Transport and deposition of indoor radon decay products—I. Model development and validation

Commonly used mathematical models of indoor radon decay product behavior are based on macroscopic mass-balances, often referred to as ‘uniformly-mixed models’. The uniformly-mixed model's applicability is limited by its inability to track the movement of pollutants from their sources to other areas within the enclosure, to permit spatial- or time-dependent sources, or to take proper account of interactions with macroscopic surfaces. Although the uniformly-mixed model parameterizes the deposition process as a constant volumetric removal rate, in reality the deposition process is actually a surface phenomenon and is strongly affected by environmental conditions.This paper describes the development of RADTRAN, a two-dimensional radon progeny transport model that begins with the differential conservation equations describing the motion of air and the transport of reactive pollutants, introduces appropriate boundary conditions to represent surface deposition, and then calculates the concentration distribution of radon progeny throughout the entire region of interest. Knowing the concentration gradient near the surface, a local mass-transfer coefficient (the deposition velocity) can be determined as a function of environmental conditions. RADTRAN simulations have been based on several flow conditions: buoyancy-driven recirculating enclosure flows, free and forced-convection boundary layer flows, and one-dimensional diffusion. Free progeny diffusivity, D^f, and attachment rate, X, were varied over representative ranges. For these conditions, RADTRAN calculated free deposition velocities of u^f = 0.014–0.079 cm s⁻¹, for ²¹⁸Po. RADTRAN predictions are compared to a range of experimental measurements. It was found that the predicted range of deposition velocities is in rough agreement with findings from experiments conducted in flow conditions similar to the simplified flows used in RADTRAN.     

Distribution and accumulation of heavy metals in Avicennia marina community in Shenzhen,China

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Geochemical fractionation and potential release behaviour of heavy metals in lead‒zinc smelting soils

The lack of understanding of heavy metal speciation and solubility control mechanisms in smelting soils limits the effective pollution control. In this study smelting soils were investigated by an advanced mineralogical analysis (AMICS), leaching tests and thermodynamic modelling. The aims were to identify the partitioning and release behaviour of Pb, Zn, Cd and As. The integration of multiple techniques was necessary and displayed coherent results. In addition to the residual fraction, Pb and Zn were predominantly associated with reducible fractions, and As primarily existed as the crystalline iron oxide-bound fractions. AMICS quantitative analysis further confirmed that Fe oxyhydroxides were the common dominant phase for As, Cd, Pb and Zn. In addition, a metal arsenate (paulmooreite) was an important mineral host for Pb and As. The pH-stat leaching indicted that the release of Pb, Zn and Cd increased towards low pH values while release of As increased towards high pH values. The separate leaching schemes were associated with the geochemical behaviour under the control of minerals and were confirmed by thermodynamic modelling. PHREEQC calculations suggested that the formation of arsenate minerals (schultenite, mimetite and koritnigite) and the binding to Fe oxyhydroxides synchronously controlled the release of Pb, Zn, Cd and As. Our results emphasized the governing role of Fe oxyhydroxides and secondary insoluble minerals in natural attenuation of heavy metals, which provides a novelty strategy for the stabilization of multi-metals in smelting sites.     

The CALGRID mesoscale photochemical grid model—I. Model formulation

A new photochemical oxidant model, CALGRID, has been developed for regulatory assessments of ozone control strategies. The model features: low numerical diffusion transport schemes that explicitly conserve mass on a terrain following mesh; modern boundary-layer representations converted to K-theory and applied to a variety of both fixed level and space-time variable vertical meshes; the ability to switch chemical schemes easily among the SAPRC hierarchy; a comprehensive resistance-based, dry deposition algorithm; and a highly-modular, streamlined FORTRAN 77 code that is highly vectorized and easily adapted to emerging parallel processor technology. The model is controlled by an easy to modify, self-documenting “control file” which also enables many consistency checks and serves to protect against a number of simple, yet common, simulation errors. The paper describes each of the model's principal technical modules in detail.     

