Mapping of Concentrations in Europe Combining Measurements and Acid Deposition Models

Measurements of air and precipitation quality have been carried out within the EMEP programme under the Convention on Long Range Transboundary Air Pollution (LRTAP) since 1978. Approximately 100 rural sites are currently in operation. The Meteorological Synthesising Centre-West (MSC-W) operates two EMEP models estimating transboundary fluxes of air pollutants, a two-dimensional Lagrangian model and a three-dimensional Eulerian model. Traditionally kriging has been used to produce gridded concentration fields from observed data for comparison with modelled data. This paper describes a method for producing optimal fields based on both point measurements and. The difference between modelled and measured values in each measurement point is interpolated to give a smooth two-dimensional expression for the discrepancy between the two data sets. A combined map is derived by adjusting the modelled values with the interpolated difference weighted by the distance to the nearest measurement point. The method has been applied to sulphur and nitrogen measurements in air and precipitation from the EMEP network and modelled results in a 150×150 km grid from the EMEP Lagrangian model. The combined maps give improved regional concentration fields combining characteristics from both the measured and modelled data sets depending on the distance to the measurement points. Comparison with results from the higher resolution Eulerian model shows good agreement.     

A comparison of models for characterizing the distribution of radionuclides with depth in soils

It is common practice to fit mathematical models to radionuclide activity–depth profiles in soils in order to quantify rates of vertical migration through the soil profile. We have fitted six such models to 21 different activity–depth profiles of radiocaesium (¹³⁷Cs) derived from Chernobyl and determined relations between the models and the values of their parameters. The advection and dispersion parameters obtained using four solutions to the advection–dispersion equation (each based on different initial and boundary conditions or different simplifications) are in good agreement. We further develop a relation between parameter values obtained using the advection–dispersion models and those determined by a simpler exponential function of the form Aexp(–Bt) where t is the time and A and B are parameters to be estimated. One of the advection–dispersion models proved to be significantly better than the others in terms of goodness-of-fit, versatility and ease of use. A simple model, using calculations based on measured characteristics of the activity–depth profile, was shown to accord well with parameters derived from more complex models based on statistical curve fitting. We have also evaluated the ‘residence time’ or ‘compartmental’ model approach to characterizing radionuclide activity–depth profiles. We relate such models to a numerical solution of a simple advection equation, and we show that apparent dispersion in compartmental models is an artefact of numerical dispersion, which can be quantified by the Courant condition. For activity profiles that have a significant advection component, using solutions to the advection–dispersion equation, we have observed a strong positive correlation between advection and dispersion in the profile.     

考虑颗粒动态尺度影响的泥沙扩散系数模型建立及应用

在欧拉两相流数值算法中,多采用类比水流涡黏性系数的半经验泥沙扩散系数模型来计算固相体积浓度分布。而在将这一模型用于悬移质固液两相流时,因忽略了颗粒动态尺度对流体湍流强度的影响导致计算精度较低。为了体现这一影响,该文针对悬移质固液两相流,基于类比水流涡黏性系数的半经验模型,以颗粒与含能涡相互作用理论判断颗粒动态尺度和固相体积浓度对流体湍流强度的作用,根据流体湍流平衡流动理论和变量间多元回归分析方法,结合现有试验数据,建立了流体湍流强度变化率与颗粒动态尺度、固相体积浓度的关系式,进而得到了新的泥沙扩散系数的计算模型。通过对圆管中悬移质固液两相流的计算表明,相比于现有泥沙扩散系数模型,该文提出的模型能够体现颗粒动态尺度对泥沙扩散系数的影响,在不同含沙工况下计算得到的固相体积浓度分布与试验结果吻合更好,计算值与试验值的最大相对误差在10%以下,远远小于现有泥沙扩散系数计算模型的最大误差。该文新发展的泥沙扩散系数模型得到的悬移质固液两相流流场的计算精度明显提高,可以用于准确预测悬移质固液两相流流场特性。     

