A geometric approach to determine adsorption and desorption kinetic constants

A geometric method based on Langmuir kinetics has been derived to determine adsorption and desorption kinetic constants. In the conventional procedure, either the adsorption kinetic constant (k(a)c) or desorption kinetic constant (k(d)c) is found from kinetic experiments and the other is calculated by their correlation with the equilibrium constant, i.e, k(d)c = Kcon/k(a)c, where Kcon has been known from equilibrium studies. The determined constants (Kcon, k(a)c, k(d)c), if based only on the conventional procedure, may not be accurate due to their mathematical dependence. Therefore, the objectives of this study are applying a geometric approach to directly determine Langmuir kinetic constants and describe adsorption behavior. In this approach, both adsorption kinetic constant (k(a)g) and desorption kinetic constant (k(d)g) are obtained only from data of kinetic experiments, and a geometric equilibrium constant (Kgeo) is calculated by Kgeo = k(a)g/k(d)g. The deviation between Kgeo and Kcon can prove the accuracy of k(a)g and k(d)g which were determined by this method. This approach was applicable to selenate, selenite and Mg2+ adsorption onto SiO2 regardless of whether the adsorbate formed inner- or outer-sphere complexes. However, this method showed some deviation between Kcon and Kgeo for Mn2+ adsorption because of the formation of surface Mn(II)-hydroxide clusters, which was inconsistent with the basic assumption of this method of monolayer adsorption.     

再生水补给河道入渗区地下水水质时空变异分析

运用聚类分析、判别分析和主成分/因子分析方法来研究潮白河流域再生水补水河段地下水水质的时空变异情况。对地下水进行剖面分析（剖面A为平行于水流场方向,剖面B垂直于水流场方向）。地下水研究结果表明除NO3-、NH4+和Mn2+外,其余指标均达到地表水Ⅱ类标准。剖面A的季节判别中由于淋溶作用筛选出pH和TDS,正确率为77.5%,说明研究区在近岸区。同时,剖面B的季节变异由于远离河岸的土壤蓄水层中氧化还原作用使得Fe3+、Mn2+、Na+、NO2-、CODMn和TP被判别出,正确率为74.4%。此外,由于非冻土期土壤蓄水层中频繁的淋溶作用和活跃的生化反应识别出CODMn、HCO3-、NO2-、pH、SO42-、Cl-、Na+和Ba2+表征了非冻土期剖面A的空间变异,而判别正确率为100%的F-、Na+和HCO3-则表征了冻土期剖面A的空间变异。冻土期剖面B的TDS和TP以及非冻土期剖面B的TN和K+的判别正确率均为100%。再生水对近岸带的影响较远岸带显著。该分析结论可归因于再生水的污染、土壤蓄水层矿物盐岩溶解污染、工农业废水排放的点源污染和降水及流域水土流失所造成的非点源污染的综合作用。     

A partially coupled, fraction-by-fraction modelling approach to the subsurface migration of gasoline spills

The subsurface spreading behaviour of gasoline, as well as several other common soil- and groundwater pollutants (e.g. diesel, creosote), is complicated by the fact that it is a mixture of hundreds of different constituents, behaving differently with respect to e.g. dissolution, volatilisation, adsorption and biodegradation. Especially for scenarios where the non-aqueous phase liquid (NAPL) phase is highly mobile, such as for sudden spills in connection with accidents, it is necessary to simultaneously analyse the migration of the NAPL and its individual components in order to assess risks and environmental impacts. Although a few fully coupled, multi-phase, multi-constituent models exist, such models are highly complex and may be time consuming to use. A new, somewhat simplified methodology for modelling the subsurface migration of gasoline while taking its multi-constituent nature into account is therefore introduced here. Constituents with similar properties are grouped together into eight fractions. The migration of each fraction in the aqueous and gaseous phases as well as adsorption is modelled separately using a single-constituent multi-phase flow model, while the movement of the free-phase gasoline is essentially the same for all fractions. The modelling is done stepwise to allow updating of the free-phase gasoline composition at certain time intervals. The output is the concentration of the eight different fractions in the aqueous, gaseous, free gasoline and solid phases with time. The approach is evaluated by comparing it to a fully coupled multi-phase, multi-constituent numerical simulator in the modelling of a typical accident-type spill scenario, based on a tanker accident in northern Sweden. Here the PCFF method produces results similar to those of the more sophisticated, fully coupled model. The benefit of the method is that it is easy to use and can be applied to any single-constituent multi-phase numerical simulator, which in turn may have different strengths in incorporating various processes. The results demonstrate that the different fractions have significantly different migration behaviours and although the methodology involves some simplifications, it is a considerable improvement compared to modelling the gasoline constituents completely individually or as one single mixture.     

