Subgrid-Scale Modeling of Reacting Scalar Fluxes in Large-Eddy Simulations of Atmospheric Boundary Layers

In large-eddy simulations of atmospheric boundary layer turbulence, the lumped coefficient in the eddy-diffusion subgrid-scale (SGS) model is known to depend on scale for the case of inert scalars. This scale dependence is predominant near the surface. In this paper, a scale-dependent dynamic SGS model for the turbulent transport of reacting scalars is implemented in large-eddy simulations of a neutral boundary layer. Since the model coefficient is computed dynamically from the dynamics of the resolved scales, the simulations are free from any parameter tuning. A set of chemical cases representative of various turbulent reacting flow regimes is examined. The reactants are involved in a first-order reaction and are injected in the atmospheric boundary layer with a constant and uniform surface flux. Emphasis is placed on studying the combined effects of resolution and chemical regime on the performance of the SGS model. Simulations with the scale-dependent dynamic model yield the expected trends of the coefficients as function of resolution, position in the flow and chemical regime, leading to resolution-independent turbulent reactant fluxes.     

Nitrate reductase for nitrate analysis in water

Nitrate analysis in water is one of the most frequently applied methods in environmental chemistry. Current methods for nitrate are generally based on toxic substances. Here, we show that a viable alternative method is to use the enzyme nitrate reductase. The key to applying this Green Chemistry solution for nitrate analysis is plentiful, inexpensive, analytical grade enzyme. We demonstrate that recombinant Arabidopsis nitrate reductase, expressed in the methylotrophic yeast Pichia pastoris, is a highly effective catalyst for nitrate analysis at 37°C. Recombinant production of enzyme ensures consistent quality and provides means to meet the needs of environmental chemistry.     

Chromium speciation in the blood of metal-on-metal hip implant patients

The objective of this study was to determine the valence state of chromium (Cr) in the blood of individuals with Cr-containing metal hip implants. Serum and red blood cell (RBC) Cr concentrations from 52 patients with Cr-containing total hip arthroplasties were measured preoperatively and at 3, 12, and 24 months postoperatively. Geometric mean and median pre-surgery serum Cr concentrations were consistently below 0.2 µg/L, while geometric mean and median pre-op RBC Cr concentrations were typically about four- to six-fold higher than the serum values. A significant 5- to 13-fold increase was found in the mean and median serum Cr concentrations three months post-surgery, with an 8- to 18-fold rise at 12 and 24 months, respectively. Steady-state serum concentrations were reached between 3 and 12 months. In contrast, there were no marked differences in mean and median RBC Cr concentrations pre- and post-surgery. Slope regression analysis for our data was similar to those reported for Cr(III) in spiked blood samples. The analysis showed that Cr released from hip implants preferentially distributed into serum and not RBC, indicating that the form of Cr present in blood of hip implant patients was in the form of non-toxic Cr(III). Our findings indicate that blood Cr concentrations Cr(III) associated with metal implants do not pose an adverse health risk to patients, which is in agreement with findings published by most investigators.     

根系分泌物对土壤重金属活化及其机理研究进展

植物通过调节根分泌物的组成来改变根际状态以适应外界环境。在重金属胁迫下,植物根系分泌物种类和量会发生显著变化。根系分泌物可通过溶解、螯合、还原等作用活化土壤重金属,提高重金属的植物有效性,或固定和钝化重金属,降低重金属的移动性。文章就根系分泌物对土壤重金属形态、有效性及其在重金属吸附解吸中的作用,根系分泌物活化土壤重金属的影响因素等国内外研究进展作了综述,并对该领域今后的研究方向进行了探讨。     

外来入侵植物化感作用与土壤相互关系研究进展

文章以全球普遍关注的外来植物入侵为背景,综述了外来入侵植物化感物质与土壤化学性质(土壤pH,土壤有机碳和有机质,土壤中的化学元素等)、土壤生物群落(土壤微生物、土壤动物)的关系。并探讨了未来研究需要加强的几个方面,包括将化感作用与野外实际情况相结合研究,更真实的反映田间状况;进一步探讨微生物在化感物质生物变化过程中的作用及其机理;化感物质作为信号物质如何影响微生物代谢,从而影响地上植物;深入研究化感作用与土壤之间的相互关系,为入侵植物生物防治的安全性提供理论指导等方面。     

