The effect of air pollution on stone decay: the decay of the Drachenfels trachyte in industrial, urban, and rural environments—a case study of the Cologne, Altenberg and Xanten cathedrals

Abstract

Severe stone deterioration is evident at the Cologne cathedral. In particular, the ''Drachenfels'' trachyte, which was the building material of the medieval construction period, shows significant structural deterioration as well as massive formation of gypsum crusts. The present article investigates crust formation on limestone, sandstone, and volcanic rock from the Cologne cathedral as well as from the Xanten and Altenberg cathedrals. These three buildings, showing varying degrees of deterioration, are located in different areas and exposed to varying industrial, urban, and rural pollution. Thin laminar and black framboidal crusts form on calcareous as well as silicate stone. The lack of a significant intrinsic calcium and sulfur source for the formation of the gypsum crusts on the Drachenfels trachyte indicates major extrinsic environmental impact: a sufficient offer of SO x from pollutant fluxes as well as external calcium sources (e.g., pollution, mortars, neighboring calcite stones). Chemical analyses reveal strong gypsum enrichment within the crusts as well as higher concentrations of lead and other pollutants (arsenic, antimony, bismuth, tin, etc.), which generally can be linked to traffic and industry. The formation of weathering crusts in an industrial environment is clearly distinguishable from that in rural areas. Scanning electron microscopy observations confirm that the total amount of pollution is less at the Altenberg cathedral than at the Cologne and Xanten cathedrals. XRF analyses show that the formation of gypsum occurs in lower amounts at Altenberg. This correlates well with the measured SO 2 content and the intensity of the decay at the different locations. Furthermore, the different types of crusts, e.g., framboidal and laminar, can be differentiated and assigned to the different locations. The black weathering crusts on the silicate Drachenfels trachyte contribute to the degradation of the historic building material. They enhance mechanical moisture-related deterioration processes and the decay by chemical corrosion of rock-forming minerals. Although SO 2 concentrations in air have shown a strong decrease over the past 30 years, degradation in connection with weathering crusts is still observed. This indicates that not only contemporary or recent emissions, but also past pollutant concentrations have to be considered.

Carbonate Neoformations on Modern Buildings and Engineering Structures in Tyumen City, Russia: Structural Features and Development Factors

“…Neoformations on the surfaces of facing materials also significantly degrade the aesthetic appeal of the urban architecture; worsen the preservation of the monuments of architectural and historical heritage; and demand expensive measures for their removal [11][12][13][14]. In addition, the weathering of building materials in the conditions of an urbanized area is intensified due to the impacts of corrosive chemical compounds occurring in the compositions of atmospheric aerosols, snowmelt, and rainfall waters [15,16].…”

Experimental Investigation of Discoloration Generated by a CI ICE's Exhaust Gas on Various Stone Types

“…The blackening process clearly related to particulate matter (Amoroso and Fassina, 1983). The blackening and formation of soiling layer have been described for various stone types including marble (Moropoulou et al, 1998;Pozo-Antonio et al, 2017), limestone (Fobe et al, 1995;Maravelaki-Kalaitzaki and Biscontin, 1999;Amoroso and Fassina 1983), travertine (Török, 2008) and even on volcanic rocks (Germinario et al, 2017;Graue et al, 2013). The soiling is related to particle deposition and incorporation into the newly formed gypsum layers (Sabbioni, 1995).…”

“…The colour change reflects air quality and thus millennium long changes can be also recorded (Brimblecombe and Grossi, 2009). In the past decades vehicles were the main causes of urban stone decay, however air pollution can cause damage in stone structures located in rural settings Graue et al, 2013). The colour change and sulfation process can be modelled under laboratory conditions where carbonate samples are exposed to exhaust gas (particulates) and SO x (Rodriguez-Navarro and Sebastian, 1996).…”

Building health assessed through environmental parameters after the OTS in the city centre of Oxford, UK

“…Varied levels of atmospheric pollution at the Altenberg versus the Cologne and Xanten cathedrals in Germany affected the formation of gypsum crusts (Graue et al . ), which are known to develop through exposure to elevated SO 2 levels. Even though atmospheric concentrations of this pollutant have decreased in the past 30 years, these weathering crusts are still evident because of the impact of past pollution levels on current weathering (cf.…”