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

A study on the Cologne Cathedral reveals that air pollution, particularly sulfur oxides (SOx), is a significant factor in the decay of its Drachenfels trachyte stone, characterized by gypsum crust formation and mechanical deterioration. The research compares stone decay at Cologne, Altenberg, and Xanten cathedrals—located in industrial, urban, and rural environments respectively—using chemical analyses and scanning electron microscopy. Findings indicate that while SO2 concentrations have decreased over the past 30 years, degradation persists due to past pollutant exposure. Additionally, the study identifies higher concentrations of pollutants like lead, arsenic, and antimony linked to traffic and industry, with distinct crust types (e.g., framboidal and laminar) correlating with pollution levels.

Graue, B., Siegesmund, S., Oyhantcabal, P., Naumann, R., Licha, T., & Simon, K. (2013). 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. Environmental Earth Sciences, 69(4), 1095–1124. https://doi.org/10.1007/s12665-012-2161-6