Famous buildings all over the world are endangered by atmospheric pollution. The aggressive components are mainly of an acidic nature. The weathering is attributed to chemical and physical processes. However, reports about the involvement of microorganisms are either not available or their involvement is denied. Nevertheless, in recent years, it has become evident that lithoautotrophic nitrifying bacteria were involved. Due to the excretion of their metabolic end-product, nitric acid, concrete is degraded. The natural process could be modeled by means of simulation experiments.