Persistence profile of polyaromatic hydrocarbons in shallow and deep Gulf waters and sediments: effect of water temperature and sediment-water partitioning characteristics

Persistence profiles of selected polyaromatic hydrocarbons (PAHs) were analyzed depending on temperature variations in the water column and water–sediment interactions in the Gulf of Mexico. The PAHs studied include anthracene, fluoranthene, pyrene, and chrysene. The half-lives of PAHs in the deep waters (over 1000 m) are about twice as long as those in the shallow areas (100–150 m), and almost 2.5 times as long as those in the top layer (0–10 m) of the water column. The half-lives of the PAHs in the sediments are significantly longer. Among the PAHs studied, chrysene is the most persistent in the water column, and pyrene is the most persistent in the sediments. The half-life of chrysene in the shallow and deep waters is over 2.5 and about 5 years, respectively. For pyrene, the half-life in the shallow and deep sediments is about 9 and 16 years, respectively.     

Characterization and low-cost treatment of an industrial arid soil polluted with lead sulfide in northern Chile

Lead (Pb) dust exposure can have detrimental environmental and human health effects. Improperly enclosed stockpiles of Pb concentrates can cause dust emissions, subsequent pollution of the soil and environmental risk. The aim of this work was to study Pb form, distribution and immobilization (by using eggshell and seashell) in an industrial arid soil near a storage area of Pb mineral concentrates in northern Chile. High amounts of sulfur (S; 9900 mg kg^?1) and Pb (6530 mg kg^?1) were found in the polluted soil. The energy-dispersive X-ray spectroscopy analysis revealed a lead sulfide (PbS: galena). Metallic Pb particles, which were between 41 and 46 µm, were identified in the soil. After eggshell and seashell (20%) were applied, the soil pH increased from 6.0 to 7.84 and 8.07, respectively. In the studied soil, the leaching test showed a 59 mg L^?1 average Pb extractable concentration. After 240 days, extractable Pb by toxicity characteristics leaching procedure decreased to 4.79 mg L^?1 (93.3%) with the application of seashell at 20% compared with a decrease of 33.33 mg L^?1 (53.6%) using eggshell. Pb in the polluted soil was mainly found in the exchangeable fraction (66%), followed by the reducible (24%), residual (7%) and oxidizable (6%) fractions. According to the risk assessment code, the contaminated soil before treatment was classified as very high risk. Adding eggshell (20%) and seashell (20%) decreased the exchangeable fractions to 39 and 35%, respectively. Applying these liming materials achieved Pb immobilization in the soil, but the soil remained in the high environmental risk category. We conclude that the application of seashell waste, resulting from high aquaculture activity, opens an interesting window to the treatment of contaminated arid soils.     

Vertical attributes of precipitation systems in West Africa and adjacent Atlantic Ocean

Summary This study reports the findings of TRMM (Tropical Rainfall Measuring Mission) satellite data analyses undertaken to investigate differences in intensity and depth of precipitating systems in the transition region from continental to maritime environments in West Africa during the rainy season of June to September in 1998–2004. The results of this study are interpreted in the context of regional thermodynamic variables such as equivalent potential temperature and equivalent convective available potential energy to discern the processes governing storm development. Over continental West Africa, convective-type precipitating storms exhibit a substantially larger vertical extent compared to the ones over the eastern Atlantic Ocean. In contrast, the stratiform precipitating systems show similar vertical reflectivity patterns, depth and intensity over both land and adjacent ocean in West Africa. The differences in the attributes of storms, as they move from the continent to the ocean, can be partly explained in terms of the surface-atmosphere interactions that provide the necessary transports of energy and water vapor from the surface to the cloud layer. Authors’ addresses: Jose D. Fuentes, Teferi Dejene, Paolo D’Odorico, Department of Environmental Sciences, University of Virginia, 291 McCormick Road, Clark Hall, Charlottesville, VA 22904, USA; Bart Geerts, Department of Atmospheric Science, University of Wyoming, Laramie, WY 82071, USA; Everette Joseph, Department of Physics, Howard University, Washington, DC 20059, USA.     

