16 research outputs found
A Balaton ásványai
A Balaton hazánk egyik legnagyobb természeti kincse, sokoldalú
tudományos kutatása a 19. században kezdődött. A Balaton
üledékének vizsgálatán keresztül számos ismerethez juthatunk a
tóban lezajló folyamatokkal kapcsolatban. A tó sekély, így vízszintje a
szabályozás ellenére is érzékenyen reagál a szezonális változásokra s
a manapság gyakori időjárási szélsőségekre. A száraz/nedves
periódusok befolyásolják a tó vízminőségét, ezáltal az ökoszisztémát.
A Balaton üledéke állandó kapcsolatban van az élő szervezetekkel,
azonban keveset tudunk az üledék összetevőinek, fizikai, kémiai,
ásványtani jellegének változásáról a szélsőséges időjárási elemekkel
jellemezhető időszakok között. E tanulmányban az üledékképződés
részletes ásványtani vizsgálatával foglalkozunk, különös tekintettel a
karbonátásványok tulajdonságaira. Rávilágítunk, hogy a szélsőséges
csapadékhelyzetek milyen hatással vannak a vízminőségre s ezen
keresztül milyen hatást gyakorolnak az üledékre
Mágneses baktériumok a Balatonban
Munkánk célja a Balaton üledékében élő mágneses baktériumok vizsgálata volt. A mágneses baktérium nem taxonómiai
kifejezés, olyan különböző baktériumok összességét jelenti, melyek mágneses taxissal rendelkeznek (a környezet
mágneses terének irányához igazodó mozgást végeznek). Azonosítottuk a különböző sejtmorfológiai típusokat és
nyomon követtük évszakos változásaikat. Transzmissziós elektronmikroszkóppal egész sejteket tanulmányoztunk, hogy
megállapítsuk, a balatoni mintákban lévő baktériumok milyen vas-ásványt választanak ki, és melyek ezen ásványok
fizikai, kémiai tulajdonságai. A magnetiten kívül a sejtek tartalmaznak amorf, P-, Ca- és S-tartalmú zárványokat is. Ezek
kémiai összetételét energiadiszperzív röntgen-spektrometriával vizsgáltuk
Light absorption properties of laboratory-generated tar ball particles
Tar balls (TBs) are a specific particle type that is
abundant in the global troposphere, in particular in biomass
smoke plumes. These particles belong to the family of atmospheric
brown carbon (BrC), which can absorb light in the
visible range of the solar spectrum. Albeit TBs are typically
present as individual particles in biomass smoke plumes,
their absorption properties have been only indirectly inferred
from field observations or calculations based on their electron
energy-loss spectra. This is because in biomass smoke
TBs coexist with various other particle types (e.g., organic
particles with inorganic inclusions and soot, the latter emitted
mainly during flaming conditions) from which they cannot
be physically separated; thus, a direct experimental determination
of their absorption properties is not feasible. Very
recently we have demonstrated that TBs can be generated
in the laboratory from droplets of wood tar that resemble
atmospheric TBs in all of their observed properties. As a
follow-up study, we have installed on-line instruments to
our laboratory set-up, which generate pure TB particles to
measure the absorption and scattering, as well as the size
distribution of the particles. In addition, samples were collected
for transmission electron microscopy (TEM) and total
carbon (TC) analysis. The effects of experimental parameters
were also studied. The mass absorption coefficients of
the laboratory-generated TBs were found to be in the range
of 0.8–3.0m2
Distribution and composition of Mg-calcite and dolomite in the water and sediments of Lake Balaton
Lake Balaton is a large and shallow lake that is of great economic and cultural importance in landlocked Hungary. Even though the lake has been studied extensively in the last century from a large number of scientific aspects, the mineralogy of its sediments has not been fully explored. The mud at the bottom of the lake consists mostly of silt-sized grains of carbonate minerals with compositions between those of calcite (CaCO3) and dolomite CaMg (CO3)2. In order to understand the processes of carbonate precipitation and the influence of water budget fluctuations on the mineralogical character of the sediment, we used X-ray powder diffraction to analyze the changes of cell parameters of carbonate minerals in the upper half meter of the sediment. The major carbonate phase is Mg-calcite that shows a distinct reduction in cell parameters from west to east, reflecting an increase of its Mg-content, in parallel with a gradient of dissolved Mg/Ca ratio in the water. Intriguingly, dolomite, the other widespread carbonate phase in the sediment, also shows a change in cell parameters from west to east, with the deviations from values of stoichiometric dolomite being largest in the Eastern Basin of the lake. The similar pattern of cell parameter changes of Mg-calcite and dolomite suggests that ordered dolomite with slightly anomalous, Ca-rich composition also forms in the lake, probably by direct precipitation from the water. In contrast, protodolomite forms within the sediment through diagenetic processes. Based on our X-ray powder diffraction measurements, we propose a model of carbonate mineral formation and transformation in Lake Balaton. Since the Mg/Ca ratio of the water appears to be the major factor in controlling the compositions of carbonate minerals, and this ratio in turn is governed by the amount of water supply, the properties of the precipitating carbonate minerals are affected by the actual level of the lake water
Atmospheric tar balls: aged primary droplets from biomass burning?
Atmospheric tar balls are particles of special morphology and composition
that are fairly abundant in the plumes of biomass smoke. These particles
form a specific subset of brown carbon (BrC) which has been shown to play a
significant role in atmospheric shortwave absorption and, by extension, climate
forcing. Here we suggest that tar balls are produced by the direct emission
of liquid tar droplets followed by heat transformation upon biomass burning.
For the first time in atmospheric chemistry we generated tar-ball particles
from liquid tar obtained previously by dry distillation of wood in an
all-glass apparatus in the laboratory with the total exclusion of flame
processes. The particles were perfectly spherical with a mean optical
diameter of 300 nm, refractory, externally mixed, and homogeneous in the
contrast of the transmission electron microscopy (TEM) images.
They lacked any graphene-like microstructure and
exhibited a mean carbon-to-oxygen ratio of 10. All of the observed
characteristics of laboratory-generated particles were very similar to those
reported for atmospheric tar-ball particles in the literature, strongly
supporting our hypothesis regarding the formation mechanism of atmospheric
tar-ball particles
Distribution and composition of Mg-calcite and dolomite in the water and sediments of Lake Balaton
Size and shape control of precipitated magnetite nanoparticles
Magnetite nanoparticles are ubiquitous in soils, sediments and mine wastes, and are also used in nanotechnological
applications. We studied the influence of synthesis conditions on the size and shape of magnetite nanoparticles that were produced in
inorganic co-precipitation processes. Variable parameters included the types of reagents and their concentrations, the pH, the
temperature (from 9 to 90 �C) and the atmosphere (O2 and N2). The mineral phases, the morphologies, size and shape distributions
of the resulting magnetite particles were characterised using transmission electron microscopy and X-ray powder diffraction. We
managed to produce magnetite nanoparticles between �11 and 120 nm and to control the mean sizes of the crystals within this range.
The morphologies of the magnetite nanocrystals were also affected by the synthesis conditions and varied according to grain size.
Crystals with diameters between 10 and 25 nm have irregular or round morphologies, whereas crystals larger than 50 nm are
octahedral. Various nucleation and growth processes are invoked to explain the influence of synthesis conditions on the sizes and
shapes of the product magnetite nanoparticles