An application of the theory of kinematics of mixing to the study of tropospheric dispersion

The most common technique used for numerical simulations of tracer mixing is that of the numerical solution of the advection–diffusion equation with the unresolved fluxes parameterized using the similarity theory. Despite correct predictions of the overall directions of transport, models based on a numerical solution of the advection–diffusion equation lack sufficient accuracy to correctly reproduce the coupling of mixing with small scale processes which are sensitive to the microstructure of the tracer distribution. The objective of this paper is to revisit the basic formalism employed in numerical models used to investigate atmospheric tracers. The main mathematical method proposed here is the theory of kinematics of mixing which could be applied effectively for simulations of atmospheric transport processes. At the beginning of the paper, we introduce simple mathematical transformations in order to demonstrate how complex topological structures are created by mixing processes. These idealistic flow systems are essential to explain transport properties of much more complex three-dimensional geophysical flows. An example of the application of the kinematics of mixing to the analysis of tracer transport on a planetary scale is presented in the following sections. The complex filamentary structures simulated in the numerical experiment are evaluated using some commonly applied statistical measures in order to compare the results with the data published in the literature. The results of the experiment are also analysed with the help of simple conceptual models of fluid filaments. The microstructure of the tracer distribution introduced in the paper is essential to increase our understanding of atmospheric transport and to develop more realistic parameterizations of small-scale mixing. The presented results could also be used to improve calculations of the coupling between microphysical processes and tracer mixing.     

Investigation of the characteristics of the reflectivity of clouds

This paper investigates some of the reflectivity characteristics that clouds (when modelled as solid bodies) must exhibit to be compatible with observations that the reflecting surface of a cloud (i) appears almost equally bright across its face, (ii) is brightest when the cloud is opposite to the Sun but decreases in brightness as the cloud moves to other positions and (iii) increases in brightness with increasing optical thickness of the cloud in the observer's line of sight. These observations, respectively, are shown to imply that the peak value of the bidirectional total reflectivity from a cloud surface (i) increases in inverse proportion to the cosine of the angle between the Sun and the normal to the cloud surface, as the incident angle increases, (ii) appears to be directed back in the direction of the incident radiation, and (iii) increases as optical thickness of the cloud in the observer's line of sight increases. The results could have application in many fields (e.g. modelling diffuse radiance distributions for cloudy skies).     

Optimization of Height of Release of Air Pollutants

A number of key projects in the Environmental Protection Agency (EPA) particulate R&;D program having applicability to industry are presented. For electrostatic precipitators (ESP) there is presented the result of work on large diameter discharge electrodes which provide a decrease in penetration of up to a factor of 4 when compared to conventional small diameter electrodes. Also discussed is the multistage ESP which provides a collection efficiency that would require a collecting plate area 4 or 5 times larger with conventional ESP technology. The E-SOX technology makes use of the multistage concept to free up space in the ESP for SO₂ removals of up to 90%. Electrostatically augmented fabric filtration provides a reduction in pressure drop of about 5 0% as compared to conventional fabric filtration. Wind tunnel modeling of windbreaks for material storage piles indicates a potential for providing engineering design data that would allow significant emission reduction caused by wind erosion     

Impact of overexploitation of shellfish: northeastern coast of India

India has a very extensive coastline of about 7515 km, rich in diverse living resources. These resources continue to deteriorate with rampant harvesting or are altered for other uses such as aquaculture and fisheries. The present paper deals with degrading coastal habitats in northeastern India, and projects the intensity of the stress arising from the collection of tiger prawn seeds (Penaeus monodon) for aquacultural farms and molluskan shells for poultry feed and edible lime. Indiscriminate exploitation of these resources leads to a heavy reduction of the species concerned and other associated marine communities. The magnitude of such destruction has been quantified. The impacts of biodiversity loss and their after-effects on the ecobalance of this coastal system have become a matter of great concern to ecologists to maintain security and sustainability. The authors propose a public awareness program on themes relating to the importance of biodiversity for human livelihoods.     

Considerations of uncertainty in setting critical loads of acidity of soils: the role of weathering rate determination

The concept of critical loads has been generally accepted throughout Europe, and increasingly in Asian countries and the rest of the world, as providing the data which forms the basis for international negotiations on abatement strategies for emissions of acidifying pollutants. Central to the determination of quantitative critical loads of acidity for forests (and other ecosystems) is the rate at which the minerals in the soil weather or dissolve. Seven methods for determining these rates on a regional basis for the production of critical load maps have been suggested by the official bodies which are responsible for co-ordinating the European critical load mapping efforts. These methods are largely correlations which require a knowledge of the soil parent material and/or the soil mineralogy. The purpose of this paper is to review these weathering rate calculation methods and to assess whether it is currently possible to calculate numerically accurate critical loads for the production of regional critical load maps. A consideration of the data used to generate these methods and comparisons of the weathering rates calculated using various methods leads to the conclusion that at present it is not. Further work is needed to develop and maintain the initial credibility of critical loads both scientifically and as an aid to policy decisions.     

