Evaluation of the diffusion size classifier (meDiSC) for the real-time measurement of particle size and number concentration of nanoaerosols in the range 20-700 nm

In the frame of assessing exposure to nanostructured particles, the aim of this work is to study the performance of a new device devoted to the real-time measurement of nanostructured aerosol: the meDiSC (Diffusion Size Classifier, Matter Engineering, Switzerland). This instrument is based on unipolar diffusion charging of particles which are then collected successively in diffusion and filtration stages. From currents measured in these stages, the instrument is capable of determining aerosol mean size and number concentration. These data were compared to reference measurements regarding monodisperse aerosols in a range from 20 to 700 nm; the relative biases were found unsatisfying. This led us to investigate the principle of the instrument. Consequently, the charging law of the diffusion charger was experimentally established, as well as the calibration curve allowing the determination of the mean size of the particles. The latter analysis was completed by a model based on diffusion theory. Our results indicate the possibility to improve the range of size measurement up to 350 nm. Measured particle size and number concentration were also used to calculate geometric surface-area concentration; the experimental data were compared to a reference calculated surface-area concentration. The results demonstrate the possibility to evaluate this parameter within acceptable uncertainty. In a second step, the meDiSC was challenged with polydisperse aerosols. It was observed that meDiSC overestimates particle size by a factor 1.7, while particle number concentrations are found within ±40% of the reference. The model applied to polydisperse aerosols indicates that polydispersity little influences particle size up to 300 nm while geometric standard deviation remains below 1.7.     

Evaluating exposure to land degradation in association with repetitive armed conflicts in North Lebanon using multi-temporal satellite data

Repetitive armed conflicts may be directly and indirectly responsible for severe biophysical modification to the environment. This, in turn, makes land more susceptible to degradation. Mapping and monitoring land degradation are essential for designing and implementing post-conflict recovery plans and informed policy decisions. The aim of this work was to evaluate the effect of repetitive armed conflicts on land degradation along the coastal zone of North Lebanon using multi-temporal satellite data. The specific objectives were to (1) identify a list of indicators for use in conjunction with satellite remote sensing, (2) monitor land cover change throughout repetitive events of armed conflicts and (3) model the effect of repetitive armed conflicts on land degradation. The methodology of work comprised the use of multi-temporal Landsat images and literature review data in GEographic Object-Based Image Analysis (GEOBIA) approach. The work resulted in the development of (1) a list of indicators to be employed, (2) land cover change detection maps with the use of multi-temporal Landsat images and, consequently, a fire risk associated with changes in vegetation cover throughout repetitive armed conflict events, and (3) an integrated approach for modelling the effect of repetitive armed conflicts on land degradation with the use of a composite land degradation index (CLDI). The final synthetic map showed four classes of exposure to land degradation associated with repetitive armed conflicts. Data collected from field visits showed that the final classification results highly reflected (average of 90 %) the effect of repetitive armed conflicts on the different classes of exposure to land degradation.     

Measurement of gas diffusion through soils: comparison of laboratory methods

Gas movement through soils is important for ecosystems and engineering in many ways such as for microbial and plant respiration, passive methane oxidation in landfill covers and oxidation of mine residues. Diffusion is one of the most important gas movement processes and the determination of the diffusion coefficient is a crucial step in any study. Five laboratory methods used for measuring the relative gas diffusion coefficient (D(s)/D(o)) were compared using a loamy sand, a porous media commonly found in agricultural fields and in several engineered structures, such as in landfill final covers. In the absence of macropores, all methods gave rather similar values of D(s)/D(o). Methods allowing the study of microscale variability indicated that the presence of macropores highly influenced gas movement, thus the value of D(s)/D(o), which, near a macropore may be one order of magnitude higher than in regions without macropores. Repacked columns do not allow the study of heterogeneity in D(s)/D(o). Natural spatial variability in D(s)/D(o) due to water distribution and preferential pathways can only be studied in large systems, but these systems are difficult to handle. Advantages and disadvantages of each method are discussed.     