Distribution and accumulation of heavy metals in A vicennia marina communi ty in Shenzhen，China

This paper deals with the absorption,accumulation and distribution of several heavy metals in Avicennia marina community at Futian Nature Reserve in Shenzhen。China．The results showed that：(1)the contents of Cu,Ph,Zn,Cd,Cr,Ni and Mn in the topsoil(O---30cm in depth)were 38．3,28．7,11．4,0．136,7 97,25．0 and 537 μg/g respectively;(2)there were significant differences in the contents of heavy metals in different fractions of Avicennia marina,and the content ranges were 1．8—13．8 for Cu,0．4—3．51 for Pb;3．4—69．5 for Zn,0．013—0．295 for Cd,0．28—0．73 for Cr,0．43—7．65 for Ni and 25一1552 μg/g for Mn;(3)The enrichment coefficient (weighted mean) of the plants to topsoil was Cd>Mn>Zn>Cu>Ni=Cr>Pb;(4)the accumulation amounts of seven elements in standing biomass of this community were 53．70,19．27,187．89,0．72,6．06,20．76 and 1631．17 mg/m² for Cu,Pb,Zn,Cd,Cr,Ni and Mn respectively．The net retention amount in the community(1993)were 4．06,1．32,16．36,1．43,107．98 rag/(m²．a)for Cu,Pb,Zn,Ni and Mn,60．21 and 431．8Oμg／(m²．a)for Cd and Cr respectively;(5)the potential amounts of the elements which existed in the residues of soil surface in the community were 2．09,1．96,5．05,1．54 and 405．54 mg／m²for Cu,Pb,Zn,Ni and Mn,and which of Cd and Cr were 19．30 and 78．00 μg/m²,respectively．     

Use of Azotobacter sp.as an indicator to detect the toxicity of heavy metals in soils

A physiological strain of microorganism - Azotobacter sp. has been adopted as an indicator to detect the toxicity of heavy metals in soils. The concentration of heavy metals to which Azotobacter sp. was behaving initially to have the resistance to heavy metals is defined as the critical poisoning concentration. The method of physiological threshold adopted can have a quantitative determination with reproducible results. The determined critical poisoning concentration is basically consistent with the results of heavy metals and arsenic toxicities to the bacteria reported recently in literatures. Total 9 typical soils, including 6 zonal soils and 3 purple soils, in the whole country were determined for the toxicities of 5 heavy metals and arsenic to Azotobacter sp. that resulted in 48 critical poisoning concentrations.     

Chemodynamics of heavy metals in long-term contaminated soils：Metal speciation in soil solution

The concentration and speciation of heavy metals in soil solution isolated from long-term contaminated soils were investigated. Thesoil solution was extracted at 70% maximum water holding capacity (MWHC) after equilibration for 24 h. The free metal concentrations(Cd2+, Cu2+, Pb2+, and Zn2+) in soil solution were determined using the Donnan membrane technique (DMT). Initially the DMT wasvalidated using artificial solutions where the percentage of free metal ions were significantly correlated with the percentages predictedusing MINTEQA2. However, there was a significant difference between the absolute free ion concentrations predicted by MINTEQA2and the values determined by the DMT. This was due to the significant metal adsorption onto the cation exchange membrane used inthe DMT with 20%, 28%, 44%, and 8% mass loss of the initial total concentration of Cd, Cu, Pb, and Zn in solution, respectively.This could result in a significant error in the determination of free metal ions when using DMT if no allowance for membrane cationadsorption was made. Relative to the total soluble metal concentrations the amounts of free Cd2+ (3%–52%) and Zn2+ (11%–72%) insoil solutions were generally higher than those of Cu2+ (0.2%–30%) and Pb2+ (0.6%–10%). Among the key soil solution properties,dissolved heavy metal concentrations were the most significant factor governing free metal ion concentrations. Soil solution pH showedonly a weak relationship with free metal ion partitioning coefficients (Kp) and dissolved organic carbon did not show any significantinfluence on Kp.     

A computational model for the rise and dispersion of wind-blown,buoyancy-driven plumes—I. Neutrally stratified atmosphere

A multi-dimensional computational model for the rise and dispersion of a wind-blown, buoyancy-driven plume in a calm, neutrally stratified atmosphere is presented. Lagrangian numerical techniques, based on the extension of the vortex method to variable density flows, are used to solve the governing equations. The plume rise trajectory and the dispersion of its material in the crosswind plane are predicted. It is found that the computed trajectory agrees well with the two-thirds power law of a buoyancy-dominated plume, modified to include the effect of the initial plume size. The effect of small-scale atmospheric turbulence, modeled in terms of eddy viscosity, on the plume trajectory is found to be negligible. For all values of buoyancy Reynolds number, the plume cross-section exhibits a kidney-shaped pattern, as observed in laboratory and field experiments. This pattern is due to the formation of two counter-rotating vortices which develop as baroclinically generated vorticity rolls up on both sides of the plume cross-section. Results show that the plume rise can be described in terms of three distinct stages: a short acceleration stage, a long double-vortex stage, and a breakup stage. The induced velocity field and engulfment are dominated by the two large vortices. The effect of a flat terrain on the plume trajectory and dispersion is found to be very small. The equivalent radii of plumes with different initial cross-sectional aspect ratios increase at almost the same rate. A large aspect-ratio plume rises slower initially and then catches up with smaller aspect-ratio plumes in the breakup stage. The Boussinesq approximation is found to be valid if the ratio of the density perturation to the reference density is less than 0.1.     

