Gas-phase reaction of CCl2F2 (CFC-12) with methane

Gas-phase reaction of CFC-12 (CCl2F2) with methane was carried out in a plug flow reactor over the temperature range of 873-1123 K. The major organic halocarbons formed during the reaction were C2F4, C2H2F2, CHClF2, CH3Cl, C3H2F6 and CCl3F. The formation of all products except C2H2F2 decreased with temperature, while the selectivity to C2H2F2 (difluoroethylene) increased with temperature and reached approximately 80% at 1123 K. Under these reaction conditions, methane acts as hydrogen and carbon source, resulting in the formation of an unsaturated C2 hydrofluorocarbon from two C1 precursors.     

Mitigation of environmental problems in Lake Victoria, East Africa: causal chain and policy options analyses

Lake Victoria is an international waterbody that offers the riparian communities a large number of extremely important environmental services. Over the past three decades or so, the lake has come under increasing and considerable pressure from a variety of interlinked human activities such as overfishing, species introductions, industrial pollution, eutrophication, and sedimentation. In this paper we examine the root causes for overfishing and pollution in Lake Victoria and give possible policy options that can help remediate or mitigate the environmental degradation.     

难降解废水生物处理中的共代谢作用

综述了共代谢作用的机理、特点及研究现状，展望了共代谢在废水生物处理中的应用前景。     

人工神经网络和遗传算法在生物载体填料生产工艺中的应用

本文应用BP人工神经网络建立了生物流化床污水处理工艺中新型生物载体填料的生产工艺参数与填料磨损破碎率和松散容重之间的关系，并运用遗传算法对填料的生产工艺进行了优化。结果表明：填料的最佳生产工艺参数为：EVA含量14％；活性炭含量3．6％；胶粉粒度18.97目。此时，填料的磨损破碎率和松散容量均达到最优值，分别为0．358％和0．226kg／L。这一优化结果对生物载体填料的实际生产加工具有指导意义。     

Evaluation of filter-based aerosol measurements during the 1987 Southern California Air Quality Study

The Southern California Air Quality Study (SCAQS) was conducted during the summer and fall of 1987 to assess the causes of elevated ozone and suspended particulate matter concentrations in California's South Coast Air Basin (SoCAB). Extensive gaseous (i.e. nitric acid, ammonia, sulfur dioxide) and particle (i.e. PM_2.5 and PM₁₀ mass, elements, ions, carbon) measurements were acquired for 11 days during the summer at nine locations, and six days during the fall at six locations. Outliers were identified so that they could be excluded from further statistical analyses. Carbon and elemental measurements were found to be negatively biased by 20% owing to inhomogenous aerosol deposits on the SCAQS filters and analysis methods which were applied to a portion of the filters. These biases seem relatively consistent, however, and should not affect conclusions drawn from data analysis efforts if they are appropriately considered. Significant fractions (30–60%) of ammonium nitrate volatilized during the summer when temperatures were higher. Less than 10% typically volatilized during the fall when temperatures were lower. Anion/cation balances support the accuracy and precision estimates of the nitrate, sulfate, and ammonium measurements. Coarse particle sulfate was generally low, while coarse particle nitrate was most pronounced at the coastal sites.This paper documents SCAQS filter-based aerosol measurement methods, and evaluates the accuracy, precision, and validity of the data set. Various comparisons were made for: (1) PM_2.5/PM₁₀ ratios for mass and major chemical species; (2) sum of chemical species versus measured mass; (3) sulfate versus sulfur ratios; (4) PM_2.5 particulate nitrate versus nitric acid-denuded nitrate; and (5) anion/cation balances. The measurement and evaluation techniques presented in this paper serve as a guideline for other data analysis and modeling studies.     

Multi-component assessment of worker exposures in a copper refinery. Part 1. Environmental monitoring

The exposure characterisation described in this paper for 135 copper refinery workers (45 females, 90 males) focuses on the concentrations of copper, nickel and other trace elements in the inhalable aerosol fractions, as well as in the water-soluble and water-insoluble subfractions. Some information is also provided on the thoracic and respirable aerosol fractions. Further, results are presented for volatile hydrides of arsenic and selenium released in the copper purification steps of the electrorefining process. For the pyrometallurgical operations, a comparison of the geometric means for the inhalable aerosol fraction indicated that water-soluble copper levels were on average 19-fold higher compared to nickel (p < 0.001) and a significant association was evident between them (r = 0.87, p < 0.001); for the insoluble subfraction, the copper : nickel ratio was 12.5 (p < 0.001) and the inter-element correlation had r = 0.98 and p < 0.001. Although for the electrorefinery workers the relative inhalable concentrations of copper and nickel were not significantly different (p > 0.05), the corresponding inter-element associations were: slope of 7.7, r= 0.54, p < or =0.001 for the water-soluble subfraction and slope of 1.3, r = 0.71 and p < or =0.001 for the water-insoluble subfraction. On average, a good proportion of the inhalable copper and nickel were found in the thoracic (40%) and respirable (20%) aerosol fractions. Cobalt air concentrations were generally low with geometric means and 95% confidence intervals of 3.1 (2.4-4.2)microg m(-3) (pyrometallurgical workers) and 0.3 (0.4-0.5) microg m(-3)(electrorefinery workers). Similarly, the maximum concentrations of cadmium and lead were low, respectively 4 and 25 microg m(-3). Of the hydrides, tellurium and antimony could not be detected, but for the arsenic (arsine) and selenium hydrides measurable exposure occurred for almost all electrorefinery workers, although the levels were generally low at 0.2 microg m(-3).     

