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881.
882.
不同方法制备的铟催化剂选择性还原NO 总被引:2,自引:0,他引:2
不同负载量的In/Al2O3催化剂分别以浸渍法、共沉淀法和溶胶-凝胶法制得,对比评价了不同方法制备的样品在富氧条件下以丙烯为还原剂,选择性催化还原NO的活性,考察了氧气浓度、H2O对活性的影响.研究表明,铟催化剂有较高的去除NO活性,制备方法对催化剂活性具有显著影响.其中,溶胶-凝胶法和共沉淀法最高活性都可达90%左右;而浸渍法样品的活性较差,最高转化率不到60%.氧气浓度对NOx最高转化率及其相应反应温度均有重要影响.随着O2浓度的提高,最高活性对应的反应温度降低.反应气氛中H2O的加入使铟催化剂活性大幅降低.铟与其他多种金属活性组分相比,一个突出的不同表现是,3种方法各自的最佳负载量相差不大. 相似文献
883.
884.
在没有密度分层的容泄水体条件下,对某污水排海工程多孔喷头的射流特性进行了实验研究。文中介绍了不同排污流量和环境流速条件下,多孔喷头附近的流速场和污水场特性;并对出流平均稀释度作了分析。最后,还对该喷头周围的冲淤形态进行了探讨.文中所得的结果对实际排污系统的设计和进一步研究有一定的参考价值。 相似文献
885.
The ecological risks of polynuclear aromatic hydrocarbons (PAH) in aquatic sediments will vary with both toxicity and bioavailability
to aquatic biota. While there are standardized protocols to test the acute toxicity of sediment-borne compounds to aquatic
invertebrates, there are none for assessing bioavailability to fish. We found that sediment-borne PAH caused an exposure-dependent
induction of cytochrome P450 (CYP1A) enzymes in rainbow trout (Oncorhynchus mykiss) fingerlings exposed in semi-static 96 h bioassays, as shown by increased activity of ethoxyresorufin-o-deethylase (EROD). Assuming that PAH are taken up by trout due to partitioning from organic and inorganic constituents of
sediments, we tested the effect of different test variables on bioaccumulation using induction as an index of exposure. EROD
activity increased with exposure of fish to increasing volumes of sediments containing PAH, i.e., with increasing ratios of
sediment to water. Uptake of single compounds from sandy sediments did not differ from uptake from clay or low organic (7%
LOI — loss on ignition) sediments, but decreased when organic content was very high (58% LOI). Maximum induction was observed
within 24~h of exposure and at 7.5^C relative to 15, 22, or 28^C. Storage and handling techniques had minor effects on sediment
EROD induction potency. Absolute EROD activity was greater in white sucker (Catostomus commersoni) a benthic species, than in trout, a pelagic species. However, when basal (negative control) activity was accounted for,
there was no difference in response between the species. Together, these experiments provide a basis for developing a standard
protocol to test the bioavailability to fish of sediment-borne PAH. 相似文献
886.
Gabbert S 《Environmental monitoring and assessment》2006,119(1-3):507-526
Abstact Ever since the Regional Acidification Information and Simulation Model (RAINS) has been constructed, the treatment of uncertainty has remained an issue of major interest. In a recent review of the model performed for the Clean Air for Europe (CAFE) programme of the European Commission, a more systematic and structured uncertainty analysis has been recommended. This paper aims at contributing to the scientific debate how this can be achieved. Because of its complex structure on the one hand and limited research resources (time, computational capacities) on the other hand a full-blown uncertainty analysis in RAINS is hardly feasible. Therefore, all types of uncertainty require more efficient ways for uncertainty analysis. With respect to parameter uncertainty, we propose to focus research efforts for uncertainty analysis on key parameters. Among different approaches to select key parameters that have been discussed in the literature screening methods seem to be particularly appropriate for complex, deterministic Integrated Assessment models such as RAINS. Surprisingly, in Integrated Assessment modelling for air pollution problems of screening design have not been taken up so far. As a case study we consider the emission module of RAINS. We show that its structure allows for a straightforward and effective screening procedure 相似文献
887.
Khaparde VV 《Environmental monitoring and assessment》2006,116(1-3):217-231
A workshop on analytical quality control (AQC) of ambient air quality measurement methods for nitrogen dioxide (NO2) and sulphur dioxide (SO2) was conducted by Central Pollution Control Board (CPCB) for officials involved in National Ambient Air Quality Monitoring
(NAAQM) in India. Concentrations of NO2 and SO2 were generated by dynamic dilution system under laboratory conditions at low and high levels and measured using static dilution
system and wet chemical methods laid down by CPCB under section 16(2)(h) of the air act 1981. CPCB provided the measured values
as reference values for comparing the means obtained by the officials participated from thirteen organizations. A tolerance
limit of ±15% of the reference values was specified to accept the results. Generated concentrations, which were unknown to
the participants, were measured using gaseous sampling assembly (Envirotech APM 411, New Delhi, India), and wet chemical methods
laid down by CPCB i.e. the same methodology which is used by the organizations to generate the data of NO2 and SO2 in ambient air. Simultaneously, concentrations were checked by CPCB using automatic analyzers as a check on reference concentration.