Estimation of pollutant concentrations in the atmosphere by measuring corrosion rates of several metals—I. Correlation between reflectance of each exposed metal and elongation of exposed rubber up to the break point

The atmospheric corrosion rates of several metals depend on the concentration of air pollutants. This premise was used to estimate the concentration of air pollutants. In this work, 12 metals and three rubber bands were exposed in 21 locations on the Osaka Plain and its surroundings for a month (July 1991) when ozone concentration on the plain was at a maximum. The correlation between the damage to the exposed rubber sample and the change of the color reflectance of the exposed metals was examined. The metals for which the obtained correlation coefficients were larger than about 0.80 were Ag, Al, Cd, Fe, Ni, Pb and Ti. In these metals, the types of surface coating Ag and Cu accorded with the results of a former investigation (Ag₂O(blue) and patinas(red)). Other metals showed as PbSO₄(green) in Pb, NiO(dark green) in Ne, FeSO₄(green) and Fe₂O₃(red) in Fe.     

Simulation of the energy budget of an urban canyon—I. Model structure and sensitivity test

This paper presents the formulation and results of a simple numerical model designed to simulate the climate of an urban canyon. The model is two-dimensional in nature and is based on the observation that ambient airflow which tranverses the long-axis of a symmetrical canyon drives a circulating vortex within the canyon air space which results in the exchange of heat, mass and momentum at the canyon top. A simple model is described which consists of two components: a semi-empirical model to relate within-canyon airflow to ambient wind velocity, and an energy budget model for canyon surfaces. The model is capable of simulating many aspects of the canyon climate, including the canyon surface and top energy budget and surface and air temperatures. Sensitivity tests with the model indicate that the canyon top energy budget is remarkably stable for many changes in canyon parameters. Canyon geometry (expressed as a height/width ratio) caused the greatest changes with increased narrowness being associated with less heat exchange across the canyon top. The model's predictions appear intuitively reasonable and compare well with existing measurement data. The results suggest that the coupling between the urban boundary and canopy layers in terms of heat exchange may be a function of canyon geometry.     

Biogenic and anthropogenic organic compounds in eolian particulates in the East Mediterranean region—I. Occurrence and origin

Lipids of biogenic and anthropogenic origin were determined in aerosol samples, collected seasonally, in a coastal area on the north of the island of Crete. Lipid classes such as n-alkanes, hopanes, polycyclic aromatic hydrocarbons, fatty alcohols, fatty acids, fatty acid salts and α,ω-dicarboxylic acids were characterized by GC/MS and GC/FID analysis, in terms of their contents of homologous compound series. The concentrations ranged between 56 and 215 ng m⁻³ for n-alkanes, 10 and 52 ng m⁻³ for polycyclic aromatic hydrocarbons, 2 and 31 ng m⁻³ for fatty alcohols, 13 and 279 ng m⁻³ for fatty acids, 24 and 220 ng m⁻³ for fatty acid salts and 0.4 and 7.5 ng m⁻³ for α, ω-dicarboxylic acid salts. The prevailing winds were influencing the composition of the eolian particles. Generally, aerosols sampled during south wind events predominantly contained lipids originating from higher plants, while when north and northwest winds prevailed the major components were of marine origin. The absence of unsaturated fatty acids in all aerosol samples is related to the presence of α,ω-dicarboxylic acids, which are believed to be their photo-oxidation products.     

GMO and sustainable development in less favoured regions—the need for alternative paths of development

The risk assessment for new technologies, like the use of GMO in the agricultural production, becomes enormously complex. It cannot be limited to purely natural–scientific analysis. Socio-economic factors need to be considered as well. The active promotion of GMO-free areas is discussed as a means for an alternative path of development. Economically less favoured and at the same time ecologically sensitive areas are suitable for the territorial application of this concept. The state of discussion on the influences of the agricultural use of GMO on the regional development of less favoured and ecologically sensitive regions is presented. The social acceptance of GMO-free areas was tested in a survey, which was conducted in 1999 in Austria. The results suggest that the idea is worth being pursued. A case study for local application is presented: GMO-free areas as part of a biosphere park stimulate economically sustainable endogenous development.     