A simple network approach to modelling dispersion among large groups of obstacles

A simple network approach has been developed to simulate the movement of pollutant within urban areas. The model uses estimates of pollutant exchange obtained from velocity measurements in experiments with various regular obstacle arrays. The transfer of tracer material was modelled using concepts of advection along streets, well-mixed flow properties within street segments and exchange velocities (akin to aerodynamic conductances) across side and top facets of the street segments.The results predicted both the centreline concentration and lateral dispersion of the tracer with reasonable accuracy for a range of packing densities and wind directions. The basic model's concentration predictions were accurate to better than a factor of two in all cases for the region from two obstacle rows behind a source located within the array to around eight rows behind, a range of distances that falls into the so-called “neighbourhood-scale” for dispersion problems. The results supported the use of parameterized rates of exchange between regions of flow as being useful for fast, approximate dispersion modelling. It was thought that the effects of re-entrainment of tracer back into the canopy were of significance, but modelling designed to incorporate these effects did not lead to general improvements to the modelling for these steady-state source experiments.The model's limitations were also investigated. Chief amongst these was that it worked poorly among tall buildings where the well-mixed assumption within street segments was inadequate.     

A simple spectroscopic method to determine dimethoate in water samples by complex formation

Abstract

A simple and rapid method for the determination of dimethoate in water was developed based on the monitoring of the complex formation between bis 5-phenyldipyrrinate of nickel (II) and the herbicide dimethoate. The method showed a short response time (10?s), high selectivity (very low interference from other sulfate and salts), high sensitivity (limit of detection (LOD) 0.45?µM, limit of quantitation (LOQ) of 1.39?µM), and a K_d of 2.4?µM. Stoichiometry experiments showed that complex formation occurred with a 1:1 relation. The method was applied to different environmental water samples such as lagoon, stream, urban, and groundwater samples. The results indicated that independently from the water source, the method exhibited high precision (0.25–2.47% variation coefficient) and accuracy (84.42–115.68% recovery). In addition, the method was also tested using an effluent from a wastewater treatment plant from Mexico; however, the results indicated that the presence of organic matter had a pronounced effect on the detection.     

A simplified approach to modelling underground migration of radionuclides from contaminated river sediments

Accidental releases of waste water from the first Czechoslovak nuclear power plant, A1, caused contamination of sediments of the Dudváh river, flowing into the Vah river, in Slovakia. Rather high concentrations of ¹³⁷Cs and ⁹⁰Sr (2150Bq dm⁻³ and 215Bq dm⁻³, respectively) were found in bottom sediments of a former channel of the re-engineered river body at a distance of about 250 m from a village, Siladice, with water-supply wells. In order to assess the possibility of contamination of the wells, underground migration of both radionuclides from the contaminated area was simulated using an original layered convection-diffusion model. K_d values determined in laboratory experiments were used. The analysis of the hydrological situation in the area reveals that the critical condition is a dominant horizontal groundwater flow near the water table in the direction from the Váh bank to Siladice, in the periods when the contaminated body lies under the water table. The simulation calculated under conservative conditions showed that the contamination of water-supply wells would not exceed permissible concentration limits.     

