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 speciation of heavy metals in sediments at Caijiawan region

Metals in different fractions in samples from surface sediments，cores，riverbank soil，islet soil and agricultural soil at Caijiawan were determined．The effect of particle size，density gradient on metal accumulation in sediments were studied．The chronology of core samples indicated that the pollution history corresponded to the development history of Dexing Copper Mine．     

Speciation and distribution characteristics of heavy metals in the Changjiang River water

ＳｐｅｃｉａｔｉｏｎａｎｄｄｉｓｔｒｉｂｕｔｉｏｎｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｈｅａｖｙｍｅｔａｌｓｉｎｔｈｅＣｈａｎｇｊｉａｎｇＲｉｖｅｒｗａｔｅｒ￥ＣｈｅｎＸｉｂａｏ；ＺｈａｎｇＳｈｅｎ；ＤｏｎｇＷｅｎｊｉａｎｇ；ＺｈａｎｇＬｉｃｈｅｎｇ（...     

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

ＤｉｓｔｒｉｂｕｔｉｏｎａｎｄａｃｃｕｍｕｌａｔｉｏｎｏｆｈｅａｖｙｍｅｔａｌｓｉｎＡｖｉｃｅｎｎｉａｍａｒｉｎａｃｏｍｍｕｎｉｔｙｉｎＳｈｅｎｚｈｅｎ，ＣｈｉｎａＬｉｎＰｅｎｇ，ＺｈｅｎｇＷｅｎｊｉａｎ，ＬｉＺｈｅｎｊｉＤｅｐａｒｔｍｅｎｔｏｆＢｉ...     

Background contents of heavy metals in sediments of theYangtze River system and their calculation methods

ＢａｃｋｇｒｏｕｎｄｃｏｎｔｅｎｔｓｏｆｈｅａｖｙｍｅｔａｌｓｉｎｓｅｄｉｍｅｎｔｓｏｆｔｈｅＹａｎｇｔｚｅＲｉｖｅｒｓｙｓｔｅｍａｎｄｔｈｅｉｒｃａｌｃｕｌａｔｉｏｎｍｅｔｈｏｄｓＺｈａｎｇＣｈａｏｓｈｅｎｇ，ＺｈａｎｇＳｈｅｎ，ＺｈａｎｇＬｉｃｈ...     

The chemical stability of heavy metals in a natural water system

A comprehensive investigation of heavy metal pollutants in Xiangjiang river was accomplished to evaluate their chemical stability through three different ways: (1) Chemical speciation by direct measurements; (2) Chemical equilibrium model simulation; (3) Sediment extraction experiments. All the results demonstrated that the directly bioavailable fraction was in a very limited amount. The metal bound to organic ligands, adsorbed particles and precipitated species presented a buffer for solution species. The majority of metals occured in the residues as solid particulates. It was inferred that the heavy metal pollutants in this aquatic system exhibited a high chemical stability. The critical limits of discharging load and pH values were suggested.     

A survey of arsenic and other heavy metals in vegetation from markets or mine tailings

This research includes two investigations. The first one is a market basket survey of the levels of arsenic （As） and trace elements in bracken fern （Pteridium aquilinum） originated from three countries： South Korea, China and North Korea. The results showed that the mean As concentrations in stems of samples were significantly higher than those in leaves. As concentrations in all samples did not exceed food safety limits for vegetables. Generally, concentrations of Fe, Mn, Cu and Zn in leaves were higher than those in stems. The second investigation is a survey on the levels of As and other heavy metals in vegetation in the vicinity of Myoungbong mine tailings. The results demonstrated that As, Pb and Cu concentrations and bioaccumulation factors （BCF） in seedlings of the fern（A splenium achilleifolium） were the highest, whereas Marsh horsetail（Equisetum polustre） accumulated the highest levels of Zn. Concentrations of As, Pb, Zn and Cu in vegetable-cress （Lepidium sativum） and the edible herb-aromatic madder （Elasholtzia splendens） were higher than food safety limits. Therefore, a risk assessment of As and other heavy metals in vegetables and herbs on local human health should be conducted in the future.     