Heavy metals in surface sediments from Minjiang Esturary—Mazu and Xiamen—Jinmen sea areas

The concentrations of Cu,Pb, Zn and Cd in surface sediments from Minjang Estuary-Mazu and Ziamen-Jinmen sea areas of China were investigated during 1995-1996.The concentration ranges of Cu,Pb ,Zn and Cd in the Minjiang Estuary-Mazu sea area were 16.4-37.2,33.4-69.6,92.1-128,0.087-0.036mg/kg(dry wt.),respectively; those for Xiamen-Jinmen sea area were 11.0-24.5,36.0-80.3,77.5-161,0.135-0.285mg/kg(dry wt.), respectively.The concentration and distributions of Cu,Pb,Zn and Cd in surface sediments of Minjiang Estuary-Mazu and Xiamen-Jinmen sea areas were analyzed and evaluated.The results showed that the values of Zn and Pb exceeded those of sediment quality criteria.The average concentration of Cu in Minjiang Estuary-Mazu sea area was higher than that in Xiamen-Jinmen sea area.The obviously higher concentrations of Cu,Pb, Zn and Cd were found at outlets of Minjiang and Jiulong River.From the estuaries to open sea, the concentrations of Cu, Pb,Zn and Cd had a decreasing trend, and then elevated in the sea areas near Mazu and Jinmen, suggesting that Cu,Pb,Zn and Cd in Minjiang Estuary-Mazu and Xiamen-Jinmen sea areas may come from both the mainland and Taiwan of China.     

Levels of airborne man-made mineral fibres in U.K. dwellings. I—Fibre levels during and after installation of insulation

This paper gives the details of airborne levels of man-made mineral fibres (MMMF) found during installation of loft insulation in 12 dwellings. About 250 samples of air were collected and analyzed by transmission electron microscopy (TEM).Respirable fibre levels measured in static samples collected in the lofts during installation generally were < 0.1 f ml⁻¹. In living spaces respirable fibre levels were< 0.006 f ml⁻¹. Personal samples on the installers gave < 1 f ml⁻¹, with the exception of a fine glass fibre blanket. A few selected samples were also analyzed by phase contrast optical microscopy (PCOM) which showed lower values than those recorded by TEM. Static gravimetric concentrations in the lofts were in the 0.3–6.5 mg m⁻³ range, and in the living spaces 0.11–0.44 mg m⁻³, but in both environments most of this dust was not MMMF.     

Integration of chemical fractionation, Mössbauer spectrometry, and magnetic methods for identification of Fe phases bonding heavy metals in street dust

Street dust is one of the most important carriers of heavy metals (HMs) originating from natural and anthropogenic sources. The main purpose of the work was to identify which of Fe-bearing phases bind HMs in street dust. Magnetic parameters of the Fe-bearing components, mainly magnetically strong iron oxides, are used to assess the level of HM pollution. Chemical sequential extraction combined with magnetic methods (magnetic susceptibility, magnetization, remanent magnetization) allowed determining the metal-bearing fractions and identifying the iron forms that are mostly associated with traffic-related HMs. The use of Mössbauer spectrometry (MS) supplemented by magnetic methods (thermomagnetic curves and psarameters of hysteresis loops) enabled precise identification and characterization of iron-containing minerals. The classification of HMs into five chemical fractions differing in mobility and bioaccessibility revealed that iron is most abundant (over 95%) in the residual fraction followed by the reducible fraction. HMs were present in reducible fraction in the following order: Pb>Zn>Mn>Cr>Ni>Fe>Cu, while they bound to the residual fraction in the following order: Fe>Ni>Cr>Mn>Pb>Cu>Zn. The signature of the anthropogenic origin of street dust is the presence of strongly nonstoichiometric and defected grains of magnetite and their porous surface. Magnetite also occurs as an admixture with maghemite, and with a significant proportion of hematite. A distinctive feature of street dust is the presence of metallic iron and iron carbides. Magnetic methods are efficient in the screening test to determine the level of HM pollution, while MS helps to identify the iron-bearing minerals through the detection of iron.     