The Longitudinal Dispersion Coefficient of Soils as Related to the Variability of Local Permeability

Solute (NaCl) miscible displacement experiments are performed on long disturbed soil columns to determine the hydrodynamic longitudinal dispersion coefficient and correlate it with the variability of the local permeability. The solute concentration, averaged over several cross-sections along the soil column, is monitored by measuring the electrical resistance between rod electrodes. The measured solute concentration breakthrough curves are fitted simultaneously with the one-region and two-region analytical models of the 1-D advection–dispersion equation to estimate the longitudinal dispersion coefficient, D _L, as a function of Peclet number, Pe, for common groundwater flow velocities (2?<?Pe?<?50). Macroscopic simulations of miscible displacement in 2-D porous media described by a periodic permeability field with low, moderate and high variability are employed to evaluate the predictability of the one-region and two-region models, and the sensitivity of the dispersion coefficients and flow velocities estimated from soil column displacement tests to the variance of local permeability. When the variability of the local permeability becomes high, the one-region model fails, while the two-region model is capable of reproducing satisfactorily the breakthrough curves, and providing reliable values of dispersion coefficients. The two mean pore velocities estimated by the two-region model represent, on average, a fast and a slow mean velocity of the dispersion front, whereas their difference is a measure of the transient evolution of the width of the equi-concentration dispersion front.     

Development and validation of a quasi-Gaussian plume model for the transport of botanical spores

Aerial dispersal of inoculum is the primary means of movement for many plant diseases. One of the challenges of modern decision support for plant health is to provide predictions of the influx of viable pathogen inoculum from sources outside a crop. Such prediction in a practical setting requires prediction tools that have modest computing and input requirements, yet provide sufficiently accurate predictions. In this paper a hybrid dispersion model is developed, combining Taylor's statistical theory of diffusion for horizontal dispersal with the eddy diffusion theory as implemented in the Lagrangian similarity diffusion model of [van Ulden, A.P., 1978. Simple estimates for vertical diffusion from sources near the ground. Atmos. Environ. 12, 2119–2124] and [Gryning, S.E., van Ulden, A.P., Larsen, S.E., 1983. Dispersion from a continuous ground-level source investigated by a K model. Q. J. Roy. Meteor. Soc. 109, 355–364]. The model is extended with a dry deposition method and an effective source strength. Model results are compared with experimental data for the transport of artificially released spores of Lycopodium clavatum above a potato canopy. The numerical results are in close agreement with the experimental data, which cover distances up to 100 m. Numerical predictions are compared to those produced by two alternative model versions and a previously published Gaussian plume model for the transport of spores above potato canopies. The potential for practical implementation of atmospheric dispersion models in plant disease decision support systems is discussed.     

Applying a Lagrangian dispersion analysis to infer carbon dioxide and latent heat fluxes in a corn canopy

Warland and Thurtell (2000) proposed an analytical dispersion Lagrangian analysis (hereafter WT analysis) to relate the mean scalar concentration field to source profiles inside the canopy. The first objective of this study was to evaluate the performance of the WT analysis with existing turbulence statistics parameterizations in a corn canopy, by comparing its inferred net ecosystem CO₂ exchange (NEE) and latent heat flux (λE) with eddy covariance measurements. The second objective was to assess the performance of the WT analysis to infer the soil CO₂ flux. Four parameterizations of turbulence statistics were used to estimate Lagrangian time scale (T_L) and standard deviation of vertical wind velocity (σ_w) profiles. The estimated T_L and σ_w profiles were then corrected for atmospheric stability conditions. The field experiment was carried out in a corn field from August to October 2007 and 2008. Profiles of water vapour and CO₂ mixing ratios were measured using a multiport sampling system connected to an infrared gas analyzer. Wind velocity within and above the canopy and eddy covariance measurements over the canopy were taken. The soil respiration, estimated using the WT analysis, was compared to estimates obtained by an empirical model. WT analysis fluxes showed good correlation (R² = 0.77-0.88) with NEE and λE obtained by the eddy covariance technique, but overestimated net fluxes, especially when corrections for atmospheric stability were applied. The optimization of T_L and σ_w profiles using in-canopy turbulence measurements improved the agreement between measured and modeled NEE and λE. Inferred soil CO₂ fluxes were underestimated and were poorly correlated (R² = 0.02-0.01) with estimates obtained using an empirical model based on soil temperature. This poor performance in estimating the soil respiration is likely caused by the decoupling between inside and above canopy flows.     