Preliminary occurrence studies of antibiotic residues in Hong Kong and Pearl River Delta

An improved liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was developed and validated to investigate the occurrence of selected antibiotic residues in Hong Kong and Pearl River Delta. LC and MS parameters were optimized to produce the maximum analytical responses for each compound. The established method targeted five groups of antibiotics, namely, macrolides, sulfonamides, tetracyclines, quinolones, and amphenicols. The method was validated for three types of environmental water matrices, namely, reservoir, river, and estuarine waters. Low detection limits of 0.17–0.18 ng/L for macrolides, 0.22–0.34 ng/L for quinolones, 0.67–1.65 ng/L for tetracyclines, and 0.27–0.56 ng/L for sulfonamides were obtained. No apparent interferences were observed in the chromatograms of all antibiotics groups. The developed method was preliminarily used to analyze water samples collected from Yuen Long River in New Territories, Hong Kong and four sites along the Pearl River Delta. Results showed that high level of tetracycline was found among the groups tested in the local river samples. In Pearl River Delta, we identified significant levels of erythromycin, roxithromycin, and sulfadiazine in Shenzhen Reservoir.     

Tradable fuel economy credits: Competition and oligopoly

Corporate average fuel economy (CAFE) regulations specify minimum standards for fuel efficiency that vehicle manufacturers must meet independently. We design a system of tradeable fuel economy credits that allows trading across vehicle classes and manufacturers with and without considering market power in the credit market. We perform numerical simulations to measure the potential cost savings from moving from the current CAFE system to one with stricter standards, but that allows vehicle manufacturers various levels of increased flexibility. We find that the ability for each manufacturer to average credits between its cars and trucks provides a large percentage of the potential savings. As expected, the greatest savings come from the greatest flexibility in the credit system. Market power lowers the potential cost savings to the industry as a whole, but only modestly. Loss in efficiency from market power does not eliminate the gains from credit trading.     

Landcare Networks in Australia: State-sponsored Participation Through Local Organizations

Landcare is an Australian success story and an important example of the potential of state-sponsored community participation. An important trend encouraged by the lead agencies is for Landcare groups to be linked through so-called networks. Linking together may appeal to groups as a way of increasing their capacity to compete for scarce resources and enhance their impact on agencies, regional catchment committees and government. Network formation is also driven by government and agency demands for efficiency, accountability and effective regional planning. In this paper the authors draw on their 1997 study of the Ovens Valley Landcare Network in Victoria. This research suggested networks are important local organisations and enhance the impact of groups by improving inter-group communication and 'pulling down' resources. Network processes also contributed to robust, productive, agency-community partnerships and suggested participation can increase community influence on decision making and be compatible with adaptive management.     

A PROPOSED APPROACH TO COORDINATION OF WATER RESOURCE DEVELOPMENT AND ENVIRONMENTAL REGULATIONS1

ABSTRACT: The planning and developing of water resources to meet the country's needs for water supply, flood control, hydroelectric power, irrigation, and navigation now needs to take more account of environmental needs and regulations. Water resource development is often beneficial to the environment, but may also be harmful, as in cases involving salmon and various other endangered species. As a national objective, the environment must be preserved and in some cases restored; but how can this be done consistent with other national objectives, relating to life and welfare of human beings? This problem has aroused the concern of many engineers and water scientists. As a result, a national conference on this subject was held in Chicago in June 1998, as an integral part of ASCE's Annual Conference on Water Resources Planning and Management and the Annual Conference on Environmental Engineering. At the conclusion of that conference, a post-conference meeting was held by a group of prominent water resource practitioners. It was concluded at this meeting that action should be taken by our government to establish a new form of interagency approach, involving the states, as a means of coordination in cases of national importance.     

Motor Vehicle Crashes on Bridges and Countermeasure Opportunities

There are approximately 600,000 highway bridges in the United States. These structures differ from surface streets and highways in terms of their physical properties and operational characteristics, which in turn, affect the risk of motor-vehicle crashes and the kinds of crashes that occur. The purpose of this study was to identify motor-vehicle crash patterns and contributing factors to bridge crashes and related countermeasure opportunities on four urban bridges in the New York metropolitan area. A crash typology was developed using the narratives and diagrams in police crash reports in addition to standard police classifications of crashes. The final dataset contained records of 1,381 police-reported crashes. The four bridges studied had higher crash rates than their respective approach roads. Four major crash types accounted for approximately 90% of the bridge crashes. Primary collision factors are reviewed, and potential countermeasures are discussed.