A two-dimensional mesoscale numerical model of an urban mixed layer—I. Model formulation,surface energy budget,and mixed layer dynamics

A two-dimensional, numerical urban mixed layer model, which takes into account differences between the urban and the rural surfaces, as well as roughness and topographical variations over the model domain, is developed. The various land use types over the metropolitan area are specified by different proportions of concrete and grassy soil surfaces. Thermal characteristics of the vegetated soil surface are parameterized in terms of the surface soil moisture content. Distinct differences in the diurnal patterns of urban and rural surface energy budgets, which are found in some observational studies, are also obtained in some of our model case studies. Dynamics of the dome-shaped urban mixed layer is studied for the case of the stationary balanced wind. The balanced wind flow simulation can explain some of the important flow perturbations due to the urban heat island and increased roughness of the urban area.     

Landscape ecolgical assessment and eco—tourism development in the South Dongting Lake Wetland,China

As an important resource and the living enivronment of mankind,wetland has become gradually a highlight ,strongly concerned and intensively studied by scientists and sociologists.The governmetns in the world and the whole society have been paying more and more attention on it.The Dongting Lake of China is regarded as an internationally important wetland.For a rational development and protection of the wetland,an investigation and studied on its resources and its value to tourism in the South Dongting Lake was conducted,to create an assessment system of the ecological landscapes,and to evaluate qualitatively and quantitatively the value of wetland landscape to the eco-tourism.The results showed that the scenic value of the South Dongting Lake Wetland satisfied the criterion of AAAA grade of China national scenic attraction.The eco-tourism value of the landscape cultures in the South Dongting Lake Wetland was discussed with emphasis.It were formulated that a principle and frame of sustainable exploitation of the wetland landscapes and it was proposed as well that establishing a Wetland Park and developing eco-tourism in the South Dongting Lake .Wetland is a fragile ecosystem with low resistance to the impact of the exploitation.Thus,we must pay intensively attention to the influence of exploitation on the landscape,take the ecological risk in account to employ a right countermeasure and avoid the negative affection.     

Volatilization of volatile organic compounds from showers—I. Analytical method and quantitative assessment

To provide data to test mathematical models developed to predict human exposure to Volatile Organic Compounds (VOCs) volatilizing from showers, an analytical method was developed to analyze the simultaneous volatilization of VOCs in the water and humid air of showers. Five VOCs with a wide range of Henry's law constants were used. Experiments, conducted in a full-scale shower, were performed at initial water concentrations nearing tap water VOC concentrations (a few μgλ⁻¹). VOCs in water and humid air samples were concentrated by purge-and-trap, thermally desorbed from a Tenax trap and analyzed with a gas chromatograph-electron capture detector. The fraction of the VOCs volatilized from showers at various water temperatures and flow rates were calculated. Mass-balane equations indicated the presence of sinks of VOCs in the experimental shower other than those due to the airflow. An experimental method to measure the residence time of the water in the shower is presented.     

Aerosol formation and growth in atmospheric organic/NOχ systems—I. Outdoor smog chamber studies of C7- and C8-hydrocarbons

Outdoor smog chamber experiments have been performed to determine the aerosol-forming potential of selected C₇- and C₈-hydrocarbons in sunlight-irradiated hydrocarbon-NO_χ mixtures. Measured aerosol size distributions were used to determine the rates of gas-to-particle conversion and to study the effects of the addition of SO₂ and/or NH₃ on aerosol formation and growth. The average aerosol yields by mass for the hydrocarbons studied were (the range of measured values for methylcyclohexane and 1-octene are in parentheses):

• •methylcyclohexane 9.2% (0.12–18.8);
• •1-octene 4.2% (0.17–6.9);
• •toluene 18.6%;
• •n-octane <0.001%.

The average yields are accompanied by large standard deviations (see Table 3) and depended strongly on the conditions, particularly the hydrocarbon to NO_χ initial concentration ratio. Addition of SO₂ to the organic/NO_χ systems led to an early nucleation burst and subsequent rapid growth of the newly formed aerosol. In the presence of NH₃, the gas-to-particle conversion rate of the organic/NO_χ system was enhanced perhaps due to the formation of NH₄NO₃ or the reaction of NH₃ with carboxylic acids. Sustained particle formation was observed when both SO₂ and NH₃ were present, presumably as a result of (NH₄)₂SO₄ formation. We have estimated the complexity of the 1-octene aerosol and identified 5-propyl furanone as a component of the aerosol.