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．     

Removal of heavy metals from sewage sludge by low costing chemical method and recycling in agriculture

ＲｅｍｏｖａｌｏｆｈｅａｖｙｍｅｔａｌｓｆｒｏｍｓｅｗａｇｅｓｌｕｄｇｅｂｙｌｏｗｃｏｓｔｉｎｇｃｈｅｍｉｃａｌｍｅｔｈｏｄａｎｄｒｅｃｙｃｌｉｎｇｉｎａｇｒｉｃｕｌｔｕｒｅＷｕＱｉｔａｎｇ，ＮｙｉｒａｎｄｅｇｅＰａｓｃａｓｉｅ，ＭｏＣｅｈｕｉＦ...     

Distribution of heavy metals in the Grand Canal (Hangzhou section) and its contributing factors

ＤｉｓｔｒｉｂｕｔｉｏｎｏｆｈｅａｖｙｍｅｔａｌｓｉｎｔｈｅＧｒａｎｄＣａｎａｌ（Ｈａｎｇｚｈｏｕｓｅｃｔｉｏｎ）ａｎｄｉｔｓｃｏｎｔｒｉｂｕｔｉｎｇｆａｃｔｏｒｓＷｅｎｇＨｕａｎｘｉｎ，ＺｈａｎｇＤｅｎｇｒｏｎｇＤｅｐａｒｔｍｅｎｔｏｆＥａｒｔｈ...     

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. The soil 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 was validated using artificial solutions where the percentage of free metal ions were significantly correlated with the percentages predicted using MINTEQA2. However, there was a significant difference between the absolute free ion concentrations predicted by MINTEQA2 and the values determined by the DMT. This was due to the significant metal adsorption onto the cation exchange membrane used in the 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 cation adsorption was made. Relative to the total soluble metal concentrations the amounts of free Cd2+ (3%–52%) and Zn2+ (11%–72%) in soil 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 showed only a weak relationship with free metal ion partitioning coefficients (Kp) and dissolved organic carbon did not show any significant influence 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.     

Selective removal of heavy metals by Zr-based MOFs in wastewater: New acid and amino functionalization strategy

Zr-based metal-organic frameworks(MOFs) have been developed in recent years to treat heavy metals,e.g.hexavalent chromium Cr⁶⁺ pollution,which damages the surrounding ecosystem and threaten human health.This kind of MOF is stable and convenient to prepare,but has the disadvantage of low adsorption capacity,limiting its wide application.To this end,a novel formic acid and amino modified MOFs were prepared,referred to as FormUiO-66-NH₂.Due to the modification of formic acid,i...     

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.     

Major environmental and ecotoxicological processes of heavy metals in Lean River polluted by discharges from mining activities

１　ＩｎｔｒｏｄｕｃｔｉｏｎＣｈｉｎａｉｓｕｎｄｅｒｇｏｉｎｇｓｕｂｓｔａｎｔｉａｌａｎｄｒａｐｉｄｃｈａｎｇｅｓｉｎｉｔｓｓｏｃｉｅｔｙａｎｄｉｔｓｅｃｏｎｏｍｉｃｐｏｌｉｃｉｅｓ．Ａｍｏｎｇｖａｒｉｏｕｓｅｎｖｉｒｏｎｍｅｎｔａｌｐｒｏｂｌｅｍｓ，ｗａｔｅｒｐｏｌｌｕｔｉｏｎｉｓｏｎｅｏｆｔｈｅｍｏｓｔｃｒｉｔｉｃａｌｉｓｓｕｅｓｆａｃｉｎｇＣｈｉｎａｔｏｄａｙ．Ｔｈｅｓｅｐｏｌｌｕｔａｎｔｓｐｏｉｓｏｎａｑｕａｔｉｃｏｒｇａｎｉｓｍｓａｎｄａｃｃｕｍｕｌａｔｅｉｎｆｉｓｈａｎｄｏｔｈｅｒｅ…     

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.     

Concentration level of heavy metals in the Great Wall Bay, Antarctica in austral summer

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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.