阳宗海沉积物中重金属生物有效性评估

通过测定和分析阳宗海表层沉积物中酸可挥发性硫化物(AVS)和同步提取重金属(SEM)的含量和分布特征,采用SEM/AVS方法对阳宗海表层沉积物中重金属的生物有效性进行评估;同时,采用生物有效阈值法评估了单一重金属的生物有效性。研究得出以下结论:阳宗海表层沉积物中AVS含量为15.09~149.74 μmol/g,平均值为49.42 μmol/g,从南向北呈递减趋势;AVS在南部和中部均与湖泊水深呈现正相关关系;∑SEM(包括Cu、Cr、Pb、Zn、Mn、As、Cd)含量分布波动较小,其范围为4.84~16.10 μmol/g,平均值为10.28 μmol/g,其分布规律为北部大于南部;阳宗海各采样点SEM/AVS<1,说明阳宗海表层沉积物中重金属不会对生物产生不良影响;从单一重金属来看,Pb可能经常产生生物毒性,Cu有可能产生生物毒性,其他金属除部分点可能产生生物毒性外,整体上几乎不会产生生物毒性。     

Optical properties of aerosols of mixed composition

A model is developed which relates the reduction in visual air quality to the chemical and physical properties of airborne aerosol particles. The aerosols are considered to be inhomogeneous and to have a mixed chemical composition which varies with particle size. The water content of the aerosol particles is derived from a semi-empirical application of the thermodynamic equations for particle growth. The model is valid for all ranges of relative humidity.The light scattering and absorption coefficients are calculated using Mie theory extended to concentric sphere scatterers. The core of each particle, which is primarily taken to be nonvolatile carbon, is enclosed in a water-soluble exterior. The soluble layer responds to changes in the relative humidity by absorbing (or releasing) water. The model predictions are in excellent agreement with experimental measurements made in Denver in the fall of 1978.     

Distribution-free estimates of quantiles of the distribution of a contaminant in environmental media

This paper examines the use of order statistics to provide distribution-free point and confidence interval estimates of quantiles of the distribution of contaminants in environmental media. These procedures are straightforward to implement and are often unaffected by the presence of observations below the detection limit. This approach to the estimation of quantiles has been implemented in the determination of the Ontario typical range of chemical parameters in soil, vegetation, moss bags and snow. These distributions range from symmetric to highly skewed to the right, with zero to 100% of observations below the detection limit.     

Classification of chemicals according to mechanism of aquatic toxicity: an evaluation of the implementation of the Verhaar scheme in Toxtree

A number of mechanisms have been identified that can lead to (acute) aquatic toxicity. The assignment of compounds to a particular mechanism of action is important in the development and utilisation of (quantitative) structure-activity relationships ((Q)SARs) for ecotoxicity. Assignment to a mechanism can be difficult; however in 1992 Verhaar et al. published a series of structural rules which aimed to classify compounds according to mechanism of action. Recent interest has seen the Verhaar rules coded into freely available software such as Toxtree available from the European Chemicals Bureau. To date, a complete critical evaluation of these rules has been lacking. Therefore, the aim of this study was to evaluate the Toxtree implementation of the Verhaar rules using two well characterised aquatic toxicity datasets (Pimephales promelas and Tetrahymena pyriformis phenol databases) for which mechanisms of toxic action are well established. The present study highlights rule, and possible coding, errors that may lead to misclassifications. Improvements to both the rules and prediction architecture are suggested. In particular further rules to improve predictions for polar narcosis (class 2) are suggested.     

Analysis of global budgets of halocarbons

It is well known that analysis of global budgets of halocarbons can provide estimates of their atmospheric lifetimes. Furthermore, such analysis may yield information on the interhemispheric mixing rate. The release rates of anthropogenic halocarbons, the average global concentrations, the ratio of hemispherical averages and the rate of change of these ratios are the principal data base for such analysis. These global averaged quantities are derived from a data base of local measurements which may or may not be sufficient to provide global coverage. A generalized analysis allows one to test the consistency of measurements and the global average theory. The sensitivity of derived results for atmospheric lifetimes is shown and the technique for analysis is illustrated with applications to CFCl₃ and CH₃CCl₃. The lifetime analysis for CFCl₃ shows considerable sensitivity to uncertainties and variabilities in the data. Nevertheless these data are shown to be consistent with an average interhemispheric transport time of 1–2 years. The data for methylchloroform are shown to be consistent with an atmospheric lifetime of 11.3 years.     

