find that a double-vortex motion, composed of a primary and a secondary vortexes, is clearly observed. As a result, the onset of SO₂ transport process occurs at the drop’s surface near where the two vortexes meet. By defining a drop mass transport number, it indicates that the mass transported via internal circulation is always much faster than that by mass diffusion and the latter is highly relevant to the drop radius. Accordingly, the SO₂ transport dynamics in a raindrop is essentially determined by drop size.     

Atmospheric pollution transport: the parallelization of a transport & chemistry code

We discuss a model for computing the chemical reactions occurring among air pollutants and predict their dispersion in the atmosphere. We consider a parallel implementation on a CRAY T3D, using up to 128 processors. A regular subdomain decomposition is considered to optimize inter-processor communications, while load balancing – the main technical difficulty to obtain a good efficiency – is achieved by re-assigning temporarily pieces of work to other processors, according to a global strategy. The performance of our implementation is described by an analytical relation whose validity is checked on realistic data sets. A speedup of 100 is obtained with 128 processors.     

ESP Bus Section Failures: Design Considerations

This paper addresses a common operation and maintenance problem encountered with sectionalized electrostatic precipitators—bus section failure. ESPs are normally designed to meet a specific minimum collection efficiency in order to comply with emission standards; the loss of several bus sections may cause the unit to be out of compliance. In this paper, the effect of bus section failure on precipitator performance is analyzed. The study is presented in two parts. First, a simplified procedure to estimate the effect of bus section failure on the overall collection efficiency is developed. An illustrative example is presented to demonstrate the use of the technique. Secondly—and this is the main thrust of this study—the technique is extended to include calculations on whether a unit is out of compliance due to the failure of a given number of bus sections. This development clearly shows that this latter effect can only be expressed in terms of a probability. Two additional examples, based on a field unit using actual test data, complement the presentation and illustrate this probability calculation.     

The Annual Average: An Alternative to the Second Highest Value as a Measure of Air Quality

It is common practice to use the second highest value both in determining compliance with the once-per-year air quality standards (AQS) and as a measure of air quality in pollutant trend studies and rollback calculations. A study of the variation in the second highest 8 hr carbon monoxide concentration observed at the CAMP stations 1962-72 is presented. It is shown that, for a given annual average, the second highest value can differ by a factor of 2 due to random variation. The annual average is linearly related to the observed average of the second highest value and is shown to be a good predictor of the percent of time the carbon monoxide AQS is exceeded. It is concluded that the annual average, which is less variable and not as greatly influenced by erroneous measurements, is the preferred measure of air quality for trend studies and air quality projections.     

Potential protective effects of Spirulina platensis on liver,kidney, and brain acrylamide toxicity in rats

Environmental Science and Pollution Research - Acrylamide (AA) is a hazardous chemical that is widely used in industrial practices. Spirulina platensis (SP) is a blue green alga that is rich in...     

On spurious water flow during numerical simulation of steam injection into water-saturated soil

Numerical simulation of steam injection into a water-saturated porous medium may be hindered by unphysical behavior causing the model to slow down. We show how spurious water flow may arise on the boundary between a steam zone and a saturated zone, giving rise to dramatic pressure drops. This is caused by the discretization of the temperature gradient coupled with the direct relation between pressure and temperature in the steam zone. The problem may be a severe limitation to numerical modeling. A solution is presented where the spurious water flow is blocked and this widely enhances the performance of the model. This new method is applied to a previously reported example exhibiting numerical problems. Furthermore, it is applied to the simulation of 2-D sandbox experiments where LNAPL is remediated from a smearing zone by steam injection. These experiments would have been difficult to analyze numerically without the adjustment to prevent spurious flow.     

Determination of aromatic hydrocarbons in submicrogram quantities in aqueous systems by means of high performance liquid chromatography

One liter of the water sample is extracted with 1,1,2-trichlorotrifluoroethane. This non-polar solvent with a low boiling point is then concentrated and a portion of the concentrated extract is injected in a high performance liquid chromatography system. Polar material is separated from the hydrocarbons by means of a silica gel column. The detector measures the UV absorbance at 254 nm at which wavelength aromatic compounds absorb especially well. The quantitative values are given as phenanthrene equivalents and amounts as small as 20 ng/l can be detected. The standard deviation of the method is ± 50 ng/l. Both these values can be improved with a limited amount of difficulty. A concentrated sample extract can be injected and evaluated in less than 6 minutes, and the method is simple enough to have been used at sea.     

Simultaneous estimation of effective and apparent diffusion coefficients in compacted bentonite

Effective diffusion coefficients (D(e)) are usually measured by means of "through-diffusion" experiments in which steady state is reached, and the "time-lag" methods are used to estimate the apparent diffusion coefficient (D(a)). For sorbing radionuclides (as caesium), the time needed to reach steady-state conditions is very large, and the precision in D(a) determinations is not satisfactory. In this paper, a method that allows determining simultaneously effective and apparent diffusion coefficients in compacted bentonite without reaching steady-state conditions is described. Basically, this method consists of an "in-diffusion" experiment in which the concentration profile in the bentonite sample is used to estimate D(a), and the temporal evolution of the solute concentration in the reservoir is used to estimate D(e). This method has several advantages over the typical "through-diffusion" experiments, in particular: (a) experiment duration is significantly shorter, (b) D(a) values are measured with greater precision and (c) it is not necessary to maintain a constant solute concentration in the reservoir. This new method has been used to estimate the effective and apparent diffusion coefficients for caesium in FEBEX bentonite and in order to validate it, the results have been compared with results previously obtained with standard methods. Experimental results have been satisfactorily modelled using a simple model of diffusion in porewater and the measured value of D(e)(Cs) is very similar to D(e)(HTO) in the same bentonite. There is no evidence of "surface diffusion" in FEBEX bentonite for caesium.