The effect of turbulence on the light environment of alfalfa

The properties of sunflecks in alfalfa canopies and their relationship to turbulence were quantified from measurements of light fluctuations and winds. Winds were measured above the canopy at 10 Hz, while light was measured at rates as high as 27 Hz inside the canopy. Power spectral analyses were used to determine the importance of various time scales of light fluctuations. Under all wind conditions a prominent spectral peak ranging from 1 to 2 Hz was observed for photosynthetically active radiation (PAR) in the canopy at LAI of 1.7. As mean winds increased from 1 to 7 ms⁻¹, the peak broadened and large increases were observed in the contribution of higher frequencies up to 10 Hz. The slope of spectral densities of PAR at the higher frequencies exhibited a linear relationship with the friction velocity or intensity of turbulence above the canopy. This implies that certain properties of sunflecks may be evaluated from measured properties of turbulence.The most prominent peaks in the PAR power spectra are likely due to stalk waving, which is triggered by gusts or turbulent structures. The strong damping effects of plants on the resonant interactions, as well as leaf flutter, account for the broad, flat peak under windy conditions. The frequency of leaf flutter is considered to be the main factor governing the slope of the linear portion of the PAR spectrum.     

Modelling of Atmospheric Transport and Deposition of Pesticides

Modelling of atmospheric transport and deposition of pesticides is presented and discussed. Modelling on regional scale builds on the existing knowledge gained in other air pollution fields. An overview of current modelling studies on transport and deposition on a regional scale (typically 30-3000 km) is given. From these studies it is concluded that the models are capable in simulating the spatial distribution of the concentrations and depositions. However, large uncertainties are present in this type of modelling and are for the greater part induced by the uncertainty in the emissions and subsequently in the exchange process parameterisations and the physicochemical properties needed in the parameterisations. Many more measurement data are needed to validate the models.     

Effects of soil properties on the kinetics of desorption of phosphate from Alfisols by anion‐exchange resins

Phosphorus‐desorption rates by anion‐exchange resins were best described by three empirical kinetic models: Elovich equation, the parabolic diffusion equation, and the fractional power equation in that order. The objective of this study was to determine the relationship between kinetic rate constants from Elovich, fractional power, and parabolic rate equations and soil physical and chemical properties from soils of different lithogenic origins from the Nigerian savanna. Phosphorus‐desorption patterns included an initial fast reaction, followed by a slow release that continued up to 20 h. Particle diffusion was observed to be the rate‐limiting step in the kinetic desorption of native P in the soils studied as opposed to ligand exchange or surface reaction. The influence of parent material is not prominent due to long history of pedogenesis over the soils. The rate coefficients from the Elovich equation, parabolic diffusion equation, and the fractional power model were best predicted from clay, pH, and extractable Al and Fe oxides and therefore exert a profound influence on the rate of P release from the soils. These soil properties together explained between 93% and 99% of the variance in the rate coefficients of P desorption from the soils.     

Dispersion number determination in waste stabilization ponds

The measurement and determination of the dispersion number in ponds is usually based on the one-dimensional diffusion equation. This paper shows that since the criterion underlying the application of this equation is not often satisfied, great error may be introduced in the determination of the dispersion number(d). The effect of this on the prediction of the bacteria reduction is also discussed.     