Downward transport and modification of tropospheric ozone through moist convection

This study estimated the largely unstudied downward transport and modification of tropospheric ozone associated with tropical moist convection using a coupled meteorology-chemistry model. High-resolution cloud resolving model simulations were conducted for deep moist convection events over West Africa during August 2006 to estimate vertical transport of ozone due to convection. Model simulations realistically reproduced the characteristics of deep convection as revealed by the estimated spatial distribution of temperature, moisture, cloud reflectivity, and vertical profiles of temperature and moisture. Also, results indicated that vertical transport reduced ozone by 50% (50 parts per billion by volume, ppbv) in the upper atmosphere (12–15 km) and enhanced ozone by 39% (10 ppbv) in the lower atmosphere (<2 km). Field observations confirmed model results and indicated that surface ozone levels abruptly increased by 10–30 ppbv in the area impacted by convection due to transport by downdrafts from the upper troposphere. Once in the lower troposphere, the lifetime of ozone decreased due to enhanced dry deposition and chemical sinks. Ozone removal via dry deposition increased by 100% compared to non-convective conditions. The redistribution of tropospheric ozone substantially changed hydroxyl radical formation in the continental tropical boundary layer. Therefore, an important conclusion of this study is that the redistribution of tropospheric ozone, due to deep convection in non-polluted tropical regions, can simultaneously reduce the atmospheric loading of ozone and substantially impact the oxidation capacity of the lower atmosphere via the enhanced formation of hydroxyl radicals.     

The new site testing survey in the Canary Islands' Observatories

The future establishment of large telescopes at the Observatorio del Roque de los Muchachos (ORM) has raised the necessity of designing a site-testing campaign, aimed specifically at selecting their emplacements, as well as characterizing correctly the local seeing behaviour and the fluctuations of the turbulent field in the area covered by the observatory.This paper describes the site evaluation programme to be carried out at the ORM during the next four years. The data obtained in this program will improve earlier tests in the critical areas of sub-are sec seeing, the size of the isoplanatic patch, the efecto Caldera and suitability for infrared astronomy, among others.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

HYD verifications using numerical methods

HYD, as described in Eurocode 7 (EC7), is related to the upward flow of water through the soil towards a free surface, such as in front of a retaining wall or in the base of an excavation. The HYD verification, using numerical analysis, can be performed with two different approaches. The first approach is the conventional soil block approach where safety may be checked by calculating the equilibrium of a rectangular block of soil. The second approach is the integration point approach where stability can be verified at every integration point in the numerical analysis by checking that the equilibrium is satisfied for a soil column of negligible width above each point. In this paper, the two approaches are described and their advantages and disadvantages are discussed. Comparisons made using benchmark geometries, extensively studied and discussed between the members of the EC7 Evolution Group 9, on Water Pressures, illustrate that the HYD verification using numerical methods seems very promising. Thorough comparisons between the factors from the two approaches allow designers to better understand the benefits of using more advanced and robust approaches for such stability verifications.     

A comparative study of different model families for the constitutive simulation of viscous clays

The simulation of the viscous behavior of some clays is of high importance in many geotechnical problems. The literature offers a vast amount of constitutive models able to simulate the rate dependence observed on these materials. Although most of these models are calibrated to very similar experimental observations and share similar definitions of material parameters, some discrepancies of their response have been detected, which are related to their mathematical formulations. In this work, the causes of these discrepancies are carefully studied. To that end, four different model families are analyzed, namely, nonstationary flow surface (NSFS) models, viscoplasticity with overstress function (OVP), viscoplasticity with Norton's power law (NVP), and visco-hypoplasticity (VHP). For the sake of a fair comparison, single constitutive models using the same set of material parameters, and following other requirements, are developed for each model family. Numerical implementations of the four resulting models are performed. Their response at different tests are carefully analyzed through simulation examples and direct examination of their constitutive equations. The set includes some basic tests at isotropic stress states and others as responses envelopes, undrained creep rupture, and an oedometer test with loading, unloading-reloading, creep, and relaxation. The article is concluded with some remarks about the observed discrepancies of these model families.     

An Improved Statistical-Dynamical Downscaling Scheme and its Application to the Alpine Precipitation Climatology

Summary An improved statistical-dynamical downscaling method for the regionalization of large-scale climate analyses or simulations is introduced. The method is based on the disaggregation of a multi-year time-series of large-scale meteorological data into multi-day episodes of quasi-stationary circulation. The episodes are subsequently grouped into a defined number of classes. A regional model is used to simulate the evolution of weather during the most typical episode of each class. These simulations consider the effects of the regional topography. Finally, the regional model results are statistically weighted with the climatological frequencies of the respective circulation classes in order to provide regional climate patterns. The statistical-dynamical downscaling procedure is applied to large-scale analyses for a 12-year climate period 1981–1992. The performance of the new method is demonstrated for winter precipitation in the Alpine region. With the help of daily precipitation analyses it was possible to validate the results and to assess the different sources of errors. It appeared that the main error originates from the regional model, whereas the error of the procedure itself was relatively unimportant. This new statistical-dynamical downscaling method turned out to be an efficient alternative to the commonly used method of nesting a regional model continuously within a general circulation model (dynamical downscaling). Received April 8, 1999 Revised July 30, 1999