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

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