Variability of enzyme system of Nocardioform bacteria as a basis of their metabolic activity

The present review describes some aspects of organization of biodegradative pathways of Nocardioform microorganisms, first of all, with respect to their ability to degrade aromatic compounds, mostly methylbenzoate, chlorosubstituted phenols, and chlorinated biphenyls and the intermediates of their transformation: 4-chlorobenzoate and para-hydroxybenzoate. Various enzyme systems induced during degradation processes are defined. The ability of microorganisms to induce a few key enzymes under the influence of xenobiotics is described. This ability may increase the biodegradative potential of strains allowing them to survive in the changing environment or demonstrate to some extent the unspecific response of microorganisms to the effect of toxicants. Nocardioform microorganisms responsible for degradation of such persistent compounds as polychlorinated biphenyls, polyaromatic hydrocarbons, chlorinated benzoates and phenols and other xenobiotics are characterized. The possibility of using Nocardioform microorganisms in some aspects of biotechnology due to their ability to produce some compounds important for industry is also estimated.     

河道底泥陶粒比表面测定

讨论了以河道底泥和生活污泥为原料烧制陶粒比表面的测定原理、方法和结果，并对生活污泥添加量、粘结刑添加量和烧结温度对陶粒比表面的影响作了进一步分析。     

Mercury accumulation in surface sediments of salt marshes of the Bay of Fundy

Mercury contamination in Canada's Bay of Fundy is a priority concern because of elevated levels observed in fish, birds and wildlife. Salt marshes constitute an important part of the Bay's coastline and are potential stores of mercury for the region. We measured the amount of mercury accumulated over a 5-yr period from 1997 to 2002 in surface sediments of seven salt marshes along the New Brunswick coast of the Bay. The seven study sites extended from outer to inner Bay, spanning a gradient in tidal range (6-12 m) and sediment characteristics such as %LOI (4-29%) and sediment deposition rate (0.27-1.76 cm yr(-1)). In each study site, mercury was measured in low and high marsh areas. Sediment mercury concentrations ranged from 7 to 79 ng g(-1) and loading rates ranged from 0.1 to 1.1 mg m(-2). Total estimated 5-yr storage of mercury in salt marsh sediments of the Bay is 854+/-465 kg. We also compared sediment mercury loading to atmospheric inputs measured at a deposition monitoring station operating in New Brunswick from 1997 to 2002 and found that direct atmospheric deposition appears to be a minor input of mercury to these sediments. We are unaware of documentation of mercury loading in salt marshes on a bay-wide scale and over a constrained (5-yr) time period elsewhere.     

温度对热水解预处理高含固污泥特性的影响

以含固率为10%的污泥为对象,研究不同温度和时间条件下热水解过程中有机物转化规律对污泥特性的影响。结果表明:随着热水解时间的延长和温度的升高,污泥中挥发性悬浮固体(VSS)的水解率逐渐升高。在热水解时间为20 min时,温度由150℃升高到180℃,VSS水解率由22.9%增至38.4%,污泥中VSS由46.28 g/L降低到40.63 g/L。水解液组分分析表明,溶解性化学需氧量(SCOD)主要组成为蛋白质(50%)、碳水化合物(15%~20%)、可挥发性脂肪酸(15%~20%)。水解液中氮主要以有机氮的形式存在。在热水解条件达到165℃、50 min时,氨氮浓度为1.16 g/L,之后,随着温度的升高和时间的延长,氨氮浓度基本不变。     

Effects of bensulfuron-methyl and cinosulfuron on growth of four freshwater species of phytoplankton

The acute toxicity of sulfonylurea herbicides bensulfuron-methyl and cinosulfuron was tested on the five species of freshwater phytoplankton: Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila. Herbicide concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 8 to 104 mg/l for cinosulfuron and from 0.015 to 6.2 mg/l for bensulfuron-methyl. The pesticides bensulfuron-methyl, atrazine and benthiocarb were more toxic than cinosulfuron, chlorsulfuron, molinate, fenitrothion and pyridaphenthion in a toxicity study with the same algal species. The transformation of effective concentrations of bensulfuron-methyl and cinosulfuron and other pesticides, obtained from toxicity measurements, into percent of the saturation level in water is used as a first evaluation of potential hazard to aquatic systems. The herbicides cinosulfuron, methyl-bensulfuron, atrazine and chlorsulfuron were more dangerous than the herbicides benthiocarb and molinate and than the insecticides fenitrothion and pyridaphenthion, in a study of hazard evaluation. The two species of Chlorella were more tolerant to both herbicides than the two species of Scenedesmus. A potential environmental hazard of sulfonylurea herbicides to aquatic systems has to be expected even at low environmental concentrations.     