盐渍化土壤光谱特征的区域异质性及盐分反演

该文通过分析中国新疆、浙江、吉林3个不同地区盐渍化土壤的高光谱特征,研究了盐渍化土壤高光谱特征的区域异质性,并对构建高精度的跨区域土壤盐分高光谱定量反演模型,应用25种数据处理方式来提高全局建模的精度,旨在提高具有光谱异质性土壤的盐分反演精度。结果表明:不同地区的盐渍化土壤,无论是反射率还是光谱曲线形态方面,均存在较明显的差异,但经过一阶微分处理后,光谱差异有所降低;对3个地区土壤盐分含量局部建模与全局建模的精度进行比较,在所选用的直线回归、主成分回归、多元线性回归、偏最小二乘回归4种建模方法中,全局建模精度均低于局部建模精度;不同地区盐渍化土壤的盐分敏感波段不一致,在所采用的25种数据处理方式中,SG3点一阶微分(savitzky golay)、SG5点一阶微分、SG7点一阶微分、线性基线校正+SG3点一阶微分、SG平滑+SG3点一阶微分、SG平滑+线性基线校正+SG3点一阶微分这6种数据处理方式对全局建模的建模精度有明显改善作用,模型的相对分析误差均达到2.0以上,其中以SG平滑+SG3点一阶微分为最佳,其决定系数、均方根误差、相对分析误差分别为0.80、0.43、2.23。研究结果为跨区域土壤盐渍化的航天高光谱遥感监测提供了一定的参考依据。     

Analytical air pollution advection and diffusion models

A review of non-Gaussian analytical solutions of the advection diffusion equation is presented. Their utilization to mathematical models of air pollution diffusion is discussed and the application of a particular solution is suggested. The suggested KAPPAG model uses the Demuth's (1978) solution and can incorporate smoothed observed vertical wind and diffusion coefficient profiles. It is shown that Demuth's solution can represent the realistic situations of the diminishing vertical exchange coefficient at the top of boundary layer.     

Invasive Freshwater Macrophyte Alligator Weed: Novel Adsorbent for Removal of Malachite Green from Aqueous Solution

The batch sorption experiments were carried out using a novel adsorbent, freshwater macrophyte alligator weed, for the removal of basic dye malachite green from aqueous solution. Effects of process parameters such as initial solution pH, contact time, adsorbent concentration, particle size, and ion strength were investigated. The adsorbent was characterized by FT-IR. The adsorption of malachite green by alligator weed was solution pH dependent. The adsorption reached equilibrium at 240 min for two particle size fractions. The pseudo-first-order equation, Ritchie second-order equation, and intraparticle diffusion models were tested. The results showed that adsorption of malachite green onto alligator weed followed the Ritchie second-order equation very well and the intraparticle diffusion played important roles in the adsorption process. The Langmuir and Freundlich equations were applied to the data related to the adsorption isotherms and the observed maximum adsorption capacity (q _max) was 185.54 mg g^?1 at 20°C according to the Langmuir model. The effects of particle size, adsorbent concentration, and ionic strength on the malachite green adsorption were very marked. The alligator weed could serve as low-cost adsorbents for removing malachite green from aqueous solution.     

Transferability and scalability of soil total carbon prediction models in Florida, USA

