11 research outputs found
Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements
This study aims to determine the mineral contribution to
PM<sub>10</sub> in the central Mediterranean Sea, based on 7 yr of daily PM<sub>10</sub>
samplings made on the island of Lampedusa (35.5° N, 12.6° E).
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The chemical composition of the PM<sub>10</sub> samples was determined by ion
chromatography for the main ions, and, on selected samples, by particle-induced
X-ray emission (PIXE) for the total content of crustal markers.
Aerosol optical depth measurements were carried out in parallel to the
PM<sub>10</sub> sampling.
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The average PM<sub>10</sub> concentration at Lampedusa over the period June
2004–December 2010 is 31.5 μg m<sup>−3</sup>, with low interannual
variability. The annual means are below the EU annual standard for
PM<sub>10</sub>, but 9.9% of the total number of daily data exceeds the daily
threshold value established by the European Commission for PM
(50 μg m<sup>−3</sup>, European Community, EC/30/1999).
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The Saharan dust contribution to PM<sub>10</sub> was derived by calculating the
contribution of Al, Si, Fe, Ti, non-sea-salt (nss) Ca, nssNa, and nssK oxides
in samples in which PIXE data were available. Cases in which crustal content
exceeded the 75th percentile of the crustal oxide content distribution were
identified as elevated dust events. Using this threshold, we obtained 175
events. Fifty-five elevated dust events (31.6%) displayed PM<sub>10</sub> higher
than 50 μg m<sup>−3</sup>, with dust contributing by 33% on average.
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The crustal contribution to PM<sub>10</sub> has an annual average value of 5.42 μg m<sup>−3</sup>,
and reaches a value as high as 67.9 μg m<sup>−3</sup> (corresponding
to 49% of PM<sub>10</sub>) during an intense Saharan dust event.
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The crustal content estimated from a single tracer, such as Al or Ca, is in
good agreement with the one calculated as the sum of the metal oxides.
Conversely, larger crustal contents are derived by applying the EU guidelines
for demonstration and subtraction of exceedances in PM<sub>10</sub> levels due to
high background of natural aerosol. The crustal aerosol amount and
contribution to PM<sub>10</sub> showed a very small seasonal dependence;
conversely, the dust columnar burden displays an evident annual cycle, with a
strong summer maximum (monthly average aerosol optical depth at 500 nm up to
0.28 in June–August). We found that 71.3% of the dust events identified
from optical properties over the atmospheric column display a high dust
content at the ground level. Conversely, the remaining 28.7% of cases
present a negligible or small impact on the surface aerosol composition due
to the transport processes over the Mediterranean Sea, where dust frequently
travels above the marine boundary layer, especially in summer.
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Based on backward trajectories, two regions, one in Algeria–Tunisia, and one
in Libya, are identified as main source areas for intense dust episodes
occurring mainly in autumn and winter. Data on the bulk composition of mineral
aerosol arising from these two source areas are scarce; results on
characteristic ratios between elements show somewhat higher values of
Ca / Al and (Ca + Mg) / Fe (2.5 ± 1.0, and 4.7 ± 2.0, respectively) for
Algeria–Tunisia than for Libyan origin (Ca / Al = 1.9 ± 0.7 and
(Ca + Mg) / Fe = 3.3 ± 1.1)
Conversion of rare earth elements to molecular oxide ions in a dynamic reaction cell and consequences on their determination by inductively coupled plasma mass spectrometry
The behaviour of rare earth elements (REEs) ions within a dynamic reaction cell (DRC) pressurized with oxygen was investigated, in order to explore their determination at m/z +16 by inductively coupled plasma mass spectrometry (ICP-MS). Under the optimized conditions, the conversion of REEs to
molecular monoxide ions was nearly quantitative (>96%), with the exception of Tm (78%), Eu (11%) and Yb (6%). Moreover, the formation of dioxide ions was generally lower than 1%. According to these results, a new method for the determination of REEs in digests from geological samples was developed.