Modulation of metabolic activity prevents degradation of sorbed toluene

The factors affecting the ability of a bacterial species to degrade different amounts of toluene (8.5 to 217 mg/g) sorbed to granular activated carbon (GAC), in an aqueous solution of mineral salts, were investigated. After 144 days the amounts of toluene remaining on one type of GAC ranged from 7.5 to 9.5 mg/g, and the aqueous concentrations of toluene ranged from 2 to 7 micrograms/L. Neither bacterial death nor an inhibition by accumulating by-products could explain why the remaining toluene had not been degraded. However, at these low concentrations of toluene, and probably because of cell starvation, bacteria were observed to be more than 100-times less efficient to degrade toluene than at high concentrations. We propose that this low degradation ability is responsible for the presence of residual toluene on the GAC, and that this mechanism may contribute to the persistence of low concentrations of sorbed pollutants in the environment.     

Characterization of products of ozonolysis of acrylonitrile in liquid phase

In order to elucidate the reaction mechanism of the ozonolysis of acrylonitrile in the liquid phase, characterization of reaction products has been attempted. One of the products, which was volatile, has been found to be formaldehyde by derivatizing with dimedone. The infrared and mass spectra of the derivative corresponded with that of alkylidene dimedone. Three other reaction products were isolated by TLC using silica gel, CHCl₃:MeOH (80:20). These have been tentatively identified as glyoxal, epoxide of acrylonitrile and acetamide from their mass spectra. Based on these findings a reaction pathway for the formation of formaldehyde is proposed to be that described by Criegee.     

Assessment of the environmental fate of linear alkylbenzenesulphonates

Fugacity models, as developed previously, are applied to the chemical linear alkylbenzenesulphonate (LAS) to predict its ultimate fate in the environment. The behaviour of LAS is illustrated using unit worlds or evaluative environments at three successive levels of complexity (Levels I, II, and III). LAS is shown to have a short environmental life of two days attributable to rapid biodegradation in water. Reported concentration data for LAS in Rapid Creek, South Dakota, downstream from a municipal sewage treatment plant, are compared to expected concentrations as generated by the QWASI (Quantitative Water Air Sediment Interaction) fugacity model; the model being based solely on the physical, chemical, reactivity and transport properties of LAS and the emission rate of the chemical into the river. The data are found to fit the model when a sediment-water mass transfer coefficient of 7.80 × 10⁻³ m/h and an effective sediment bed depth of 3 mm are used. The generally satisfying agreement between environmental observations and the QWASI fugacity models lends credibility to the use of evaluative models.     

双基质层绿化屋面的雨水水文水质特征分析

绿化屋面作为低冲击开发的常用措施之一,能有效削减暴雨径流、延缓产流时间,从而缓减城市市政管网的压力。但绿色屋面暴雨径流的水质特征依然存在很多不确定性。在天津市气候条件下,通过搭建不同厚度的“双基质层”绿化屋面小试实验装置开展人工降雨实验,着重研究分析了不同降雨条件下,绿化屋面的产流过程以及绿化屋面暴雨径流中污染物的平均出水浓度与吸附基质层厚度、降雨强度的关系。结果表明,产流阶段的产流速度与降雨总量无关,只与降雨强度有关,径流累积量与降雨强度无关,与填料层厚度和降雨总量有关;污染物径流平均浓度与吸附基质层厚度、降雨强度有关;绿色屋顶能够有效降低雨水的COD和浊度,且对酸雨有较好的中和作用。     

Application of ground-based Lidar for studies of the dynamics of ozone in a mountainous basin

A ground-based Differential Absorption Lidar was employed to study the dynamics of atmospheric O3 within the planetary boundary layer of a basin in the 'Fichtelgebirge' mountains, NE Bavaria. In particular, the night-time dynamics of O3 linked to the ground were investigated. The Lidar system measured vertical profiles of O3 up to 1 km above ground. For detailed analysis of the night-time dynamics of ozone, supplementary data from three ground-based stations (measuring mixing ratios of O3 and NO(x), as well as meteorological parameters) are essential. The Lidar results could be evaluated with these data from various altitudes above the basin floor. For the station with the largest (vertical) distance to the ground-based Lidar, the agreement was very good at all times. The Lidar method proved to be useful for examining the spatial distribution of O3. The observed night-time decrease of O3 at the bottom of the basin was due to deposition and to advection of air masses containing less O3 from the mountain slopes.