It is observed that results of automatic analyzers for NO2 and SO2 were within a tolerance of ±5% with %RSD below 3. On the other hand, results of most of the participants showed variability
in the measurements with %RSD ranging between ±0.8 and ±88.6 and exceedences of means from the tolerance limit with bias ranging
between 1.4 and −59%. To check the cause of high variability in the measurements obtained under identical conditions, duplicate
sampling was performed by one of the participants for SO2 at low concentration level. In this study, results of wet chemical methods, automatic analyzers and results of duplicate
sampling are analysed statistically to assess the cause of high variability in the measurements. Analysis of t-test and analysis of variance (ANOVA) showed highly significant results for NO2 and SO2 at high concentration levels (α 0.05) and for SO2 at both the levels (α 0.01) respectively indicating some bias is existing either in the sampling or in analytical technique.
Duplicate sampling performed to check precision in parallel measurements showed high %RSD indicating the presence of systematic
error in sampling technique as the same calibration factor (CF) was used to measure the concentration of duplicate samples.
Statistical analysis of flow rates of duplicate sampling showed that the sampling assembly could not maintain the constant
flow rate within the ±10% with that measured at the start of the sampling. This resulted in high %RSD and deviation from the
reference values for the results of most of the participants, even after accepting ±15% tolerance limit. There is a need to
improve and evaluate this gaseous sample collection device under laboratory conditions to generate reliable database of NO2 and SO2 in ambient air. 相似文献
888.
Tessa Artruc Desiree Tullos Ben Leshchinsky 《Journal of the American Water Resources Association》2023,59(1):86-106
The drawdown of reservoirs behind dams is an important management strategy (e.g., for removal of aging infrastructure, flushing of sediment), and an opportunity to study erosional processes. A numerical model was developed to examine retrogressive bank erosion across reservoir drawdown scenarios and to evaluate factors controlling the rate, volume, and mechanisms of lateral erosion. Modeled processes included dynamic drawdown of groundwater, sequential slope failures via limit equilibrium analysis, and retrogression considering stress interaction between failing blocks. Field measurements were coupled with Staged, Slow, and Rapid drawdown scenarios. Results highlight the importance of including retrogression as an avenue for lateral erosion, as sequential block failures were found to occur in all scenarios except Slow drawdown. This result indicates that bank stability models without some means of characterizing the evolution of slope failure during drawdown are likely underestimating bank failure rates and volumes. In contrast, dynamic groundwater was not found to be a dominant control for any drawdown scenario. Model results also demonstrate that the drawdown increment is a first-order control on slope instability via the development of drained or undrained conditions. A majority of failures occurred under undrained conditions. To maximize slope stability, using slow drawdown to activate internal friction under drained conditions is essential. The design of the drawdown rate created a tradeoff between the amount of impact created and when the impact is produced. The study also articulated the need for coupling models and field observations for rapidly changing systems. 相似文献
889.
The central objectives of the European Forum on Integrated Environmental Assessment (EFIEA) include improving the scientific
quality of Integrated Environmental Assessments (IEA) as well as strengthening the interactions between science and policy
making in environmental matters. This paper is intended to provide a concise assessment of the evolution of IEA methods and
present it as a background to current thinking on and practice in IEA. Historical roots of IEA concepts and applications are
explored. Common elements and distinctive features in recent proposals to define IEA are sorted and a liberal definition is
proposed for the purposes of the present methodological study. This definition emphasizes the interdisciplinary character
and environmental policy orientation of IEAs. Changes in the nature, social perception, and management of environmental problems
are identified as the major factors driving methodological development in IEAs. A simple scheme is proposed to arrange the
main elements of IEA: disciplinary tools, integration tools, and assessment frameworks. The role of IEAs in environmental
management is examined by adopting the concept of risk management functions. Due to the varying needs for interdisciplinary
research and diverging degrees of policy involvement across those functions, the potential contribution of IEAs to activities
belonging to different functions also varies. The flexibility and diversity of IEAs are demonstrated by a sampler of frameworks
that have been developed to address profoundly different problems and audiences.
This revised version was published online in July 2006 with corrections to the Cover Date.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
890.
ABSTRACTHouzhai (Guizhou Province, Southwest China) is a typical karstification area, with dolomite and limestone constituting the major rock types. The aim of this study was to utilize major element mass-balance and multivariate statistical methods to analyze the chemical composition of water in the Houzhai River catchment area with regard to seasonal variations in ion content, dissolution reactions, and rates. Data demonstrated that the Houzhai's hydrochemical composition is dominated by calcium (Ca2+), magnesium (Mg2+), bicarbonate (HCO3?), and sulfate (SO42?) which predominantly originated from chemical weathering of carbonate rocks like limestone and dolomite. Carbonate weathering contributes 83% of the dissolved Ca2+. Sulfuric acid also plays an important role in rock weathering. Our analysis identified three principal sources of hydrochemical variation in the study area, including dolomite dissolution, limestone dissolution, and anthropogenic activities. In addition, the identified two main hydrochemical facies were characterized by the predominance of Ca-Mg-HCO3 and Ca-Mg-HCO3-SO4. In terms of temporal variation, all of the examined parameters showed strong inter-annual and seasonal variations of concentration distribution, except pH levels and potassium and sodium (K++Na+). The dissolution rate of carbonate was estimated using the concentration of Ca2+ and discharge rate, which constitutes a simple, practical, and innovative method. Compared with other research methods, our strategy was found to be simple, feasible, readily adaptable, and less demanding of data inputs. 相似文献