After microwave-assisted acid digestion, the solutions were directly analyzed by ICP-MS, determining REEs at m/z +16. The interferences due to dioxide and un-reacted ions were carefully evaluated by taking into account the actual concentration of REEs in sediment samples. In addition, the possible interferences due to other constituents of sediments (e.g. barium) were considered. The accurate determination of Y, La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er and Tm was achieved, as demonstrated by the
analysis of both certified reference materials and Antarctic marine sediment samples, using ICP sector field mass spectrometry (ICP-SFMS) for comparison. On the other hand, Eu, Gd, Yb and Lu could not be measured by the O-atom addition approach and their separate determination in the standard mode
using mathematical correction is hence necessary to obtain the complete REE pattern. The quantification limits (10 times the standard deviation of 10 procedural blanks) were at least two orders of magnitude lower than the REEs concentrations in sediment samples. Precision of the procedure ranged from 1.6% to 6.4%
Development of new analytical methods based on ICP-MS for the determination of rare earth elements in geological samples
none5noneF. Ardini; M. Grotti; F. Soggia; R. Udisti; F. RugiArdini, Francisco; Grotti, Marco; Soggia, Francesco; R., Udisti; F., Rug
Reactivity of an antimetastatic organometallic ruthenium compound with metallothionein-2: relevance to the mechanism of action
Dolomite highlights glacial to interglacial transitions in Ross Sea deposits investigated in AND-1B core, Antarctica
The retreats of Antarctica's ice masses during the Plio-Pleistocene were characterized by large-scale environmental changes at the continental margin. Increased melt water got in contact with seawater and build up particular conditions for a huge variety of chemical reactions. The precipitates of these reactions, within the sediment deposits, are reliable tools to reconstruct specific paleoenvironmental changes. Discrete horizons with high dolomite and calcite content (up to ~20 and ~30 % respectively) were detected in the AND-1B core from the ANDRILL McMurdo Sound Project. We measured the split core in the field during the austral summer 2006/2007 with a non-destructive AVAATECH XRF-Core Scanner. On discrete samples chemical analysis were carried out and the mineral composition was examined by X-ray diffraction measurements. At the depth of 162.71, 182.10, 224.59 and 292.15 mbsf these high dolomite values were found within the glacial to interglacial transition zones. Our hypothesis states that calcite and dolomite formation in the transition zones is possible under cold glaciomarine conditions with an increased melt-water runoff and a high amount of dissolved HCO3- in contact with Mg+ and Ca+ rich seawater at the grounding line region or in the sub-ice hydrological system. We also detected horizons containing other carbonates like ankerite (i.e. 143.23, 449.26 mbsf) and low Mg calcite that support this hypothesis. Whether in this environment the dolomite was (I) precipitated in the water column, or (II) in the pore water system where sub-ice freshwater was replaced and overlaid by heavier seawater during glacial to interglacial transitions, is under investigation. Anyhow, most of the dolomite formations in the AND-1B core could be related to shelf ice retreats and (bio?)geochemical processes at or close to the sediment surface
Exploring the Effect of Co Doping in Fine Maghemite Nanoparticles
We present a study of the structural, magnetic, and magneto-optical
properties of a series of Co-substituted ferrite nanoparticles (NPs)
prepared by thermal decomposition of metallo-organic precursors in
high boiling solvents. The structural characterization, carried out
by using several techniques (transmission electron microscopy (TEM),
X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and
magnetic circular dichroism measurements), showed all the samples
are high crystalline, 5–6 nm spherical NPs with the cubic spinel
structure typical of ferrites. The evolution of lattice parameters
with cobalt content suggests that the material is Co-substituted maghemite,
also confirmed by XAS and magneto optical (MO) characterizations.
The investigation of the magnetic and magneto-optical properties displays
peculiar trends with the cobalt content, the main features being the
large increase of the saturation magnetization and the anomalous dependence
of magnetic anisotropy which reaches its maximum values for intermediate
compositions. The large tuneability of this material makes it possible
to implement the performances of devices used in biomedical and sensing
applications