The applicability, transferability, and scalability of visible/near-infrared (VNIR)-derived soil total carbon (TC) models are still poorly understood. The objectives of this study were to: i) compare models of three multivariate statistical methods, partial least squares regression (PLSR), support vector machine (SVM), and random forest methods, to predict soil logarithm-transformed TC (logTC) using five fields (local scale) and a pooled (regional-scale) VNIR spectral dataset (a total of 560 TC spectral datasets), ii) assess the model transferability among fields, and iii) evaluate their up- and downscaling behaviors in Florida, USA. The transferability and up- and downscaling of the models were limited by the following factors: i) the spectral data domain, ii) soil attribute domain, iii) methods that describe the internal model structure of VNIR-TC relationships, and iv) environmental domain space of attributes that control soil carbon dynamics. All soil logTC models showed excellent performance based on all three methods with R² > 0.86, bias < 0.01%, root mean squared error (RMSE) = 0.09%, residual predication deviation (RPD) > 2.70%, and ratio of prediction error to interquartile range (RPIQ) > 4.54. The PLSR method performed substantially better than the SVM method to scale and transfer the TC models. This could be attributed to the tendency of SVM to overfit models, while the asset of the PLSR method was its robustness when the models were validated with independent datasets, transferred, and/or scaled. The upscaled soil TC models performed somewhat better in terms of model fit (R²), RPD, and RPIQ, whereas the downscaled models showed less bias and smaller RMSE based on PLSR. We found no universal trend indicating which of the four limiting factors mentioned above had the most impact that constrained the transferability and scalability of the models. Given that several factors can impinge on the empirically derived soil spectral prediction models, as demonstrated by this study, more focus on their applicability and scalability is needed.     

Modelling water transfer by rain-splash in a 3D canopy using Monte Carlo integration

Rain-splash is a very effective process in the short distance dispersal of biotic and abiotic particles leading to potential biological or chemical contamination within crop ecosystems. A physical approach to simulate water transfer by rain-splash in a 3D canopy structure is presented. This new approach is based on the explicit parameterisations of the mechanisms such as raindrop propagation, production and transport of splash droplets and their interception by canopy elements. The model theory and its numerical solution were based on the Monte Carlo integration technique. The calculation of droplet trajectories was validated by comparison with the previous published measured data (R²=0.99 for the terminal velocity and R²=0.93 for the distance travelled by droplets). Simulated patterns of splash dispersal through artificial canopies consisting of vertical cylinders compared well with measured patterns (R²=0.90). This new modelling approach is promising for studying particle dispersal by rain-splash in complex canopy structures.     

Miscible displacement studies in capillary tubes,sand and soil columns

Misciple displacement studies were conducted in the laboratory to determine the dispersion and diffusion coefficients of nitrate and bicarbonate ions in capillary tubes, sand and soil columns. Necessary mathematical equations used for the evaluation of the dispersion coefficients are discussed. The dispersion coefficients evaluated with use of two different models are compared, particularly with reference to their velocity dependence. The values of the dispersion coefficients (D₁ and D₂) and molecular diffusion coefficients (D₀₁ and D₀₂) were found to be several times higher in the Kirkham and Powers' moving coordinate model than those in a probability model.     

Equilibrium, Kinetics and Mechanism of Removal of Methylene Blue from Aqueous Solution by Adsorption onto Pine Cone Biomass of Pinus radiata

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R _L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (?G ⁰), standard enthalpy (?H ⁰), standard entropy (?S ⁰) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.     

Equilibrium, Kinetics, and Thermodynamics of Methylene Blue Adsorption by Pine Tree Leaves

The adsorption capacity of pine tree leaves for removal of methylene blue (MB) from aqueous solution was investigated in a batch system. The effects of the process variables, such as solution pH, contact time, initial dye concentration, amount of adsorbent, agitation speed, salt concentration, and system temperature on the adsorption process were studied. The extent of methylene blue dye adsorption increased with increase in initial dye concentration, contact time, agitation speed, temperature, and solution pH but decreased with increased in amount of adsorbent and salt concentration. Equilibrium data were best described by both Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine tree leaves biomass was 126.58?mg/g at 30?°C. The value of separation factor, R _L , from Langmuir equation and Freundlich constant, n, both give an indication of favorable adsorption. The intrapartical diffusion model, liquid film diffusion model, double exponential model, pseudo-first and second order model were used to describe the kinetic and mechanism of adsorption process. A single stage bath adsorber design for the MB adsorption onto pine tree leaves has been presented based on the Langmuir isotherm model equation. Thermodynamic parameters such as standard Gibbs free energy (??G ⁰), standard enthalpy (??H ⁰), and standard entropy (??S ⁰) were calculated.