A hybrid modeling approach to resolve pollutant concentrations in an urban area

A modeling tool that can resolve contributions from individual sources to the urban environment is critical for air-toxics exposure assessments. Air toxics are often chemically reactive and may have background concentrations originated from distant sources. Grid models are the best-suited tools to handle the regional features of these chemicals. However, these models are not designed to resolve pollutant concentrations on local scales. Moreover, for many species of interest, having reaction time scales that are longer than the travel time across an urban area, chemical reactions can be ignored in describing local dispersion from strong individual sources making Lagrangian and plume-dispersion models practical. In this study, we test the feasibility of developing an urban hybrid simulation system. In this combination, the Community Multi-scale Air Quality model (CMAQ) provides the regional background concentrations and urban-scale photochemistry, and local models such as Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) and AMS/EPA Regulatory Model (AERMOD) provide the more spatially resolved concentrations due to local emission sources. In the initial application, the HYSPLIT, AERMOD, and CMAQ models are used in combination to calculate high-resolution benzene concentrations in the Houston area. The study period is from 18 August to 4 September of 2000. The Mesoscale Model 5 (MM5) is used to create meteorological fields with a horizontal resolution of 1×1 km². In another variation to this approach, multiple HYSPLIT simulations are used to create a concentration ensemble to estimate the contribution to the concentration variability from point sources. HYSPLIT simulations are used to model two sources of concentration variability; one due to variability created by different particle trajectory pathways in the turbulent atmosphere and the other due to different flow regimes that might be introduced when using gridded data to represent meteorological data fields. The ensemble mean concentrations determined by HYSPLIT plus the concentrations estimated by AERMOD are added to the CMAQ calculated background to estimate the total mean benzene concentration. These estimated hourly mean concentrations are also compared with available field measurements.     

An integrated approach to identify the origin of PM10 exceedances

Purpose

This study was aimed to the development of an integrated approach for the characterization of particulate matter (PM) pollution events in the South of Italy.

Methods

PM₁₀ and PM_2.5 daily samples were collected from June to November 2008 at an urban background site located in Bari (Puglia Region, South of Italy). Meteorological data, particle size distributions and atmospheric dispersion conditions were also monitored in order to provide information concerning the different features of PM sources.

Results

The collected data allowed suggesting four indicators to characterize different PM₁₀ exceedances. PM_2.5/PM₁₀ ratio, natural radioactivity, aerosol maps and back-trajectory analysis and particle distributions were considered in order to evaluate the contribution of local anthropogenic sources and to determine the different origins of intrusive air mass coming from long-range transport, such as African dust outbreaks and aerosol particles from Central and Eastern Europe. The obtained results were confirmed by applying principal component analysis to the number particle concentration dataset and by the chemical characterization of the samples (PM₁₀ and PM_2.5).

Conclusions

The integrated approach for PM study suggested in this paper can be useful to support the air quality managers for the development of cost-effective control strategies and the application of more suitable risk management approaches.     

A Lagrangian approach for modelling turbulent transport and chemistry

A Lagrangian two-particle model for the relative diffusion and mixing of two reactive species is proposed. The model has been tested for consistency in simple geometrical configurations and has been compared to experimental data, Eulerian first- and second-order closure models as well as to other Lagrangian models. The model includes the covariance between the two species and therefore gives better predictions of both diffusion and chemistry than first-order closure models or the one-particle model proposed by Chock and Winkler (1994a,b, Journal of Geophysical Research, 99 D1, 1019–1031, 99 D1, 1033–1041). The model is a generalisation of the model presented by Komori et al. (1991, Journal of Fluid Mechanics 228, 629–659). The results of the calculations, although preliminary in character, indicate that the proposed algorithm is robust and efficient, and yields satisfactory results in turbulence with slow to moderate chemistry.     

