Dust has a significant contribution to the formation the formation of black weathering crusts. Various limestone buildings showing black soiling were studied in Germany and in Hungary. Dust, crust and limestone samples were collected and analysed to understand the contribution of dust to black crust formation. Test methods included microscopic and SEM analyses and detection of mineralogical composition by using XRD. Since some elements and organic carbon act as catalyst for crust formation trace element distribution (LA-ICPMS) and organic carbon content were also detected.
According to analyses gypsum is the main secondary mineral of limestone weathering crusts both in rural and urban areas, although there are different concentrations detected in Germany and Hungary. Siliceous and carbonaceous fly-ash particles were found in both countries with the prevalence of the former one. Lead mostly accumulates in dust, but also common in the black crust. Surprising high concentrations were found at the crust/limestone boundary in the samples of Budapest and Cologne city centre. The dust composition reflects the setting but does not necessarily a good indicator of the environmental conditions.