Design and performance of a field exposure system for evaluation of the ecological effects of SO2 on native grassland

We describe the design and performance of two replicate field exposure systems for evaluating the ecological effects of chronic SO₂ exposure on 0.5 ha plots of native Montana grassland. The SO₂ was supplied at a constant rate to each plot through a network of 2.5-cm inside diameter aluminum pipes set parallel to and approximately 0.7 m above the ground with 0.8-mm SO₂ release holes at 3-m intervals. The resulting SO₂ concentrations on the plots varied with micrometeorological conditions. Fumigations were essentially continuous from April through October for 5 yr on one set of four plots and for 4 yr on another set of four plots. Frequency distributions of SO₂ concentrations were approximately log-normal and qualitatively similar to those from various area and point sources. The diurnal pattern of SO₂ concentrations was strongly correlated with the reciprocal of windspeed. Nighttime concentrations averaged almost double daytime concentrations. The diurnal concentration pattern resembled an area source more closely than a point source, a direct result of using constant SO₂ source strength. Plume strikes could be simulated by turning the system on only during pre-specified meteorological conditions. Similarly, seasonal variations in area source concentrations could be simulated by varying source strength on the plots. The data from 5 years use of the system indicate that the fine-scale behavior of SO₂ concentrations would be realistic.     

双子型复配增强两性膨润土吸附Cr(VI)的效应

在两性修饰剂十二烷基二甲基甜菜碱（BS）修饰膨润土的基础上,采用双子型阳离子修饰剂乙撑基双十四烷基二甲基氯化铵（EB）对其进行复配修饰,以批处理法研究了不同修饰比例、温度、pH值和离子强度条件下,BS+EB复配修饰膨润土对Cr（VI）的吸附规律和热力学特征,并通过吸附Cr（VI）前后BS+EB复配修饰膨润土的红外光谱和表面电荷探讨了其吸附机制.结果表明,与BS两性修饰膨润土比较,EB复配修饰显著增强了其对Cr（VI）的吸附能力,吸附量增加了2.02~27.25倍,30℃时吸附量呈现BS+150EB（BS和150%比例的EB复配修饰膨润土） > BS+100EB > BS+50EB > BS+25EB > BS > CK（膨润土）的趋势,对Cr（VI）的吸附量随EB修饰比例增加而上升.CK、BS修饰膨润土对Cr（VI）呈现自发、熵增和焓增的特征,而BS+EB复配修饰膨润土对Cr（VI）吸附量随着温度的升高而降低,呈现出增温负效应.随着pH值的升高、离子强度增加,各供试土样对Cr（VI）的吸附量逐渐降低.红外光谱和土壤表面电荷结果证实电荷引力是BS+EB复配修饰土吸附Cr（VI）的主要机制.     

Spatial Convergence in Major Dissolved Ion Concentrations and Implications of Headwater Mining for Downstream Water Quality

Spatial patterns in major dissolved solute concentrations were examined to better understand impact of surface coal mining in headwaters on downstream water chemistry. Sixty sites were sampled seasonally from 2012 to 2014 in an eastern Kentucky watershed. Watershed areas (WA) ranged from 1.6 to 400.5 km² and were mostly forested (58%–95%), but some drained as much as 31% surface mining. Measures of total dissolved solutes and most component ions were positively correlated with mining. Analytes showed strong convergent spatial patterns with high variability in headwaters (<15 km² WA) that stabilized downstream (WA > 75 km²), indicating hydrologic mixing primarily controls downstream values. Mean headwater solute concentrations were a good predictor of downstream values, with % differences ranging from 0.55% (Na⁺) to 28.78% (Mg²⁺). In a mined scenario where all headwaters had impacts, downstream solute concentrations roughly doubled. Alternatively, if mining impacts to headwaters were minimized, downstream solute concentrations better approximated the 300 μS/cm conductivity criterion deemed protective of aquatic life. Temporal variability also had convergent spatial patterns and mined streams were less variable due to unnaturally stable hydrology. The highly conserved nature of dissolved solutes from mining activities and lack of viable treatment options suggest forested, unmined watersheds would provide dilution that would be protective of downstream aquatic life.