城市内河综合水质对再生水补水的响应

为解析再生水补水对城市内河水质的影响,以合肥市塘西河为例,采用一维水动力水质模型,结合模糊模式识别方法,研究再生水补水位置、水质和补水量对塘西河水质的影响。模拟结果表明：再生水补水改变了河流水动力特征、污染物负荷及其扩散降解过程,影响河流水质空间分布,且对补给点附近的河流水质影响最为显著;通过模糊模式识别分析发现,补给点越靠近上游对河流水质的改善作用越大,提高补水水质或增大补水水量均可进一步改善河流水质。     

Reverse quantitative structure-activity relationship for modelling the sorption of esfenvalerate to dissolved organic matter. A multivariate approach

The sorption of the pyrethroid, esfenvalerate, to the dissolved and/or dispersed fraction of eight different natural humic compounds has been investigated. The dissolved organic matters (DOMs) included in this study originate from ground water, soil pore water, and surface waters. Sorption was modelled at DOM concentration levels where equilibrium partitioning of esfenvalerate between DOM and the aqueous bulk phase prevails. The inherent characteristics of the eight different humic materials, quantified in the preceding paper by Thomsen et al. (2002, this issue (PII: S0045-6535(02)00335-1)), have been used as explanatory variables for modelling this equilibrium partitioning. Using a reverse QSAR approach based on by projection-into-latent-structure regression (PLS-R) inherent sorbent properties determining for the sorption affinity of esfenvalerate to DOM were analysed. For all humic substances a decrease in the DOM-normalised equilibrium-partitioning coefficient, K_DOM, with increasing concentration of DOM was observed. Significant variations in K_DOM values, as function of the inherent characteristics of the individual humic substances, were found at DOM concentrations of 75 and 100 ppm, respectively. The latter is a strong indication of variations in sorption mechanisms of esfenvalerate to DOM of varying inherent properties. Groupings in the principal property space quantifying DOMs may indicate that separate models are needed for quantifying the equilibrium partitioning to different classes of DOM.     

Application of encapsulation (pH-sensitive polymer and phosphate buffer macrocapsules): a novel approach to remediation of acidic ground water

Macrocapsules, composed of a pH-sensitive polymer and phosphate buffer, offer a novel remediation alternative for acidic ground waters. To test their potential effectiveness, laboratory experiments were carried out followed by a field trial within a coal pile runoff (CPR) acidic contaminant plume. Results of traditional limestone and macrocapsule treatments were compared in both laboratory and field experiments. Macrocapsules were more effective than limestone as a passive treatment for raising pH in well water from 2.5 to 6 in both laboratory and field experiments. The limestone treatments had limited impact on pH, only increasing pH as high as 3.3, and armoring by iron was evident in the field trial. Aluminum, iron and sulfate concentrations remained relatively constant throughout the experiments, but phosphate increased (0.15-32 mg/L), indicating macrocapsule release. This research confirmed that macrocapsules may be an effective alternative to limestone to treat highly acidic ground water.     

Analysis of radon origin by backward atmospheric transport modelling

This work shows how ambient radon concentrations measured at Cabauw station in central Netherlands are influenced by transport from different regions under typical transport conditions occurring during April and November, 2007 by means of atmospheric Lagrangian particle dispersion modelling in a receptor-oriented approach. Four specific regions have been isolated to assess their contribution to the modelled radon ambient concentrations at Cabauw, and two different radon flux assumptions. Westerly flows coming from the ocean are poor in radon and do not increase radon air concentrations unless there is some fetch over the British Isles. Continental transport, mainly from eastern and southern Europe, significantly increases radon background concentrations, reaching increments of 3 Bq m^?3. A constant 0.66 atoms cm^?2 s^?1 radon flux over land and zero over water bodies is a good approximation for the source term in order to study regional contributions and modulation of the radon background.     

