A statistical characterization for two-point temperature fluctuations in the planetary boundary layer (PBL) is analyzed and its implications on the long-standing closure problem discussed. Despite the non-triviality of the dynamics of temperature fluctuations, our analysis supports the idea that the most relevant statistical properties can be captured solely in terms of two scaling exponents. They turned out to be weakly dependent on the stability properties of the PBL. Its statistics have been investigated by collecting data from a field experiment carried out in the urban area of Turin (Italy) from January 2007 to March 2008. Our results confirm those from a large-eddy simulation (LES) analysis carried out for the convective PBL with different level of convection. We extend the scenario to the stable PBL, a regime much more difficult to simulate when exploiting LES. 相似文献
The kaolin deposits of the Amazon region of Brazil are of lateritic origin, modified by subsequent reduced lacustrine and/or swamp environment. They are contemporaneous with lateritic bauxites found in the same region, all formed from aluminium silicate rocks. These are principally sedimentary rocks from the Cretaceous period (Itapecuru and Alter do Chão), but also include metamorphic and felsic volcanic rocks. After erosion of the upper part of these profiles they became locally a substratum for swampy and/or lacustrine environments mostly developed over the clayey saprolitic horizon where kaolin occurs. The saprolitic horizon is made up mainly of iron-mottled kaolinite which has been subject to an intense deferrification, which has increased the kaolin brightness and thickness. The kaolins are basically made up of well-crystallized kaolinite, quartz, sometimes illite-muscovite, anatase and hematite. In certain locations, crandallite-goyazite is also present. The deposits studied differ from each other in the mineral content levels, concentration of principal elements and in trace element distribution. The greatest quantity of quartz and, consequently SiO2, is intrinsically related to the type of parent rock. Small sedimentary deposits occur in alluvial flood plains located not very far from the lateritic source. 相似文献
The main purposes of this study are the textural, chemical and mineralogical characterization of the urban soils of Lisbon
and the identification of probable relations between the several soil properties. The results are used to infer which soil
properties control the superficial dispersion of potential harmful elements to human health. Soil sampling was carried out
in 51 selected sites all through the city, under the criterion that such sites should be spaces usually frequented by children.
The concentrations of 42 elements in the >2 mm soil size fraction were determined at a commercial laboratory in Canada (ActLabs,
LTD), by ICP-MS/ICP-OES after an acid digestion with aqua regia. The soil mineralogy was determined by X-ray diffraction in
the <2 and <62 μm size fractions. The results indicate that the urban soils have mainly a sandy texture and a main mineralogical
assemblage of quartz, K-feldspar, plagioclase and calcite. In terms of clay minerals, smectite, illite and kaolinite are the
main clays in the soil. Smectite and illite show a dichotomy in their distribution, with the smectites prevailing in the soils
of the volcanic complex of Lisbon, which are classified as being residual, and illite prevailing in the remaining soils, which
are considered mainly as man-made soils. Smectite seems to exert an important role in the fixation of Ni and Cr. The results
of the geochemical study show that Ni and Cr have concentrations above the soil guideline value established to the UK and
pose a probable risk to human health. 相似文献
Laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA-MC-ICP-MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr-baseline subtraction, Rb-peak-stripping using βRb derived from a bracketing glass reference material, and a CaCa or CaAr correction for plagioclase and CaCa or CaAr + REE2+ correction for rock glasses, yields the most accurate and precise 87Sr/86Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50–65 μm diameter beam can readily achieve < 100 ppm 2SE repeatability ("internal") precision for 87Sr/86Sr measurements for materials with < 1000 μg g-1 Sr. 相似文献
The Cerrado biome is the second largest in Brazil, but the evolution of the Cerrado during the late Quaternary is not yet fully known. This study identifies paleoenvironmental changes during the last 23 000 years, based on a tropical mountain peatland record, in the Serra do Espinhaço Meridional in central-eastern Brazil. A multi-proxy approach was used that involved palynological analysis, stable isotopes (δ13C, δ15N), geochemistry, radiocarbon dating and multivariate statistics derived from a peatland core from Rio Preto (Minas Gerais state). The study reveals a very humid and cold climate during the late Pleistocene, with an increase in temperature and decrease in humidity at the Pleistocene–Holocene transition. During this period there was strong instability in the landscape (episodes of erosion). At the beginning of the Holocene there was a reduction in humidity with greater landscape stability. The current sub-humid climatic conditions seem to have been established in the mid-/late Holocene, with periods of landscape instability. Our findings agree with other Cerrado records that contradict previously established hypotheses, such as the Amazonian Refuge and the Pleistocene Arc. 相似文献
The mineral water of Vilajuïga village in Alt Empordà (NE Catalonia, Spain) owes its uniqueness to an emanation of geogenic CO2 that modifies groundwater hydrochemistry to produce a differentiated HCO3–Na- and CO2-rich groundwater among the usual Ca–HCO3 type found in this region. A hydrogeological conceptual model attributes its occurrence to the intersection of two faults: La Valleta and Garriguella-Roses. The former provides a thrust of metamorphic over igneous rocks, formed during the Paleozoic, over a layer of ampelitic shale that, from a hydrogeological perspective, acts as a confining layer. The Garriguella-Roses normal fault, which originated during the Neogene, permits the degassing of geogenic CO2 that is attributed to volcanic activity occurring in the Neogene. Groundwater mixing from the metamorphic and igneous rock units plus the local occurrence of CO2 creates a HCO3–Na water that still holds free-CO2 in solution. Interaction with the gas phase is restricted at the intersection of the two faults. Radiocarbon dating, after correcting for geogenic dead carbon, estimates an age of 8,000 years BP. The low tritium content (0.7 TU) indicates that Vilajuïga water is a mix of “older” groundwater recharged in the metamorphic rocks of the Albera range and “younger” groundwater from the igneous rocks of the Rodes range, over a recharge area of 45 km2 and a maximum elevation of 600 m. Given its origin as rare groundwater in the southern slope of the Eastern Pyrenees, purposeful monitoring is necessary to evaluate the groundwater vulnerability and anticipate impacts from nearby wells and climate-change effects.