Characterization of decomposition forms of carbonate natural stones i̇n the experimentally generated acid rain environment

This study aims to characterize the degradation patterns of carbonate natural stones in an experimentally created acid rain environment. Acid rain refers to precipitation containing high levels of nitric and sulfuric acids, which result from pollutants accumulating in the atmosphere due to human activities such as coal-burning power plants, factories, and automobiles. Natural rain is mildly acidic with a pH of approximately 5.6; however, the pH of acid rain generally ranges from 4.2 to 4.4. The main components of acid rain, sulfur dioxide (SO2) and nitrogen oxides (NOx), combine with precipitation to form sulfuric acid (H2SO4) and nitric acid (HNO3). These acids cause significant deterioration in the microstructural, color, and chemical properties of natural stones. Carbonate-based metamorphic natural stones with fine crystalline, coarse crystalline and dolomitic structure were used in the study. Chemical analyses (XRF), petrographic characterizations, assessments of resistance to SO2 weathering in a humid environment, and scanning electron microscope (SEM) analyses were conducted on these natural stones. Petrographic examinations were performed to identify microstructural changes on the surfaces before and after the aging process. SEM analyses were used to detail the microscopic level degradation occurring on stone surfaces. The research findings indicate that there are distinct microstructural deteriorations on the surfaces of carbonate natural stones in an acid rain environment. Under the influence of sulfuric and nitric acids, degradation patterns such as deposition, crack formation, and mineral loss were observed on the stone surfaces. Petrographic analyses revealed that these deteriorations could progress into the internal structure of the natural stones. SEM results showed significant roughness and microcrack formations on the stone surfaces after acid exposure. In conclusion, this study provides detailed insights into the adverse effects of acid rain on carbonate natural stones and their degradation processes, offering valuable information for conservation and restoration efforts. These findings contribute to the development of strategies for mitigating the effects of acid rain and preserving natural stones.