A case study of optical and chemical ground apportionment for urban aerosols in Thessaloniki

Urban aerosol characterization gathering ground-based in situ and sunphotometer measurements have been performed for the city of Thessaloniki for two specific days: the 12th and 13th of June 1997. A representative aerosol model for Thessaloniki aerosols was tentatively constructed for each day. Four components have been selected from our chemical measurements: black carbon (BC), particulate organic matter (POM), inorganic fine water soluble particles (WS) and a residue coarse component which mainly contains coarse dust and sea-salt particles (CC). Size distribution and complex refractive index for (WS) and (CC) components were determined from published data. (CC) has been shown to have a small optical effect compared to the submicron components. Size distribution for carbonaceous particles was obtained from sensitivity tests on particulate number and visible Angström exponent. The impact of relative humidity on extinction and scattering coefficients has been calculated on 13 June with Mie theory and Hänel relationships. Parameters needed for this calculation were well known for WS particles only. For POM particles we have used the experimental curve of hygroscopic factors obtained by Hobbs et al. (1997) for urban aerosols sampled on the East coast of United States to determine the hydrophilic dependency of POM particles. Relative humidity has been shown to be an important parameter even for values lower than 50%. Optical apportionment calculation has been realized pointing out that more than 45% of the total extinction coefficient is due to (POM) particles and about 20 and 30% to (WS) and (BC), respectively.     

Road traffic impact on urban water quality: a step towards integrated traffic,air and stormwater modelling

Methods for simulating air pollution due to road traffic and the associated effects on stormwater runoff quality in an urban environment are examined with particular emphasis on the integration of the various simulation models into a consistent modelling chain. To that end, the models for traffic, pollutant emissions, atmospheric dispersion and deposition, and stormwater contamination are reviewed. The present study focuses on the implementation of a modelling chain for an actual urban case study, which is the contamination of water runoff by cadmium (Cd), lead (Pb), and zinc (Zn) in the Grigny urban catchment near Paris, France. First, traffic emissions are calculated with traffic inputs using the COPERT4 methodology. Next, the atmospheric dispersion of pollutants is simulated with the Polyphemus line source model and pollutant deposition fluxes in different subcatchment areas are calculated. Finally, the SWMM water quantity and quality model is used to estimate the concentrations of pollutants in stormwater runoff. The simulation results are compared to mass flow rates and concentrations of Cd, Pb and Zn measured at the catchment outlet. The contribution of local traffic to stormwater contamination is estimated to be significant for Pb and, to a lesser extent, for Zn and Cd; however, Pb is most likely overestimated due to outdated emissions factors. The results demonstrate the importance of treating distributed traffic emissions from major roadways explicitly since the impact of these sources on concentrations in the catchment outlet is underestimated when those traffic emissions are spatially averaged over the catchment area.     

A prediction-based approach to modelling temporal and spatial variability of traffic-related air pollution in Montreal, Canada

Concentrations of traffic-related air pollution can be highly variable at the local scale and can have substantial seasonal variability. This study was designed to provide estimates of intra-urban concentrations of ambient nitrogen dioxide (NO₂) in Montreal, Canada, that would be used subsequently in health studies of chronic diseases and long-term exposures to traffic-related air pollution. We measured concentrations of NO₂ at 133 locations in Montreal with passive diffusion samplers in three seasons during 2005 and 2006. We then used land use regression, a proven statistical prediction method for describing spatial patterns of air pollution, to develop separate estimates of spatial variability across the city by regressing NO₂ against available land-use variables in each of these three periods. We also developed a “pooled” model across these sampling periods to provide an estimate of an annual average. Our modelling strategy was to develop a predictive model that maximized the model R². This strategy is different from other strategies whose goal is to identify causal relationships between predictors and concentrations of NO₂.Observed concentrations of NO₂ ranged from 2.6 ppb to 31.5 ppb, with mean values of 12.6 ppb in December 2005, 14.0 ppb in May 2006, and 8.9 ppb in August 2006. The greatest variability was observed during May. Concentrations of NO₂ were highest downtown and near major highways, and they were lowest in the western part of the city. Our pooled model explained approximately 80% of the variability in concentrations of NO₂. Although there were differences in concentrations of NO₂ between the three sampling periods, we found that the spatial variability did not vary significantly across the three sampling periods and that the pooled model was representative of mean annual spatial patterns.