Spatial patterns of tungsten and cobalt in surface dust of Fallon,Nevada

Spatial patterns of tungsten and cobalt are described for surface dust of Fallon, Nevada, where a cluster of childhood leukemia has been ongoing since 1997. In earlier research, airborne tungsten and cobalt was shown to be elevated in total suspended particulates in Fallon. To fine-tune the spatial patterns of tungsten and cobalt deposition in Fallon, surface dust was collected in a grid pattern within as well as outside of Fallon to establish background concentrations of metals. In surface dust, tungsten and cobalt show sharp peaks (934 ppm and 98 ppm, respectively) within Fallon just north of highway 50 and west of highway 95. These two peaks overlap spatially, and given the grid pattern used for collecting surface dust, the source area of these two airborne metals can be pinpointed to the vicinity of hard-metal industry located north of highway 50 and west of highway 95. Fallon is distinctive in west central Nevada because of high airborne tungsten and cobalt particulates, and given its cluster of childhood leukemia, it stands to reason that additional biomedical research is in order to test directly the leukogenicity of combined airborne tungsten and cobalt particulates.     

Development of a nonlocal convective mixing scheme with varying upward mixing rates for use in air quality and chemical transport models

BACKGROUND, AIM, AND SCOPE: Asymmetrical convective non-local scheme (CON) with varying upward mixing rates is developed for simulation of vertical turbulent mixing in the convective boundary layer in air quality and chemical transport models. MATERIALS AND METHODS: The upward mixing rate form the surface layer is parameterized using the sensible heat flux and the friction and convective velocities. Upward mixing rates varying with height are scaled with an amount of turbulent kinetic energy in layer, while the downward mixing rates are derived from mass conservation. RESULTS: This scheme provides a less rapid mass transport out of surface layer into other layers than other asymmetrical convective mixing schemes. DISCUSSION: In this paper, we studied the performance of a nonlocal convective mixing scheme with varying upward mixing in the atmospheric boundary layer and its impact on the concentration of pollutants calculated with chemical and air-quality models. This scheme was additionally compared versus a local eddy-diffusivity scheme (KSC). Simulated concentrations of NO(2) and the nitrate wet deposition by the CON scheme are closer to the observations when compared to those obtained from using the KSC scheme. CONCLUSIONS: Concentrations calculated with the CON scheme are in general higher and closer to the observations than those obtained by the KSC scheme (of the order of 15-20%). Nitrate wet deposition calculated with the CON scheme are in general higher and closer to the observations than those obtained by the KSC scheme. RECOMMENDATIONS AND PERSPECTIVES: To examine the performance of the scheme, simulated and measured concentrations of a pollutant (NO(2)) and nitrate wet deposition was compared for the year 2002. The comparison was made for the whole domain used in simulations performed by the chemical European Monitoring and Evaluation Programme Unified model (version UNI-ACID, rv2.0) where schemes were incorporated.     

污水处理中的恶臭对周边环境的污染及其治理

就污水处理厂运行过程中产生的臭气对周边环境产生的污染情况,针对臭气的治理方法,重点介绍了物理脱臭法、化学脱臭法、生物脱臭法的作用原理、工艺流程及设计参数。     

用煤矸石合成4A沸石分子筛处理氨氮废水

以煤矸石为原料,采用碱熔一水热法合成4A沸石分子筛。由于煤矸石中铝、硅主要以高岭土形式存在,其活化过程是合成4A沸石分子筛关键环节。为提高4A沸石分子筛钙离子的交换能力,增加对模拟废水氨氮的去除率,实验考察了碳酸钠与煤矸石质量比、活化温度、活化时间、晶化温度和晶化时间对4A沸石分子筛钙离子交换能力的影响,同时也考察了模拟废水的pH、4A沸石分子筛加入量及吸附时间对氨氮去除率的影响。结果表明,最佳工艺条件为,碳酸钠与煤矸石质量比为0．9、活化温度为800％、活化时间1．5h、晶化温度90％和晶化时间3h。合成4A沸石分子筛的钙离子交换能力为310mg／g,在pH为6的100mL模拟氨氮废水中加入6g4A沸石分子筛吸附40min后,废水中氨氮的去除率达到86％。通过最佳工艺条件合成4A沸石分子筛,在处理氨氮废水方面具有一定的应用前景。