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Coupling of Speciation and Transport Models
Published in Herbert E. Allen, E. Michael Perdue, David S. Brown, Metals in Groundwater, 2020
Charles J. Hostetler, Robert L. Erikson
The chemical transport model (CTM) uses a two-step algorithm to model mass transport of aqueous solutes in the presence of chemically reactive sub-surface media. The CTM model offers an alternative to the classical ADR equation: advection and dispersion are modeled using a probability density function approach and retardation is modeled using chemical attenuation reactions. The description of retardation in terms of interphase mass transfer reactions leads to variable solute velocities. For situations involving complex trace metal/sediment interactions, the mechanistic treatment used in CTM (and other reactive solute transport models) represents an improvement over the lumped parameter approach used in the classical transport equation.
Disposal of Spent Fuel and High-Level Waste
Published in James H. Saling, Audeen W. Fentiman, Radioactive Waste Management, 2018
James H. Saling, Audeen W. Fentiman
Other mathematical models have been reported in the literature: Models of radionuclide transport in porous media were adapted to the analysis of transport in jointed porous rock.17 Radionuclide transport in jointed porous rock can be approximated as occurring in an equivalent porous medium.A chemical transport model, CHEMTRN, includes advection, dispersion/diffusion, complexation, sorption, precipitation or dissolution of solids, and dissolution in water.18 The transport, mass action, and site constraint equations were expressed in a differential/algebraic form with the sorption process modeled by either ion exchange or surface complexation.The effects of several variables and model assumptions have been assessed in the calculation of radionuclide discharge from hypothetical repositories in tuff and bedded salt.19 The repository sites were modeled in a way consistent with the current understanding of the characteristics of the geologic environments being studied by the DOE.As part of a program to develop a methodology for use in assessing the long-term risk of disposal of radwaste in deep geologic formations, the dynamic network (DNET) model was developed to investigate waste/near-field interactions associated with the disposal of radwaste in bedded salt formations.20The coupled thermomechanical, thermohydrologic, and hydromechanical processes were studied with a numerical code, ROCMAS, for a radwaste repository in a fractured rock medium.21A probabilistic source-term code, AREST, has been developed to provide a quantiative assessment of the performance of the engineered barrier system relative to the regulatory requirements.22Using uncertainty analysis techniques to quantify the level of confidence and to assess the long-term risk, probabilistic systems assessment codes (PSACs) are being developed in several member countries of the Nuclear Energy Agency (NEA) within the PSAC user group.23 The work carried out on the application of PSAC in these countries is reported in reference.23
Expansion of a size disaggregation profile library for particulate matter emissions processing from three generic profiles to 36 source-type-specific profiles
Published in Journal of the Air & Waste Management Association, 2020
Elisa I. Boutzis, Junhua Zhang, Michael D. Moran
Chemical transport models with size-resolved representations of atmospheric particulate matter need the primary PM emissions input by the models to be size-resolved. The emissions processing systems that are typically used to prepare model-ready emissions input files employ PM size disaggregation profiles to allocate bulk PM emissions to the model’s PM size distribution representation. The Environment and Climate Change Canada GEM-MACH chemical transport model uses a sectional or size-bin representation of the PM size distribution and one of the two sectional configurations for PM: two-bin or 12-bin. For the GEM-MACH 12-bin configuration, a small library of three generic PM size disaggregation profiles is currently applied for three broad source categories (area, mobile, and point) in order to allocate PM2.5 and PM10 inventory emissions to the 10 model size bins smaller than 10 µm (eight of which represent bulk PM2.5). These three profiles are aggregates of 10 source-specific PM size distribution profiles discussed in a paper by Eldering and Cass (1996). However, such a small number of profiles cannot well represent the size distribution of PM emissions from all of the PM source types considered by the GEM-MACH model (e.g., unpaved road dust, residential wood combustion, electric arc furnaces, and ocean-going marine vessels).
Comparison of discrete, discrete-sectional, modal and moment models for aerosol dynamics simulations
Published in Aerosol Science and Technology, 2020
Huang Zhang, Girish Sharma, Sukrant Dhawan, David Dhanraj, Zhichao Li, Pratim Biswas
The understanding of aerosol dynamics is essential in many applications, such as aerosol reactors (Wang et al. 2014), combustion (Sharma, Dhawan, et al. 2019; Sharma, Wang, et al. 2019), air quality control (Zhu, Sartelet, and Seigneur 2015), etc. It can also be used to predict the evolution of particulate systems, which is useful for in-depth understanding of the experimental measurements. Aerosol dynamic models (ADMs) permit the interaction of complex physical processes through simulation, and can be used to understand the experimental observations in aerosol systems. Panda and Pratsinis (1995) and Chadha et al. (2017) used ADM to predict the properties of particles formed via vapor phase synthesis processes and based their recommendations for industrial scale up of the synthesis process on these predictions. Biswas et al. (1997), Gao et al. (2017), and Sharma, Dhawan, et al. (2019) used ADM to predict the evolution of aerosol size distribution, in order to understand the underlying physics of particle formation by gas or solid combustion. In several atmospheric models, ADMs are often coupled with a chemical-transport model to simulate the aerosol transport and deposition in a large scale region to predict the impact of aerosols on air quality (Korhonen, Lehtinen, and Kulmala 2004; Zhang et al. 1999). ADMs are also employed for nuclear reactor safety analysis to determine the release and evolution of radioactive materials in the unlikely case of an accident (Williams 1986).
Study of nitrogen pollution in the Republic of North Macedonia by moss biomonitoring and Kjeldahl method
Published in Journal of Environmental Science and Health, Part A, 2020
Trajče Stafilov, Zdravko Špirić, Marin Glad, Lambe Barandovski, Katerina Bačeva Andonovska, Robert Šajn, Oleg Antonić
In Europe, the control of reactive nitrogen emissions to air is regulated under several European Union directives, such as the National Emission Ceilings Directive and Nitrates Directive, and protocols of the Long-Range Transboundary Air Pollution (LRTAP) Convention, such as the Gothenburg Protocol. Under the LRTAP Convention, the European Monitoring and Evaluation Programme (EMEP) collects emission data from European countries in order to model atmospheric transport and deposition of air pollutants. Deposition of nitrogen compounds is currently calculated using the EMEP Unified Eulerian chemical transport model with a grid size of 50 km × 50 km.[7,8] Passive biomonitoring of atmospheric nitrogen deposition using mosses could be a step forward toward a higher spatial resolution in determining nitrogen deposition in Europe.[9–14] The European moss survey has been repeated at five-yearly intervals. In 2005/6 moss survey, for the first time, 16 countries determined the nitrogen concentration in mosses to establish whether mosses can be used as biomonitors of atmospheric nitrogen deposition across Europe, identify the main polluted areas and produce European maps.[9,10] The lowest total nitrogen concentrations in mosses were found in northern Finland and northern parts of the UK, whilst the highest concentrations were found in parts of Western, Central and Eastern Europe.