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231.
Luis Carlos Belalcazar Alain Clappier Nadège Blond Thomas Flassak Joachim Eichhorn 《Atmospheric environment (Oxford, England : 1994)》2010,44(31):3814-3822
Road traffic emission factors (EFs) are one of the main sources of uncertainties in emission inventories; it is necessary to develop methods to reduce these uncertainties to manage air quality more efficiently. Recently an alternative method has been proposed to estimate the EFs. In that work the emission factors were estimated from a long term tracer study developed in Ho Chi Minh City (HCMC) Vietnam. A passive tracer was continuously emitted from a finite line source placed in one side of an urban street canyon. Simultaneously, the resulting tracer concentrations were monitored at the other side of the street. The results of this experiment were used to calculate the dispersion factors and afterwards, these dispersion factors were used to estimate the EFs. In this paper we use the Computational Fluids Dynamics (CFD) model WinMISKAM to critically evaluate the proposed methodology.In a first step, we use the results of the tracer study to validate the CFD model. Results show that the model is able to simulate quite well the tracer dispersion in most of the cases. The model is then used to evaluate the effect of varying the source configuration and to correct the EFs. A comparison with available studies shows that the corrected EFs are within the range of the EFs reported in other studies. Finally, the CFD model is used to find a source configuration that better represents the vehicle emissions and that may be used in future studies to estimate the EFs more accurately. Results show that a 200 m line placed in the center of the street would represent very well the vehicle emissions. This work shows that it is possible to accurately estimate the EFs from tracer studies. 相似文献
232.
Marco Vervliet-Scheebaum Alain Straus Mick Hamer Edgar Wagner 《Environmental pollution (Barking, Essex : 1987)》2010,158(2):615-623
This study evaluates the effects of the triazine herbicide simazine in an outdoor pond microcosm test system that contained two submerged rooted species (Myriophyllum spicatum and Elodea canadensis) and two emergent rooted species (Persicaria amphibia and Glyceria maxima) over a period of 84 days. Simazine was applied to the microcosms at nominal concentrations of 0.05, 0.5 and 5 mg/L. General biological endpoints and physiological endpoints were used to evaluate herbicide toxicity on macrophytes and the algae developing naturally in the system.Concentration-related responses of macrophytes and algae were obtained for the endpoints selected, resulting in a no observed ecologically adverse effect concentration (NOEAEC) at simazine concentrations of 0.05 mg active ingredient/L after 84 days. E. canadensis was the most negatively affected species based on length increase, which was consistently a very sensitive parameter for all macrophytes. The experimental design presented might constitute a suitable alternative to conventional laboratory single-species testing. 相似文献
233.
Tsuji LJ Martin ID Martin ES LeBlanc A Dumas P 《Environmental monitoring and assessment》2008,146(1-3):91-104
We examined matched-tissue samples (the right pectoral muscle plus the associated skin and fat was considered a breast portion) of 81 spring-harvested waterfowl and 19 summer-harvested godwits (Limosa spp.) to assess the potential of these water birds contributing to the body burden of PCBs and DDT noted in First Nation people of the western James Bay region, northern Ontario, Canada. In general, the dabbling ducks (mallard duck, Anas platyrhynchos; and northern pintail, A. acuta) had significantly lower percent lipid (gravimetrically determined) values in skin tissue, fat tissue, and breast muscle compared to the goose species (Canada goose, Branta canadensis; lesser snow goose, Chen caerulescens); godwits had percent lipid values not significantly different than ducks and geese. Also, the percent lipid values in skin for all species of birds examined approached those found in fat tissue. Organochlorine data were expressed as the amount (microg) of each contaminant per breast portion to show contaminant consumption in terms of typical and easily recognizable dietary portions; direct comparisons were made to acceptable daily intake (ADI) or tolerable daily intake (TDI) values as recommended by Health Canada. Significant differences in the amount of organochlorines between bird species for skin, fat tissue, and breast muscle samples were found. In general, breast portions from snow geese contained the least amount of organochlorines, followed by godwits (except for mirex) and then Canada geese; the dabbling ducks had the greatest amount of organochlorines on a breast portion basis. However, on average, no 60 kg person would exceed the calculated organochlorine ADI/TDI values consuming one breast portion (i.e., breast + associated skin and fat), but the maximum value of SigmaPCBs for skin tissue alone in male mallards (47 microg) was more than twice the ADI/TDI (18 microg/day); while, that in fat tissue alone (17 microg) approached the ADI/TDI. Thus, the consumption of dabbling ducks by children is an issue that should be explored further, if tissue other than breast muscle is eaten. Lastly, the consumption of waterfowl was a source of PCBs for people of Fort Albany and Kashechewan, but not DDT, as this organochlorine was infrequently detected. 相似文献
234.
This paper tackles the increasingly significant problem of irrigation-induced soil salinity within a groundwater management model. Irrigation can result not only in heavier salt concentrations but also in the removal of salt from the soil through return flows. Given these contradictory observations, we are interested in the effects on soil salt concentration if irrigation efficiency is improved. We develop a model of salt concentration patterns in both soil and groundwater. We introduce a negative externality to the production process by assuming that soil degradation due to higher soil salinity affects total factor productivity. Within this framework, we show that in the presence of this externality, increasing irrigation efficiency can lead to higher or lower soil salt concentration, depending on the social cost of transferring salt from one reservoir to another. 相似文献