Urban and rural limestone weathering; the contribution of dust to black crust formation |
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Authors: | Ákos Török Tobias Licha Klaus Simon Siegfried Siegesmund |
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Institution: | 1.Department of Construction Materials and Engineering Geology,Budapest University of Technology and Economics,Budapest,Hungary;2.Department of Applied Geology,Geoscience Center,G?ttingen,Germany;3.Department of Geochemistry,Geoscience Center,G?ttingen,Germany;4.Department of Structural Geology,Geoscience Center,G?ttingen,Germany |
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Abstract: | A novel approach of studying dust, black crust and host limestones by using various techniques is presented in this paper.
Samples were collected from limestone monuments located in rural, urban and industrial areas in Germany and Hungary. The paper
focuses on differences in the mineralogical composition, major and trace element distribution of materials and their total
polyaromatic hydrocarbons (PAH) concentration having different exposure to air pollutants. High concentration of gypsum was
found in laminar and dendritic black crusts and even in the dust of both urban and rural areas, despite the low concentration
of SO2 in rural atmospheric environments. The black crusts show a typical microfabric with distinct layers of various gypsum–calcite
mineral associations, silt-sized mineral fragments and black particle content. In dust, newly formed gypsum crystals were
found along with mineral fragments, and siliceous and, less frequently, carbonaceous fly ash particles. High concentration
of lead was found both in the samples of urban and rural areas of Germany and Hungary. Lead mostly accumulates in dust and
also in the black crust. Highest lead concentrations were found not on the surface of the black crust, but close to the crust/limestone
boundary according to LA-ICPMS analyses. It indicates that despite the ban of leaded petrol, lead is still present in the
dust and the in the soiled zones of the built environment. Similarly to lead, no significant difference in the total PAH content
of dust and crust samples were found in the two countries. Dusts are equally enriched in PAH in both countries, whereas black
crusts contain fewer amounts. Most of the aqueous extracts of the samples were saturated with respect to sulphate, which also
indicate the presence of gypsum, whilst in some German samples unsaturated conditions were detected. In summary, by using
a combination of these analytical techniques, it was possible to distinguish rural and urban samples and to outline the role
of dust in bringing pollutants to the stone surface. It is suggested that the analysed dust and stone samples indicate not
only present, but also the past, pollution fluxes and as a consequence stones similar to sediments or surface waters can be
used as environment indicators. |
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