Air pollution effect on the decay of carbonate building stones in old town of Tallinn

For a long time the local Ordovician carbonate rocks were widely used for the building of many historical buildings, churches and strongholds in Tallinn. The chemical and mineralogical composition of building stone and gypsum black crust from five historical objects of Old Town of Tallinn were examined in order to reveal the weathering behaviour of the limestone and estimate the influence of pollution on the decay processes. The ICP-MS analysis and X-ray difractometry were performed to provide a quantitative analysis of the processes, which are responsible for building stone decay. The enrichment factor and R-mode factor analyses were applied in order to improve the understanding the nature and sources of elements and assess the pollution effect. The obtained results confirmed a natural origin for Ca, Mg, Si, Al, Ti, K, Na and Fe. The black crust is elevated in Cu, Pb, Sb, Sn and Zn concentrations as a result of the pollution effect. The highest increase of Cu, Pb and Zn content was determined in the samples from gypsum crust at St. Olaf's church. The enrichment factors calculation and factor analysis confirm the input of these elements from anthropic sources. Sulphur isotope composition in damaged building stone and black crust was used to discriminate the anthropic and natural sources of sulphur. The impact of technogenous sulphur in the gypsum formation in the black crust was revealed. The contribution of sulphur dissoluted from limestone is reflected in the positive delta values of sulphur. Comparison of obtained data to those for similar objects in European cities was carried out.