## 1 Introduction
However, real-world exposure of sandstone structures involves both static and dynamic dissolution processes, including alternating cycles of rainfall and drying. This underscores the need for a more comprehensive approach incorporating dynamic dissolution conditions to better simulate natural environmental interactions and their impact on sandstone deterioration. Such an approach would enable a more accurate understanding of degradation mechanisms and guide effective conservation strategies for sandstone-based heritage structures. For sandstone, static dissolution occurs under humid conditions with accumulated rainwater, while dynamic dissolution simulates the effects of rainfall. The dynamic testing device generates an unsaturated dynamic flow of the chemical solution, exposing sandstone to its effects and simulating acid rain precipitation on grotto stone carvings. [PERSON] et al. [14] comprehensively simulated carbonate rock dissolution under static and dynamic conditions to study the effects of condensed water. Their experimental results showed that dynamic dissolution, mimicking water vapor condensation, causes stronger microscopic water vapor intrusion, significantly increasing the dissolution rate and porosity of dolomite compared to static conditions. Similarly, [PERSON] et al. [15] found that limestone porosity increased by 66% under dynamic acid rain erosion compared to only 28% under static immersion, indicating that dynamic dissolution significantly exacerbates rock degradation. These findings highlight the importance of considering both static and dynamic dissolution mechanisms in studying building material deterioration, as dynamic processes often significantly worsen rock property degradation. This dual approach is crucial for accurately assessing the long-term durability of sandstone and other rock-based structures in natural environments. Previous studies have shown that the physical and mechanical properties of carbonate rocks change distinctly under dynamic and static dissolution conditions. Sandstone-based rock-cut caves and stone carvings frequently experience alternating cycles of rainfall (dynamic dissolution) and water accumulation (static dissolution). Therefore, comparative studies on sandstone's physical and mechanical properties under these two dissolution modes are essential. This research is vital for understanding the different degradation mechanisms and their effects on sandstone structures. A systematic comparison of dynamic and static dissolution effects enables the development of more accurate models for predicting sandstone's long-term behavior in natural environments. This knowledge lays a scientific foundation for developing targeted conservation strategies to mitigate the deterioration of sandstone-based heritage sites and ensure their long-term preservation. To fully understand the impact of acid rain on the surface layers of rock-cut caves and stone carvings, this study simulates dynamic dissolution during acid rainfall and static immersion dissolution caused by residual water accumulation. Controlled laboratory experiments with dilute sulfuric acid solutions of identical concentration but different dissolution modes (dynamic and static) are conducted to elucidate key patterns of sandstone degradation under dynamic dissolution and compare its effects on pore structure, surface mechanical properties, and hygroscopic characteristics with those of static dissolution. This approach captures the distinct mechanisms of sandstone deterioration under realistic environmental conditions and provides critical insights into the differential impacts of dynamic and static dissolution. The findings enhance the understanding of sandstone degradation mechanisms and support the development of effective preservation strategies tailored to the challenges of acid rain and water accumulation.