As a result of a tragic industrial accident, a highly alkaline red mud sludge inundated settlements and agricultural areas near Ajka, Hungary on October 4, 2010. One of the major concerns about the aftermaths of the accident is the potential health effects of vast amounts of fugitive dust from red mud sediment. Thus, we studied the chemical and physical properties of particles of red mud and its respirable fugitive dust, and performed toxicity measurements. Under unfavorable meteorological conditions dry red mud sediment could emit very high amounts of respirable alkaline particles into the air. The number size distribution of fugitive dust peaks above 1 μm aerodynamic diameter; therefore, its inhalation is unlikely to affect the deep regions of the lungs. No significant mineralogical or elemental fractionation was observed between the sediment and dust, with the major minerals being hematite, cancrinite, calcite, and hydrogarnet. Although the high resuspension potential and alkalinity might pose some problems such as the irritation of the upper respiratory tract and eyes, based on its size distribution and composition red mud dust appears to be less hazardous to human health than urban particulate matter.

Abstract. 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 0.8-3.0 m 2 g −1 at 550 nm, with absorption Ångström exponents (AAE) between 2.7 and 3.4 (average 2.9) in the wavelength range 467-652 nm. The refractive index of TBs as derived from Mie calculations was about 1.84 − 0.21i at 550 nm. In the brown carbon continuum, these values fall closer to those of soot than to other light-absorbing species such as humic-like substances (HULIS). Considering the abundance of TBs in biomass smoke and the global magnitude of biomass burning emissions, these findings may have substantial influence on the understanding of global radiative energy fluxes.

Abstract. 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.

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 (CaCO 3 ) and dolomite CaMg (CO 3 ) 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.

No abstract